mesa: Import libtxc_dxtn sources

Imported from master (commit ef07298391c6dcad843e0b13e985090c1dd76e76)
of https://cgit.freedesktop.org/~mareko/libtxc_dxtn/

Acked-by: Nicolai Hähnle <[email protected]>
Acked-by: Emil Velikov <[email protected]>

3 files changed, 1141 insertions, 0 deletions

diff --git a/src/mesa/main/txc_compress_dxtn.c b/src/mesa/main/txc_compress_dxtn.c
new file mode 100644
index 00000000000..cf83d08eeac
--- /dev/null
+++ b/src/mesa/main/txc_compress_dxtn.c
@@ -0,0 +1,843 @@
+/*
+ * libtxc_dxtn
+ * Version:  1.0
+ *
+ * Copyright (C) 2004  Roland Scheidegger   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.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "txc_dxtn.h"
+
+/* weights used for error function, basically weights (unsquared 2/4/1) according to rgb->luminance conversion
+   not sure if this really reflects visual perception */
+#define REDWEIGHT 4
+#define GREENWEIGHT 16
+#define BLUEWEIGHT 1
+
+#define ALPHACUT 127
+
+static void fancybasecolorsearch( GLubyte *blkaddr, GLubyte srccolors[4][4][4], GLubyte *bestcolor[2],
+                           GLint numxpixels, GLint numypixels, GLint type, GLboolean haveAlpha)
+{
+   /* use same luminance-weighted distance metric to determine encoding as for finding the base colors */
+
+   /* TODO could also try to find a better encoding for the 3-color-encoding type, this really should be done
+      if it's rgba_dxt1 and we have alpha in the block, currently even values which will be mapped to black
+      due to their alpha value will influence the result */
+   GLint i, j, colors, z;
+   GLuint pixerror, pixerrorred, pixerrorgreen, pixerrorblue, pixerrorbest;
+   GLint colordist, blockerrlin[2][3];
+   GLubyte nrcolor[2];
+   GLint pixerrorcolorbest[3];
+   GLubyte enc = 0;
+   GLubyte cv[4][4];
+   GLubyte testcolor[2][3];
+
+/*   fprintf(stderr, "color begin 0 r/g/b %d/%d/%d, 1 r/g/b %d/%d/%d\n",
+      bestcolor[0][0], bestcolor[0][1], bestcolor[0][2], bestcolor[1][0], bestcolor[1][1], bestcolor[1][2]);*/
+   if (((bestcolor[0][0] & 0xf8) << 8 | (bestcolor[0][1] & 0xfc) << 3 | bestcolor[0][2] >> 3) <
+      ((bestcolor[1][0] & 0xf8) << 8 | (bestcolor[1][1] & 0xfc) << 3 | bestcolor[1][2] >> 3)) {
+      testcolor[0][0] = bestcolor[0][0];
+      testcolor[0][1] = bestcolor[0][1];
+      testcolor[0][2] = bestcolor[0][2];
+      testcolor[1][0] = bestcolor[1][0];
+      testcolor[1][1] = bestcolor[1][1];
+      testcolor[1][2] = bestcolor[1][2];
+   }
+   else {
+      testcolor[1][0] = bestcolor[0][0];
+      testcolor[1][1] = bestcolor[0][1];
+      testcolor[1][2] = bestcolor[0][2];
+      testcolor[0][0] = bestcolor[1][0];
+      testcolor[0][1] = bestcolor[1][1];
+      testcolor[0][2] = bestcolor[1][2];
+   }
+
+   for (i = 0; i < 3; i ++) {
+      cv[0][i] = testcolor[0][i];
+      cv[1][i] = testcolor[1][i];
+      cv[2][i] = (testcolor[0][i] * 2 + testcolor[1][i]) / 3;
+      cv[3][i] = (testcolor[0][i] + testcolor[1][i] * 2) / 3;
+   }
+
+   blockerrlin[0][0] = 0;
+   blockerrlin[0][1] = 0;
+   blockerrlin[0][2] = 0;
+   blockerrlin[1][0] = 0;
+   blockerrlin[1][1] = 0;
+   blockerrlin[1][2] = 0;
+
+   nrcolor[0] = 0;
+   nrcolor[1] = 0;
+
+   for (j = 0; j < numypixels; j++) {
+      for (i = 0; i < numxpixels; i++) {
+         pixerrorbest = 0xffffffff;
+         for (colors = 0; colors < 4; colors++) {
+            colordist = srccolors[j][i][0] - (cv[colors][0]);
+            pixerror = colordist * colordist * REDWEIGHT;
+            pixerrorred = colordist;
+            colordist = srccolors[j][i][1] - (cv[colors][1]);
+            pixerror += colordist * colordist * GREENWEIGHT;
+            pixerrorgreen = colordist;
+            colordist = srccolors[j][i][2] - (cv[colors][2]);
+            pixerror += colordist * colordist * BLUEWEIGHT;
+            pixerrorblue = colordist;
+            if (pixerror < pixerrorbest) {
+               enc = colors;
+               pixerrorbest = pixerror;
+               pixerrorcolorbest[0] = pixerrorred;
+               pixerrorcolorbest[1] = pixerrorgreen;
+               pixerrorcolorbest[2] = pixerrorblue;
+            }
+         }
+         if (enc == 0) {
+            for (z = 0; z < 3; z++) {
+               blockerrlin[0][z] += 3 * pixerrorcolorbest[z];
+            }
+            nrcolor[0] += 3;
+         }
+         else if (enc == 2) {
+            for (z = 0; z < 3; z++) {
+               blockerrlin[0][z] += 2 * pixerrorcolorbest[z];
+            }
+            nrcolor[0] += 2;
+            for (z = 0; z < 3; z++) {
+               blockerrlin[1][z] += 1 * pixerrorcolorbest[z];
+            }
+            nrcolor[1] += 1;
+         }
+         else if (enc == 3) {
+            for (z = 0; z < 3; z++) {
+               blockerrlin[0][z] += 1 * pixerrorcolorbest[z];
+            }
+            nrcolor[0] += 1;
+            for (z = 0; z < 3; z++) {
+               blockerrlin[1][z] += 2 * pixerrorcolorbest[z];
+            }
+            nrcolor[1] += 2;
+         }
+         else if (enc == 1) {
+            for (z = 0; z < 3; z++) {
+               blockerrlin[1][z] += 3 * pixerrorcolorbest[z];
+            }
+            nrcolor[1] += 3;
+         }
+      }
+   }
+   if (nrcolor[0] == 0) nrcolor[0] = 1;
+   if (nrcolor[1] == 0) nrcolor[1] = 1;
+   for (j = 0; j < 2; j++) {
+      for (i = 0; i < 3; i++) {
+	 GLint newvalue = testcolor[j][i] + blockerrlin[j][i] / nrcolor[j];
+	 if (newvalue <= 0)
+	    testcolor[j][i] = 0;
+	 else if (newvalue >= 255)
+	    testcolor[j][i] = 255;
+	 else testcolor[j][i] = newvalue;
+      }
+   }
+
+   if ((abs(testcolor[0][0] - testcolor[1][0]) < 8) &&
+       (abs(testcolor[0][1] - testcolor[1][1]) < 4) &&
+       (abs(testcolor[0][2] - testcolor[1][2]) < 8)) {
+       /* both colors are so close they might get encoded as the same 16bit values */
+      GLubyte coldiffred, coldiffgreen, coldiffblue, coldiffmax, factor, ind0, ind1;
+
+      coldiffred = abs(testcolor[0][0] - testcolor[1][0]);
+      coldiffgreen = 2 * abs(testcolor[0][1] - testcolor[1][1]);
+      coldiffblue = abs(testcolor[0][2] - testcolor[1][2]);
+      coldiffmax = coldiffred;
+      if (coldiffmax < coldiffgreen) coldiffmax = coldiffgreen;
+      if (coldiffmax < coldiffblue) coldiffmax = coldiffblue;
+      if (coldiffmax > 0) {
+         if (coldiffmax > 4) factor = 2;
