FXT1 texture compression (initial draft)

1 files changed, 640 insertions, 35 deletions

diff --git a/src/mesa/main/texcompress_fxt1.c b/src/mesa/main/texcompress_fxt1.c
index 5a37a259c7..cd5b0c3d60 100644
--- a/src/mesa/main/texcompress_fxt1.c
+++ b/src/mesa/main/texcompress_fxt1.c
@@ -26,6 +26,7 @@
 /**
  * \file texcompress_fxt1.c
  * GL_EXT_texture_compression_fxt1 support.
+ * \author Daniel Borca
  */
 
 
@@ -40,15 +41,15 @@
 #include "texstore.h"
 
 
-static GLuint
-compress_fxt1 (GLcontext *ctx,
-               GLsizei srcWidth,
-               GLsizei srcHeight,
-               GLenum srcFormat,
-               const GLchan *source,
-               GLint srcRowStride,
-               GLubyte *dest,
-               GLint dstRowStride);
+int
+fxt1_encode (GLcontext *ctx,
+             unsigned int width, unsigned int height,
+             int srcFormat,
+             const void *source, int srcRowStride,
+             void *dest, int destRowStride);
+void
+fxt1_decode_1 (const void *texture, int width,
+               int i, int j, unsigned char *rgba);
 
 
 /**
@@ -77,17 +78,14 @@ texstore_rgb_fxt1(STORE_PARAMS)
    ASSERT(dstYoffset % 4 == 0);
    ASSERT(dstZoffset     == 0);
 
-   /* [dBorca]
-    * we still need to pass 4byte/texel to the codec
-    */
-   if (1 || srcFormat != GL_RGB ||
+   if (srcFormat != GL_RGB ||
        srcType != CHAN_TYPE ||
        ctx->_ImageTransferState ||
        srcPacking->SwapBytes) {
       /* convert image to RGB/GLchan */
       tempImage = _mesa_make_temp_chan_image(ctx, dims,
                                              baseInternalFormat,
-                                             /*dstFormat->BaseFormat*/GL_RGBA,
+                                             dstFormat->BaseFormat,
                                              srcWidth, srcHeight, srcDepth,
                                              srcFormat, srcType, srcAddr,
                                              srcPacking);
@@ -95,7 +93,7 @@ texstore_rgb_fxt1(STORE_PARAMS)
          return GL_FALSE; /* out of memory */
       _mesa_adjust_image_for_convolution(ctx, dims, &srcWidth, &srcHeight);
       pixels = tempImage;
-      srcRowStride = /*3*/4 * srcWidth;
+      srcRowStride = 3 * srcWidth;
       srcFormat = GL_RGB;
    }
    else {
@@ -108,11 +106,11 @@ texstore_rgb_fxt1(STORE_PARAMS)
                                         GL_COMPRESSED_RGB_FXT1_3DFX,
                                         texWidth, (GLubyte *) dstAddr);
 
-   compress_fxt1(ctx, srcWidth, srcHeight, srcFormat, pixels, srcRowStride,
-                 dst, dstRowStride);
+   fxt1_encode(ctx, srcWidth, srcHeight, srcFormat, pixels, srcRowStride,
+               dst, dstRowStride);
 
    if (tempImage)
-      _mesa_free((void *) tempImage);
+      _mesa_free((void*) tempImage);
 
    return GL_TRUE;
 }
@@ -163,8 +161,8 @@ texstore_rgba_fxt1(STORE_PARAMS)
                                         GL_COMPRESSED_RGBA_FXT1_3DFX,
                                         texWidth, (GLubyte *) dstAddr);
 
-   compress_fxt1(ctx, srcWidth, srcHeight, srcFormat, pixels, srcRowStride,
-                 dst, dstRowStride);
+   fxt1_encode(ctx, srcWidth, srcHeight, srcFormat, pixels, srcRowStride,
+               dst, dstRowStride);
 
    if (tempImage)
       _mesa_free((void*) tempImage);
@@ -177,7 +175,7 @@ static void
 fetch_texel_2d_rgba_fxt1( const struct gl_texture_image *texImage,
                           GLint i, GLint j, GLint k, GLchan *texel )
 {
-   /* XXX to do */
+   fxt1_decode_1(texImage->Data, texImage->Width, i, j, texel);
 }
 
