text: /* libs/pixelflinger/scanline.cpp
  **
  ** Copyright 2006-2011, The Android Open Source Project
  **
  ** Licensed under the Apache License, Version 2.0 (the "License"); 
  ** you may not use this file except in compliance with the License. 
  ** You may obtain a copy of the License at 
  **
  **     http://www.apache.org/licenses/LICENSE-2.0 
  **
  ** Unless required by applicable law or agreed to in writing, software 
  ** distributed under the License is distributed on an "AS IS" BASIS, 
  ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
  ** See the License for the specific language governing permissions and 
  ** limitations under the License.
  */
  
  
  #define LOG_TAG "pixelflinger"
  
  #include <assert.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <string.h>
  
  #include <cutils/memory.h>
  #include <cutils/log.h>
  
  #include "buffer.h"
  #include "scanline.h"
  
  #include "codeflinger/CodeCache.h"
  #include "codeflinger/GGLAssembler.h"
  #include "codeflinger/ARMAssembler.h"
  //#include "codeflinger/ARMAssemblerOptimizer.h"
  
  // ----------------------------------------------------------------------------
  
  #define ANDROID_CODEGEN_GENERIC     0   // force generic pixel pipeline
  #define ANDROID_CODEGEN_C           1   // hand-written C, fallback generic 
  #define ANDROID_CODEGEN_ASM         2   // hand-written asm, fallback generic
  #define ANDROID_CODEGEN_GENERATED   3   // hand-written asm, fallback codegen
  
  #ifdef NDEBUG
  #   define ANDROID_RELEASE
  #   define ANDROID_CODEGEN      ANDROID_CODEGEN_GENERATED
  #else
  #   define ANDROID_DEBUG
  #   define ANDROID_CODEGEN      ANDROID_CODEGEN_GENERATED
  #endif
  
  #if defined(__arm__)
  #   define ANDROID_ARM_CODEGEN  1
  #else
  #   define ANDROID_ARM_CODEGEN  0
  #endif
  
  #define DEBUG__CODEGEN_ONLY     0
  
  /* Set to 1 to dump to the log the states that need a new
   * code-generated scanline callback, i.e. those that don't
   * have a corresponding shortcut function.
   */
  #define DEBUG_NEEDS  0
  
  #define ASSEMBLY_SCRATCH_SIZE   2048
  
  // ----------------------------------------------------------------------------
  namespace android {
  // ----------------------------------------------------------------------------
  
  static void init_y(context_t*, int32_t);
  static void init_y_noop(context_t*, int32_t);
  static void init_y_packed(context_t*, int32_t);
  static void init_y_error(context_t*, int32_t);
  
  static void step_y__generic(context_t* c);
  static void step_y__nop(context_t*);
  static void step_y__smooth(context_t* c);
  static void step_y__tmu(context_t* c);
  static void step_y__w(context_t* c);
  
  static void scanline(context_t* c);
  static void scanline_perspective(context_t* c);
  static void scanline_perspective_single(context_t* c);
  static void scanline_t32cb16blend(context_t* c);
  static void scanline_t32cb16blend_dither(context_t* c);
  static void scanline_t32cb16blend_srca(context_t* c);
  static void scanline_t32cb16blend_clamp(context_t* c);
  static void scanline_t32cb16blend_clamp_dither(context_t* c);
  static void scanline_t32cb16blend_clamp_mod(context_t* c);
  static void scanline_x32cb16blend_clamp_mod(context_t* c);
  static void scanline_t32cb16blend_clamp_mod_dither(context_t* c);
  static void scanline_x32cb16blend_clamp_mod_dither(context_t* c);
  static void scanline_t32cb16(context_t* c);
  static void scanline_t32cb16_dither(context_t* c);
  static void scanline_t32cb16_clamp(context_t* c);
  static void scanline_t32cb16_clamp_dither(context_t* c);
  static void scanline_col32cb16blend(context_t* c);
  static void scanline_t16cb16_clamp(context_t* c);
  static void scanline_t16cb16blend_clamp_mod(context_t* c);
  static void scanline_memcpy(context_t* c);
  static void scanline_memset8(context_t* c);
  static void scanline_memset16(context_t* c);
  static void scanline_memset32(context_t* c);
  static void scanline_noop(context_t* c);
  static void scanline_set(context_t* c);
  static void scanline_clear(context_t* c);
  
  static void rect_generic(context_t* c, size_t yc);
  static void rect_memcpy(context_t* c, size_t yc);
  
  extern "C" void scanline_t32cb16blend_arm(uint16_t*, uint32_t*, size_t);
  extern "C" void scanline_t32cb16_arm(uint16_t *dst, uint32_t *src, size_t ct);
  extern "C" void scanline_col32cb16blend_neon(uint16_t *dst, uint32_t *col, size_t ct);
  extern "C" void scanline_col32cb16blend_arm(uint16_t *dst, uint32_t col, size_t ct);
  
  // ----------------------------------------------------------------------------
  
  static inline uint16_t  convertAbgr8888ToRgb565(uint32_t  pix)
  {
      return uint16_t( ((pix << 8) & 0xf800) |
                        ((pix >> 5) & 0x07e0) |
                        ((pix >> 19) & 0x001f) );
  }
  
  struct shortcut_t {
      needs_filter_t  filter;
      const char*     desc;
      void            (*scanline)(context_t*);
      void            (*init_y)(context_t*, int32_t);
  };
  
  // Keep in sync with needs
  
  /* To understand the values here, have a look at:
   *     system/core/include/private/pixelflinger/ggl_context.h
   *
   * Especially the lines defining and using GGL_RESERVE_NEEDS
   *
   * Quick reminders:
   *   - the last nibble of the first value is the destination buffer format.
   *   - the last nibble of the third value is the source texture format
   *   - formats: 4=rgb565 1=abgr8888 2=xbgr8888
   *
   * In the descriptions below:
   *
   *   SRC      means we copy the source pixels to the destination
   *
   *   SRC_OVER means we blend the source pixels to the destination
   *            with dstFactor = 1-srcA, srcFactor=1  (premultiplied source).
   *            This mode is otherwise called 'blend'.
   *
   *   SRCA_OVER means we blend the source pixels to the destination
   *             with dstFactor=srcA*(1-srcA) srcFactor=srcA (non-premul source).
   *             This mode is otherwise called 'blend_srca'
   *
   *   clamp    means we fetch source pixels from a texture with u/v clamping
   *
   *   mod      means the source pixels are modulated (multiplied) by the
   *            a/r/g/b of the current context's color. Typically used for
   *            fade-in / fade-out.
   *
   *   dither   means we dither 32 bit values to 16 bits
   */
  static shortcut_t shortcuts[] = {
      { { { 0x03515104, 0x00000077, { 0x00000A01, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, blend SRC_OVER", scanline_t32cb16blend, init_y_noop },
      { { { 0x03010104, 0x00000077, { 0x00000A01, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC", scanline_t32cb16, init_y_noop  },
      /* same as first entry, but with dithering */
      { { { 0x03515104, 0x00000177, { 0x00000A01, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, blend SRC_OVER dither", scanline_t32cb16blend_dither, init_y_noop },
      /* same as second entry, but with dithering */
      { { { 0x03010104, 0x00000177, { 0x00000A01, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC dither", scanline_t32cb16_dither, init_y_noop  },
      /* this is used during the boot animation - CHEAT: ignore dithering */
      { { { 0x03545404, 0x00000077, { 0x00000A01, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFEFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, blend dst:ONE_MINUS_SRCA src:SRCA", scanline_t32cb16blend_srca, init_y_noop },
      /* special case for arbitrary texture coordinates (think scaling) */
      { { { 0x03515104, 0x00000077, { 0x00000001, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC_OVER clamp", scanline_t32cb16blend_clamp, init_y },
      { { { 0x03515104, 0x00000177, { 0x00000001, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC_OVER clamp dither", scanline_t32cb16blend_clamp_dither, init_y },
      /* another case used during emulation */
      { { { 0x03515104, 0x00000077, { 0x00001001, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC_OVER clamp modulate", scanline_t32cb16blend_clamp_mod, init_y },
      /* and this */
      { { { 0x03515104, 0x00000077, { 0x00001002, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, x888 tx, SRC_OVER clamp modulate", scanline_x32cb16blend_clamp_mod, init_y },
      { { { 0x03515104, 0x00000177, { 0x00001001, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC_OVER clamp modulate dither", scanline_t32cb16blend_clamp_mod_dither, init_y },
      { { { 0x03515104, 0x00000177, { 0x00001002, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, x888 tx, SRC_OVER clamp modulate dither", scanline_x32cb16blend_clamp_mod_dither, init_y },
      { { { 0x03010104, 0x00000077, { 0x00000001, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC clamp", scanline_t32cb16_clamp, init_y  },
      { { { 0x03010104, 0x00000077, { 0x00000002, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, x888 tx, SRC clamp", scanline_t32cb16_clamp, init_y  },
      { { { 0x03010104, 0x00000177, { 0x00000001, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 8888 tx, SRC clamp dither", scanline_t32cb16_clamp_dither, init_y  },
      { { { 0x03010104, 0x00000177, { 0x00000002, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, x888 tx, SRC clamp dither", scanline_t32cb16_clamp_dither, init_y  },
      { { { 0x03010104, 0x00000077, { 0x00000004, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 565 tx, SRC clamp", scanline_t16cb16_clamp, init_y  },
      { { { 0x03515104, 0x00000077, { 0x00001004, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0x0000003F } } },
          "565 fb, 565 tx, SRC_OVER clamp", scanline_t16cb16blend_clamp_mod, init_y  },
      { { { 0x03515104, 0x00000077, { 0x00000000, 0x00000000 } },
          { 0xFFFFFFFF, 0xFFFFFFFF, { 0xFFFFFFFF, 0xFFFFFFFF } } },
          "565 fb, 8888 fixed color", scanline_col32cb16blend, init_y_packed  },  
      { { { 0x00000000, 0x00000000, { 0x00000000, 0x00000000 } },
          { 0x00000000, 0x00000007, { 0x00000000, 0x00000000 } } },
          "(nop) alpha test", scanline_noop, init_y_noop },
      { { { 0x00000000, 0x00000000, { 0x00000000, 0x00000000 } },
          { 0x00000000, 0x00000070, { 0x00000000, 0x00000000 } } },
          "(nop) depth test", scanline_noop, init_y_noop },
      { { { 0x05000000, 0x00000000, { 0x00000000, 0x00000000 } },
          { 0x0F000000, 0x00000080, { 0x00000000, 0x00000000 } } },
          "(nop) logic_op", scanline_noop, init_y_noop },
      { { { 0xF0000000, 0x00000000, { 0x00000000, 0x00000000 } },
          { 0xF0000000, 0x00000080, { 0x00000000, 0x00000000 } } },
          "(nop) color mask", scanline_noop, init_y_noop },
      { { { 0x0F000000, 0x00000077, { 0x00000000, 0x00000000 } },
          { 0xFF000000, 0x000000F7, { 0x00000000, 0x00000000 } } },
          "(set) logic_op", scanline_set, init_y_noop },
      { { { 0x00000000, 0x00000077, { 0x00000000, 0x00000000 } },
          { 0xFF000000, 0x000000F7, { 0x00000000, 0x00000000 } } },
          "(clear) logic_op", scanline_clear, init_y_noop },
      { { { 0x03000000, 0x00000077, { 0x00000000, 0x00000000 } },
          { 0xFFFFFF00, 0x000000F7, { 0x00000000, 0x00000000 } } },
          "(clear) blending 0/0", scanline_clear, init_y_noop },
      { { { 0x00000000, 0x00000000, { 0x00000000, 0x00000000 } },
          { 0x0000003F, 0x00000000, { 0x00000000, 0x00000000 } } },
          "(error) invalid color-buffer format", scanline_noop, init_y_error },
  };
  static const needs_filter_t noblend1to1 = {
          // (disregard dithering, see below)
          { 0x03010100, 0x00000077, { 0x00000A00, 0x00000000 } },
          { 0xFFFFFFC0, 0xFFFFFEFF, { 0xFFFFFFC0, 0x0000003F } }
  };
  static  const needs_filter_t fill16noblend = {
          { 0x03010100, 0x00000077, { 0x00000000, 0x00000000 } },
          { 0xFFFFFFC0, 0xFFFFFFFF, { 0x0000003F, 0x0000003F } }
  };
  