+         else if (coldiffmax > 2) factor = 3;
+         else factor = 4;
+         /* Won't do much if the color value is near 255... */
+         /* argh so many ifs */
+         if (testcolor[1][1] >= testcolor[0][1]) {
+            ind1 = 1; ind0 = 0;
+         }
+         else {
+            ind1 = 0; ind0 = 1;
+         }
+         if ((testcolor[ind1][1] + factor * coldiffgreen) <= 255)
+            testcolor[ind1][1] += factor * coldiffgreen;
+         else testcolor[ind1][1] = 255;
+         if ((testcolor[ind1][0] - testcolor[ind0][1]) > 0) {
+            if ((testcolor[ind1][0] + factor * coldiffred) <= 255)
+               testcolor[ind1][0] += factor * coldiffred;
+            else testcolor[ind1][0] = 255;
+         }
+         else {
+            if ((testcolor[ind0][0] + factor * coldiffred) <= 255)
+               testcolor[ind0][0] += factor * coldiffred;
+            else testcolor[ind0][0] = 255;
+         }
+         if ((testcolor[ind1][2] - testcolor[ind0][2]) > 0) {
+            if ((testcolor[ind1][2] + factor * coldiffblue) <= 255)
+               testcolor[ind1][2] += factor * coldiffblue;
+            else testcolor[ind1][2] = 255;
+         }
+         else {
+            if ((testcolor[ind0][2] + factor * coldiffblue) <= 255)
+               testcolor[ind0][2] += factor * coldiffblue;
+            else testcolor[ind0][2] = 255;
+         }
+      }
+   }
+
+   if (((testcolor[0][0] & 0xf8) << 8 | (testcolor[0][1] & 0xfc) << 3 | testcolor[0][2] >> 3) <
+      ((testcolor[1][0] & 0xf8) << 8 | (testcolor[1][1] & 0xfc) << 3 | testcolor[1][2]) >> 3) {
+      for (i = 0; i < 3; i++) {
+         bestcolor[0][i] = testcolor[0][i];
+         bestcolor[1][i] = testcolor[1][i];
+      }
+   }
+   else {
+      for (i = 0; i < 3; i++) {
+         bestcolor[0][i] = testcolor[1][i];
+         bestcolor[1][i] = testcolor[0][i];
+      }
+   }
+
+/*     fprintf(stderr, "color end 0 r/g/b %d/%d/%d, 1 r/g/b %d/%d/%d\n",
+     bestcolor[0][0], bestcolor[0][1], bestcolor[0][2], bestcolor[1][0], bestcolor[1][1], bestcolor[1][2]);*/
+}
+
+
+
+static void storedxtencodedblock( GLubyte *blkaddr, GLubyte srccolors[4][4][4], GLubyte *bestcolor[2],
+                           GLint numxpixels, GLint numypixels, GLuint type, GLboolean haveAlpha)
+{
+   /* use same luminance-weighted distance metric to determine encoding as for finding the base colors */
+
+   GLint i, j, colors;
+   GLuint testerror, testerror2, pixerror, pixerrorbest;
+   GLint colordist;
+   GLushort color0, color1, tempcolor;
+   GLuint bits = 0, bits2 = 0;
+   GLubyte *colorptr;
+   GLubyte enc = 0;
+   GLubyte cv[4][4];
+
+   bestcolor[0][0] = bestcolor[0][0] & 0xf8;
+   bestcolor[0][1] = bestcolor[0][1] & 0xfc;
+   bestcolor[0][2] = bestcolor[0][2] & 0xf8;
+   bestcolor[1][0] = bestcolor[1][0] & 0xf8;
+   bestcolor[1][1] = bestcolor[1][1] & 0xfc;
+   bestcolor[1][2] = bestcolor[1][2] & 0xf8;
+
+   color0 = bestcolor[0][0] << 8 | bestcolor[0][1] << 3 | bestcolor[0][2] >> 3;
+   color1 = bestcolor[1][0] << 8 | bestcolor[1][1] << 3 | bestcolor[1][2] >> 3;
+   if (color0 < color1) {
+      tempcolor = color0; color0 = color1; color1 = tempcolor;
+      colorptr = bestcolor[0]; bestcolor[0] = bestcolor[1]; bestcolor[1] = colorptr;
+   }
+
+
+   for (i = 0; i < 3; i++) {
+      cv[0][i] = bestcolor[0][i];
+      cv[1][i] = bestcolor[1][i];
+      cv[2][i] = (bestcolor[0][i] * 2 + bestcolor[1][i]) / 3;
+      cv[3][i] = (bestcolor[0][i] + bestcolor[1][i] * 2) / 3;
+   }
+
+   testerror = 0;
+   for (j = 0; j < numypixels; j++) {
+      for (i = 0; i < numxpixels; i++) {
+         pixerrorbest = 0xffffffff;
+         for (colors = 0; colors < 4; colors++) {
+            colordist = srccolors[j][i][0] - cv[colors][0];
+            pixerror = colordist * colordist * REDWEIGHT;
+            colordist = srccolors[j][i][1] - cv[colors][1];
+            pixerror += colordist * colordist * GREENWEIGHT;
+            colordist = srccolors[j][i][2] - cv[colors][2];
+            pixerror += colordist * colordist * BLUEWEIGHT;
+            if (pixerror < pixerrorbest) {
+               pixerrorbest = pixerror;
+               enc = colors;
+            }
+         }
+         testerror += pixerrorbest;
+         bits |= enc << (2 * (j * 4 + i));
+      }
+   }
+   /* some hw might disagree but actually decoding should always use 4-color encoding
+      for non-dxt1 formats */
+   if (type == GL_COMPRESSED_RGB_S3TC_DXT1_EXT || type == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) {
+      for (i = 0; i < 3; i++) {
+         cv[2][i] = (bestcolor[0][i] + bestcolor[1][i]) / 2;
+         /* this isn't used. Looks like the black color constant can only be used
+            with RGB_DXT1 if I read the spec correctly (note though that the radeon gpu disagrees,
+            it will decode 3 to black even with DXT3/5), and due to how the color searching works
+            it won't get used even then */
+         cv[3][i] = 0;
+      }
+      testerror2 = 0;
+      for (j = 0; j < numypixels; j++) {
+         for (i = 0; i < numxpixels; i++) {
+            pixerrorbest = 0xffffffff;
+            if ((type == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) && (srccolors[j][i][3] <= ALPHACUT)) {
+               enc = 3;
+               pixerrorbest = 0; /* don't calculate error */
+            }
+            else {
+               /* we're calculating the same what we have done already for colors 0-1 above... */
+               for (colors = 0; colors < 3; colors++) {
+                  colordist = srccolors[j][i][0] - cv[colors][0];
+                  pixerror = colordist * colordist * REDWEIGHT;
+                  colordist = srccolors[j][i][1] - cv[colors][1];
+                  pixerror += colordist * colordist * GREENWEIGHT;
+                  colordist = srccolors[j][i][2] - cv[colors][2];
+                  pixerror += colordist * colordist * BLUEWEIGHT;
+                  if (pixerror < pixerrorbest) {
+                     pixerrorbest = pixerror;
+                     /* need to exchange colors later */
+                     if (colors > 1) enc = colors;
+                     else enc = colors ^ 1;
+                  }
+               }
+            }
+            testerror2 += pixerrorbest;
+            bits2 |= enc << (2 * (j * 4 + i));