 
@@ -187,7 +185,7 @@ fetch_texel_2d_f_rgba_fxt1( const struct gl_texture_image *texImage,
 {
    /* just sample as GLchan and convert to float here */
    GLchan rgba[4];
-   fetch_texel_2d_rgba_fxt1(texImage, i, j, k, rgba);
+   fxt1_decode_1(texImage->Data, texImage->Width, i, j, rgba);
    texel[RCOMP] = CHAN_TO_FLOAT(rgba[RCOMP]);
    texel[GCOMP] = CHAN_TO_FLOAT(rgba[GCOMP]);
    texel[BCOMP] = CHAN_TO_FLOAT(rgba[BCOMP]);
@@ -199,7 +197,8 @@ static void
 fetch_texel_2d_rgb_fxt1( const struct gl_texture_image *texImage,
                          GLint i, GLint j, GLint k, GLchan *texel )
 {
-   /* XXX to do */
+   fxt1_decode_1(texImage->Data, texImage->Width, i, j, texel);
+   texel[ACOMP] = 255;
 }
 
 
@@ -209,11 +208,11 @@ fetch_texel_2d_f_rgb_fxt1( const struct gl_texture_image *texImage,
 {
    /* just sample as GLchan and convert to float here */
    GLchan rgba[4];
-   fetch_texel_2d_rgb_fxt1(texImage, i, j, k, rgba);
+   fxt1_decode_1(texImage->Data, texImage->Width, i, j, rgba);
    texel[RCOMP] = CHAN_TO_FLOAT(rgba[RCOMP]);
    texel[GCOMP] = CHAN_TO_FLOAT(rgba[GCOMP]);
    texel[BCOMP] = CHAN_TO_FLOAT(rgba[BCOMP]);
-   texel[ACOMP] = CHAN_TO_FLOAT(rgba[ACOMP]);
+   texel[ACOMP] = 1.0;
 }
 
 
@@ -263,16 +262,622 @@ const struct gl_texture_format _mesa_texformat_rgba_fxt1 = {
 };
 
