text: /*
   * Mesa 3-D graphics library
   *
   * Copyright (C) 1999-2008  Brian Paul   All Rights Reserved.
   * Copyright (C) 2009  VMware, Inc.  All Rights Reserved.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a
   * copy of this software and associated documentation files (the "Software"),
   * to deal in the Software without restriction, including without limitation
   * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   * and/or sell copies of the Software, and to permit persons to whom the
   * Software is furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included
   * in all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
   * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
   * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
   * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
   * OTHER DEALINGS IN THE SOFTWARE.
   */
  
  
  /**
   * \file swrast/s_span.c
   * \brief Span processing functions used by all rasterization functions.
   * This is where all the per-fragment tests are performed
   * \author Brian Paul
   */
  
  #include "c99_math.h"
  #include "main/glheader.h"
  #include "main/format_pack.h"
  #include "main/format_unpack.h"
  #include "main/macros.h"
  #include "main/imports.h"
  #include "main/image.h"
  #include "main/samplerobj.h"
  #include "main/teximage.h"
  
  #include "s_atifragshader.h"
  #include "s_alpha.h"
  #include "s_blend.h"
  #include "s_context.h"
  #include "s_depth.h"
  #include "s_fog.h"
  #include "s_logic.h"
  #include "s_masking.h"
  #include "s_fragprog.h"
  #include "s_span.h"
  #include "s_stencil.h"
  #include "s_texcombine.h"
  
  #include <stdbool.h>
  
  /**
   * Set default fragment attributes for the span using the
   * current raster values.  Used prior to glDraw/CopyPixels
   * and glBitmap.
   */
  void
  _swrast_span_default_attribs(struct gl_context *ctx, SWspan *span)
  {
     GLchan r, g, b, a;
     /* Z*/
     {
        const GLfloat depthMax = ctx->DrawBuffer->_DepthMaxF;
        if (ctx->DrawBuffer->Visual.depthBits <= 16)
           span->z = FloatToFixed(ctx->Current.RasterPos[2] * depthMax + 0.5F);
        else {
           GLfloat tmpf = ctx->Current.RasterPos[2] * depthMax; 
           tmpf = MIN2(tmpf, depthMax);
           span->z = (GLint)tmpf;
        }
        span->zStep = 0;
        span->interpMask |= SPAN_Z;
     }
  
     /* W (for perspective correction) */
     span->attrStart[VARYING_SLOT_POS][3] = 1.0;
     span->attrStepX[VARYING_SLOT_POS][3] = 0.0;
     span->attrStepY[VARYING_SLOT_POS][3] = 0.0;
  
     /* primary color, or color index */
     UNCLAMPED_FLOAT_TO_CHAN(r, ctx->Current.RasterColor[0]);
     UNCLAMPED_FLOAT_TO_CHAN(g, ctx->Current.RasterColor[1]);
     UNCLAMPED_FLOAT_TO_CHAN(b, ctx->Current.RasterColor[2]);
     UNCLAMPED_FLOAT_TO_CHAN(a, ctx->Current.RasterColor[3]);
  #if CHAN_TYPE == GL_FLOAT
     span->red = r;
     span->green = g;
     span->blue = b;
     span->alpha = a;
  #else
     span->red   = IntToFixed(r);
     span->green = IntToFixed(g);
     span->blue  = IntToFixed(b);
     span->alpha = IntToFixed(a);
  #endif
     span->redStep = 0;
     span->greenStep = 0;
     span->blueStep = 0;
     span->alphaStep = 0;
     span->interpMask |= SPAN_RGBA;
  
     COPY_4V(span->attrStart[VARYING_SLOT_COL0], ctx->Current.RasterColor);
     ASSIGN_4V(span->attrStepX[VARYING_SLOT_COL0], 0.0, 0.0, 0.0, 0.0);
     ASSIGN_4V(span->attrStepY[VARYING_SLOT_COL0], 0.0, 0.0, 0.0, 0.0);
  
     /* Secondary color */
     if (ctx->Light.Enabled || ctx->Fog.ColorSumEnabled)
     {
        COPY_4V(span->attrStart[VARYING_SLOT_COL1], ctx->Current.RasterSecondaryColor);
        ASSIGN_4V(span->attrStepX[VARYING_SLOT_COL1], 0.0, 0.0, 0.0, 0.0);
        ASSIGN_4V(span->attrStepY[VARYING_SLOT_COL1], 0.0, 0.0, 0.0, 0.0);
     }
  
     /* fog */
     {
        const SWcontext *swrast = SWRAST_CONTEXT(ctx);
        GLfloat fogVal; /* a coord or a blend factor */
        if (swrast->_PreferPixelFog) {
           /* fog blend factors will be computed from fog coordinates per pixel */
           fogVal = ctx->Current.RasterDistance;
        }
        else {
           /* fog blend factor should be computed from fogcoord now */
           fogVal = _swrast_z_to_fogfactor(ctx, ctx->Current.RasterDistance);
        }
        span->attrStart[VARYING_SLOT_FOGC][0] = fogVal;
        span->attrStepX[VARYING_SLOT_FOGC][0] = 0.0;
        span->attrStepY[VARYING_SLOT_FOGC][0] = 0.0;
     }
  
     /* texcoords */
     {
        GLuint i;
        for (i = 0; i < ctx->Const.MaxTextureCoordUnits; i++) {
           const GLuint attr = VARYING_SLOT_TEX0 + i;
           const GLfloat *tc = ctx->Current.RasterTexCoords[i];
           if (_swrast_use_fragment_program(ctx) ||
               ctx->ATIFragmentShader._Enabled) {
              COPY_4V(span->attrStart[attr], tc);
           }
           else if (tc[3] > 0.0F) {
              /* use (s/q, t/q, r/q, 1) */
              span->attrStart[attr][0] = tc[0] / tc[3];
              span->attrStart[attr][1] = tc[1] / tc[3];
              span->attrStart[attr][2] = tc[2] / tc[3];
              span->attrStart[attr][3] = 1.0;
           }
           else {
              ASSIGN_4V(span->attrStart[attr], 0.0F, 0.0F, 0.0F, 1.0F);
           }
           ASSIGN_4V(span->attrStepX[attr], 0.0F, 0.0F, 0.0F, 0.0F);
           ASSIGN_4V(span->attrStepY[attr], 0.0F, 0.0F, 0.0F, 0.0F);
        }
     }
  }
  
  
  /**
   * Interpolate the active attributes (and'd with attrMask) to
   * fill in span->array->attribs[].
   * Perspective correction will be done.  The point/line/triangle function
   * should have computed attrStart/Step values for VARYING_SLOT_POS[3]!
   */
  static inline void
  interpolate_active_attribs(struct gl_context *ctx, SWspan *span,
                             GLbitfield64 attrMask)
  {
     const SWcontext *swrast = SWRAST_CONTEXT(ctx);
  
     /*
      * Don't overwrite existing array values, such as colors that may have
      * been produced by glDraw/CopyPixels.
      */
     attrMask &= ~span->arrayAttribs;
  