+         }
+      }
+   } else {
+      testerror2 = 0xffffffff;
+   }
+
+   /* finally we're finished, write back colors and bits */
+   if ((testerror > testerror2) || (haveAlpha)) {
+      *blkaddr++ = color1 & 0xff;
+      *blkaddr++ = color1 >> 8;
+      *blkaddr++ = color0 & 0xff;
+      *blkaddr++ = color0 >> 8;
+      *blkaddr++ = bits2 & 0xff;
+      *blkaddr++ = ( bits2 >> 8) & 0xff;
+      *blkaddr++ = ( bits2 >> 16) & 0xff;
+      *blkaddr = bits2 >> 24;
+   }
+   else {
+      *blkaddr++ = color0 & 0xff;
+      *blkaddr++ = color0 >> 8;
+      *blkaddr++ = color1 & 0xff;
+      *blkaddr++ = color1 >> 8;
+      *blkaddr++ = bits & 0xff;
+      *blkaddr++ = ( bits >> 8) & 0xff;
+      *blkaddr++ = ( bits >> 16) & 0xff;
+      *blkaddr = bits >> 24;
+   }
+}
+
+static void encodedxtcolorblockfaster( GLubyte *blkaddr, GLubyte srccolors[4][4][4],
+                         GLint numxpixels, GLint numypixels, GLuint type )
+{
+/* simplistic approach. We need two base colors, simply use the "highest" and the "lowest" color
+   present in the picture as base colors */
+
+   /* define lowest and highest color as shortest and longest vector to 0/0/0, though the
+      vectors are weighted similar to their importance in rgb-luminance conversion
+      doesn't work too well though...
+      This seems to be a rather difficult problem */
+
+   GLubyte *bestcolor[2];
+   GLubyte basecolors[2][3];
+   GLubyte i, j;
+   GLuint lowcv, highcv, testcv;
+   GLboolean haveAlpha = GL_FALSE;
+
+   lowcv = highcv = srccolors[0][0][0] * srccolors[0][0][0] * REDWEIGHT +
+                          srccolors[0][0][1] * srccolors[0][0][1] * GREENWEIGHT +
+                          srccolors[0][0][2] * srccolors[0][0][2] * BLUEWEIGHT;
+   bestcolor[0] = bestcolor[1] = srccolors[0][0];
+   for (j = 0; j < numypixels; j++) {
+      for (i = 0; i < numxpixels; i++) {
+         /* don't use this as a base color if the pixel will get black/transparent anyway */
+         if ((type != GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) || (srccolors[j][i][3] > ALPHACUT)) {
+            testcv = srccolors[j][i][0] * srccolors[j][i][0] * REDWEIGHT +
+                     srccolors[j][i][1] * srccolors[j][i][1] * GREENWEIGHT +
+                     srccolors[j][i][2] * srccolors[j][i][2] * BLUEWEIGHT;
+            if (testcv > highcv) {
+               highcv = testcv;
+               bestcolor[1] = srccolors[j][i];
+            }
+            else if (testcv < lowcv) {
+               lowcv = testcv;
+               bestcolor[0] = srccolors[j][i];
+            }
+         }
+         else haveAlpha = GL_TRUE;
+      }
+   }
+   /* make sure the original color values won't get touched... */
+   for (j = 0; j < 2; j++) {
+      for (i = 0; i < 3; i++) {
+         basecolors[j][i] = bestcolor[j][i];
+      }
+   }
+   bestcolor[0] = basecolors[0];
+   bestcolor[1] = basecolors[1];
+
+   /* try to find better base colors */
+   fancybasecolorsearch(blkaddr, srccolors, bestcolor, numxpixels, numypixels, type, haveAlpha);
+   /* find the best encoding for these colors, and store the result */
+   storedxtencodedblock(blkaddr, srccolors, bestcolor, numxpixels, numypixels, type, haveAlpha);
+}
+
+static void writedxt5encodedalphablock( GLubyte *blkaddr, GLubyte alphabase1, GLubyte alphabase2,
+                         GLubyte alphaenc[16])
+{
+   *blkaddr++ = alphabase1;
+   *blkaddr++ = alphabase2;
+   *blkaddr++ = alphaenc[0] | (alphaenc[1] << 3) | ((alphaenc[2] & 3) << 6);
+   *blkaddr++ = (alphaenc[2] >> 2) | (alphaenc[3] << 1) | (alphaenc[4] << 4) | ((alphaenc[5] & 1) << 7);
+   *blkaddr++ = (alphaenc[5] >> 1) | (alphaenc[6] << 2) | (alphaenc[7] << 5);
+   *blkaddr++ = alphaenc[8] | (alphaenc[9] << 3) | ((alphaenc[10] & 3) << 6);
+   *blkaddr++ = (alphaenc[10] >> 2) | (alphaenc[11] << 1) | (alphaenc[12] << 4) | ((alphaenc[13] & 1) << 7);
+   *blkaddr++ = (alphaenc[13] >> 1) | (alphaenc[14] << 2) | (alphaenc[15] << 5);
+}
+
+static void encodedxt5alpha(GLubyte *blkaddr, GLubyte srccolors[4][4][4],
+                            GLint numxpixels, GLint numypixels)
+{
+   GLubyte alphabase[2], alphause[2];
+   GLshort alphatest[2];
+   GLuint alphablockerror1, alphablockerror2, alphablockerror3;
+   GLubyte i, j, aindex, acutValues[7];
+   GLubyte alphaenc1[16], alphaenc2[16], alphaenc3[16];
+   GLboolean alphaabsmin = GL_FALSE;
+   GLboolean alphaabsmax = GL_FALSE;
+   GLshort alphadist;
+
+   /* find lowest and highest alpha value in block, alphabase[0] lowest, alphabase[1] highest */
+   alphabase[0] = 0xff; alphabase[1] = 0x0;
+   for (j = 0; j < numypixels; j++) {
+      for (i = 0; i < numxpixels; i++) {
+         if (srccolors[j][i][3] == 0)
+            alphaabsmin = GL_TRUE;
+         else if (srccolors[j][i][3] == 255)
+            alphaabsmax = GL_TRUE;
+         else {
+            if (srccolors[j][i][3] > alphabase[1])
+               alphabase[1] = srccolors[j][i][3];
+            if (srccolors[j][i][3] < alphabase[0])
+               alphabase[0] = srccolors[j][i][3];
+         }
+      }
+   }
+
+
+   if ((alphabase[0] > alphabase[1]) && !(alphaabsmin && alphaabsmax)) { /* one color, either max or min */
+      /* shortcut here since it is a very common case (and also avoids later problems) */
+      /* || (alphabase[0] == alphabase[1] && !alphaabsmin && !alphaabsmax) */
+      /* could also thest for alpha0 == alpha1 (and not min/max), but probably not common, so don't bother */
+
+      *blkaddr++ = srccolors[0][0][3];
+      blkaddr++;
+      *blkaddr++ = 0;
+      *blkaddr++ = 0;
+      *blkaddr++ = 0;
+      *blkaddr++ = 0;
+      *blkaddr++ = 0;
+      *blkaddr++ = 0;
+/*      fprintf(stderr, "enc0 used\n");*/
+      return;
+   }
+
+   /* find best encoding for alpha0 > alpha1 */
+   /* it's possible this encoding is better even if both alphaabsmin and alphaabsmax are true */
+   alphablockerror1 = 0x0;
+   alphablockerror2 = 0xffffffff;
+   alphablockerror3 = 0xffffffff;
+   if (alphaabsmin) alphause[0] = 0;
+   else alphause[0] = alphabase[0];
+   if (alphaabsmax) alphause[1] = 255;
+   else alphause[1] = alphabase[1];
+   /* calculate the 7 cut values, just the middle between 2 of the computed alpha values */
+   for (aindex = 0; aindex < 7; aindex++) {
+      /* don't forget here is always rounded down */