 
-static GLuint
-compress_fxt1 (GLcontext *ctx,
-               GLsizei srcWidth,
-               GLsizei srcHeight,
-               GLenum srcFormat,
-               const GLchan *source,
-               GLint srcRowStride,
-               GLubyte *dest,
-               GLint dstRowStride)
+/***************************************************************************\
+ * FXT1 encoder
+ *
+ * The encoder was built by reversing the decoder,
+ * and is vaguely based on Texus2 by 3dfx. Note that this code
+ * is merely a proof of concept, since it is higly UNoptimized;
+ * moreover it is sub-optimal due to Lloyd's algorithm.
+ * Only CHROMA and non-lerp ALPHA is implemented!
+\***************************************************************************/
+
+
+#define MAX_COMP 4 /* ever meeded maximum number of components in texel */
+#define MAX_VECT 4 /* ever needed maximum number of base vectors to find */
+#define N_TEXELS 32 /* number of texels in a block (always 32) */
+#define LL_N_REP 50 /* number of iterations in lloyd's vq */
+#define LL_MAX_E 255 /* fault tolerance (maximum error) */
+
+
+static int
+fxt1_besterr (float vec[][MAX_COMP], int nv,
+              unsigned char input[MAX_COMP], int nc,
+              float *d)
+{
+   int i, j, best = -1;
+   float err = 1e5; /* big enough */
+
+   for (j = 0; j < nv; j++) {
+      float e = 0;
+      for (i = 0; i < nc; i++) {
+         e += (vec[j][i] - input[i]) * (vec[j][i] - input[i]);
+      }
+      if (e < err) {
+         err = e;
+         best = j;
+      }
+   }
+
+   *d = err;
+   return best;
+}
+
+
+static int
+fxt1_worsterr (float vec[MAX_COMP],
+               unsigned char input[N_TEXELS][MAX_COMP], int nc, int n)
+{
+   int i, k, worst = -1;
+   float err = -1; /* small enough */
+
+   for (k = 0; k < n; k++) {
+      float e = 0;
+      for (i = 0; i < nc; i++) {
+         e += (vec[i] - input[k][i]) * (vec[i] - input[k][i]);
+      }
+      if (e > err) {
+         err = e;
+         worst = k;
+      }
+   }
+
+   return worst;
+}
+
+
+static void
+fxt1_lloyd (float vec[][MAX_COMP], int nv,
+            unsigned char input[N_TEXELS][MAX_COMP], int nc, int n)
+{
+   /* Use the generalized lloyd's algorithm for VQ:
+    *     find 4 color vectors.
+    *
+    *     for each sample color
+    *         sort to nearest vector.
+    *
+    *     replace each vector with the centroid of it's matching colors.
+    *
+    *     repeat until RMS doesn't improve.
+    *
+    *     if a color vector has no samples, or becomes the same as another
+    *     vector, replace it with the color which is farthest from a sample.
+    *
+    * vec[][MAX_COMP]           resulting colors
+    * nv                        number of resulting colors required
+    * input[N_TEXELS][MAX_COMP] input texels
+    * nc                        number of components in input / vec
+    * n                         number of input samples
+    */
+
+   int sum[MAX_VECT][MAX_COMP]; /* used to accumulate closest texels */
+   int cnt[MAX_VECT]; /* how many times a certain vector was chosen */
+   float error;
+
+   int i, j, k, rep;
+
+   /* choose the base vectors from input */
+   for (j = 0; j < nv; j++) {
+      int m = j * (n - 1) / (nv - 1);
+      for (i = 0; i < nc; i++) {
+         vec[j][i] = input[m][i];
+      }
+   }
+
+   /* the quantizer */
+   for (rep = 0; rep < LL_N_REP; rep++) {
+      /* reset sums & counters */
+      for (j = 0; j < nv; j++) {
+         for (i = 0; i < nc; i++) {
+            sum[j][i] = 0;
+         }
+         cnt[j] = 0;
+      }
+      error = 0;
+
+      /* scan whole block */
+      for (k = 0; k < n; k++) {
+         float d;
+         int best = fxt1_besterr(vec, nv, input[k], nc, &d);
+         /* add in closest color */
+         for (i = 0; i < nc; i++) {
+            sum[best][i] += input[k][i];
+         }
+         /* mark this vector as used */
+         cnt[best]++;
+         /* accumulate error */
+         error += d;
+      }
+
+      /* accumulated distance (error) small enough? */
+      if (error < LL_MAX_E) {
+         break;
+      }
+
+      /* move each vector to the barycenter of its closest colors */
+      for (j = 0; j < nv; j++) {
+         if (cnt[j]) {
+            float div = 1.0 / cnt[j];
+            for (i = 0; i < nc; i++) {
+               vec[j][i] = div * sum[j][i];
+            }
+         } else {
+            /* this vec has no samples or is identical with a previous vec */
+            int worst = fxt1_worsterr(vec[j], input, nc, n);
+            for (i = 0; i < nc; i++) {
+               vec[j][i] = input[worst][i];
+            }
+         }
+      }
+   }
+}
+
+
+static void
+fxt1_quantize_CHROMA (unsigned long *cc,
+                      unsigned char input[N_TEXELS][MAX_COMP])
+{
+   const int n_vect = 4; /* 4 base vectors to find */