  // ----------------------------------------------------------------------------
  
  #if ANDROID_ARM_CODEGEN
  static CodeCache gCodeCache(12 * 1024);
  
  class ScanlineAssembly : public Assembly {
      AssemblyKey<needs_t> mKey;
  public:
      ScanlineAssembly(needs_t needs, size_t size)
          : Assembly(size), mKey(needs) { }
      const AssemblyKey<needs_t>& key() const { return mKey; }
  };
  #endif
  
  // ----------------------------------------------------------------------------
  
  void ggl_init_scanline(context_t* c)
  {
      c->init_y = init_y;
      c->step_y = step_y__generic;
      c->scanline = scanline;
  }
  
  void ggl_uninit_scanline(context_t* c)
  {
      if (c->state.buffers.coverage)
          free(c->state.buffers.coverage);
  #if ANDROID_ARM_CODEGEN
      if (c->scanline_as)
          c->scanline_as->decStrong(c);
  #endif
  }
  
  // ----------------------------------------------------------------------------
  
  static void pick_scanline(context_t* c)
  {
  #if (!defined(DEBUG__CODEGEN_ONLY) || (DEBUG__CODEGEN_ONLY == 0))
  
  #if ANDROID_CODEGEN == ANDROID_CODEGEN_GENERIC
      c->init_y = init_y;
      c->step_y = step_y__generic;
      c->scanline = scanline;
      return;
  #endif
  
      //printf("*** needs [%08lx:%08lx:%08lx:%08lx]\n",
      //    c->state.needs.n, c->state.needs.p,
      //    c->state.needs.t[0], c->state.needs.t[1]);
  
      // first handle the special case that we cannot test with a filter
      const uint32_t cb_format = GGL_READ_NEEDS(CB_FORMAT, c->state.needs.n);
      if (GGL_READ_NEEDS(T_FORMAT, c->state.needs.t[0]) == cb_format) {
          if (c->state.needs.match(noblend1to1)) {
              // this will match regardless of dithering state, since both
              // src and dest have the same format anyway, there is no dithering
              // to be done.
              const GGLFormat* f =
                  &(c->formats[GGL_READ_NEEDS(T_FORMAT, c->state.needs.t[0])]);
              if ((f->components == GGL_RGB) ||
                  (f->components == GGL_RGBA) ||
                  (f->components == GGL_LUMINANCE) ||
                  (f->components == GGL_LUMINANCE_ALPHA))
              {
                  // format must have all of RGB components
                  // (so the current color doesn't show through)
                  c->scanline = scanline_memcpy;
                  c->init_y = init_y_noop;
                  return;
              }
          }
      }
  
      if (c->state.needs.match(fill16noblend)) {
          c->init_y = init_y_packed;
          switch (c->formats[cb_format].size) {
          case 1: c->scanline = scanline_memset8;  return;
          case 2: c->scanline = scanline_memset16; return;
          case 4: c->scanline = scanline_memset32; return;
          }
      }
  
      const int numFilters = sizeof(shortcuts)/sizeof(shortcut_t);
      for (int i=0 ; i<numFilters ; i++) {
          if (c->state.needs.match(shortcuts[i].filter)) {
              c->scanline = shortcuts[i].scanline;
              c->init_y = shortcuts[i].init_y;
              return;
          }
      }
  
  #if DEBUG_NEEDS
      ALOGI("Needs: n=0x%08x p=0x%08x t0=0x%08x t1=0x%08x",
           c->state.needs.n, c->state.needs.p,
           c->state.needs.t[0], c->state.needs.t[1]);
  #endif
  
  #endif // DEBUG__CODEGEN_ONLY
  
      c->init_y = init_y;
      c->step_y = step_y__generic;
  
  #if ANDROID_ARM_CODEGEN
      // we're going to have to generate some code...
      // here, generate code for our pixel pipeline
      const AssemblyKey<needs_t> key(c->state.needs);
      sp<Assembly> assembly = gCodeCache.lookup(key);
      if (assembly == 0) {
          // create a new assembly region
          sp<ScanlineAssembly> a = new ScanlineAssembly(c->state.needs, 
                  ASSEMBLY_SCRATCH_SIZE);
          // initialize our assembler
          GGLAssembler assembler( new ARMAssembler(a) );
          //GGLAssembler assembler(
          //        new ARMAssemblerOptimizer(new ARMAssembler(a)) );
          // generate the scanline code for the given needs
          int err = assembler.scanline(c->state.needs, c);
          if (ggl_likely(!err)) {
              // finally, cache this assembly
              err = gCodeCache.cache(a->key(), a);
          }
          if (ggl_unlikely(err)) {
              ALOGE("error generating or caching assembly. Reverting to NOP.");
              c->scanline = scanline_noop;
              c->init_y = init_y_noop;
              c->step_y = step_y__nop;
              return;
          }
          assembly = a;
      }
  
      // release the previous assembly
      if (c->scanline_as) {
          c->scanline_as->decStrong(c);
      }
  
      //ALOGI("using generated pixel-pipeline");
      c->scanline_as = assembly.get();
      c->scanline_as->incStrong(c); //  hold on to assembly
      c->scanline = (void(*)(context_t* c))assembly->base();
  #else
  //    ALOGW("using generic (slow) pixel-pipeline");
      c->scanline = scanline;
  #endif
  }
  
  void ggl_pick_scanline(context_t* c)
  {
      pick_scanline(c);
      if ((c->state.enables & GGL_ENABLE_W) &&
          (c->state.enables & GGL_ENABLE_TMUS))
      {
          c->span = c->scanline;
          c->scanline = scanline_perspective;
          if (!(c->state.enabled_tmu & (c->state.enabled_tmu - 1))) {
              // only one TMU enabled
              c->scanline = scanline_perspective_single;
          }
      }
  }
  
  // ----------------------------------------------------------------------------
  
  static void blending(context_t* c, pixel_t* fragment, pixel_t* fb);
  static void blend_factor(context_t* c, pixel_t* r, uint32_t factor,
          const pixel_t* src, const pixel_t* dst);
  static void rescale(uint32_t& u, uint8_t& su, uint32_t& v, uint8_t& sv);
  
  #if ANDROID_ARM_CODEGEN && (ANDROID_CODEGEN == ANDROID_CODEGEN_GENERATED)
  
  // no need to compile the generic-pipeline, it can't be reached
  void scanline(context_t*)
  {
  }
  
  #else
  
  void rescale(uint32_t& u, uint8_t& su, uint32_t& v, uint8_t& sv)
  {
      if (su && sv) {
          if (su > sv) {
              v = ggl_expand(v, sv, su);
              sv = su;
          } else if (su < sv) {
              u = ggl_expand(u, su, sv);
              su = sv;
          }
      }
  }
  
  void blending(context_t* c, pixel_t* fragment, pixel_t* fb)
  {
      rescale(fragment->c[0], fragment->s[0], fb->c[0], fb->s[0]);
      rescale(fragment->c[1], fragment->s[1], fb->c[1], fb->s[1]);
      rescale(fragment->c[2], fragment->s[2], fb->c[2], fb->s[2]);
      rescale(fragment->c[3], fragment->s[3], fb->c[3], fb->s[3]);
  
      pixel_t sf, df;
      blend_factor(c, &sf, c->state.blend.src, fragment, fb);
      blend_factor(c, &df, c->state.blend.dst, fragment, fb);
  
      fragment->c[1] =
              gglMulAddx(fragment->c[1], sf.c[1], gglMulx(fb->c[1], df.c[1]));
      fragment->c[2] =
              gglMulAddx(fragment->c[2], sf.c[2], gglMulx(fb->c[2], df.c[2]));
      fragment->c[3] =
              gglMulAddx(fragment->c[3], sf.c[3], gglMulx(fb->c[3], df.c[3]));
  
      if (c->state.blend.alpha_separate) {
          blend_factor(c, &sf, c->state.blend.src_alpha, fragment, fb);
          blend_factor(c, &df, c->state.blend.dst_alpha, fragment, fb);
      }
  
      fragment->c[0] =
              gglMulAddx(fragment->c[0], sf.c[0], gglMulx(fb->c[0], df.c[0]));
  
      // clamp to 1.0
      if (fragment->c[0] >= (1LU<<fragment->s[0]))
          fragment->c[0] = (1<<fragment->s[0])-1;
      if (fragment->c[1] >= (1LU<<fragment->s[1]))
          fragment->c[1] = (1<<fragment->s[1])-1;
      if (fragment->c[2] >= (1LU<<fragment->s[2]))
          fragment->c[2] = (1<<fragment->s[2])-1;
      if (fragment->c[3] >= (1LU<<fragment->s[3]))
          fragment->c[3] = (1<<fragment->s[3])-1;
  }
  
  static inline int blendfactor(uint32_t x, uint32_t size, uint32_t def = 0)
  {
      if (!size)
          return def;
  