+      acutValues[aindex] = (alphause[0] * (2*aindex + 1) + alphause[1] * (14 - (2*aindex + 1))) / 14;
+   }
+
+   for (j = 0; j < numypixels; j++) {
+      for (i = 0; i < numxpixels; i++) {
+         /* maybe it's overkill to have the most complicated calculation just for the error
+            calculation which we only need to figure out if encoding1 or encoding2 is better... */
+         if (srccolors[j][i][3] > acutValues[0]) {
+            alphaenc1[4*j + i] = 0;
+            alphadist = srccolors[j][i][3] - alphause[1];
+         }
+         else if (srccolors[j][i][3] > acutValues[1]) {
+            alphaenc1[4*j + i] = 2;
+            alphadist = srccolors[j][i][3] - (alphause[1] * 6 + alphause[0] * 1) / 7;
+         }
+         else if (srccolors[j][i][3] > acutValues[2]) {
+            alphaenc1[4*j + i] = 3;
+            alphadist = srccolors[j][i][3] - (alphause[1] * 5 + alphause[0] * 2) / 7;
+         }
+         else if (srccolors[j][i][3] > acutValues[3]) {
+            alphaenc1[4*j + i] = 4;
+            alphadist = srccolors[j][i][3] - (alphause[1] * 4 + alphause[0] * 3) / 7;
+         }
+         else if (srccolors[j][i][3] > acutValues[4]) {
+            alphaenc1[4*j + i] = 5;
+            alphadist = srccolors[j][i][3] - (alphause[1] * 3 + alphause[0] * 4) / 7;
+         }
+         else if (srccolors[j][i][3] > acutValues[5]) {
+            alphaenc1[4*j + i] = 6;
+            alphadist = srccolors[j][i][3] - (alphause[1] * 2 + alphause[0] * 5) / 7;
+         }
+         else if (srccolors[j][i][3] > acutValues[6]) {
+            alphaenc1[4*j + i] = 7;
+            alphadist = srccolors[j][i][3] - (alphause[1] * 1 + alphause[0] * 6) / 7;
+         }
+         else {
+            alphaenc1[4*j + i] = 1;
+            alphadist = srccolors[j][i][3] - alphause[0];
+         }
+         alphablockerror1 += alphadist * alphadist;
+      }
+   }
+/*      for (i = 0; i < 16; i++) {
+         fprintf(stderr, "%d ", alphaenc1[i]);
+      }
+      fprintf(stderr, "cutVals ");
+      for (i = 0; i < 8; i++) {
+         fprintf(stderr, "%d ", acutValues[i]);
+      }
+      fprintf(stderr, "srcVals ");
+      for (j = 0; j < numypixels; j++)
+         for (i = 0; i < numxpixels; i++) {
+            fprintf(stderr, "%d ", srccolors[j][i][3]);
+         }
+
+      fprintf(stderr, "\n");
+   }*/
+   /* it's not very likely this encoding is better if both alphaabsmin and alphaabsmax
+      are false but try it anyway */
+   if (alphablockerror1 >= 32) {
+
+      /* don't bother if encoding is already very good, this condition should also imply
+      we have valid alphabase colors which we absolutely need (alphabase[0] <= alphabase[1]) */
+      alphablockerror2 = 0;
+      for (aindex = 0; aindex < 5; aindex++) {
+         /* don't forget here is always rounded down */
+         acutValues[aindex] = (alphabase[0] * (10 - (2*aindex + 1)) + alphabase[1] * (2*aindex + 1)) / 10;
+      }
+      for (j = 0; j < numypixels; j++) {
+         for (i = 0; i < numxpixels; i++) {
+             /* maybe it's overkill to have the most complicated calculation just for the error
+               calculation which we only need to figure out if encoding1 or encoding2 is better... */
+            if (srccolors[j][i][3] == 0) {
+               alphaenc2[4*j + i] = 6;
+               alphadist = 0;
+            }
+            else if (srccolors[j][i][3] == 255) {
+               alphaenc2[4*j + i] = 7;
+               alphadist = 0;
+            }
+            else if (srccolors[j][i][3] <= acutValues[0]) {
+               alphaenc2[4*j + i] = 0;
+               alphadist = srccolors[j][i][3] - alphabase[0];
+            }
+            else if (srccolors[j][i][3] <= acutValues[1]) {
+               alphaenc2[4*j + i] = 2;
+               alphadist = srccolors[j][i][3] - (alphabase[0] * 4 + alphabase[1] * 1) / 5;
+            }
+            else if (srccolors[j][i][3] <= acutValues[2]) {
+               alphaenc2[4*j + i] = 3;
+               alphadist = srccolors[j][i][3] - (alphabase[0] * 3 + alphabase[1] * 2) / 5;
+            }
+            else if (srccolors[j][i][3] <= acutValues[3]) {
+               alphaenc2[4*j + i] = 4;
+               alphadist = srccolors[j][i][3] - (alphabase[0] * 2 + alphabase[1] * 3) / 5;
+            }
+            else if (srccolors[j][i][3] <= acutValues[4]) {
+               alphaenc2[4*j + i] = 5;
+               alphadist = srccolors[j][i][3] - (alphabase[0] * 1 + alphabase[1] * 4) / 5;
+            }
+            else {
+               alphaenc2[4*j + i] = 1;
+               alphadist = srccolors[j][i][3] - alphabase[1];
+            }
+            alphablockerror2 += alphadist * alphadist;
+         }
+      }
+
+
+      /* skip this if the error is already very small
+         this encoding is MUCH better on average than #2 though, but expensive! */
+      if ((alphablockerror2 > 96) && (alphablockerror1 > 96)) {
+         GLshort blockerrlin1 = 0;
+         GLshort blockerrlin2 = 0;
+         GLubyte nralphainrangelow = 0;
+         GLubyte nralphainrangehigh = 0;
+         alphatest[0] = 0xff;
+         alphatest[1] = 0x0;
+         /* if we have large range it's likely there are values close to 0/255, try to map them to 0/255 */
+         for (j = 0; j < numypixels; j++) {
+            for (i = 0; i < numxpixels; i++) {
+               if ((srccolors[j][i][3] > alphatest[1]) && (srccolors[j][i][3] < (255 -(alphabase[1] - alphabase[0]) / 28)))
+                  alphatest[1] = srccolors[j][i][3];
+               if ((srccolors[j][i][3] < alphatest[0]) && (srccolors[j][i][3] > (alphabase[1] - alphabase[0]) / 28))
+                  alphatest[0] = srccolors[j][i][3];
+            }
+         }
+          /* shouldn't happen too often, don't really care about those degenerated cases */
+          if (alphatest[1] <= alphatest[0]) {
+             alphatest[0] = 1;
+             alphatest[1] = 254;
+/*             fprintf(stderr, "only 1 or 0 colors for encoding!\n");*/
+         }
+         for (aindex = 0; aindex < 5; aindex++) {
+         /* don't forget here is always rounded down */
+            acutValues[aindex] = (alphatest[0] * (10 - (2*aindex + 1)) + alphatest[1] * (2*aindex + 1)) / 10;
+         }
+
+         /* find the "average" difference between the alpha values and the next encoded value.