     ATTRIB_LOOP_BEGIN
        if (attrMask & BITFIELD64_BIT(attr)) {
           const GLfloat dwdx = span->attrStepX[VARYING_SLOT_POS][3];
           GLfloat w = span->attrStart[VARYING_SLOT_POS][3];
           const GLfloat dv0dx = span->attrStepX[attr][0];
           const GLfloat dv1dx = span->attrStepX[attr][1];
           const GLfloat dv2dx = span->attrStepX[attr][2];
           const GLfloat dv3dx = span->attrStepX[attr][3];
           GLfloat v0 = span->attrStart[attr][0] + span->leftClip * dv0dx;
           GLfloat v1 = span->attrStart[attr][1] + span->leftClip * dv1dx;
           GLfloat v2 = span->attrStart[attr][2] + span->leftClip * dv2dx;
           GLfloat v3 = span->attrStart[attr][3] + span->leftClip * dv3dx;
           GLuint k;
           for (k = 0; k < span->end; k++) {
              const GLfloat invW = 1.0f / w;
              span->array->attribs[attr][k][0] = v0 * invW;
              span->array->attribs[attr][k][1] = v1 * invW;
              span->array->attribs[attr][k][2] = v2 * invW;
              span->array->attribs[attr][k][3] = v3 * invW;
              v0 += dv0dx;
              v1 += dv1dx;
              v2 += dv2dx;
              v3 += dv3dx;
              w += dwdx;
           }
           assert((span->arrayAttribs & BITFIELD64_BIT(attr)) == 0);
           span->arrayAttribs |= BITFIELD64_BIT(attr);
        }
     ATTRIB_LOOP_END
  }
  
  
  /**
   * Interpolate primary colors to fill in the span->array->rgba8 (or rgb16)
   * color array.
   */
  static inline void
  interpolate_int_colors(struct gl_context *ctx, SWspan *span)
  {
  #if CHAN_BITS != 32
     const GLuint n = span->end;
     GLuint i;
  
     assert(!(span->arrayMask & SPAN_RGBA));
  #endif
  
     switch (span->array->ChanType) {
  #if CHAN_BITS != 32
     case GL_UNSIGNED_BYTE:
        {
           GLubyte (*rgba)[4] = span->array->rgba8;
           if (span->interpMask & SPAN_FLAT) {
              GLubyte color[4];
              color[RCOMP] = FixedToInt(span->red);
              color[GCOMP] = FixedToInt(span->green);
              color[BCOMP] = FixedToInt(span->blue);
              color[ACOMP] = FixedToInt(span->alpha);
              for (i = 0; i < n; i++) {
                 COPY_4UBV(rgba[i], color);
              }
           }
           else {
              GLfixed r = span->red;
              GLfixed g = span->green;
              GLfixed b = span->blue;
              GLfixed a = span->alpha;
              GLint dr = span->redStep;
              GLint dg = span->greenStep;
              GLint db = span->blueStep;
              GLint da = span->alphaStep;
              for (i = 0; i < n; i++) {
                 rgba[i][RCOMP] = FixedToChan(r);
                 rgba[i][GCOMP] = FixedToChan(g);
                 rgba[i][BCOMP] = FixedToChan(b);
                 rgba[i][ACOMP] = FixedToChan(a);
                 r += dr;
                 g += dg;
                 b += db;
                 a += da;
              }
           }
        }
        break;
     case GL_UNSIGNED_SHORT:
        {
           GLushort (*rgba)[4] = span->array->rgba16;
           if (span->interpMask & SPAN_FLAT) {
              GLushort color[4];
              color[RCOMP] = FixedToInt(span->red);
              color[GCOMP] = FixedToInt(span->green);
              color[BCOMP] = FixedToInt(span->blue);
              color[ACOMP] = FixedToInt(span->alpha);
              for (i = 0; i < n; i++) {
                 COPY_4V(rgba[i], color);
              }
           }
           else {
              GLushort (*rgba)[4] = span->array->rgba16;
              GLfixed r, g, b, a;
              GLint dr, dg, db, da;
              r = span->red;
              g = span->green;
              b = span->blue;
              a = span->alpha;
              dr = span->redStep;
              dg = span->greenStep;
              db = span->blueStep;
              da = span->alphaStep;
              for (i = 0; i < n; i++) {
                 rgba[i][RCOMP] = FixedToChan(r);
                 rgba[i][GCOMP] = FixedToChan(g);
                 rgba[i][BCOMP] = FixedToChan(b);
                 rgba[i][ACOMP] = FixedToChan(a);
                 r += dr;
                 g += dg;
                 b += db;
                 a += da;
              }
           }
        }
        break;
  #endif
     case GL_FLOAT:
        interpolate_active_attribs(ctx, span, VARYING_BIT_COL0);
        break;
     default:
        _mesa_problem(ctx, "bad datatype 0x%x in interpolate_int_colors",
                      span->array->ChanType);
     }
     span->arrayMask |= SPAN_RGBA;
  }
  
  
  /**
   * Populate the VARYING_SLOT_COL0 array.
   */
  static inline void
  interpolate_float_colors(SWspan *span)
  {
     GLfloat (*col0)[4] = span->array->attribs[VARYING_SLOT_COL0];
     const GLuint n = span->end;
     GLuint i;
  
     assert(!(span->arrayAttribs & VARYING_BIT_COL0));
  
     if (span->arrayMask & SPAN_RGBA) {
        /* convert array of int colors */
        for (i = 0; i < n; i++) {
           col0[i][0] = UBYTE_TO_FLOAT(span->array->rgba8[i][0]);
           col0[i][1] = UBYTE_TO_FLOAT(span->array->rgba8[i][1]);
           col0[i][2] = UBYTE_TO_FLOAT(span->array->rgba8[i][2]);
           col0[i][3] = UBYTE_TO_FLOAT(span->array->rgba8[i][3]);
        }
     }
     else {
        /* interpolate red/green/blue/alpha to get float colors */
        assert(span->interpMask & SPAN_RGBA);
        if (span->interpMask & SPAN_FLAT) {
           GLfloat r = FixedToFloat(span->red);
           GLfloat g = FixedToFloat(span->green);
           GLfloat b = FixedToFloat(span->blue);
           GLfloat a = FixedToFloat(span->alpha);
           for (i = 0; i < n; i++) {
              ASSIGN_4V(col0[i], r, g, b, a);
           }
        }
        else {
           GLfloat r = FixedToFloat(span->red);
           GLfloat g = FixedToFloat(span->green);
           GLfloat b = FixedToFloat(span->blue);
           GLfloat a = FixedToFloat(span->alpha);
           GLfloat dr = FixedToFloat(span->redStep);
           GLfloat dg = FixedToFloat(span->greenStep);
           GLfloat db = FixedToFloat(span->blueStep);
           GLfloat da = FixedToFloat(span->alphaStep);
           for (i = 0; i < n; i++) {
              col0[i][0] = r;
              col0[i][1] = g;
              col0[i][2] = b;
              col0[i][3] = a;
              r += dr;
              g += dg;
              b += db;
              a += da;
           }
        }
     }
  
     span->arrayAttribs |= VARYING_BIT_COL0;
     span->array->ChanType = GL_FLOAT;
  }
  
  
  