      // scale to 16 bits
      if (size > 16) {
          x >>= (size - 16);
      } else if (size < 16) {
          x = ggl_expand(x, size, 16);
      }
      x += x >> 15;
      return x;
  }
  
  void blend_factor(context_t* c, pixel_t* r, 
          uint32_t factor, const pixel_t* src, const pixel_t* dst)
  {
      switch (factor) {
          case GGL_ZERO:
              r->c[1] = 
              r->c[2] = 
              r->c[3] = 
              r->c[0] = 0;
              break;
          case GGL_ONE:
              r->c[1] = 
              r->c[2] = 
              r->c[3] = 
              r->c[0] = FIXED_ONE;
              break;
          case GGL_DST_COLOR:
              r->c[1] = blendfactor(dst->c[1], dst->s[1]);
              r->c[2] = blendfactor(dst->c[2], dst->s[2]);
              r->c[3] = blendfactor(dst->c[3], dst->s[3]);
              r->c[0] = blendfactor(dst->c[0], dst->s[0]);
              break;
          case GGL_SRC_COLOR:
              r->c[1] = blendfactor(src->c[1], src->s[1]);
              r->c[2] = blendfactor(src->c[2], src->s[2]);
              r->c[3] = blendfactor(src->c[3], src->s[3]);
              r->c[0] = blendfactor(src->c[0], src->s[0]);
              break;
          case GGL_ONE_MINUS_DST_COLOR:
              r->c[1] = FIXED_ONE - blendfactor(dst->c[1], dst->s[1]);
              r->c[2] = FIXED_ONE - blendfactor(dst->c[2], dst->s[2]);
              r->c[3] = FIXED_ONE - blendfactor(dst->c[3], dst->s[3]);
              r->c[0] = FIXED_ONE - blendfactor(dst->c[0], dst->s[0]);
              break;
          case GGL_ONE_MINUS_SRC_COLOR:
              r->c[1] = FIXED_ONE - blendfactor(src->c[1], src->s[1]);
              r->c[2] = FIXED_ONE - blendfactor(src->c[2], src->s[2]);
              r->c[3] = FIXED_ONE - blendfactor(src->c[3], src->s[3]);
              r->c[0] = FIXED_ONE - blendfactor(src->c[0], src->s[0]);
              break;
          case GGL_SRC_ALPHA:
              r->c[1] = 
              r->c[2] = 
              r->c[3] = 
              r->c[0] = blendfactor(src->c[0], src->s[0], FIXED_ONE);
              break;
          case GGL_ONE_MINUS_SRC_ALPHA:
              r->c[1] = 
              r->c[2] = 
              r->c[3] = 
              r->c[0] = FIXED_ONE - blendfactor(src->c[0], src->s[0], FIXED_ONE);
              break;
          case GGL_DST_ALPHA:
              r->c[1] = 
              r->c[2] = 
              r->c[3] = 
              r->c[0] = blendfactor(dst->c[0], dst->s[0], FIXED_ONE);
              break;
          case GGL_ONE_MINUS_DST_ALPHA:
              r->c[1] = 
              r->c[2] = 
              r->c[3] = 
              r->c[0] = FIXED_ONE - blendfactor(dst->c[0], dst->s[0], FIXED_ONE);
              break;
          case GGL_SRC_ALPHA_SATURATE:
              // XXX: GGL_SRC_ALPHA_SATURATE
              break;
      }
  }
  
  static GGLfixed wrapping(int32_t coord, uint32_t size, int tx_wrap)
  {
      GGLfixed d;
      if (tx_wrap == GGL_REPEAT) {
          d = (uint32_t(coord)>>16) * size;
      } else if (tx_wrap == GGL_CLAMP) { // CLAMP_TO_EDGE semantics
          const GGLfixed clamp_min = FIXED_HALF;
          const GGLfixed clamp_max = (size << 16) - FIXED_HALF;
          if (coord < clamp_min)     coord = clamp_min;
          if (coord > clamp_max)     coord = clamp_max;
          d = coord;
      } else { // 1:1
          const GGLfixed clamp_min = 0;
          const GGLfixed clamp_max = (size << 16);
          if (coord < clamp_min)     coord = clamp_min;
          if (coord > clamp_max)     coord = clamp_max;
          d = coord;
      }
      return d;
  }
  
  static inline
  GGLcolor ADJUST_COLOR_ITERATOR(GGLcolor v, GGLcolor dvdx, int len)
  {
      const int32_t end = dvdx * (len-1) + v;
      if (end < 0)
          v -= end;
      v &= ~(v>>31);
      return v;
  }
  
  void scanline(context_t* c)
  {
      const uint32_t enables = c->state.enables;
      const int xs = c->iterators.xl;
      const int x1 = c->iterators.xr;
  	int xc = x1 - xs;
      const int16_t* covPtr = c->state.buffers.coverage + xs;
  
      // All iterated values are sampled at the pixel center
  
      // reset iterators for that scanline...
      GGLcolor r, g, b, a;
      iterators_t& ci = c->iterators;
      if (enables & GGL_ENABLE_SMOOTH) {
          r = (xs * c->shade.drdx) + ci.ydrdy;
          g = (xs * c->shade.dgdx) + ci.ydgdy;
          b = (xs * c->shade.dbdx) + ci.ydbdy;
          a = (xs * c->shade.dadx) + ci.ydady;
          r = ADJUST_COLOR_ITERATOR(r, c->shade.drdx, xc);
          g = ADJUST_COLOR_ITERATOR(g, c->shade.dgdx, xc);
          b = ADJUST_COLOR_ITERATOR(b, c->shade.dbdx, xc);
          a = ADJUST_COLOR_ITERATOR(a, c->shade.dadx, xc);
      } else {
          r = ci.ydrdy;
          g = ci.ydgdy;
          b = ci.ydbdy;
          a = ci.ydady;
      }
  
      // z iterators are 1.31
      GGLfixed z = (xs * c->shade.dzdx) + ci.ydzdy;
      GGLfixed f = (xs * c->shade.dfdx) + ci.ydfdy;
  
      struct {
          GGLfixed s, t;
      } tc[GGL_TEXTURE_UNIT_COUNT];
      if (enables & GGL_ENABLE_TMUS) {
          for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
              if (c->state.texture[i].enable) {
                  texture_iterators_t& ti = c->state.texture[i].iterators;
                  if (enables & GGL_ENABLE_W) {
                      tc[i].s = ti.ydsdy;
                      tc[i].t = ti.ydtdy;
                  } else {
                      tc[i].s = (xs * ti.dsdx) + ti.ydsdy;
                      tc[i].t = (xs * ti.dtdx) + ti.ydtdy;
                  }
              }
          }
      }
  
      pixel_t fragment;
      pixel_t texel;
      pixel_t fb;
  
  	uint32_t x = xs;
  	uint32_t y = c->iterators.y;
  
  	while (xc--) {
      
          { // just a scope
  
  		// read color (convert to 8 bits by keeping only the integer part)
          fragment.s[1] = fragment.s[2] =
          fragment.s[3] = fragment.s[0] = 8;
          fragment.c[1] = r >> (GGL_COLOR_BITS-8);
          fragment.c[2] = g >> (GGL_COLOR_BITS-8);
          fragment.c[3] = b >> (GGL_COLOR_BITS-8);
          fragment.c[0] = a >> (GGL_COLOR_BITS-8);
  
  		// texturing
          if (enables & GGL_ENABLE_TMUS) {
              for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
                  texture_t& tx = c->state.texture[i];
                  if (!tx.enable)
                      continue;
                  texture_iterators_t& ti = tx.iterators;
                  int32_t u, v;
  
                  // s-coordinate
                  if (tx.s_coord != GGL_ONE_TO_ONE) {
                      const int w = tx.surface.width;
                      u = wrapping(tc[i].s, w, tx.s_wrap);
                      tc[i].s += ti.dsdx;
                  } else {
                      u = (((tx.shade.is0>>16) + x)<<16) + FIXED_HALF;
                  }
  
                  // t-coordinate
                  if (tx.t_coord != GGL_ONE_TO_ONE) {
                      const int h = tx.surface.height;
                      v = wrapping(tc[i].t, h, tx.t_wrap);
                      tc[i].t += ti.dtdx;
                  } else {
                      v = (((tx.shade.it0>>16) + y)<<16) + FIXED_HALF;
                  }
  
                  // read texture
                  if (tx.mag_filter == GGL_NEAREST &&
                      tx.min_filter == GGL_NEAREST)
                  {
                      u >>= 16;
                      v >>= 16;
                      tx.surface.read(&tx.surface, c, u, v, &texel);
                  } else {
                      const int w = tx.surface.width;
                      const int h = tx.surface.height;
                      u -= FIXED_HALF;
                      v -= FIXED_HALF;
                      int u0 = u >> 16;
                      int v0 = v >> 16;
                      int u1 = u0 + 1;
                      int v1 = v0 + 1;
                      if (tx.s_wrap == GGL_REPEAT) {
                          if (u0<0)  u0 += w;
                          if (u1<0)  u1 += w;
                          if (u0>=w) u0 -= w;
                          if (u1>=w) u1 -= w;
                      } else {
                          if (u0<0)  u0 = 0;
                          if (u1<0)  u1 = 0;
                          if (u0>=w) u0 = w-1;
                          if (u1>=w) u1 = w-1;
                      }
                      if (tx.t_wrap == GGL_REPEAT) {
                          if (v0<0)  v0 += h;
                          if (v1<0)  v1 += h;
                          if (v0>=h) v0 -= h;
                          if (v1>=h) v1 -= h;
                      } else {
                          if (v0<0)  v0 = 0;
                          if (v1<0)  v1 = 0;
                          if (v0>=h) v0 = h-1;
                          if (v1>=h) v1 = h-1;
                      }
                      pixel_t texels[4];
                      uint32_t mm[4];
                      tx.surface.read(&tx.surface, c, u0, v0, &texels[0]);
                      tx.surface.read(&tx.surface, c, u0, v1, &texels[1]);
                      tx.surface.read(&tx.surface, c, u1, v0, &texels[2]);
                      tx.surface.read(&tx.surface, c, u1, v1, &texels[3]);
                      u = (u >> 12) & 0xF; 
                      v = (v >> 12) & 0xF;
                      u += u>>3;
                      v += v>>3;
                      mm[0] = (0x10 - u) * (0x10 - v);
                      mm[1] = (0x10 - u) * v;
                      mm[2] = u * (0x10 - v);
                      mm[3] = 0x100 - (mm[0] + mm[1] + mm[2]);
                      for (int j=0 ; j<4 ; j++) {
                          texel.s[j] = texels[0].s[j];
                          if (!texel.s[j]) continue;
                          texel.s[j] += 8;
                          texel.c[j] =    texels[0].c[j]*mm[0] +
                                          texels[1].c[j]*mm[1] +
                                          texels[2].c[j]*mm[2] +
                                          texels[3].c[j]*mm[3] ;
                      }
                  }
  
                  // Texture environnement...
                  for (int j=0 ; j<4 ; j++) {
                      uint32_t& Cf = fragment.c[j];
                      uint32_t& Ct = texel.c[j];
                      uint8_t& sf  = fragment.s[j];
                      uint8_t& st  = texel.s[j];
                      uint32_t At = texel.c[0];
                      uint8_t sat = texel.s[0];
                      switch (tx.env) {
                      case GGL_REPLACE:
                          if (st) {
                              Cf = Ct;
                              sf = st;
                          }
                          break;
                      case GGL_MODULATE:
                          if (st) {
                              uint32_t factor = Ct + (Ct>>(st-1));
                              Cf = (Cf * factor) >> st;
                          }
                          break;
                      case GGL_DECAL:
                          if (sat) {
                              rescale(Cf, sf, Ct, st);
                              Cf += ((Ct - Cf) * (At + (At>>(sat-1)))) >> sat;
                          }
                          break;
                      case GGL_BLEND:
                          if (st) {
                              uint32_t Cc = tx.env_color[i];
                              if (sf>8)       Cc = (Cc * ((1<<sf)-1))>>8;
                              else if (sf<8)  Cc = (Cc - (Cc>>(8-sf)))>>(8-sf);
                              uint32_t factor = Ct + (Ct>>(st-1));
                              Cf = ((((1<<st) - factor) * Cf) + Ct*Cc)>>st;
                          }
                          break;
                      case GGL_ADD:
                          if (st) {
                              rescale(Cf, sf, Ct, st);
                              Cf += Ct;
                          }
                          break;
                      }
                  }
              }
  		}
      