+            This is then used to calculate new base values.
+            Should there be some weighting, i.e. those values closer to alphatest[x] have more weight,
+            since they will see more improvement, and also because the values in the middle are somewhat
+            likely to get no improvement at all (because the base values might move in different directions)?
+            OTOH it would mean the values in the middle are even less likely to get an improvement
+         */
+         for (j = 0; j < numypixels; j++) {
+            for (i = 0; i < numxpixels; i++) {
+               if (srccolors[j][i][3] <= alphatest[0] / 2) {
+               }
+               else if (srccolors[j][i][3] > ((255 + alphatest[1]) / 2)) {
+               }
+               else if (srccolors[j][i][3] <= acutValues[0]) {
+                  blockerrlin1 += (srccolors[j][i][3] - alphatest[0]);
+                  nralphainrangelow += 1;
+               }
+               else if (srccolors[j][i][3] <= acutValues[1]) {
+                  blockerrlin1 += (srccolors[j][i][3] - (alphatest[0] * 4 + alphatest[1] * 1) / 5);
+                  blockerrlin2 += (srccolors[j][i][3] - (alphatest[0] * 4 + alphatest[1] * 1) / 5);
+                  nralphainrangelow += 1;
+                  nralphainrangehigh += 1;
+               }
+               else if (srccolors[j][i][3] <= acutValues[2]) {
+                  blockerrlin1 += (srccolors[j][i][3] - (alphatest[0] * 3 + alphatest[1] * 2) / 5);
+                  blockerrlin2 += (srccolors[j][i][3] - (alphatest[0] * 3 + alphatest[1] * 2) / 5);
+                  nralphainrangelow += 1;
+                  nralphainrangehigh += 1;
+               }
+               else if (srccolors[j][i][3] <= acutValues[3]) {
+                  blockerrlin1 += (srccolors[j][i][3] - (alphatest[0] * 2 + alphatest[1] * 3) / 5);
+                  blockerrlin2 += (srccolors[j][i][3] - (alphatest[0] * 2 + alphatest[1] * 3) / 5);
+                  nralphainrangelow += 1;
+                  nralphainrangehigh += 1;
+               }
+               else if (srccolors[j][i][3] <= acutValues[4]) {
+                  blockerrlin1 += (srccolors[j][i][3] - (alphatest[0] * 1 + alphatest[1] * 4) / 5);
+                  blockerrlin2 += (srccolors[j][i][3] - (alphatest[0] * 1 + alphatest[1] * 4) / 5);
+                  nralphainrangelow += 1;
+                  nralphainrangehigh += 1;
+                  }
+               else {
+                  blockerrlin2 += (srccolors[j][i][3] - alphatest[1]);
+                  nralphainrangehigh += 1;
+               }
+            }
+         }
+         /* shouldn't happen often, needed to avoid div by zero */
+         if (nralphainrangelow == 0) nralphainrangelow = 1;
+         if (nralphainrangehigh == 0) nralphainrangehigh = 1;
+         alphatest[0] = alphatest[0] + (blockerrlin1 / nralphainrangelow);
+/*         fprintf(stderr, "block err lin low %d, nr %d\n", blockerrlin1, nralphainrangelow);
+         fprintf(stderr, "block err lin high %d, nr %d\n", blockerrlin2, nralphainrangehigh);*/
+         /* again shouldn't really happen often... */
+         if (alphatest[0] < 0) {
+            alphatest[0] = 0;
+/*            fprintf(stderr, "adj alpha base val to 0\n");*/
+         }
+         alphatest[1] = alphatest[1] + (blockerrlin2 / nralphainrangehigh);
+         if (alphatest[1] > 255) {
+            alphatest[1] = 255;
+/*            fprintf(stderr, "adj alpha base val to 255\n");*/
+         }
+
+         alphablockerror3 = 0;
+         for (aindex = 0; aindex < 5; aindex++) {
+         /* don't forget here is always rounded down */
+            acutValues[aindex] = (alphatest[0] * (10 - (2*aindex + 1)) + alphatest[1] * (2*aindex + 1)) / 10;
+         }
+         for (j = 0; j < numypixels; j++) {
+            for (i = 0; i < numxpixels; i++) {
+                /* maybe it's overkill to have the most complicated calculation just for the error
+                  calculation which we only need to figure out if encoding1 or encoding2 is better... */
+               if (srccolors[j][i][3] <= alphatest[0] / 2) {
+                  alphaenc3[4*j + i] = 6;
+                  alphadist = srccolors[j][i][3];
+               }
+               else if (srccolors[j][i][3] > ((255 + alphatest[1]) / 2)) {
+                  alphaenc3[4*j + i] = 7;
+                  alphadist = 255 - srccolors[j][i][3];
+               }
+               else if (srccolors[j][i][3] <= acutValues[0]) {
+                  alphaenc3[4*j + i] = 0;
+                  alphadist = srccolors[j][i][3] - alphatest[0];
+               }
+               else if (srccolors[j][i][3] <= acutValues[1]) {
+                 alphaenc3[4*j + i] = 2;
+                 alphadist = srccolors[j][i][3] - (alphatest[0] * 4 + alphatest[1] * 1) / 5;
+               }
+               else if (srccolors[j][i][3] <= acutValues[2]) {
+                  alphaenc3[4*j + i] = 3;
+                  alphadist = srccolors[j][i][3] - (alphatest[0] * 3 + alphatest[1] * 2) / 5;
+               }
+               else if (srccolors[j][i][3] <= acutValues[3]) {
+                  alphaenc3[4*j + i] = 4;
+                  alphadist = srccolors[j][i][3] - (alphatest[0] * 2 + alphatest[1] * 3) / 5;
+               }
+               else if (srccolors[j][i][3] <= acutValues[4]) {
+                  alphaenc3[4*j + i] = 5;
+                  alphadist = srccolors[j][i][3] - (alphatest[0] * 1 + alphatest[1] * 4) / 5;
+               }
+               else {
+                  alphaenc3[4*j + i] = 1;
+                  alphadist = srccolors[j][i][3] - alphatest[1];
+               }
+               alphablockerror3 += alphadist * alphadist;