  /**
   * Fill in the span.zArray array from the span->z, zStep values.
   */
  void
  _swrast_span_interpolate_z( const struct gl_context *ctx, SWspan *span )
  {
     const GLuint n = span->end;
     GLuint i;
  
     assert(!(span->arrayMask & SPAN_Z));
  
     if (ctx->DrawBuffer->Visual.depthBits <= 16) {
        GLfixed zval = span->z;
        GLuint *z = span->array->z; 
        for (i = 0; i < n; i++) {
           z[i] = FixedToInt(zval);
           zval += span->zStep;
        }
     }
     else {
        /* Deep Z buffer, no fixed->int shift */
        GLuint zval = span->z;
        GLuint *z = span->array->z;
        for (i = 0; i < n; i++) {
           z[i] = zval;
           zval += span->zStep;
        }
     }
     span->interpMask &= ~SPAN_Z;
     span->arrayMask |= SPAN_Z;
  }
  
  
  /**
   * Compute mipmap LOD from partial derivatives.
   * This the ideal solution, as given in the OpenGL spec.
   */
  GLfloat
  _swrast_compute_lambda(GLfloat dsdx, GLfloat dsdy, GLfloat dtdx, GLfloat dtdy,
                         GLfloat dqdx, GLfloat dqdy, GLfloat texW, GLfloat texH,
                         GLfloat s, GLfloat t, GLfloat q, GLfloat invQ)
  {
     GLfloat dudx = texW * ((s + dsdx) / (q + dqdx) - s * invQ);
     GLfloat dvdx = texH * ((t + dtdx) / (q + dqdx) - t * invQ);
     GLfloat dudy = texW * ((s + dsdy) / (q + dqdy) - s * invQ);
     GLfloat dvdy = texH * ((t + dtdy) / (q + dqdy) - t * invQ);
     GLfloat x = sqrtf(dudx * dudx + dvdx * dvdx);
     GLfloat y = sqrtf(dudy * dudy + dvdy * dvdy);
     GLfloat rho = MAX2(x, y);
     GLfloat lambda = LOG2(rho);
     return lambda;
  }
  
  
  /**
   * Compute mipmap LOD from partial derivatives.
   * This is a faster approximation than above function.
   */
  #if 0
  GLfloat
  _swrast_compute_lambda(GLfloat dsdx, GLfloat dsdy, GLfloat dtdx, GLfloat dtdy,
                       GLfloat dqdx, GLfloat dqdy, GLfloat texW, GLfloat texH,
                       GLfloat s, GLfloat t, GLfloat q, GLfloat invQ)
  {
     GLfloat dsdx2 = (s + dsdx) / (q + dqdx) - s * invQ;
     GLfloat dtdx2 = (t + dtdx) / (q + dqdx) - t * invQ;
     GLfloat dsdy2 = (s + dsdy) / (q + dqdy) - s * invQ;
     GLfloat dtdy2 = (t + dtdy) / (q + dqdy) - t * invQ;
     GLfloat maxU, maxV, rho, lambda;
     dsdx2 = fabsf(dsdx2);
     dsdy2 = fabsf(dsdy2);
     dtdx2 = fabsf(dtdx2);
     dtdy2 = fabsf(dtdy2);
     maxU = MAX2(dsdx2, dsdy2) * texW;
     maxV = MAX2(dtdx2, dtdy2) * texH;
     rho = MAX2(maxU, maxV);
     lambda = LOG2(rho);
     return lambda;
  }
  #endif
  
  
  /**
   * Fill in the span.array->attrib[VARYING_SLOT_TEXn] arrays from the
   * using the attrStart/Step values.
   *
   * This function only used during fixed-function fragment processing.
   *
   * Note: in the places where we divide by Q (or mult by invQ) we're
   * really doing two things: perspective correction and texcoord
   * projection.  Remember, for texcoord (s,t,r,q) we need to index
   * texels with (s/q, t/q, r/q).
   */
  static void
  interpolate_texcoords(struct gl_context *ctx, SWspan *span)
  {
     const GLuint maxUnit
        = (ctx->Texture._EnabledCoordUnits > 1) ? ctx->Const.MaxTextureUnits : 1;
     GLuint u;
  
     /* XXX CoordUnits vs. ImageUnits */
     for (u = 0; u < maxUnit; u++) {
        if (ctx->Texture._EnabledCoordUnits & (1 << u)) {
           const GLuint attr = VARYING_SLOT_TEX0 + u;
           const struct gl_texture_object *obj = ctx->Texture.Unit[u]._Current;
           GLfloat texW, texH;
           GLboolean needLambda;
           GLfloat (*texcoord)[4] = span->array->attribs[attr];
           GLfloat *lambda = span->array->lambda[u];
           const GLfloat dsdx = span->attrStepX[attr][0];
           const GLfloat dsdy = span->attrStepY[attr][0];
           const GLfloat dtdx = span->attrStepX[attr][1];
           const GLfloat dtdy = span->attrStepY[attr][1];
           const GLfloat drdx = span->attrStepX[attr][2];
           const GLfloat dqdx = span->attrStepX[attr][3];
           const GLfloat dqdy = span->attrStepY[attr][3];
           GLfloat s = span->attrStart[attr][0] + span->leftClip * dsdx;
           GLfloat t = span->attrStart[attr][1] + span->leftClip * dtdx;
           GLfloat r = span->attrStart[attr][2] + span->leftClip * drdx;
           GLfloat q = span->attrStart[attr][3] + span->leftClip * dqdx;
  
           if (obj) {
              const struct gl_texture_image *img = _mesa_base_tex_image(obj);
              const struct swrast_texture_image *swImg =
                 swrast_texture_image_const(img);
              const struct gl_sampler_object *samp = _mesa_get_samplerobj(ctx, u);
  
              needLambda = (samp->MinFilter != samp->MagFilter)
                 || _swrast_use_fragment_program(ctx);
              /* LOD is calculated directly in the ansiotropic filter, we can
               * skip the normal lambda function as the result is ignored.
               */
              if (samp->MaxAnisotropy > 1.0F &&
                  samp->MinFilter == GL_LINEAR_MIPMAP_LINEAR) {
                 needLambda = GL_FALSE;
              }
              texW = swImg->WidthScale;
              texH = swImg->HeightScale;
           }
           else {
              /* using a fragment program */
              texW = 1.0;
              texH = 1.0;
              needLambda = GL_FALSE;
           }
  