          // coverage application
          if (enables & GGL_ENABLE_AA) {
              int16_t cf = *covPtr++;
              fragment.c[0] = (int64_t(fragment.c[0]) * cf) >> 15;
          }
          
          // alpha-test
          if (enables & GGL_ENABLE_ALPHA_TEST) {
              GGLcolor ref = c->state.alpha_test.ref;
              GGLcolor alpha = (uint64_t(fragment.c[0]) *
                      ((1<<GGL_COLOR_BITS)-1)) / ((1<<fragment.s[0])-1);
              switch (c->state.alpha_test.func) {
              case GGL_NEVER:     goto discard;
              case GGL_LESS:      if (alpha<ref)  break; goto discard;
              case GGL_EQUAL:     if (alpha==ref) break; goto discard;
              case GGL_LEQUAL:    if (alpha<=ref) break; goto discard;
              case GGL_GREATER:   if (alpha>ref)  break; goto discard;
              case GGL_NOTEQUAL:  if (alpha!=ref) break; goto discard;
              case GGL_GEQUAL:    if (alpha>=ref) break; goto discard;
              }
          }
          
          // depth test
          if (c->state.buffers.depth.format) {
              if (enables & GGL_ENABLE_DEPTH_TEST) {
                  surface_t* cb = &(c->state.buffers.depth);
                  uint16_t* p = (uint16_t*)(cb->data)+(x+(cb->stride*y));
                  uint16_t zz = uint32_t(z)>>(16);
                  uint16_t depth = *p;
                  switch (c->state.depth_test.func) {
                  case GGL_NEVER:     goto discard;
                  case GGL_LESS:      if (zz<depth)    break; goto discard;
                  case GGL_EQUAL:     if (zz==depth)   break; goto discard;
                  case GGL_LEQUAL:    if (zz<=depth)   break; goto discard;
                  case GGL_GREATER:   if (zz>depth)    break; goto discard;
                  case GGL_NOTEQUAL:  if (zz!=depth)   break; goto discard;
                  case GGL_GEQUAL:    if (zz>=depth)   break; goto discard;
                  }
                  // depth buffer is not enabled, if depth-test is not enabled
  /*
          fragment.s[1] = fragment.s[2] =
          fragment.s[3] = fragment.s[0] = 8;
          fragment.c[1] = 
          fragment.c[2] = 
          fragment.c[3] = 
          fragment.c[0] = 255 - (zz>>8);
  */
                  if (c->state.mask.depth) {
                      *p = zz;
                  }
              }
          }
  
          // fog
          if (enables & GGL_ENABLE_FOG) {
              for (int i=1 ; i<=3 ; i++) {
                  GGLfixed fc = (c->state.fog.color[i] * 0x10000) / 0xFF;
                  uint32_t& c = fragment.c[i];
                  uint8_t& s  = fragment.s[i];
                  c = (c * 0x10000) / ((1<<s)-1);
                  c = gglMulAddx(c, f, gglMulx(fc, 0x10000 - f));
                  s = 16;
              }
          }
  
          // blending
          if (enables & GGL_ENABLE_BLENDING) {
              fb.c[1] = fb.c[2] = fb.c[3] = fb.c[0] = 0; // placate valgrind
              fb.s[1] = fb.s[2] = fb.s[3] = fb.s[0] = 0;
              c->state.buffers.color.read(
                      &(c->state.buffers.color), c, x, y, &fb);
              blending( c, &fragment, &fb );
          }
  
  		// write
          c->state.buffers.color.write(
                  &(c->state.buffers.color), c, x, y, &fragment);
          }
  
  discard:
  		// iterate...
          x += 1;
          if (enables & GGL_ENABLE_SMOOTH) {
              r += c->shade.drdx;
              g += c->shade.dgdx;
              b += c->shade.dbdx;
              a += c->shade.dadx;
          }
          z += c->shade.dzdx;
          f += c->shade.dfdx;
  	}
  }
  
  #endif // ANDROID_ARM_CODEGEN && (ANDROID_CODEGEN == ANDROID_CODEGEN_GENERATED)
  
  // ----------------------------------------------------------------------------
  #if 0
  #pragma mark -
  #pragma mark Scanline
  #endif
  
  /* Used to parse a 32-bit source texture linearly. Usage is:
   *
   * horz_iterator32  hi(context);
   * while (...) {
   *    uint32_t  src_pixel = hi.get_pixel32();
   *    ...
   * }
   *
   * Use only for one-to-one texture mapping.
   */
  struct horz_iterator32 {
      horz_iterator32(context_t* c) {
          const int x = c->iterators.xl;
          const int y = c->iterators.y;
          texture_t& tx = c->state.texture[0];
          const int32_t u = (tx.shade.is0>>16) + x;
          const int32_t v = (tx.shade.it0>>16) + y;
          m_src = reinterpret_cast<uint32_t*>(tx.surface.data)+(u+(tx.surface.stride*v));
      }
      uint32_t  get_pixel32() {
          return *m_src++;
      }
  protected:
      uint32_t* m_src;
  };
  
  /* A variant for 16-bit source textures. */
  struct horz_iterator16 {
      horz_iterator16(context_t* c) {
          const int x = c->iterators.xl;
          const int y = c->iterators.y;
          texture_t& tx = c->state.texture[0];
          const int32_t u = (tx.shade.is0>>16) + x;
          const int32_t v = (tx.shade.it0>>16) + y;
          m_src = reinterpret_cast<uint16_t*>(tx.surface.data)+(u+(tx.surface.stride*v));
      }
      uint16_t  get_pixel16() {
          return *m_src++;
      }
  protected:
      uint16_t* m_src;
  };
  
  /* A clamp iterator is used to iterate inside a texture with GGL_CLAMP.
   * After initialization, call get_src16() or get_src32() to get the current
   * texture pixel value.
   */
  struct clamp_iterator {
      clamp_iterator(context_t* c) {
          const int xs = c->iterators.xl;
          texture_t& tx = c->state.texture[0];
          texture_iterators_t& ti = tx.iterators;
          m_s = (xs * ti.dsdx) + ti.ydsdy;
          m_t = (xs * ti.dtdx) + ti.ydtdy;
          m_ds = ti.dsdx;
          m_dt = ti.dtdx;
          m_width_m1 = tx.surface.width - 1;
          m_height_m1 = tx.surface.height - 1;
          m_data = tx.surface.data;
          m_stride = tx.surface.stride;
      }
      uint16_t get_pixel16() {
          int  u, v;
          get_uv(u, v);
          uint16_t* src = reinterpret_cast<uint16_t*>(m_data) + (u + (m_stride*v));
          return src[0];
      }
      uint32_t get_pixel32() {
          int  u, v;
          get_uv(u, v);
          uint32_t* src = reinterpret_cast<uint32_t*>(m_data) + (u + (m_stride*v));
          return src[0];
      }
  private:
      void   get_uv(int& u, int& v) {
          int  uu = m_s >> 16;
          int  vv = m_t >> 16;
          if (uu < 0)
              uu = 0;
          if (uu > m_width_m1)
              uu = m_width_m1;
          if (vv < 0)
              vv = 0;
          if (vv > m_height_m1)
              vv = m_height_m1;
          u = uu;
          v = vv;
          m_s += m_ds;
          m_t += m_dt;
      }
  
      GGLfixed  m_s, m_t;
      GGLfixed  m_ds, m_dt;
      int       m_width_m1, m_height_m1;
      uint8_t*  m_data;
      int       m_stride;
  };
  
  /*
   * The 'horizontal clamp iterator' variant corresponds to the case where
   * the 'v' coordinate doesn't change. This is useful to avoid one mult and
   * extra adds / checks per pixels, if the blending/processing operation after
   * this is very fast.
   */
  static int is_context_horizontal(const context_t* c) {
      return (c->state.texture[0].iterators.dtdx == 0);
  }
  
  struct horz_clamp_iterator {
      uint16_t  get_pixel16() {
          int  u = m_s >> 16;
          m_s += m_ds;
          if (u < 0)
              u = 0;
          if (u > m_width_m1)
              u = m_width_m1;
          const uint16_t* src = reinterpret_cast<const uint16_t*>(m_data);
          return src[u];
      }
      uint32_t  get_pixel32() {
          int  u = m_s >> 16;
          m_s += m_ds;
          if (u < 0)
              u = 0;
          if (u > m_width_m1)
              u = m_width_m1;
          const uint32_t* src = reinterpret_cast<const uint32_t*>(m_data);
          return src[u];
      }
  protected:
      void init(const context_t* c, int shift);
      GGLfixed       m_s;
      GGLfixed       m_ds;
      int            m_width_m1;
      const uint8_t* m_data;
  };
  
  void horz_clamp_iterator::init(const context_t* c, int shift)
  {
      const int xs = c->iterators.xl;
      const texture_t& tx = c->state.texture[0];
      const texture_iterators_t& ti = tx.iterators;
      m_s = (xs * ti.dsdx) + ti.ydsdy;
      m_ds = ti.dsdx;
      m_width_m1 = tx.surface.width-1;
      m_data = tx.surface.data;
  
      GGLfixed t = (xs * ti.dtdx) + ti.ydtdy;
      int      v = t >> 16;
      if (v < 0)
          v = 0;
      else if (v >= (int)tx.surface.height)
          v = (int)tx.surface.height-1;
  
      m_data += (tx.surface.stride*v) << shift;
  }
  
  struct horz_clamp_iterator16 : horz_clamp_iterator {
      horz_clamp_iterator16(const context_t* c) {
          init(c,1);
      };
  };
  
  struct horz_clamp_iterator32 : horz_clamp_iterator {
      horz_clamp_iterator32(context_t* c) {
          init(c,2);
      };
  };
  