+            }
+         }
+      }
+   }
+  /* write the alpha values and encoding back. */
+   if ((alphablockerror1 <= alphablockerror2) && (alphablockerror1 <= alphablockerror3)) {
+/*      if (alphablockerror1 > 96) fprintf(stderr, "enc1 used, error %d\n", alphablockerror1);*/
+      writedxt5encodedalphablock( blkaddr, alphause[1], alphause[0], alphaenc1 );
+   }
+   else if (alphablockerror2 <= alphablockerror3) {
+/*      if (alphablockerror2 > 96) fprintf(stderr, "enc2 used, error %d\n", alphablockerror2);*/
+      writedxt5encodedalphablock( blkaddr, alphabase[0], alphabase[1], alphaenc2 );
+   }
+   else {
+/*      fprintf(stderr, "enc3 used, error %d\n", alphablockerror3);*/
+      writedxt5encodedalphablock( blkaddr, (GLubyte)alphatest[0], (GLubyte)alphatest[1], alphaenc3 );
+   }
+}
+
+static void extractsrccolors( GLubyte srcpixels[4][4][4], const GLchan *srcaddr,
+                         GLint srcRowStride, GLint numxpixels, GLint numypixels, GLint comps)
+{
+   GLubyte i, j, c;
+   const GLchan *curaddr;
+   for (j = 0; j < numypixels; j++) {
+      curaddr = srcaddr + j * srcRowStride * comps;
+      for (i = 0; i < numxpixels; i++) {
+         for (c = 0; c < comps; c++) {
+            srcpixels[j][i][c] = *curaddr++ / (CHAN_MAX / 255);
+         }
+      }
+   }
+}
+
+
+void tx_compress_dxtn(GLint srccomps, GLint width, GLint height, const GLubyte *srcPixData,
+                     GLenum destFormat, GLubyte *dest, GLint dstRowStride)
+{
+      GLubyte *blkaddr = dest;
+      GLubyte srcpixels[4][4][4];
+      const GLchan *srcaddr = srcPixData;
+      GLint numxpixels, numypixels;
+      GLint i, j;
+      GLint dstRowDiff;
+
+   switch (destFormat) {
+   case GL_COMPRESSED_RGB_S3TC_DXT1_EXT:
+   case GL_COMPRESSED_RGBA_S3TC_DXT1_EXT:
+      /* hmm we used to get called without dstRowStride... */
+      dstRowDiff = dstRowStride >= (width * 2) ? dstRowStride - (((width + 3) & ~3) * 2) : 0;
+/*      fprintf(stderr, "dxt1 tex width %d tex height %d dstRowStride %d\n",
+              width, height, dstRowStride); */
+      for (j = 0; j < height; j += 4) {
+         if (height > j + 3) numypixels = 4;
+         else numypixels = height - j;
+         srcaddr = srcPixData + j * width * srccomps;
+         for (i = 0; i < width; i += 4) {
+            if (width > i + 3) numxpixels = 4;
+            else numxpixels = width - i;
+            extractsrccolors(srcpixels, srcaddr, width, numxpixels, numypixels, srccomps);
+            encodedxtcolorblockfaster(blkaddr, srcpixels, numxpixels, numypixels, destFormat);
+            srcaddr += srccomps * numxpixels;
+            blkaddr += 8;
+         }
+         blkaddr += dstRowDiff;
+      }
+      break;
+   case GL_COMPRESSED_RGBA_S3TC_DXT3_EXT:
+      dstRowDiff = dstRowStride >= (width * 4) ? dstRowStride - (((width + 3) & ~3) * 4) : 0;
+/*      fprintf(stderr, "dxt3 tex width %d tex height %d dstRowStride %d\n",
+              width, height, dstRowStride); */
+      for (j = 0; j < height; j += 4) {
+         if (height > j + 3) numypixels = 4;
+         else numypixels = height - j;
+         srcaddr = srcPixData + j * width * srccomps;
+         for (i = 0; i < width; i += 4) {
+            if (width > i + 3) numxpixels = 4;
+            else numxpixels = width - i;
+            extractsrccolors(srcpixels, srcaddr, width, numxpixels, numypixels, srccomps);
+            *blkaddr++ = (srcpixels[0][0][3] >> 4) | (srcpixels[0][1][3] & 0xf0);
+            *blkaddr++ = (srcpixels[0][2][3] >> 4) | (srcpixels[0][3][3] & 0xf0);
+            *blkaddr++ = (srcpixels[1][0][3] >> 4) | (srcpixels[1][1][3] & 0xf0);
+            *blkaddr++ = (srcpixels[1][2][3] >> 4) | (srcpixels[1][3][3] & 0xf0);
+            *blkaddr++ = (srcpixels[2][0][3] >> 4) | (srcpixels[2][1][3] & 0xf0);
+            *blkaddr++ = (srcpixels[2][2][3] >> 4) | (srcpixels[2][3][3] & 0xf0);
+            *blkaddr++ = (srcpixels[3][0][3] >> 4) | (srcpixels[3][1][3] & 0xf0);
+            *blkaddr++ = (srcpixels[3][2][3] >> 4) | (srcpixels[3][3][3] & 0xf0);
+            encodedxtcolorblockfaster(blkaddr, srcpixels, numxpixels, numypixels, destFormat);
+            srcaddr += srccomps * numxpixels;
+            blkaddr += 8;
+         }
+         blkaddr += dstRowDiff;
+      }
+      break;
+   case GL_COMPRESSED_RGBA_S3TC_DXT5_EXT:
+      dstRowDiff = dstRowStride >= (width * 4) ? dstRowStride - (((width + 3) & ~3) * 4) : 0;
+/*      fprintf(stderr, "dxt5 tex width %d tex height %d dstRowStride %d\n",
+              width, height, dstRowStride); */
+      for (j = 0; j < height; j += 4) {
+         if (height > j + 3) numypixels = 4;
+         else numypixels = height - j;
+         srcaddr = srcPixData + j * width * srccomps;
+         for (i = 0; i < width; i += 4) {
+            if (width > i + 3) numxpixels = 4;
+            else numxpixels = width - i;
+            extractsrccolors(srcpixels, srcaddr, width, numxpixels, numypixels, srccomps);
+            encodedxt5alpha(blkaddr, srcpixels, numxpixels, numypixels);
+            encodedxtcolorblockfaster(blkaddr + 8, srcpixels, numxpixels, numypixels, destFormat);
+            srcaddr += srccomps * numxpixels;
+            blkaddr += 16;
+         }
+         blkaddr += dstRowDiff;
+      }
+      break;
+   default:
+      fprintf(stderr, "libdxtn: Bad dstFormat %d in tx_compress_dxtn\n", destFormat);
+      return;
+   }
+}
+
+
diff --git a/src/mesa/main/txc_dxtn.h b/src/mesa/main/txc_dxtn.h
new file mode 100644
index 00000000000..ef352aabe55
--- /dev/null
+++ b/src/mesa/main/txc_dxtn.h
@@ -0,0 +1,55 @@
+/*
+ * libtxc_dxtn
+ * Version:  1.0
+ *
+ * Copyright (C) 2004  Roland Scheidegger   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.
