text: /*
   * Mesa 3-D graphics library
   * Version:  6.1
   *
   * Copyright (C) 1999-2004  Brian Paul   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
   * BRIAN PAUL 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 texcompress.c
   * Helper functions for texture compression.
   */
  
  
  #include "glheader.h"
  #include "imports.h"
  #include "colormac.h"
  #include "context.h"
  #include "image.h"
  #include "texcompress.h"
  #include "texformat.h"
  #include "texstore.h"
  
  /**
   * Get the list of supported internal compression formats.
   *
   * \param ctx GL context.
   * \param formats the resulting format list (may be NULL).
   *
   * \return number of formats.
   */
  GLuint
  _mesa_get_compressed_formats( GLcontext *ctx, GLint *formats )
  {
     GLuint n = 0;
     if (ctx->Extensions.ARB_texture_compression) {
        if (ctx->Extensions.TDFX_texture_compression_FXT1) {
           if (formats) {
              formats[n++] = GL_COMPRESSED_RGB_FXT1_3DFX;
              formats[n++] = GL_COMPRESSED_RGBA_FXT1_3DFX;
           }
           else {
              n += 2;
           }
        }
        if (ctx->Extensions.EXT_texture_compression_s3tc) {
           if (formats) {
              formats[n++] = GL_COMPRESSED_RGB_S3TC_DXT1_EXT;
              /* Skip this one because it has a restriction (all transparent
               * pixels become black).  See the texture compressions spec for
               * a detailed explanation.  This is what NVIDIA does.
              formats[n++] = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
              */
              formats[n++] = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
              formats[n++] = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
           }
           else {
              n += 3;
           }
        }
        if (ctx->Extensions.S3_s3tc) {
           if (formats) {
              formats[n++] = GL_RGB_S3TC;
              formats[n++] = GL_RGB4_S3TC;
              formats[n++] = GL_RGBA_S3TC;
              formats[n++] = GL_RGBA4_S3TC;
           }
           else {
              n += 4;
           }
        }
     }
     return n;
  }
  
  
  
  /**
   * Return number of bytes needed to store a texture of the given size
   * using the specified compressed format.
   * This is called via the ctx->Driver.CompressedTextureSize function,
   * unless a device driver overrides it.
   *
   * \param width texture width in texels.
   * \param height texture height in texels.
   * \param depth texture depth in texels.
   * \param format - one of the specific compressed texture formats
   *
   * \return size in bytes, or zero if bad format
   */
  GLuint
  _mesa_compressed_texture_size( GLcontext *ctx,
                                 GLsizei width, GLsizei height, GLsizei depth,
                                 GLenum format )
  {
     GLuint size;
  
     ASSERT(depth == 1);
     (void) depth;
  
     switch (format) {
     case GL_COMPRESSED_RGB_FXT1_3DFX:
     case GL_COMPRESSED_RGBA_FXT1_3DFX:
        /* round up width to next multiple of 8, height to next multiple of 4 */
        width = (width + 7) & ~7;
        height = (height + 3) & ~3;
        /* 16 bytes per 8x4 tile of RGB[A] texels */
        size = width * height / 2;
        /* Textures smaller than 8x4 will effectively be made into 8x4 and
         * take 16 bytes.
         */
        if (size < 16)
           size = 16;
        return size;
     case GL_COMPRESSED_RGB_S3TC_DXT1_EXT:
     case GL_COMPRESSED_RGBA_S3TC_DXT1_EXT:
     case GL_RGB_S3TC:
     case GL_RGB4_S3TC:
        /* round up width, height to next multiple of 4 */
        width = (width + 3) & ~3;
        height = (height + 3) & ~3;
        /* 8 bytes per 4x4 tile of RGB[A] texels */
        size = width * height / 2;
        /* Textures smaller than 4x4 will effectively be made into 4x4 and
         * take 8 bytes.
         */
        if (size < 8)
           size = 8;
        return size;
     case GL_COMPRESSED_RGBA_S3TC_DXT3_EXT:
     case GL_COMPRESSED_RGBA_S3TC_DXT5_EXT:
     case GL_RGBA_S3TC:
     case GL_RGBA4_S3TC:
        /* round up width, height to next multiple of 4 */
        width = (width + 3) & ~3;
        height = (height + 3) & ~3;
        /* 16 bytes per 4x4 tile of RGBA texels */
        size = width * height; /* simple! */
        /* Textures smaller than 4x4 will effectively be made into 4x4 and
         * take 16 bytes.
         */
        if (size < 16)
           size = 16;
        return size;
     default:
        _mesa_problem(ctx, "bad texformat in compressed_texture_size");
        return 0;
     }
  }
  