  /* This is used to perform dithering operations.
   */
  struct ditherer {
      ditherer(const context_t* c) {
          const int x = c->iterators.xl;
          const int y = c->iterators.y;
          m_line = &c->ditherMatrix[ ((y & GGL_DITHER_MASK)<<GGL_DITHER_ORDER_SHIFT) ];
          m_index = x & GGL_DITHER_MASK;
      }
      void step(void) {
          m_index++;
      }
      int  get_value(void) {
          int ret = m_line[m_index & GGL_DITHER_MASK];
          m_index++;
          return ret;
      }
      uint16_t abgr8888ToRgb565(uint32_t s) {
          uint32_t r = s & 0xff;
          uint32_t g = (s >> 8) & 0xff;
          uint32_t b = (s >> 16) & 0xff;
          return rgb888ToRgb565(r,g,b);
      }
      /* The following assumes that r/g/b are in the 0..255 range each */
      uint16_t rgb888ToRgb565(uint32_t& r, uint32_t& g, uint32_t &b) {
          int threshold = get_value();
          /* dither in on GGL_DITHER_BITS, and each of r, g, b is on 8 bits */
          r += (threshold >> (GGL_DITHER_BITS-8 +5));
          g += (threshold >> (GGL_DITHER_BITS-8 +6));
          b += (threshold >> (GGL_DITHER_BITS-8 +5));
          if (r > 0xff)
              r = 0xff;
          if (g > 0xff)
              g = 0xff;
          if (b > 0xff)
              b = 0xff;
          return uint16_t(((r & 0xf8) << 8) | ((g & 0xfc) << 3) | (b >> 3));
      }
  protected:
      const uint8_t* m_line;
      int            m_index;
  };
  
  /* This structure is used to blend (SRC_OVER) 32-bit source pixels
   * onto 16-bit destination ones. Usage is simply:
   *
   *   blender.blend(<32-bit-src-pixel-value>,<ptr-to-16-bit-dest-pixel>)
   */
  struct blender_32to16 {
      blender_32to16(context_t* c) { }
      void write(uint32_t s, uint16_t* dst) {
          if (s == 0)
              return;
          s = GGL_RGBA_TO_HOST(s);
          int sA = (s>>24);
          if (sA == 0xff) {
              *dst = convertAbgr8888ToRgb565(s);
          } else {
              int f = 0x100 - (sA + (sA>>7));
              int sR = (s >> (   3))&0x1F;
              int sG = (s >> ( 8+2))&0x3F;
              int sB = (s >> (16+3))&0x1F;
              uint16_t d = *dst;
              int dR = (d>>11)&0x1f;
              int dG = (d>>5)&0x3f;
              int dB = (d)&0x1f;
              sR += (f*dR)>>8;
              sG += (f*dG)>>8;
              sB += (f*dB)>>8;
              *dst = uint16_t((sR<<11)|(sG<<5)|sB);
          }
      }
      void write(uint32_t s, uint16_t* dst, ditherer& di) {
          if (s == 0) {
              di.step();
              return;
          }
          s = GGL_RGBA_TO_HOST(s);
          int sA = (s>>24);
          if (sA == 0xff) {
              *dst = di.abgr8888ToRgb565(s);
          } else {
              int threshold = di.get_value() << (8 - GGL_DITHER_BITS);
              int f = 0x100 - (sA + (sA>>7));
              int sR = (s >> (   3))&0x1F;
              int sG = (s >> ( 8+2))&0x3F;
              int sB = (s >> (16+3))&0x1F;
              uint16_t d = *dst;
              int dR = (d>>11)&0x1f;
              int dG = (d>>5)&0x3f;
              int dB = (d)&0x1f;
              sR = ((sR << 8) + f*dR + threshold)>>8;
              sG = ((sG << 8) + f*dG + threshold)>>8;
              sB = ((sB << 8) + f*dB + threshold)>>8;
              if (sR > 0x1f) sR = 0x1f;
              if (sG > 0x3f) sG = 0x3f;
              if (sB > 0x1f) sB = 0x1f;
              *dst = uint16_t((sR<<11)|(sG<<5)|sB);
          }
      }
  };
  
  /* This blender does the same for the 'blend_srca' operation.
   * where dstFactor=srcA*(1-srcA) srcFactor=srcA
   */
  struct blender_32to16_srcA {
      blender_32to16_srcA(const context_t* c) { }
      void write(uint32_t s, uint16_t* dst) {
          if (!s) {
              return;
          }
          uint16_t d = *dst;
          s = GGL_RGBA_TO_HOST(s);
          int sR = (s >> (   3))&0x1F;
          int sG = (s >> ( 8+2))&0x3F;
          int sB = (s >> (16+3))&0x1F;
          int sA = (s>>24);
          int f1 = (sA + (sA>>7));
          int f2 = 0x100-f1;
          int dR = (d>>11)&0x1f;
          int dG = (d>>5)&0x3f;
          int dB = (d)&0x1f;
          sR = (f1*sR + f2*dR)>>8;
          sG = (f1*sG + f2*dG)>>8;
          sB = (f1*sB + f2*dB)>>8;
          *dst = uint16_t((sR<<11)|(sG<<5)|sB);
      }
  };
  
  /* Common init code the modulating blenders */
  struct blender_modulate {
      void init(const context_t* c) {
          const int r = c->iterators.ydrdy >> (GGL_COLOR_BITS-8);
          const int g = c->iterators.ydgdy >> (GGL_COLOR_BITS-8);
          const int b = c->iterators.ydbdy >> (GGL_COLOR_BITS-8);
          const int a = c->iterators.ydady >> (GGL_COLOR_BITS-8);
          m_r = r + (r >> 7);
          m_g = g + (g >> 7);
          m_b = b + (b >> 7);
          m_a = a + (a >> 7);
      }
  protected:
      int m_r, m_g, m_b, m_a;
  };
  
  /* This blender does a normal blend after modulation.
   */
  struct blender_32to16_modulate : blender_modulate {
      blender_32to16_modulate(const context_t* c) {
          init(c);
      }
      void write(uint32_t s, uint16_t* dst) {
          // blend source and destination
          if (!s) {
              return;
          }
          s = GGL_RGBA_TO_HOST(s);
  
          /* We need to modulate s */
          uint32_t  sA = (s >> 24);
          uint32_t  sB = (s >> 16) & 0xff;
          uint32_t  sG = (s >> 8) & 0xff;
          uint32_t  sR = s & 0xff;
  
          sA = (sA*m_a) >> 8;
          /* Keep R/G/B scaled to 5.8 or 6.8 fixed float format */
          sR = (sR*m_r) >> (8 - 5);
          sG = (sG*m_g) >> (8 - 6);
          sB = (sB*m_b) >> (8 - 5);
  
          /* Now do a normal blend */
          int f = 0x100 - (sA + (sA>>7));
          uint16_t d = *dst;
          int dR = (d>>11)&0x1f;
          int dG = (d>>5)&0x3f;
          int dB = (d)&0x1f;
          sR = (sR + f*dR)>>8;
          sG = (sG + f*dG)>>8;
          sB = (sB + f*dB)>>8;
          *dst = uint16_t((sR<<11)|(sG<<5)|sB);
      }
      void write(uint32_t s, uint16_t* dst, ditherer& di) {
          // blend source and destination
          if (!s) {
              di.step();
              return;
          }
          s = GGL_RGBA_TO_HOST(s);
  
          /* We need to modulate s */
          uint32_t  sA = (s >> 24);
          uint32_t  sB = (s >> 16) & 0xff;
          uint32_t  sG = (s >> 8) & 0xff;
          uint32_t  sR = s & 0xff;
  
          sA = (sA*m_a) >> 8;
          /* keep R/G/B scaled to 5.8 or 6.8 fixed float format */
          sR = (sR*m_r) >> (8 - 5);
          sG = (sG*m_g) >> (8 - 6);
          sB = (sB*m_b) >> (8 - 5);
  
          /* Scale threshold to 0.8 fixed float format */
          int threshold = di.get_value() << (8 - GGL_DITHER_BITS);
          int f = 0x100 - (sA + (sA>>7));
          uint16_t d = *dst;
          int dR = (d>>11)&0x1f;
          int dG = (d>>5)&0x3f;
          int dB = (d)&0x1f;
          sR = (sR + f*dR + threshold)>>8;
          sG = (sG + f*dG + threshold)>>8;
          sB = (sB + f*dB + threshold)>>8;
          if (sR > 0x1f) sR = 0x1f;
          if (sG > 0x3f) sG = 0x3f;
          if (sB > 0x1f) sB = 0x1f;
          *dst = uint16_t((sR<<11)|(sG<<5)|sB);
      }
  };
  
  /* same as 32to16_modulate, except that the input is xRGB, instead of ARGB */
  struct blender_x32to16_modulate : blender_modulate {
      blender_x32to16_modulate(const context_t* c) {
          init(c);
      }
      void write(uint32_t s, uint16_t* dst) {
          s = GGL_RGBA_TO_HOST(s);
  
          uint32_t  sB = (s >> 16) & 0xff;
          uint32_t  sG = (s >> 8) & 0xff;
          uint32_t  sR = s & 0xff;
  
          /* Keep R/G/B in 5.8 or 6.8 format */
          sR = (sR*m_r) >> (8 - 5);
          sG = (sG*m_g) >> (8 - 6);
          sB = (sB*m_b) >> (8 - 5);
  
          int f = 0x100 - m_a;
          uint16_t d = *dst;
          int dR = (d>>11)&0x1f;
          int dG = (d>>5)&0x3f;
          int dB = (d)&0x1f;
          sR = (sR + f*dR)>>8;
          sG = (sG + f*dG)>>8;
          sB = (sB + f*dB)>>8;
          *dst = uint16_t((sR<<11)|(sG<<5)|sB);
      }
      void write(uint32_t s, uint16_t* dst, ditherer& di) {
          s = GGL_RGBA_TO_HOST(s);
  
          uint32_t  sB = (s >> 16) & 0xff;
          uint32_t  sG = (s >> 8) & 0xff;
          uint32_t  sR = s & 0xff;
  
          sR = (sR*m_r) >> (8 - 5);
          sG = (sG*m_g) >> (8 - 6);
          sB = (sB*m_b) >> (8 - 5);
  
          /* Now do a normal blend */
          int threshold = di.get_value() << (8 - GGL_DITHER_BITS);
          int f = 0x100 - m_a;
          uint16_t d = *dst;
          int dR = (d>>11)&0x1f;
          int dG = (d>>5)&0x3f;
          int dB = (d)&0x1f;
          sR = (sR + f*dR + threshold)>>8;
          sG = (sG + f*dG + threshold)>>8;
          sB = (sB + f*dB + threshold)>>8;
          if (sR > 0x1f) sR = 0x1f;
          if (sG > 0x3f) sG = 0x3f;
          if (sB > 0x1f) sB = 0x1f;
          *dst = uint16_t((sR<<11)|(sG<<5)|sB);
      }
  };
  
  /* Same as above, but source is 16bit rgb565 */
  struct blender_16to16_modulate : blender_modulate {
      blender_16to16_modulate(const context_t* c) {
          init(c);
      }
      void write(uint16_t s16, uint16_t* dst) {
          uint32_t  s = s16;
  
          uint32_t  sR = s >> 11;
          uint32_t  sG = (s >> 5) & 0x3f;
          uint32_t  sB = s & 0x1f;
  
          sR = (sR*m_r);
          sG = (sG*m_g);
          sB = (sB*m_b);
  
          int f = 0x100 - m_a;
          uint16_t d = *dst;
          int dR = (d>>11)&0x1f;
          int dG = (d>>5)&0x3f;
          int dB = (d)&0x1f;
          sR = (sR + f*dR)>>8;
          sG = (sG + f*dG)>>8;
          sB = (sB + f*dB)>>8;
          *dst = uint16_t((sR<<11)|(sG<<5)|sB);
      }
  };
  