+ */
+
+#ifndef _TXC_DXTN_H
+#define _TXC_DXTN_H
+
+#ifdef __APPLE__
+#include <OpenGL/gl.h>
+#else
+#include <GL/gl.h>
+#endif
+
+typedef GLubyte GLchan;
+#define UBYTE_TO_CHAN(b)  (b)
+#define CHAN_MAX 255
+#define RCOMP 0
+#define GCOMP 1
+#define BCOMP 2
+#define ACOMP 3
+
+void fetch_2d_texel_rgb_dxt1(GLint srcRowStride, const GLubyte *pixdata,
+			     GLint i, GLint j, GLvoid *texel);
+void fetch_2d_texel_rgba_dxt1(GLint srcRowStride, const GLubyte *pixdata,
+			     GLint i, GLint j, GLvoid *texel);
+void fetch_2d_texel_rgba_dxt3(GLint srcRowStride, const GLubyte *pixdata,
+			     GLint i, GLint j, GLvoid *texel);
+void fetch_2d_texel_rgba_dxt5(GLint srcRowStride, const GLubyte *pixdata,
+			     GLint i, GLint j, GLvoid *texel);
+
+void tx_compress_dxtn(GLint srccomps, GLint width, GLint height,
+		      const GLubyte *srcPixData, GLenum destformat,
+		      GLubyte *dest, GLint dstRowStride);
+
+#endif /* _TXC_DXTN_H */
diff --git a/src/mesa/main/txc_fetch_dxtn.c b/src/mesa/main/txc_fetch_dxtn.c
new file mode 100644
index 00000000000..7f0db56a155
--- /dev/null
+++ b/src/mesa/main/txc_fetch_dxtn.c
@@ -0,0 +1,243 @@
+/*
+ * libtxc_dxtn
+ * Version:  1.0
+ *
+ * Copyright (C) 2004  Roland Scheidegger   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.
+ */
+
+#include <stdio.h>
+#include "txc_dxtn.h"
+
+#define EXP5TO8R(packedcol)					\
+   ((((packedcol) >> 8) & 0xf8) | (((packedcol) >> 13) & 0x7))
+
+#define EXP6TO8G(packedcol)					\
+   ((((packedcol) >> 3) & 0xfc) | (((packedcol) >>  9) & 0x3))
+
+#define EXP5TO8B(packedcol)					\
+   ((((packedcol) << 3) & 0xf8) | (((packedcol) >>  2) & 0x7))
+
+#define EXP4TO8(col)						\
+   ((col) | ((col) << 4))
+
+/* inefficient. To be efficient, it would be necessary to decode 16 pixels at once */
+
+static void dxt135_decode_imageblock ( const GLubyte *img_block_src,
+                         GLint i, GLint j, GLuint dxt_type, GLvoid *texel ) {
+   GLchan *rgba = (GLchan *) texel;
+   const GLushort color0 = img_block_src[0] | (img_block_src[1] << 8);
+   const GLushort color1 = img_block_src[2] | (img_block_src[3] << 8);
+   const GLuint bits = img_block_src[4] | (img_block_src[5] << 8) |
+      (img_block_src[6] << 16) | (img_block_src[7] << 24);
+   /* What about big/little endian? */
+   GLubyte bit_pos = 2 * (j * 4 + i) ;
+   GLubyte code = (GLubyte) ((bits >> bit_pos) & 3);
+
+   rgba[ACOMP] = CHAN_MAX;
+   switch (code) {
+   case 0:
+      rgba[RCOMP] = UBYTE_TO_CHAN( EXP5TO8R(color0) );
+      rgba[GCOMP] = UBYTE_TO_CHAN( EXP6TO8G(color0) );
+      rgba[BCOMP] = UBYTE_TO_CHAN( EXP5TO8B(color0) );
+      break;
+   case 1:
+      rgba[RCOMP] = UBYTE_TO_CHAN( EXP5TO8R(color1) );
+      rgba[GCOMP] = UBYTE_TO_CHAN( EXP6TO8G(color1) );
+      rgba[BCOMP] = UBYTE_TO_CHAN( EXP5TO8B(color1) );
+      break;
+   case 2:
+      if ((dxt_type > 1) || (color0 > color1)) {
+         rgba[RCOMP] = UBYTE_TO_CHAN( ((EXP5TO8R(color0) * 2 + EXP5TO8R(color1)) / 3) );
+         rgba[GCOMP] = UBYTE_TO_CHAN( ((EXP6TO8G(color0) * 2 + EXP6TO8G(color1)) / 3) );
+         rgba[BCOMP] = UBYTE_TO_CHAN( ((EXP5TO8B(color0) * 2 + EXP5TO8B(color1)) / 3) );
+      }
+      else {
+         rgba[RCOMP] = UBYTE_TO_CHAN( ((EXP5TO8R(color0) + EXP5TO8R(color1)) / 2) );
+         rgba[GCOMP] = UBYTE_TO_CHAN( ((EXP6TO8G(color0) + EXP6TO8G(color1)) / 2) );
+         rgba[BCOMP] = UBYTE_TO_CHAN( ((EXP5TO8B(color0) + EXP5TO8B(color1)) / 2) );
+      }
+      break;
+   case 3:
+      if ((dxt_type > 1) || (color0 > color1)) {
+         rgba[RCOMP] = UBYTE_TO_CHAN( ((EXP5TO8R(color0) + EXP5TO8R(color1) * 2) / 3) );
+         rgba[GCOMP] = UBYTE_TO_CHAN( ((EXP6TO8G(color0) + EXP6TO8G(color1) * 2) / 3) );
+         rgba[BCOMP] = UBYTE_TO_CHAN( ((EXP5TO8B(color0) + EXP5TO8B(color1) * 2) / 3) );
+      }
+      else {
+         rgba[RCOMP] = 0;
+         rgba[GCOMP] = 0;
+         rgba[BCOMP] = 0;
+         if (dxt_type == 1) rgba[ACOMP] = UBYTE_TO_CHAN(0);
+      }
+      break;
+   default:
+   /* CANNOT happen (I hope) */
+      break;
+   }
+}
+
+
+void fetch_2d_texel_rgb_dxt1(GLint srcRowStride, const GLubyte *pixdata,
+                         GLint i, GLint j, GLvoid *texel)
+{
+   /* Extract the (i,j) pixel from pixdata and return it
+    * in texel[RCOMP], texel[GCOMP], texel[BCOMP], texel[ACOMP].