           if (needLambda) {
              GLuint i;
              if (_swrast_use_fragment_program(ctx)
                  || ctx->ATIFragmentShader._Enabled) {
                 /* do perspective correction but don't divide s, t, r by q */
                 const GLfloat dwdx = span->attrStepX[VARYING_SLOT_POS][3];
                 GLfloat w = span->attrStart[VARYING_SLOT_POS][3] + span->leftClip * dwdx;
                 for (i = 0; i < span->end; i++) {
                    const GLfloat invW = 1.0F / w;
                    texcoord[i][0] = s * invW;
                    texcoord[i][1] = t * invW;
                    texcoord[i][2] = r * invW;
                    texcoord[i][3] = q * invW;
                    lambda[i] = _swrast_compute_lambda(dsdx, dsdy, dtdx, dtdy,
                                                       dqdx, dqdy, texW, texH,
                                                       s, t, q, invW);
                    s += dsdx;
                    t += dtdx;
                    r += drdx;
                    q += dqdx;
                    w += dwdx;
                 }
              }
              else {
                 for (i = 0; i < span->end; i++) {
                    const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
                    texcoord[i][0] = s * invQ;
                    texcoord[i][1] = t * invQ;
                    texcoord[i][2] = r * invQ;
                    texcoord[i][3] = q;
                    lambda[i] = _swrast_compute_lambda(dsdx, dsdy, dtdx, dtdy,
                                                       dqdx, dqdy, texW, texH,
                                                       s, t, q, invQ);
                    s += dsdx;
                    t += dtdx;
                    r += drdx;
                    q += dqdx;
                 }
              }
              span->arrayMask |= SPAN_LAMBDA;
           }
           else {
              GLuint i;
              if (_swrast_use_fragment_program(ctx) ||
                  ctx->ATIFragmentShader._Enabled) {
                 /* do perspective correction but don't divide s, t, r by q */
                 const GLfloat dwdx = span->attrStepX[VARYING_SLOT_POS][3];
                 GLfloat w = span->attrStart[VARYING_SLOT_POS][3] + span->leftClip * dwdx;
                 for (i = 0; i < span->end; i++) {
                    const GLfloat invW = 1.0F / w;
                    texcoord[i][0] = s * invW;
                    texcoord[i][1] = t * invW;
                    texcoord[i][2] = r * invW;
                    texcoord[i][3] = q * invW;
                    lambda[i] = 0.0;
                    s += dsdx;
                    t += dtdx;
                    r += drdx;
                    q += dqdx;
                    w += dwdx;
                 }
              }
              else if (dqdx == 0.0F) {
                 /* Ortho projection or polygon's parallel to window X axis */
                 const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
                 for (i = 0; i < span->end; i++) {
                    texcoord[i][0] = s * invQ;
                    texcoord[i][1] = t * invQ;
                    texcoord[i][2] = r * invQ;
                    texcoord[i][3] = q;
                    lambda[i] = 0.0;
                    s += dsdx;
                    t += dtdx;
                    r += drdx;
                 }
              }
              else {
                 for (i = 0; i < span->end; i++) {
                    const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
                    texcoord[i][0] = s * invQ;
                    texcoord[i][1] = t * invQ;
                    texcoord[i][2] = r * invQ;
                    texcoord[i][3] = q;
                    lambda[i] = 0.0;
                    s += dsdx;
                    t += dtdx;
                    r += drdx;
                    q += dqdx;
                 }
              }
           } /* lambda */
        } /* if */
     } /* for */
  }
  
  
  /**
   * Fill in the arrays->attribs[VARYING_SLOT_POS] array.
   */
  static inline void
  interpolate_wpos(struct gl_context *ctx, SWspan *span)
  {
     GLfloat (*wpos)[4] = span->array->attribs[VARYING_SLOT_POS];
     GLuint i;
     const GLfloat zScale = 1.0F / ctx->DrawBuffer->_DepthMaxF;
     GLfloat w, dw;
  
     if (span->arrayMask & SPAN_XY) {
        for (i = 0; i < span->end; i++) {
           wpos[i][0] = (GLfloat) span->array->x[i];
           wpos[i][1] = (GLfloat) span->array->y[i];
        }
     }
     else {
        for (i = 0; i < span->end; i++) {
           wpos[i][0] = (GLfloat) span->x + i;
           wpos[i][1] = (GLfloat) span->y;
        }
     }
  
     dw = span->attrStepX[VARYING_SLOT_POS][3];
     w = span->attrStart[VARYING_SLOT_POS][3] + span->leftClip * dw;
     for (i = 0; i < span->end; i++) {
        wpos[i][2] = (GLfloat) span->array->z[i] * zScale;
        wpos[i][3] = w;
        w += dw;
     }
  }
  
  
  /**
   * Apply the current polygon stipple pattern to a span of pixels.
   */
  static inline void
  stipple_polygon_span(struct gl_context *ctx, SWspan *span)
  {
     GLubyte *mask = span->array->mask;
  
     assert(ctx->Polygon.StippleFlag);
  
     if (span->arrayMask & SPAN_XY) {
        /* arrays of x/y pixel coords */
        GLuint i;
        for (i = 0; i < span->end; i++) {
           const GLint col = span->array->x[i] % 32;
           const GLint row = span->array->y[i] % 32;
           const GLuint stipple = ctx->PolygonStipple[row];
           if (((1 << col) & stipple) == 0) {
              mask[i] = 0;
           }
        }
     }
     else {
        /* horizontal span of pixels */
        const GLuint highBit = 1 << 31;
        const GLuint stipple = ctx->PolygonStipple[span->y % 32];
        GLuint i, m = highBit >> (GLuint) (span->x % 32);
        for (i = 0; i < span->end; i++) {
           if ((m & stipple) == 0) {
              mask[i] = 0;
           }
           m = m >> 1;
           if (m == 0) {
              m = highBit;
           }
        }
     }
     span->writeAll = GL_FALSE;
  }
  
  
  /**
   * Clip a pixel span to the current buffer/window boundaries:
   * DrawBuffer->_Xmin, _Xmax, _Ymin, _Ymax.  This will accomplish
   * window clipping and scissoring.
   * Return:   GL_TRUE   some pixels still visible
   *           GL_FALSE  nothing visible
   */
  static inline GLuint
  clip_span( struct gl_context *ctx, SWspan *span )
  {
     const GLint xmin = ctx->DrawBuffer->_Xmin;
     const GLint xmax = ctx->DrawBuffer->_Xmax;
     const GLint ymin = ctx->DrawBuffer->_Ymin;
     const GLint ymax = ctx->DrawBuffer->_Ymax;
  
     span->leftClip = 0;
  
     if (span->arrayMask & SPAN_XY) {
        /* arrays of x/y pixel coords */
        const GLint *x = span->array->x;
        const GLint *y = span->array->y;
        const GLint n = span->end;
        GLubyte *mask = span->array->mask;
        GLint i;
        GLuint passed = 0;
        if (span->arrayMask & SPAN_MASK) {
           /* note: using & intead of && to reduce branches */
           for (i = 0; i < n; i++) {
              mask[i] &= (x[i] >= xmin) & (x[i] < xmax)
                       & (y[i] >= ymin) & (y[i] < ymax);
              passed += mask[i];
           }
        }
        else {
           /* note: using & intead of && to reduce branches */
           for (i = 0; i < n; i++) {
              mask[i] = (x[i] >= xmin) & (x[i] < xmax)
                      & (y[i] >= ymin) & (y[i] < ymax);
              passed += mask[i];
           }
        }
        return passed > 0;
     }
     else {
        /* horizontal span of pixels */
        const GLint x = span->x;
        const GLint y = span->y;
        GLint n = span->end;
  
        /* Trivial rejection tests */
        if (y < ymin || y >= ymax || x + n <= xmin || x >= xmax) {
           span->end = 0;
           return GL_FALSE;  /* all pixels clipped */
        }
  
        /* Clip to right */
        if (x + n > xmax) {
           assert(x < xmax);
           n = span->end = xmax - x;
        }
  
        /* Clip to the left */
        if (x < xmin) {
           const GLint leftClip = xmin - x;
           GLuint i;
  
           assert(leftClip > 0);
           assert(x + n > xmin);
  