  /* This is used to iterate over a 16-bit destination color buffer.
   * Usage is:
   *
   *   dst_iterator16  di(context);
   *   while (di.count--) {
   *       <do stuff with dest pixel at di.dst>
   *       di.dst++;
   *   }
   */
  struct dst_iterator16 {
      dst_iterator16(const context_t* c) {
          const int x = c->iterators.xl;
          const int width = c->iterators.xr - x;
          const int32_t y = c->iterators.y;
          const surface_t* cb = &(c->state.buffers.color);
          count = width;
          dst = reinterpret_cast<uint16_t*>(cb->data) + (x+(cb->stride*y));
      }
      int        count;
      uint16_t*  dst;
  };
  
  
  static void scanline_t32cb16_clamp(context_t* c)
  {
      dst_iterator16  di(c);
  
      if (is_context_horizontal(c)) {
          /* Special case for simple horizontal scaling */
          horz_clamp_iterator32 ci(c);
          while (di.count--) {
              uint32_t s = ci.get_pixel32();
              *di.dst++ = convertAbgr8888ToRgb565(s);
          }
      } else {
          /* General case */
          clamp_iterator ci(c);
          while (di.count--) {
              uint32_t s = ci.get_pixel32();
              *di.dst++ = convertAbgr8888ToRgb565(s);
          }
      }
  }
  
  static void scanline_t32cb16_dither(context_t* c)
  {
      horz_iterator32 si(c);
      dst_iterator16  di(c);
      ditherer        dither(c);
  
      while (di.count--) {
          uint32_t s = si.get_pixel32();
          *di.dst++ = dither.abgr8888ToRgb565(s);
      }
  }
  
  static void scanline_t32cb16_clamp_dither(context_t* c)
  {
      dst_iterator16  di(c);
      ditherer        dither(c);
  
      if (is_context_horizontal(c)) {
          /* Special case for simple horizontal scaling */
          horz_clamp_iterator32 ci(c);
          while (di.count--) {
              uint32_t s = ci.get_pixel32();
              *di.dst++ = dither.abgr8888ToRgb565(s);
          }
      } else {
          /* General case */
          clamp_iterator ci(c);
          while (di.count--) {
              uint32_t s = ci.get_pixel32();
              *di.dst++ = dither.abgr8888ToRgb565(s);
          }
      }
  }
  
  static void scanline_t32cb16blend_dither(context_t* c)
  {
      dst_iterator16 di(c);
      ditherer       dither(c);
      blender_32to16 bl(c);
      horz_iterator32  hi(c);
      while (di.count--) {
          uint32_t s = hi.get_pixel32();
          bl.write(s, di.dst, dither);
          di.dst++;
      }
  }
  
  static void scanline_t32cb16blend_clamp(context_t* c)
  {
      dst_iterator16  di(c);
      blender_32to16  bl(c);
  
      if (is_context_horizontal(c)) {
          horz_clamp_iterator32 ci(c);
          while (di.count--) {
              uint32_t s = ci.get_pixel32();
              bl.write(s, di.dst);
              di.dst++;
          }
      } else {
          clamp_iterator ci(c);
          while (di.count--) {
              uint32_t s = ci.get_pixel32();
              bl.write(s, di.dst);
              di.dst++;
          }
      }
  }
  
  static void scanline_t32cb16blend_clamp_dither(context_t* c)
  {
      dst_iterator16 di(c);
      ditherer       dither(c);
      blender_32to16 bl(c);
  
      clamp_iterator ci(c);
      while (di.count--) {
          uint32_t s = ci.get_pixel32();
          bl.write(s, di.dst, dither);
          di.dst++;
      }
  }
  
  void scanline_t32cb16blend_clamp_mod(context_t* c)
  {
      dst_iterator16 di(c);
      blender_32to16_modulate bl(c);
  
      clamp_iterator ci(c);
      while (di.count--) {
          uint32_t s = ci.get_pixel32();
          bl.write(s, di.dst);
          di.dst++;
      }
  }
  
  void scanline_t32cb16blend_clamp_mod_dither(context_t* c)
  {
      dst_iterator16 di(c);
      blender_32to16_modulate bl(c);
      ditherer dither(c);
  
      clamp_iterator ci(c);
      while (di.count--) {
          uint32_t s = ci.get_pixel32();
          bl.write(s, di.dst, dither);
          di.dst++;
      }
  }
  
  /* Variant of scanline_t32cb16blend_clamp_mod with a xRGB texture */
  void scanline_x32cb16blend_clamp_mod(context_t* c)
  {
      dst_iterator16 di(c);
      blender_x32to16_modulate  bl(c);
  
      clamp_iterator ci(c);
      while (di.count--) {
          uint32_t s = ci.get_pixel32();
          bl.write(s, di.dst);
          di.dst++;
      }
  }
  
  void scanline_x32cb16blend_clamp_mod_dither(context_t* c)
  {
      dst_iterator16 di(c);
      blender_x32to16_modulate  bl(c);
      ditherer dither(c);
  
      clamp_iterator ci(c);
      while (di.count--) {
          uint32_t s = ci.get_pixel32();
          bl.write(s, di.dst, dither);
          di.dst++;
      }
  }
  
  void scanline_t16cb16_clamp(context_t* c)
  {
      dst_iterator16  di(c);
  
      /* Special case for simple horizontal scaling */
      if (is_context_horizontal(c)) {
          horz_clamp_iterator16 ci(c);
          while (di.count--) {
              *di.dst++ = ci.get_pixel16();
          }
      } else {
          clamp_iterator ci(c);
          while (di.count--) {
              *di.dst++ = ci.get_pixel16();
          }
      }
  }
  
  
  
  template <typename T, typename U>
  static inline __attribute__((const))
  T interpolate(int y, T v0, U dvdx, U dvdy) {
      // interpolates in pixel's centers
      // v = v0 + (y + 0.5) * dvdy + (0.5 * dvdx)
      return (y * dvdy) + (v0 + ((dvdy + dvdx) >> 1));
  }
  
  // ----------------------------------------------------------------------------
  #if 0
  #pragma mark -
  #endif
  
  void init_y(context_t* c, int32_t ys)
  {
      const uint32_t enables = c->state.enables;
  
      // compute iterators...
      iterators_t& ci = c->iterators;
      
      // sample in the center
      ci.y = ys;
  
      if (enables & (GGL_ENABLE_DEPTH_TEST|GGL_ENABLE_W|GGL_ENABLE_FOG)) {
          ci.ydzdy = interpolate(ys, c->shade.z0, c->shade.dzdx, c->shade.dzdy);
          ci.ydwdy = interpolate(ys, c->shade.w0, c->shade.dwdx, c->shade.dwdy);
          ci.ydfdy = interpolate(ys, c->shade.f0, c->shade.dfdx, c->shade.dfdy);
      }
  
      if (ggl_unlikely(enables & GGL_ENABLE_SMOOTH)) {
          ci.ydrdy = interpolate(ys, c->shade.r0, c->shade.drdx, c->shade.drdy);
          ci.ydgdy = interpolate(ys, c->shade.g0, c->shade.dgdx, c->shade.dgdy);
          ci.ydbdy = interpolate(ys, c->shade.b0, c->shade.dbdx, c->shade.dbdy);
          ci.ydady = interpolate(ys, c->shade.a0, c->shade.dadx, c->shade.dady);
          c->step_y = step_y__smooth;
      } else {
          ci.ydrdy = c->shade.r0;
          ci.ydgdy = c->shade.g0;
          ci.ydbdy = c->shade.b0;
          ci.ydady = c->shade.a0;
          // XXX: do only if needed, or make sure this is fast
          c->packed = ggl_pack_color(c, c->state.buffers.color.format,
                  ci.ydrdy, ci.ydgdy, ci.ydbdy, ci.ydady);
          c->packed8888 = ggl_pack_color(c, GGL_PIXEL_FORMAT_RGBA_8888, 
                  ci.ydrdy, ci.ydgdy, ci.ydbdy, ci.ydady);
      }
  
      // initialize the variables we need in the shader
      generated_vars_t& gen = c->generated_vars;
      gen.argb[GGLFormat::ALPHA].c  = ci.ydady;
      gen.argb[GGLFormat::ALPHA].dx = c->shade.dadx;
      gen.argb[GGLFormat::RED  ].c  = ci.ydrdy;
      gen.argb[GGLFormat::RED  ].dx = c->shade.drdx;
      gen.argb[GGLFormat::GREEN].c  = ci.ydgdy;
      gen.argb[GGLFormat::GREEN].dx = c->shade.dgdx;
      gen.argb[GGLFormat::BLUE ].c  = ci.ydbdy;
      gen.argb[GGLFormat::BLUE ].dx = c->shade.dbdx;
      gen.dzdx = c->shade.dzdx;
      gen.f    = ci.ydfdy;
      gen.dfdx = c->shade.dfdx;
  
      if (enables & GGL_ENABLE_TMUS) {
          for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
              texture_t& t = c->state.texture[i];
              if (!t.enable) continue;
  
              texture_iterators_t& ti = t.iterators;
              if (t.s_coord == GGL_ONE_TO_ONE && t.t_coord == GGL_ONE_TO_ONE) {
                  // we need to set all of these to 0 because in some cases
                  // step_y__generic() or step_y__tmu() will be used and
                  // therefore will update dtdy, however, in 1:1 mode
                  // this is always done by the scanline rasterizer.
                  ti.dsdx = ti.dsdy = ti.dtdx = ti.dtdy = 0;
                  ti.ydsdy = t.shade.is0;
                  ti.ydtdy = t.shade.it0;
              } else {
                  const int adjustSWrap = ((t.s_wrap==GGL_CLAMP)?0:16);
                  const int adjustTWrap = ((t.t_wrap==GGL_CLAMP)?0:16);
                  ti.sscale = t.shade.sscale + adjustSWrap;
                  ti.tscale = t.shade.tscale + adjustTWrap;
                  if (!(enables & GGL_ENABLE_W)) {
                      // S coordinate
                      const int32_t sscale = ti.sscale;
                      const int32_t sy = interpolate(ys,
                              t.shade.is0, t.shade.idsdx, t.shade.idsdy);
                      if (sscale>=0) {
                          ti.ydsdy= sy            << sscale;
                          ti.dsdx = t.shade.idsdx << sscale; 
                          ti.dsdy = t.shade.idsdy << sscale;
                      } else {
                          ti.ydsdy= sy            >> -sscale;
                          ti.dsdx = t.shade.idsdx >> -sscale; 
                          ti.dsdy = t.shade.idsdy >> -sscale;
                      }
                      // T coordinate
                      const int32_t tscale = ti.tscale;
                      const int32_t ty = interpolate(ys,
                              t.shade.it0, t.shade.idtdx, t.shade.idtdy);
                      if (tscale>=0) {
                          ti.ydtdy= ty            << tscale;
                          ti.dtdx = t.shade.idtdx << tscale; 
                          ti.dtdy = t.shade.idtdy << tscale;
                      } else {
                          ti.ydtdy= ty            >> -tscale;
                          ti.dtdx = t.shade.idtdx >> -tscale; 
                          ti.dtdy = t.shade.idtdy >> -tscale;
                      }
                  }
              }
              // mirror for generated code...
              generated_tex_vars_t& gen = c->generated_vars.texture[i];
              gen.width   = t.surface.width;
              gen.height  = t.surface.height;
              gen.stride  = t.surface.stride;
              gen.data    = int32_t(t.surface.data);
              gen.dsdx = ti.dsdx;
              gen.dtdx = ti.dtdx;
          }
      }
  