+    */
+
+   const GLubyte *blksrc = (pixdata + ((srcRowStride + 3) / 4 * (j / 4) + (i / 4)) * 8);
+   dxt135_decode_imageblock(blksrc, (i&3), (j&3), 0, texel);
+}
+
+
+void fetch_2d_texel_rgba_dxt1(GLint srcRowStride, const GLubyte *pixdata,
+                         GLint i, GLint j, GLvoid *texel)
+{
+   /* Extract the (i,j) pixel from pixdata and return it
+    * in texel[RCOMP], texel[GCOMP], texel[BCOMP], texel[ACOMP].
+    */
+
+   const GLubyte *blksrc = (pixdata + ((srcRowStride + 3) / 4 * (j / 4) + (i / 4)) * 8);
+   dxt135_decode_imageblock(blksrc, (i&3), (j&3), 1, texel);
+}
+
+void fetch_2d_texel_rgba_dxt3(GLint srcRowStride, const GLubyte *pixdata,
+                         GLint i, GLint j, GLvoid *texel) {
+
+   /* Extract the (i,j) pixel from pixdata and return it
+    * in texel[RCOMP], texel[GCOMP], texel[BCOMP], texel[ACOMP].
+    */
+
+   GLchan *rgba = (GLchan *) texel;
+   const GLubyte *blksrc = (pixdata + ((srcRowStride + 3) / 4 * (j / 4) + (i / 4)) * 16);
+#if 0
+   /* Simple 32bit version. */
+/* that's pretty brain-dead for a single pixel, isn't it? */
+   const GLubyte bit_pos = 4 * ((j&3) * 4 + (i&3));
+   const GLuint alpha_low = blksrc[0] | (blksrc[1] << 8) | (blksrc[2] << 16) | (blksrc[3] << 24);
+   const GLuint alpha_high = blksrc[4] | (blksrc[5] << 8) | (blksrc[6] << 16) | (blksrc[7] << 24);
+
+   dxt135_decode_imageblock(blksrc + 8, (i&3), (j&3), 2, texel);
+   if (bit_pos < 32)
+      rgba[ACOMP] = UBYTE_TO_CHAN( (GLubyte)(EXP4TO8((alpha_low >> bit_pos) & 15)) );
+   else
+      rgba[ACOMP] = UBYTE_TO_CHAN( (GLubyte)(EXP4TO8((alpha_high >> (bit_pos - 32)) & 15)) );
+#endif
+#if 1
+/* TODO test this! */
+   const GLubyte anibble = (blksrc[((j&3) * 4 + (i&3)) / 2] >> (4 * (i&1))) & 0xf;
+   dxt135_decode_imageblock(blksrc + 8, (i&3), (j&3), 2, texel);
+   rgba[ACOMP] = UBYTE_TO_CHAN( (GLubyte)(EXP4TO8(anibble)) );
+#endif
+
+}
+
+void fetch_2d_texel_rgba_dxt5(GLint srcRowStride, const GLubyte *pixdata,
+                         GLint i, GLint j, GLvoid *texel) {
+
+   /* Extract the (i,j) pixel from pixdata and return it
+    * in texel[RCOMP], texel[GCOMP], texel[BCOMP], texel[ACOMP].
+    */
+
+   GLchan *rgba = (GLchan *) texel;
+   const GLubyte *blksrc = (pixdata + ((srcRowStride + 3) / 4 * (j / 4) + (i / 4)) * 16);
+   const GLubyte alpha0 = blksrc[0];
+   const GLubyte alpha1 = blksrc[1];
+#if 0
+   const GLubyte bit_pos = 3 * ((j&3) * 4 + (i&3));
+   /* simple 32bit version */
+   const GLuint bits_low = blksrc[2] | (blksrc[3] << 8) | (blksrc[4] << 16) | (blksrc[5] << 24);
+   const GLuint bits_high = blksrc[6] | (blksrc[7] << 8);
+   GLubyte code;
+
+   if (bit_pos < 30)
+      code = (GLubyte) ((bits_low >> bit_pos) & 7);
+   else if (bit_pos == 30)
+      code = (GLubyte) ((bits_low >> 30) & 3) | ((bits_high << 2) & 4);
+   else
+      code = (GLubyte) ((bits_high >> (bit_pos - 32)) & 7);
+#endif
+#if 1
+/* TODO test this! */
+   const GLubyte bit_pos = ((j&3) * 4 + (i&3)) * 3;
+   const GLubyte acodelow = blksrc[2 + bit_pos / 8];
+   const GLubyte acodehigh = blksrc[3 + bit_pos / 8];
+   const GLubyte code = (acodelow >> (bit_pos & 0x7) |
+      (acodehigh  << (8 - (bit_pos & 0x7)))) & 0x7;
+#endif
+   dxt135_decode_imageblock(blksrc + 8, (i&3), (j&3), 2, texel);
+#if 0
+   if (alpha0 > alpha1) {
+      switch (code) {
+      case 0:
+         rgba[ACOMP] = UBYTE_TO_CHAN( alpha0 );
+         break;
+      case 1:
+         rgba[ACOMP] = UBYTE_TO_CHAN( alpha1 );
+         break;
+      case 2:
+      case 3:
+      case 4:
+      case 5:
+      case 6:
+      case 7:
+         rgba[ACOMP] = UBYTE_TO_CHAN( ((alpha0 * (8 - code) + (alpha1 * (code - 1))) / 7) );
+         break;
+      }
+   }
+   else {
+      switch (code) {
+      case 0:
+         rgba[ACOMP] = UBYTE_TO_CHAN( alpha0 );
+         break;
+      case 1:
+         rgba[ACOMP] = UBYTE_TO_CHAN( alpha1 );
+         break;
+      case 2:
+      case 3:
+      case 4:
+      case 5:
+         rgba[ACOMP] = UBYTE_TO_CHAN( ((alpha0 * (6 - code) + (alpha1 * (code - 1))) / 5) );
+         break;
+      case 6:
+         rgba[ACOMP] = 0;
+         break;
+      case 7:
+         rgba[ACOMP] = CHAN_MAX;
+         break;
+      }
+   }
+#endif
+/* not sure. Which version is faster? */
+#if 1
+/* TODO test this */
+   if (code == 0)
+      rgba[ACOMP] = UBYTE_TO_CHAN( alpha0 );
+   else if (code == 1)
+      rgba[ACOMP] = UBYTE_TO_CHAN( alpha1 );
+   else if (alpha0 > alpha1)
+      rgba[ACOMP] = UBYTE_TO_CHAN( ((alpha0 * (8 - code) + (alpha1 * (code - 1))) / 7) );
+   else if (code < 6)
+      rgba[ACOMP] = UBYTE_TO_CHAN( ((alpha0 * (6 - code) + (alpha1 * (code - 1))) / 5) );
+   else if (code == 6)
+      rgba[ACOMP] = 0;
+   else
+      rgba[ACOMP] = CHAN_MAX;
+#endif
+}