           /* Clip 'leftClip' pixels from the left side.
            * The span->leftClip field will be applied when we interpolate
            * fragment attributes.
            * For arrays of values, shift them left.
            */
           for (i = 0; i < VARYING_SLOT_MAX; i++) {
              if (span->interpMask & (1 << i)) {
                 GLuint j;
                 for (j = 0; j < 4; j++) {
                    span->attrStart[i][j] += leftClip * span->attrStepX[i][j];
                 }
              }
           }
  
           span->red += leftClip * span->redStep;
           span->green += leftClip * span->greenStep;
           span->blue += leftClip * span->blueStep;
           span->alpha += leftClip * span->alphaStep;
           span->index += leftClip * span->indexStep;
           span->z += leftClip * span->zStep;
           span->intTex[0] += leftClip * span->intTexStep[0];
           span->intTex[1] += leftClip * span->intTexStep[1];
  
  #define SHIFT_ARRAY(ARRAY, SHIFT, LEN) \
           memmove(ARRAY, ARRAY + (SHIFT), (LEN) * sizeof(ARRAY[0]))
  
           for (i = 0; i < VARYING_SLOT_MAX; i++) {
              if (span->arrayAttribs & BITFIELD64_BIT(i)) {
                 /* shift array elements left by 'leftClip' */
                 SHIFT_ARRAY(span->array->attribs[i], leftClip, n - leftClip);
              }
           }
  
           SHIFT_ARRAY(span->array->mask, leftClip, n - leftClip);
           SHIFT_ARRAY(span->array->rgba8, leftClip, n - leftClip);
           SHIFT_ARRAY(span->array->rgba16, leftClip, n - leftClip);
           SHIFT_ARRAY(span->array->x, leftClip, n - leftClip);
           SHIFT_ARRAY(span->array->y, leftClip, n - leftClip);
           SHIFT_ARRAY(span->array->z, leftClip, n - leftClip);
           SHIFT_ARRAY(span->array->index, leftClip, n - leftClip);
           for (i = 0; i < MAX_TEXTURE_COORD_UNITS; i++) {
              SHIFT_ARRAY(span->array->lambda[i], leftClip, n - leftClip);
           }
           SHIFT_ARRAY(span->array->coverage, leftClip, n - leftClip);
  
  #undef SHIFT_ARRAY
  
           span->leftClip = leftClip;
           span->x = xmin;
           span->end -= leftClip;
           span->writeAll = GL_FALSE;
        }
  
        assert(span->x >= xmin);
        assert(span->x + span->end <= xmax);
        assert(span->y >= ymin);
        assert(span->y < ymax);
  
        return GL_TRUE;  /* some pixels visible */
     }
  }
  
  
  /**
   * Add specular colors to primary colors.
   * Only called during fixed-function operation.
   * Result is float color array (VARYING_SLOT_COL0).
   */
  static inline void
  add_specular(struct gl_context *ctx, SWspan *span)
  {
     const SWcontext *swrast = SWRAST_CONTEXT(ctx);
     const GLubyte *mask = span->array->mask;
     GLfloat (*col0)[4] = span->array->attribs[VARYING_SLOT_COL0];
     GLfloat (*col1)[4] = span->array->attribs[VARYING_SLOT_COL1];
     GLuint i;
  
     assert(!_swrast_use_fragment_program(ctx));
     assert(span->arrayMask & SPAN_RGBA);
     assert(swrast->_ActiveAttribMask & VARYING_BIT_COL1);
     (void) swrast; /* silence warning */
  
     if (span->array->ChanType == GL_FLOAT) {
        if ((span->arrayAttribs & VARYING_BIT_COL0) == 0) {
           interpolate_active_attribs(ctx, span, VARYING_BIT_COL0);
        }
     }
     else {
        /* need float colors */
        if ((span->arrayAttribs & VARYING_BIT_COL0) == 0) {
           interpolate_float_colors(span);
        }
     }
  
     if ((span->arrayAttribs & VARYING_BIT_COL1) == 0) {
        /* XXX could avoid this and interpolate COL1 in the loop below */
        interpolate_active_attribs(ctx, span, VARYING_BIT_COL1);
     }
  
     assert(span->arrayAttribs & VARYING_BIT_COL0);
     assert(span->arrayAttribs & VARYING_BIT_COL1);
  
     for (i = 0; i < span->end; i++) {
        if (mask[i]) {
           col0[i][0] += col1[i][0];
           col0[i][1] += col1[i][1];
           col0[i][2] += col1[i][2];
        }
     }
  
     span->array->ChanType = GL_FLOAT;
  }
  
  
  /**
   * Apply antialiasing coverage value to alpha values.
   */
  static inline void
  apply_aa_coverage(SWspan *span)
  {
     const GLfloat *coverage = span->array->coverage;
     GLuint i;
     if (span->array->ChanType == GL_UNSIGNED_BYTE) {
        GLubyte (*rgba)[4] = span->array->rgba8;
        for (i = 0; i < span->end; i++) {
           const GLfloat a = rgba[i][ACOMP] * coverage[i];
           rgba[i][ACOMP] = (GLubyte) CLAMP(a, 0.0F, 255.0F);
           assert(coverage[i] >= 0.0F);
           assert(coverage[i] <= 1.0F);
        }
     }
     else if (span->array->ChanType == GL_UNSIGNED_SHORT) {
        GLushort (*rgba)[4] = span->array->rgba16;
        for (i = 0; i < span->end; i++) {
           const GLfloat a = rgba[i][ACOMP] * coverage[i];
           rgba[i][ACOMP] = (GLushort) CLAMP(a, 0.0F, 65535.0F);
        }
     }
     else {
        GLfloat (*rgba)[4] = span->array->attribs[VARYING_SLOT_COL0];
        for (i = 0; i < span->end; i++) {
           rgba[i][ACOMP] = rgba[i][ACOMP] * coverage[i];
           /* clamp later */
        }
     }
  }
  
  
  /**
   * Clamp span's float colors to [0,1]
   */
  static inline void
  clamp_colors(SWspan *span)
  {
     GLfloat (*rgba)[4] = span->array->attribs[VARYING_SLOT_COL0];
     GLuint i;
     assert(span->array->ChanType == GL_FLOAT);
     for (i = 0; i < span->end; i++) {
        rgba[i][RCOMP] = CLAMP(rgba[i][RCOMP], 0.0F, 1.0F);
        rgba[i][GCOMP] = CLAMP(rgba[i][GCOMP], 0.0F, 1.0F);
        rgba[i][BCOMP] = CLAMP(rgba[i][BCOMP], 0.0F, 1.0F);
        rgba[i][ACOMP] = CLAMP(rgba[i][ACOMP], 0.0F, 1.0F);
     }
  }
  
  
  /**
   * Convert the span's color arrays to the given type.
   * The only way 'output' can be greater than zero is when we have a fragment
   * program that writes to gl_FragData[1] or higher.
   * \param output  which fragment program color output is being processed
   */
  static inline void
  convert_color_type(SWspan *span, GLenum srcType, GLenum newType, GLuint output)
  {
     GLvoid *src, *dst;
  
     if (output > 0 || srcType == GL_FLOAT) {
        src = span->array->attribs[VARYING_SLOT_COL0 + output];
        span->array->ChanType = GL_FLOAT;
     }
     else if (srcType == GL_UNSIGNED_BYTE) {
        src = span->array->rgba8;
     }
     else {
        assert(srcType == GL_UNSIGNED_SHORT);
        src = span->array->rgba16;
     }
  
     if (newType == GL_UNSIGNED_BYTE) {
        dst = span->array->rgba8;
     }
     else if (newType == GL_UNSIGNED_SHORT) {
        dst = span->array->rgba16;
     }
     else {
        dst = span->array->attribs[VARYING_SLOT_COL0];
     }
  