      // choose the y-stepper
      c->step_y = step_y__nop;
      if (enables & GGL_ENABLE_FOG) {
          c->step_y = step_y__generic;
      } else if (enables & GGL_ENABLE_TMUS) {
          if (enables & GGL_ENABLE_SMOOTH) {
              c->step_y = step_y__generic;
          } else if (enables & GGL_ENABLE_W) {
              c->step_y = step_y__w;
          } else {
              c->step_y = step_y__tmu;
          }
      } else {
          if (enables & GGL_ENABLE_SMOOTH) {
              c->step_y = step_y__smooth;
          }
      }
      
      // choose the rectangle blitter
      c->rect = rect_generic;
      if ((c->step_y == step_y__nop) &&
          (c->scanline == scanline_memcpy))
      {
          c->rect = rect_memcpy;
      }
  }
  
  void init_y_packed(context_t* c, int32_t y0)
  {
      uint8_t f = c->state.buffers.color.format;
      c->packed = ggl_pack_color(c, f,
              c->shade.r0, c->shade.g0, c->shade.b0, c->shade.a0);
      c->packed8888 = ggl_pack_color(c, GGL_PIXEL_FORMAT_RGBA_8888,
              c->shade.r0, c->shade.g0, c->shade.b0, c->shade.a0);
      c->iterators.y = y0;
      c->step_y = step_y__nop;
      // choose the rectangle blitter
      c->rect = rect_generic;
      if (c->scanline == scanline_memcpy) {
          c->rect = rect_memcpy;
      }
  }
  
  void init_y_noop(context_t* c, int32_t y0)
  {
      c->iterators.y = y0;
      c->step_y = step_y__nop;
      // choose the rectangle blitter
      c->rect = rect_generic;
      if (c->scanline == scanline_memcpy) {
          c->rect = rect_memcpy;
      }
  }
  
  void init_y_error(context_t* c, int32_t y0)
  {
      // woooops, shoud never happen,
      // fail gracefully (don't display anything)
      init_y_noop(c, y0);
      ALOGE("color-buffer has an invalid format!");
  }
  
  // ----------------------------------------------------------------------------
  #if 0
  #pragma mark -
  #endif
  
  void step_y__generic(context_t* c)
  {
      const uint32_t enables = c->state.enables;
  
      // iterate...
      iterators_t& ci = c->iterators;
      ci.y += 1;
                  
      if (enables & GGL_ENABLE_SMOOTH) {
          ci.ydrdy += c->shade.drdy;
          ci.ydgdy += c->shade.dgdy;
          ci.ydbdy += c->shade.dbdy;
          ci.ydady += c->shade.dady;
      }
  
      const uint32_t mask =
              GGL_ENABLE_DEPTH_TEST |
              GGL_ENABLE_W |
              GGL_ENABLE_FOG;
      if (enables & mask) {
          ci.ydzdy += c->shade.dzdy;
          ci.ydwdy += c->shade.dwdy;
          ci.ydfdy += c->shade.dfdy;
      }
  
      if ((enables & GGL_ENABLE_TMUS) && (!(enables & GGL_ENABLE_W))) {
          for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
              if (c->state.texture[i].enable) {
                  texture_iterators_t& ti = c->state.texture[i].iterators;
                  ti.ydsdy += ti.dsdy;
                  ti.ydtdy += ti.dtdy;
              }
          }
      }
  }
  
  void step_y__nop(context_t* c)
  {
      c->iterators.y += 1;
      c->iterators.ydzdy += c->shade.dzdy;
  }
  
  void step_y__smooth(context_t* c)
  {
      iterators_t& ci = c->iterators;
      ci.y += 1;
      ci.ydrdy += c->shade.drdy;
      ci.ydgdy += c->shade.dgdy;
      ci.ydbdy += c->shade.dbdy;
      ci.ydady += c->shade.dady;
      ci.ydzdy += c->shade.dzdy;
  }
  
  void step_y__w(context_t* c)
  {
      iterators_t& ci = c->iterators;
      ci.y += 1;
      ci.ydzdy += c->shade.dzdy;
      ci.ydwdy += c->shade.dwdy;
  }
  
  void step_y__tmu(context_t* c)
  {
      iterators_t& ci = c->iterators;
      ci.y += 1;
      ci.ydzdy += c->shade.dzdy;
      for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
          if (c->state.texture[i].enable) {
              texture_iterators_t& ti = c->state.texture[i].iterators;
              ti.ydsdy += ti.dsdy;
              ti.ydtdy += ti.dtdy;
          }
      }
  }
  
  // ----------------------------------------------------------------------------
  #if 0
  #pragma mark -
  #endif
  
  void scanline_perspective(context_t* c)
  {
      struct {
          union {
              struct {
                  int32_t s, sq;
                  int32_t t, tq;
              };
              struct {
                  int32_t v, q;
              } st[2];
          };
      } tc[GGL_TEXTURE_UNIT_COUNT] __attribute__((aligned(16)));
  
      // XXX: we should have a special case when dwdx = 0
  
      // 32 pixels spans works okay. 16 is a lot better,
      // but hey, it's a software renderer...
      const uint32_t SPAN_BITS = 5; 
      const uint32_t ys = c->iterators.y;
      const uint32_t xs = c->iterators.xl;
      const uint32_t x1 = c->iterators.xr;
  	const uint32_t xc = x1 - xs;
      uint32_t remainder = xc & ((1<<SPAN_BITS)-1);
      uint32_t numSpans = xc >> SPAN_BITS;
  
      const iterators_t& ci = c->iterators;
      int32_t w0 = (xs * c->shade.dwdx) + ci.ydwdy;
      int32_t q0 = gglRecipQ(w0, 30);
      const int iwscale = 32 - gglClz(q0);
  
      const int32_t dwdx = c->shade.dwdx << SPAN_BITS;
      int32_t xl = c->iterators.xl;
  
      // We process s & t with a loop to reduce the code size
      // (and i-cache pressure).
  
      for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
          const texture_t& tmu = c->state.texture[i];
          if (!tmu.enable) continue;
          int32_t s =   tmu.shade.is0 +
                       (tmu.shade.idsdy * ys) + (tmu.shade.idsdx * xs) +
                       ((tmu.shade.idsdx + tmu.shade.idsdy)>>1);
          int32_t t =   tmu.shade.it0 +
                       (tmu.shade.idtdy * ys) + (tmu.shade.idtdx * xs) +
                       ((tmu.shade.idtdx + tmu.shade.idtdy)>>1);
          tc[i].s  = s;
          tc[i].t  = t;
          tc[i].sq = gglMulx(s, q0, iwscale);
          tc[i].tq = gglMulx(t, q0, iwscale);
      }
  
      int32_t span = 0;
      do {
          int32_t w1;
          if (ggl_likely(numSpans)) {
              w1 = w0 + dwdx;
          } else {
              if (remainder) {
                  // finish off the scanline...
                  span = remainder;
                  w1 = (c->shade.dwdx * span) + w0;
              } else {
                  break;
              }
          }
          int32_t q1 = gglRecipQ(w1, 30);
          for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
              texture_t& tmu = c->state.texture[i];
              if (!tmu.enable) continue;
              texture_iterators_t& ti = tmu.iterators;
  
              for (int j=0 ; j<2 ; j++) {
                  int32_t v = tc[i].st[j].v;
                  if (span)   v += (tmu.shade.st[j].dx)*span;
                  else        v += (tmu.shade.st[j].dx)<<SPAN_BITS;
                  const int32_t v0 = tc[i].st[j].q;
                  const int32_t v1 = gglMulx(v, q1, iwscale);
                  int32_t dvdx = v1 - v0;
                  if (span)   dvdx /= span;
                  else        dvdx >>= SPAN_BITS;
                  tc[i].st[j].v = v;
                  tc[i].st[j].q = v1;
  
                  const int scale = ti.st[j].scale + (iwscale - 30);
                  if (scale >= 0) {
                      ti.st[j].ydvdy = v0   << scale;
                      ti.st[j].dvdx  = dvdx << scale;
                  } else {
                      ti.st[j].ydvdy = v0   >> -scale;
                      ti.st[j].dvdx  = dvdx >> -scale;
                  }
              }
              generated_tex_vars_t& gen = c->generated_vars.texture[i];
              gen.dsdx = ti.st[0].dvdx;
              gen.dtdx = ti.st[1].dvdx;
          }
          c->iterators.xl = xl;
          c->iterators.xr = xl = xl + (span ? span : (1<<SPAN_BITS));
          w0 = w1;
          q0 = q1;
          c->span(c);
      } while(numSpans--);
  }
  
  void scanline_perspective_single(context_t* c)
  {
      // 32 pixels spans works okay. 16 is a lot better,
      // but hey, it's a software renderer...
      const uint32_t SPAN_BITS = 5; 
      const uint32_t ys = c->iterators.y;
      const uint32_t xs = c->iterators.xl;
      const uint32_t x1 = c->iterators.xr;
  	const uint32_t xc = x1 - xs;
  
      const iterators_t& ci = c->iterators;
      int32_t w = (xs * c->shade.dwdx) + ci.ydwdy;
      int32_t iw = gglRecipQ(w, 30);
      const int iwscale = 32 - gglClz(iw);
  
      const int i = 31 - gglClz(c->state.enabled_tmu);
      generated_tex_vars_t& gen = c->generated_vars.texture[i];
      texture_t& tmu = c->state.texture[i];
      texture_iterators_t& ti = tmu.iterators;
      const int sscale = ti.sscale + (iwscale - 30);
      const int tscale = ti.tscale + (iwscale - 30);
      int32_t s =   tmu.shade.is0 +
                   (tmu.shade.idsdy * ys) + (tmu.shade.idsdx * xs) +
                   ((tmu.shade.idsdx + tmu.shade.idsdy)>>1);
      int32_t t =   tmu.shade.it0 +
                   (tmu.shade.idtdy * ys) + (tmu.shade.idtdx * xs) +
                   ((tmu.shade.idtdx + tmu.shade.idtdy)>>1);
      int32_t s0 = gglMulx(s, iw, iwscale);
      int32_t t0 = gglMulx(t, iw, iwscale);
      int32_t xl = c->iterators.xl;
  