  
  /*
   * Compute the bytes per row in a compressed texture image.
   * We use this for computing the destination address for sub-texture updates.
   * \param format  one of the specific texture compression formats
   * \param width  image width in pixels
   * \return stride, in bytes, between rows for compressed image
   */
  GLint
  _mesa_compressed_row_stride(GLenum format, GLsizei width)
  {
     GLint stride;
  
     switch (format) {
     case GL_COMPRESSED_RGB_FXT1_3DFX:
     case GL_COMPRESSED_RGBA_FXT1_3DFX:
        stride = ((width + 7) / 8) * 16; /* 16 bytes per 8x4 tile */
        break;
     case GL_COMPRESSED_RGB_S3TC_DXT1_EXT:
     case GL_COMPRESSED_RGBA_S3TC_DXT1_EXT:
     case GL_RGB_S3TC:
     case GL_RGB4_S3TC:
        stride = ((width + 3) / 4) * 8; /* 8 bytes per 4x4 tile */
        break;
     case GL_COMPRESSED_RGBA_S3TC_DXT3_EXT:
     case GL_COMPRESSED_RGBA_S3TC_DXT5_EXT:
     case GL_RGBA_S3TC:
     case GL_RGBA4_S3TC:
        stride = ((width + 3) / 4) * 16; /* 16 bytes per 4x4 tile */
        break;
     default:
        return 0;
     }
  
     return stride;
  }
  
  
  /*
   * Return the address of the pixel at (col, row, img) in a
   * compressed texture image.
   * \param col, row, img - image position (3D)
   * \param format - compressed image format
   * \param width - image width
   * \param image - the image address
   * \return address of pixel at (row, col)
   */
  GLubyte *
  _mesa_compressed_image_address(GLint col, GLint row, GLint img,
                                 GLenum format,
                                 GLsizei width, const GLubyte *image)
  {
     GLubyte *addr;
  
     (void) img;
  
     /* We try to spot a "complete" subtexture "above" ROW, COL;
      * this texture is given by appropriate rounding of WIDTH x ROW.
      * Then we just add the amount left (usually on the left).
      *
      * Example for X*Y microtiles (Z bytes each)
      * offset = Z * (((width + X - 1) / X) * (row / Y) + col / X);
      */
  
     switch (format) {
     case GL_COMPRESSED_RGB_FXT1_3DFX:
     case GL_COMPRESSED_RGBA_FXT1_3DFX:
        addr = (GLubyte *) image + 16 * (((width + 7) / 8) * (row / 4) + col / 8);
        break;
     case GL_COMPRESSED_RGB_S3TC_DXT1_EXT:
     case GL_COMPRESSED_RGBA_S3TC_DXT1_EXT:
     case GL_RGB_S3TC:
     case GL_RGB4_S3TC:
        addr = (GLubyte *) image + 8 * (((width + 3) / 4) * (row / 4) + col / 4);
        break;
     case GL_COMPRESSED_RGBA_S3TC_DXT3_EXT:
     case GL_COMPRESSED_RGBA_S3TC_DXT5_EXT:
     case GL_RGBA_S3TC:
     case GL_RGBA4_S3TC:
        addr = (GLubyte *) image + 16 * (((width + 3) / 4) * (row / 4) + col / 4);
        break;
     default:
        return NULL;
     }
  
     return addr;
  }
  