     _mesa_convert_colors(span->array->ChanType, src,
                          newType, dst,
                          span->end, span->array->mask);
  
     span->array->ChanType = newType;
     span->array->rgba = dst;
  }
  
  
  
  /**
   * Apply fragment shader, fragment program or normal texturing to span.
   */
  static inline void
  shade_texture_span(struct gl_context *ctx, SWspan *span)
  {
     if (_swrast_use_fragment_program(ctx) ||
         ctx->ATIFragmentShader._Enabled) {
        /* programmable shading */
        if (span->primitive == GL_BITMAP && span->array->ChanType != GL_FLOAT) {
           convert_color_type(span, span->array->ChanType, GL_FLOAT, 0);
        }
        else {
           span->array->rgba = (void *) span->array->attribs[VARYING_SLOT_COL0];
        }
  
        if (span->primitive != GL_POINT ||
  	  (span->interpMask & SPAN_RGBA) ||
  	  ctx->Point.PointSprite) {
           /* for single-pixel points, we populated the arrays already */
           interpolate_active_attribs(ctx, span, ~0);
        }
        span->array->ChanType = GL_FLOAT;
  
        if (!(span->arrayMask & SPAN_Z))
           _swrast_span_interpolate_z (ctx, span);
  
  #if 0
        if (inputsRead & VARYING_BIT_POS)
  #else
        /* XXX always interpolate wpos so that DDX/DDY work */
  #endif
           interpolate_wpos(ctx, span);
  
        /* Run fragment program/shader now */
        if (_swrast_use_fragment_program(ctx)) {
           _swrast_exec_fragment_program(ctx, span);
        }
        else {
           assert(ctx->ATIFragmentShader._Enabled);
           _swrast_exec_fragment_shader(ctx, span);
        }
     }
     else if (ctx->Texture._EnabledCoordUnits) {
        /* conventional texturing */
  
  #if CHAN_BITS == 32
        if ((span->arrayAttribs & VARYING_BIT_COL0) == 0) {
           interpolate_int_colors(ctx, span);
        }
  #else
        if (!(span->arrayMask & SPAN_RGBA))
           interpolate_int_colors(ctx, span);
  #endif
        if ((span->arrayAttribs & VARYING_BITS_TEX_ANY) == 0x0)
           interpolate_texcoords(ctx, span);
  
        _swrast_texture_span(ctx, span);
     }
  }
  
  
  /** Put colors at x/y locations into a renderbuffer */
  static void
  put_values(struct gl_context *ctx, struct gl_renderbuffer *rb,
             GLenum datatype,
             GLuint count, const GLint x[], const GLint y[],
             const void *values, const GLubyte *mask)
  {
     gl_pack_ubyte_rgba_func pack_ubyte = NULL;
     gl_pack_float_rgba_func pack_float = NULL;
     GLuint i;
  
     if (datatype == GL_UNSIGNED_BYTE)
        pack_ubyte = _mesa_get_pack_ubyte_rgba_function(rb->Format);
     else
        pack_float = _mesa_get_pack_float_rgba_function(rb->Format);
  
     for (i = 0; i < count; i++) {
        if (mask[i]) {
           GLubyte *dst = _swrast_pixel_address(rb, x[i], y[i]);
  
           if (datatype == GL_UNSIGNED_BYTE) {
              pack_ubyte((const GLubyte *) values + 4 * i, dst);
           }
           else {
              assert(datatype == GL_FLOAT);
              pack_float((const GLfloat *) values + 4 * i, dst);
           }
        }
     }
  }
  
  
  /** Put row of colors into renderbuffer */
  void
  _swrast_put_row(struct gl_context *ctx, struct gl_renderbuffer *rb,
                  GLenum datatype,
                  GLuint count, GLint x, GLint y,
                  const void *values, const GLubyte *mask)
  {
     GLubyte *dst = _swrast_pixel_address(rb, x, y);
  
     if (!mask) {
        if (datatype == GL_UNSIGNED_BYTE) {
           _mesa_pack_ubyte_rgba_row(rb->Format, count,
                                     (const GLubyte (*)[4]) values, dst);
        }
        else {
           assert(datatype == GL_FLOAT);
           _mesa_pack_float_rgba_row(rb->Format, count,
                                     (const GLfloat (*)[4]) values, dst);
        }
     }
     else {
        const GLuint bpp = _mesa_get_format_bytes(rb->Format);
        GLuint i, runLen, runStart;
        /* We can't pass a 'mask' array to the _mesa_pack_rgba_row() functions
         * so look for runs where mask=1...
         */
        runLen = runStart = 0;
        for (i = 0; i < count; i++) {
           if (mask[i]) {
              if (runLen == 0)
                 runStart = i;
              runLen++;
           }
  
           if (!mask[i] || i == count - 1) {
              /* might be the end of a run of pixels */
              if (runLen > 0) {
                 if (datatype == GL_UNSIGNED_BYTE) {
                    _mesa_pack_ubyte_rgba_row(rb->Format, runLen,
                                       (const GLubyte (*)[4]) values + runStart,
                                       dst + runStart * bpp);
                 }
                 else {
                    assert(datatype == GL_FLOAT);
                    _mesa_pack_float_rgba_row(rb->Format, runLen,
                                     (const GLfloat (*)[4]) values + runStart,
                                     dst + runStart * bpp);
                 }
                 runLen = 0;
              }
           }
        }
     }
  }
  
  
  
  /**
   * Apply all the per-fragment operations to a span.
   * This now includes texturing (_swrast_write_texture_span() is history).
   * This function may modify any of the array values in the span.
   * span->interpMask and span->arrayMask may be changed but will be restored
   * to their original values before returning.
   */
  void
  _swrast_write_rgba_span( struct gl_context *ctx, SWspan *span)
  {
     const SWcontext *swrast = SWRAST_CONTEXT(ctx);
     const GLuint *colorMask = (GLuint *) ctx->Color.ColorMask;
     const GLbitfield origInterpMask = span->interpMask;
     const GLbitfield origArrayMask = span->arrayMask;
     const GLbitfield64 origArrayAttribs = span->arrayAttribs;
     const GLenum origChanType = span->array->ChanType;
     void * const origRgba = span->array->rgba;
     const GLboolean shader = (_swrast_use_fragment_program(ctx)
                               || ctx->ATIFragmentShader._Enabled);
     const GLboolean shaderOrTexture = shader || ctx->Texture._EnabledCoordUnits;
     struct gl_framebuffer *fb = ctx->DrawBuffer;
  
     /*
     printf("%s()  interp 0x%x  array 0x%x\n", __func__,
            span->interpMask, span->arrayMask);
     */
  
     assert(span->primitive == GL_POINT ||
            span->primitive == GL_LINE ||
  	  span->primitive == GL_POLYGON ||
            span->primitive == GL_BITMAP);
  