      int32_t sq, tq, dsdx, dtdx;
      int32_t premainder = xc & ((1<<SPAN_BITS)-1);
      uint32_t numSpans = xc >> SPAN_BITS;
      if (c->shade.dwdx == 0) {
          // XXX: we could choose to do this if the error is small enough
          numSpans = 0;
          premainder = xc;
          goto no_perspective;
      }
  
      if (premainder) {
          w += c->shade.dwdx   * premainder;
          iw = gglRecipQ(w, 30);
  no_perspective:        
          s += tmu.shade.idsdx * premainder;
          t += tmu.shade.idtdx * premainder;
          sq = gglMulx(s, iw, iwscale);
          tq = gglMulx(t, iw, iwscale);
          dsdx = (sq - s0) / premainder;
          dtdx = (tq - t0) / premainder;
          c->iterators.xl = xl;
          c->iterators.xr = xl = xl + premainder;
          goto finish;
      }
  
      while (numSpans--) {
          w += c->shade.dwdx   << SPAN_BITS;
          s += tmu.shade.idsdx << SPAN_BITS;
          t += tmu.shade.idtdx << SPAN_BITS;
          iw = gglRecipQ(w, 30);
          sq = gglMulx(s, iw, iwscale);
          tq = gglMulx(t, iw, iwscale);
          dsdx = (sq - s0) >> SPAN_BITS;
          dtdx = (tq - t0) >> SPAN_BITS;
          c->iterators.xl = xl;
          c->iterators.xr = xl = xl + (1<<SPAN_BITS);
  finish:
          if (sscale >= 0) {
              ti.ydsdy = s0   << sscale;
              ti.dsdx  = dsdx << sscale;
          } else {
              ti.ydsdy = s0   >>-sscale;
              ti.dsdx  = dsdx >>-sscale;
          }
          if (tscale >= 0) {
              ti.ydtdy = t0   << tscale;
              ti.dtdx  = dtdx << tscale;
          } else {
              ti.ydtdy = t0   >>-tscale;
              ti.dtdx  = dtdx >>-tscale;
          }
          s0 = sq;
          t0 = tq;
          gen.dsdx = ti.dsdx;
          gen.dtdx = ti.dtdx;
          c->span(c);
      }
  }
  
  // ----------------------------------------------------------------------------
  
  void scanline_col32cb16blend(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      union {
          uint16_t* dst;
          uint32_t* dst32;
      };
      dst = reinterpret_cast<uint16_t*>(cb->data) + (x+(cb->stride*y));
  
  #if ((ANDROID_CODEGEN >= ANDROID_CODEGEN_ASM) && defined(__arm__))
  #if defined(__ARM_HAVE_NEON) && BYTE_ORDER == LITTLE_ENDIAN
      scanline_col32cb16blend_neon(dst, &(c->packed8888), ct);
  #else  // defined(__ARM_HAVE_NEON) && BYTE_ORDER == LITTLE_ENDIAN
      scanline_col32cb16blend_arm(dst, GGL_RGBA_TO_HOST(c->packed8888), ct);
  #endif // defined(__ARM_HAVE_NEON) && BYTE_ORDER == LITTLE_ENDIAN
  #else
      uint32_t s = GGL_RGBA_TO_HOST(c->packed8888);
      int sA = (s>>24);
      int f = 0x100 - (sA + (sA>>7));
      while (ct--) {
          uint16_t d = *dst;
          int dR = (d>>11)&0x1f;
          int dG = (d>>5)&0x3f;
          int dB = (d)&0x1f;
          int sR = (s >> (   3))&0x1F;
          int sG = (s >> ( 8+2))&0x3F;
          int sB = (s >> (16+3))&0x1F;
          sR += (f*dR)>>8;
          sG += (f*dG)>>8;
          sB += (f*dB)>>8;
          *dst++ = uint16_t((sR<<11)|(sG<<5)|sB);
      }
  #endif
  
  }
  
  void scanline_t32cb16(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;    
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      union {
          uint16_t* dst;
          uint32_t* dst32;
      };
      dst = reinterpret_cast<uint16_t*>(cb->data) + (x+(cb->stride*y));
  
      surface_t* tex = &(c->state.texture[0].surface);
      const int32_t u = (c->state.texture[0].shade.is0>>16) + x;
      const int32_t v = (c->state.texture[0].shade.it0>>16) + y;
      uint32_t *src = reinterpret_cast<uint32_t*>(tex->data)+(u+(tex->stride*v));
      int sR, sG, sB;
      uint32_t s, d;
  
      if (ct==1 || uint32_t(dst)&2) {
  last_one:
          s = GGL_RGBA_TO_HOST( *src++ );
          *dst++ = convertAbgr8888ToRgb565(s);
          ct--;
      }
  
      while (ct >= 2) {
  #if BYTE_ORDER == BIG_ENDIAN
          s = GGL_RGBA_TO_HOST( *src++ );
          d = convertAbgr8888ToRgb565_hi16(s);
  
          s = GGL_RGBA_TO_HOST( *src++ );
          d |= convertAbgr8888ToRgb565(s);
  #else
          s = GGL_RGBA_TO_HOST( *src++ );
          d = convertAbgr8888ToRgb565(s);
  
          s = GGL_RGBA_TO_HOST( *src++ );
          d |= convertAbgr8888ToRgb565(s) << 16;
  #endif
          *dst32++ = d;
          ct -= 2;
      }
      
      if (ct > 0) {
          goto last_one;
      }
  }
  
  void scanline_t32cb16blend(context_t* c)
  {
  #if ((ANDROID_CODEGEN >= ANDROID_CODEGEN_ASM) && defined(__arm__))
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      uint16_t* dst = reinterpret_cast<uint16_t*>(cb->data) + (x+(cb->stride*y));
  
      surface_t* tex = &(c->state.texture[0].surface);
      const int32_t u = (c->state.texture[0].shade.is0>>16) + x;
      const int32_t v = (c->state.texture[0].shade.it0>>16) + y;
      uint32_t *src = reinterpret_cast<uint32_t*>(tex->data)+(u+(tex->stride*v));
  
      scanline_t32cb16blend_arm(dst, src, ct);
  #else
      dst_iterator16  di(c);
      horz_iterator32  hi(c);
      blender_32to16  bl(c);
      while (di.count--) {
          uint32_t s = hi.get_pixel32();
          bl.write(s, di.dst);
          di.dst++;
      }
  #endif
  }
  
  void scanline_t32cb16blend_srca(context_t* c)
  {
      dst_iterator16  di(c);
      horz_iterator32  hi(c);
      blender_32to16_srcA  blender(c);
  
      while (di.count--) {
          uint32_t s = hi.get_pixel32();
          blender.write(s,di.dst);
          di.dst++;
      }
  }
  
  void scanline_t16cb16blend_clamp_mod(context_t* c)
  {
      const int a = c->iterators.ydady >> (GGL_COLOR_BITS-8);
      if (a == 0) {
          return;
      }
  
      if (a == 255) {
          scanline_t16cb16_clamp(c);
          return;
      }
  
      dst_iterator16  di(c);
      blender_16to16_modulate  blender(c);
      clamp_iterator  ci(c);
  
      while (di.count--) {
          uint16_t s = ci.get_pixel16();
          blender.write(s, di.dst);
          di.dst++;
      }
  }
  
  void scanline_memcpy(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      const GGLFormat* fp = &(c->formats[cb->format]);
      uint8_t* dst = reinterpret_cast<uint8_t*>(cb->data) +
                              (x + (cb->stride * y)) * fp->size;
  
      surface_t* tex = &(c->state.texture[0].surface);
      const int32_t u = (c->state.texture[0].shade.is0>>16) + x;
      const int32_t v = (c->state.texture[0].shade.it0>>16) + y;
      uint8_t *src = reinterpret_cast<uint8_t*>(tex->data) +
                              (u + (tex->stride * v)) * fp->size;
  
      const size_t size = ct * fp->size;
      memcpy(dst, src, size);
  }
  
  void scanline_memset8(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      uint8_t* dst = reinterpret_cast<uint8_t*>(cb->data) + (x+(cb->stride*y));
      uint32_t packed = c->packed;
      memset(dst, packed, ct);
  }
  
  void scanline_memset16(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      uint16_t* dst = reinterpret_cast<uint16_t*>(cb->data) + (x+(cb->stride*y));
      uint32_t packed = c->packed;
      android_memset16(dst, packed, ct*2);
  }
  
  void scanline_memset32(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      uint32_t* dst = reinterpret_cast<uint32_t*>(cb->data) + (x+(cb->stride*y));
      uint32_t packed = GGL_HOST_TO_RGBA(c->packed);
      android_memset32(dst, packed, ct*4);
  }
  
  void scanline_clear(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      const GGLFormat* fp = &(c->formats[cb->format]);
      uint8_t* dst = reinterpret_cast<uint8_t*>(cb->data) +
                              (x + (cb->stride * y)) * fp->size;
      const size_t size = ct * fp->size;
      memset(dst, 0, size);
  }
  
  void scanline_set(context_t* c)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      const GGLFormat* fp = &(c->formats[cb->format]);
      uint8_t* dst = reinterpret_cast<uint8_t*>(cb->data) +
                              (x + (cb->stride * y)) * fp->size;
      const size_t size = ct * fp->size;
      memset(dst, 0xFF, size);
  }
  
  void scanline_noop(context_t* c)
  {
  }
  
  void rect_generic(context_t* c, size_t yc)
  {
      do {
          c->scanline(c);
          c->step_y(c);
      } while (--yc);
  }
  
  void rect_memcpy(context_t* c, size_t yc)
  {
      int32_t x = c->iterators.xl;
      size_t ct = c->iterators.xr - x;
      int32_t y = c->iterators.y;
      surface_t* cb = &(c->state.buffers.color);
      const GGLFormat* fp = &(c->formats[cb->format]);
      uint8_t* dst = reinterpret_cast<uint8_t*>(cb->data) +
                              (x + (cb->stride * y)) * fp->size;
  
      surface_t* tex = &(c->state.texture[0].surface);
      const int32_t u = (c->state.texture[0].shade.is0>>16) + x;
      const int32_t v = (c->state.texture[0].shade.it0>>16) + y;
      uint8_t *src = reinterpret_cast<uint8_t*>(tex->data) +
                              (u + (tex->stride * v)) * fp->size;
  
      if (cb->stride == tex->stride && ct == size_t(cb->stride)) {
          memcpy(dst, src, ct * fp->size * yc);
      } else {
          const size_t size = ct * fp->size;
          const size_t dbpr = cb->stride  * fp->size;
          const size_t sbpr = tex->stride * fp->size;
          do {
              memcpy(dst, src, size);
              dst += dbpr;
              src += sbpr;        
          } while (--yc);
      }
  }
  // ----------------------------------------------------------------------------
  }; // namespace android
  
  