     /* Fragment write masks */
     if (span->arrayMask & SPAN_MASK) {
        /* mask was initialized by caller, probably glBitmap */
        span->writeAll = GL_FALSE;
     }
     else {
        memset(span->array->mask, 1, span->end);
        span->writeAll = GL_TRUE;
     }
  
     /* Clip to window/scissor box */
     if (!clip_span(ctx, span)) {
        return;
     }
  
     assert(span->end <= SWRAST_MAX_WIDTH);
  
     /* Depth bounds test */
     if (ctx->Depth.BoundsTest && fb->Visual.depthBits > 0) {
        if (!_swrast_depth_bounds_test(ctx, span)) {
           return;
        }
     }
  
  #ifdef DEBUG
     /* Make sure all fragments are within window bounds */
     if (span->arrayMask & SPAN_XY) {
        /* array of pixel locations */
        GLuint i;
        for (i = 0; i < span->end; i++) {
           if (span->array->mask[i]) {
              assert(span->array->x[i] >= fb->_Xmin);
              assert(span->array->x[i] < fb->_Xmax);
              assert(span->array->y[i] >= fb->_Ymin);
              assert(span->array->y[i] < fb->_Ymax);
           }
        }
     }
  #endif
  
     /* Polygon Stippling */
     if (ctx->Polygon.StippleFlag && span->primitive == GL_POLYGON) {
        stipple_polygon_span(ctx, span);
     }
  
     /* This is the normal place to compute the fragment color/Z
      * from texturing or shading.
      */
     if (shaderOrTexture && !swrast->_DeferredTexture) {
        shade_texture_span(ctx, span);
     }
  
     /* Do the alpha test */
     if (ctx->Color.AlphaEnabled) {
        if (!_swrast_alpha_test(ctx, span)) {
           /* all fragments failed test */
           goto end;
        }
     }
  
     /* Stencil and Z testing */
     if (ctx->Stencil._Enabled || ctx->Depth.Test) {
        if (!(span->arrayMask & SPAN_Z))
           _swrast_span_interpolate_z(ctx, span);
  
        if (ctx->Transform.DepthClamp)
  	 _swrast_depth_clamp_span(ctx, span);
  
        if (ctx->Stencil._Enabled) {
           /* Combined Z/stencil tests */
           if (!_swrast_stencil_and_ztest_span(ctx, span)) {
              /* all fragments failed test */
              goto end;
           }
        }
        else if (fb->Visual.depthBits > 0) {
           /* Just regular depth testing */
           assert(ctx->Depth.Test);
           assert(span->arrayMask & SPAN_Z);
           if (!_swrast_depth_test_span(ctx, span)) {
              /* all fragments failed test */
              goto end;
           }
        }
     }
  
     if (ctx->Query.CurrentOcclusionObject) {
        /* update count of 'passed' fragments */
        struct gl_query_object *q = ctx->Query.CurrentOcclusionObject;
        GLuint i;
        for (i = 0; i < span->end; i++)
           q->Result += span->array->mask[i];
     }
  
     /* We had to wait until now to check for glColorMask(0,0,0,0) because of
      * the occlusion test.
      */
     if (fb->_NumColorDrawBuffers == 1 && colorMask[0] == 0x0) {
        /* no colors to write */
        goto end;
     }
  
     /* If we were able to defer fragment color computation to now, there's
      * a good chance that many fragments will have already been killed by
      * Z/stencil testing.
      */
     if (shaderOrTexture && swrast->_DeferredTexture) {
        shade_texture_span(ctx, span);
     }
  
  #if CHAN_BITS == 32
     if ((span->arrayAttribs & VARYING_BIT_COL0) == 0) {
        interpolate_active_attribs(ctx, span, VARYING_BIT_COL0);
     }
  #else
     if ((span->arrayMask & SPAN_RGBA) == 0) {
        interpolate_int_colors(ctx, span);
     }
  #endif
  
     assert(span->arrayMask & SPAN_RGBA);
  
     if (span->primitive == GL_BITMAP || !swrast->SpecularVertexAdd) {
        /* Add primary and specular (diffuse + specular) colors */
        if (!shader) {
           if (ctx->Fog.ColorSumEnabled ||
               (ctx->Light.Enabled &&
                ctx->Light.Model.ColorControl == GL_SEPARATE_SPECULAR_COLOR)) {
              add_specular(ctx, span);
           }
        }
     }
  
     /* Fog */
     if (swrast->_FogEnabled) {
        _swrast_fog_rgba_span(ctx, span);
     }
  
     /* Antialias coverage application */
     if (span->arrayMask & SPAN_COVERAGE) {
        apply_aa_coverage(span);
     }
  
     /* Clamp color/alpha values over the range [0.0, 1.0] before storage */
     if (ctx->Color.ClampFragmentColor == GL_TRUE &&
         span->array->ChanType == GL_FLOAT) {
        clamp_colors(span);
     }
  
     /*
      * Write to renderbuffers.
      * Depending on glDrawBuffer() state and the which color outputs are
      * written by the fragment shader, we may either replicate one color to
      * all renderbuffers or write a different color to each renderbuffer.
      * multiFragOutputs=TRUE for the later case.
      */
     {
        const GLuint numBuffers = fb->_NumColorDrawBuffers;
        const struct gl_fragment_program *fp = ctx->FragmentProgram._Current;
        const GLboolean multiFragOutputs = 
           _swrast_use_fragment_program(ctx)
           && fp->Base.OutputsWritten >= (1 << FRAG_RESULT_DATA0);
        /* Save srcColorType because convert_color_type() can change it */
        const GLenum srcColorType = span->array->ChanType;
        GLuint buf;
  
        for (buf = 0; buf < numBuffers; buf++) {
           struct gl_renderbuffer *rb = fb->_ColorDrawBuffers[buf];
  
           /* color[fragOutput] will be written to buffer[buf] */
  
           if (rb) {
              /* re-use one of the attribute array buffers for rgbaSave */
              GLchan (*rgbaSave)[4] = (GLchan (*)[4]) span->array->attribs[0];
              struct swrast_renderbuffer *srb = swrast_renderbuffer(rb);
              const GLenum dstColorType = srb->ColorType;
  
              assert(dstColorType == GL_UNSIGNED_BYTE ||
                     dstColorType == GL_FLOAT);
  
              /* set span->array->rgba to colors for renderbuffer's datatype */
              if (srcColorType != dstColorType) {
                 convert_color_type(span, srcColorType, dstColorType,
                                    multiFragOutputs ? buf : 0);
              }
              else {
                 if (srcColorType == GL_UNSIGNED_BYTE) {
                    span->array->rgba = span->array->rgba8;
                 }
                 else {
                    span->array->rgba = (void *)
                       span->array->attribs[VARYING_SLOT_COL0];
                 }
              }
  
              if (!multiFragOutputs && numBuffers > 1) {
                 /* save colors for second, third renderbuffer writes */
                 memcpy(rgbaSave, span->array->rgba,
                        4 * span->end * sizeof(GLchan));
              }
  
              assert(rb->_BaseFormat == GL_RGBA ||
                     rb->_BaseFormat == GL_RGB ||
                     rb->_BaseFormat == GL_RED ||
                     rb->_BaseFormat == GL_RG ||
  		   rb->_BaseFormat == GL_ALPHA);
  
              if (ctx->Color.ColorLogicOpEnabled) {
                 _swrast_logicop_rgba_span(ctx, rb, span);
              }
              else if ((ctx->Color.BlendEnabled >> buf) & 1) {
                 _swrast_blend_span(ctx, rb, span);
              }
  
              if (colorMask[buf] != 0xffffffff) {
                 _swrast_mask_rgba_span(ctx, rb, span, buf);
              }
  
              if (span->arrayMask & SPAN_XY) {
                 /* array of pixel coords */
                 put_values(ctx, rb,
                            span->array->ChanType, span->end,
                            span->array->x, span->array->y,
                            span->array->rgba, span->array->mask);
              }
              else {
                 /* horizontal run of pixels */
                 _swrast_put_row(ctx, rb,
                                 span->array->ChanType,
                                 span->end, span->x, span->y,
                                 span->array->rgba,
                                 span->writeAll ? NULL: span->array->mask);
              }
  
              if (!multiFragOutputs && numBuffers > 1) {
                 /* restore original span values */
                 memcpy(span->array->rgba, rgbaSave,
                        4 * span->end * sizeof(GLchan));
              }
  
           } /* if rb */
        } /* for buf */
     }
  
  end:
     /* restore these values before returning */
     span->interpMask = origInterpMask;
     span->arrayMask = origArrayMask;
     span->arrayAttribs = origArrayAttribs;
     span->array->ChanType = origChanType;
     span->array->rgba = origRgba;
  }
  
  
  /**
   * Read float RGBA pixels from a renderbuffer.  Clipping will be done to
   * prevent reading ouside the buffer's boundaries.
   * \param rgba  the returned colors
   */
  void
  _swrast_read_rgba_span( struct gl_context *ctx, struct gl_renderbuffer *rb,
                          GLuint n, GLint x, GLint y,
                          GLvoid *rgba)
  {
     struct swrast_renderbuffer *srb = swrast_renderbuffer(rb);
     GLenum dstType = GL_FLOAT;
     const GLint bufWidth = (GLint) rb->Width;
     const GLint bufHeight = (GLint) rb->Height;
  
     if (y < 0 || y >= bufHeight || x + (GLint) n < 0 || x >= bufWidth) {
        /* completely above, below, or right */
        /* XXX maybe leave rgba values undefined? */
        memset(rgba, 0, 4 * n * sizeof(GLchan));
     }
     else {
        GLint skip, length;
        GLubyte *src;
  
        if (x < 0) {
           /* left edge clipping */
           skip = -x;
           length = (GLint) n - skip;
           if (length < 0) {
              /* completely left of window */
              return;
           }
           if (length > bufWidth) {
              length = bufWidth;
           }
        }
        else if ((GLint) (x + n) > bufWidth) {
           /* right edge clipping */
           skip = 0;
           length = bufWidth - x;
           if (length < 0) {
              /* completely to right of window */
              return;
           }
        }
        else {
           /* no clipping */
           skip = 0;
           length = (GLint) n;
        }
  
        assert(rb);
        assert(rb->_BaseFormat == GL_RGBA ||
  	     rb->_BaseFormat == GL_RGB ||
  	     rb->_BaseFormat == GL_RG ||
  	     rb->_BaseFormat == GL_RED ||
  	     rb->_BaseFormat == GL_LUMINANCE ||
  	     rb->_BaseFormat == GL_INTENSITY ||
  	     rb->_BaseFormat == GL_LUMINANCE_ALPHA ||
  	     rb->_BaseFormat == GL_ALPHA);
  
        assert(srb->Map);
        (void) srb; /* silence unused var warning */
  
        src = _swrast_pixel_address(rb, x + skip, y);
  
        if (dstType == GL_UNSIGNED_BYTE) {
           _mesa_unpack_ubyte_rgba_row(rb->Format, length, src,
                                       (GLubyte (*)[4]) rgba + skip);
        }
        else if (dstType == GL_FLOAT) {
           _mesa_unpack_rgba_row(rb->Format, length, src,
                                 (GLfloat (*)[4]) rgba + skip);
        }
        else {
           _mesa_problem(ctx, "unexpected type in _swrast_read_rgba_span()");
        }
     }
  }
  
  
  /**
   * Get colors at x/y positions with clipping.
   * \param type  type of values to return
   */
  static void
  get_values(struct gl_context *ctx, struct gl_renderbuffer *rb,
             GLuint count, const GLint x[], const GLint y[],
             void *values, GLenum type)
  {
     GLuint i;
  
     for (i = 0; i < count; i++) {
        if (x[i] >= 0 && y[i] >= 0 &&
  	  x[i] < (GLint) rb->Width && y[i] < (GLint) rb->Height) {
           /* inside */
           const GLubyte *src = _swrast_pixel_address(rb, x[i], y[i]);
  
           if (type == GL_UNSIGNED_BYTE) {
              _mesa_unpack_ubyte_rgba_row(rb->Format, 1, src,
                                          (GLubyte (*)[4]) values + i);
           }
           else if (type == GL_FLOAT) {
              _mesa_unpack_rgba_row(rb->Format, 1, src,
                                    (GLfloat (*)[4]) values + i);
           }
           else {
              _mesa_problem(ctx, "unexpected type in get_values()");
           }
        }
     }
  }
  
  
  /**
   * Get row of colors with clipping.
   * \param type  type of values to return
   */
  static void
  get_row(struct gl_context *ctx, struct gl_renderbuffer *rb,
          GLuint count, GLint x, GLint y,
          GLvoid *values, GLenum type)
  {
     GLint skip = 0;
     GLubyte *src;
  
     if (y < 0 || y >= (GLint) rb->Height)
        return; /* above or below */
  
     if (x + (GLint) count <= 0 || x >= (GLint) rb->Width)
        return; /* entirely left or right */
  
     if (x + count > rb->Width) {
        /* right clip */
        GLint clip = x + count - rb->Width;
        count -= clip;
     }
  
     if (x < 0) {
        /* left clip */
        skip = -x;
        x = 0;
        count -= skip;
     }
  
     src = _swrast_pixel_address(rb, x, y);
  
     if (type == GL_UNSIGNED_BYTE) {
        _mesa_unpack_ubyte_rgba_row(rb->Format, count, src,
                                    (GLubyte (*)[4]) values + skip);
     }
     else if (type == GL_FLOAT) {
        _mesa_unpack_rgba_row(rb->Format, count, src,
                              (GLfloat (*)[4]) values + skip);
     }
     else {
        _mesa_problem(ctx, "unexpected type in get_row()");
     }
  }
  
  
  /**
   * Get RGBA pixels from the given renderbuffer.
   * Used by blending, logicop and masking functions.
   * \return pointer to the colors we read.
   */
  void *
  _swrast_get_dest_rgba(struct gl_context *ctx, struct gl_renderbuffer *rb,
                        SWspan *span)
  {
     void *rbPixels;
  
     /* Point rbPixels to a temporary space */
     rbPixels = span->array->attribs[VARYING_SLOT_MAX - 1];
  
     /* Get destination values from renderbuffer */
     if (span->arrayMask & SPAN_XY) {
        get_values(ctx, rb, span->end, span->array->x, span->array->y,
                   rbPixels, span->array->ChanType);
     }
     else {
        get_row(ctx, rb, span->end, span->x, span->y,
                rbPixels, span->array->ChanType);
     }
  
     return rbPixels;
  }
  