+   const int n_comp = 3; /* 3 components: R, G, B */
+   float vec[MAX_VECT][MAX_COMP];
+   int i, j, k;
+   unsigned long long hihi; /* high quadword */
+   unsigned long lohi, lolo; /* low quadword: hi dword, lo dword */
+   float d;
+
+   fxt1_lloyd(vec, n_vect, input, n_comp, N_TEXELS);
+
+   hihi = 4; /* cc-chroma = "010" + unused bit */
+   for (j = 0; j < n_vect; j++) {
+      for (i = 0; i < n_comp; i++) {
+         /* add in colors */
+         hihi <<= 5;
+         hihi |= (unsigned int)vec[n_vect - 1 - j][i] >> 3;
+      }
+   }
+   ((unsigned long long *)cc)[1] = hihi;
+
+   lohi = lolo = 0;
+   /* right microtile */
+   for (k = N_TEXELS - 1; k >= N_TEXELS/2; k--) {
+      lohi <<= 2;
+      lohi |= fxt1_besterr(vec, n_vect, input[k], n_comp, &d);
+   }
+   /* left microtile */
+   for (; k >= 0; k--) {
+      lolo <<= 2;
+      lolo |= fxt1_besterr(vec, n_vect, input[k], n_comp, &d);
+   }
+   cc[1] = lohi;
+   cc[0] = lolo;
+}
+
+
+static void
+fxt1_quantize_ALPHA0 (unsigned long *cc,
+                      unsigned char input[N_TEXELS][MAX_COMP],
+                      unsigned char reord[N_TEXELS][MAX_COMP], int n)
+{
+   const int n_vect = 3; /* 3 base vectors to find */
+   const int n_comp = 4; /* 4 components: R, G, B, A */
+   float vec[MAX_VECT][MAX_COMP];
+   int i, j, k;
+   unsigned long long hihi; /* high quadword */
+   unsigned long lohi, lolo; /* low quadword: hi dword, lo dword */
+   float d;
+
+   /* the last vector indicates zero */
+   for (i = 0; i < n_comp; i++) {
+      vec[n_vect][i] = 0;
+   }
+
+   /* the first n texels in reord are guaranteed to be non-zero */
+   fxt1_lloyd(vec, n_vect, reord, n_comp, n);
+
+   hihi = 6; /* alpha = "011" + lerp = 0 */
+   for (j = 0; j < n_vect; j++) {
+      /* add in alphas */
+      hihi <<= 5;
+      hihi |= (unsigned int)vec[n_vect - 1 - j][n_comp - 1] >> 3;
+   }
+   for (j = 0; j < n_vect; j++) {
+      for (i = 0; i < n_comp - 1; i++) {
+         /* add in colors */
+         hihi <<= 5;
+         hihi |= (unsigned int)vec[n_vect - 1 - j][i] >> 3;
+      }
+   }
+   ((unsigned long long *)cc)[1] = hihi;
+
+   lohi = lolo = 0;
+   /* right microtile */
+   for (k = N_TEXELS - 1; k >= N_TEXELS/2; k--) {
+      lohi <<= 2;
+      lohi |= fxt1_besterr(vec, n_vect + 1, input[k], n_comp, &d);
+   }
+   /* left microtile */
+   for (; k >= 0; k--) {
+      lolo <<= 2;
+      lolo |= fxt1_besterr(vec, n_vect + 1, input[k], n_comp, &d);
+   }
+   cc[1] = lohi;
+   cc[0] = lolo;
+}
+
+
+static void
+fxt1_quantize (unsigned long *cc, const unsigned char *lines[], int comps)
 {
-   /* here be dragons */
+   int trualpha = 0;
+   unsigned char reord[N_TEXELS][MAX_COMP];
+
+   unsigned char input[N_TEXELS][MAX_COMP];
+   int i, k, l;
+
+   /* 8 texels each line */
+   for (l = 0; l < 4; l++) {
+      for (k = 0; k < 4; k++) {
+         for (i = 0; i < comps; i++) {
+            input[k + l * 4][i] = *lines[l]++;
+         }
+         for (; i < MAX_COMP; i++) {
+            input[k + l * 4][i] = 255;
+         }
+      }
+      for (k = 0; k < 4; k++) {
+         for (i = 0; i < comps; i++) {
+            input[k + l * 4 + 16][i] = *lines[l]++;
+         }
+         for (; i < MAX_COMP; i++) {
+            input[k + l * 4 + 16][i] = 255;
+         }
+      }
+   }
+
+   /* [dBorca]
+    * stupidity flows forth from this
+    */
+
+   if (comps == 4) {
+      /* skip all transparent black texels */
+      l = 0;
+      for (k = 0; k < N_TEXELS; k++) {
+         int t = 0;
+         /* test all components against 0 */
+         for (i = 0; i < comps; i++) {
+            reord[l][i] = input[k][i];
+            t += input[k][i];
+         }
+         if (t) {
+            /* texel is not transparent black */
+            if (reord[l][comps - 1] < 255) {
+               /* non-opaque texel */
+               trualpha = !0;
+            }
+            l++;
+         } else {
+            /* transparent black texel */
+            trualpha = !0;
+         }
+      }
+   }
+
+   if (trualpha) {
+      fxt1_quantize_ALPHA0(cc, input, reord, l);
+   } else {
+      fxt1_quantize_CHROMA(cc, input);
+   }
+}
+
+
+int
+fxt1_encode (GLcontext *ctx,
+             unsigned int width, unsigned int height,
+             int srcFormat,
+             const void *source, int srcRowStride,
+             void *dest, int destRowStride)
+{
+   const int comps = (srcFormat == GL_RGB) ? 3 : 4;
+   unsigned int x, y;
+   const unsigned char *data = source;
+   unsigned long *encoded = dest;
+   GLubyte *newSource = NULL;
+
+   /*
+    * Rescale image if width is less than 8 or height is less than 4.
+    */
+   if (width < 8 || height < 4) {
+      GLint newWidth = (width + 7) & ~7;
+      GLint newHeight = (height + 3) & ~3;
+      newSource = MALLOC(comps * newWidth * newHeight * sizeof(GLchan));
+      _mesa_upscale_teximage2d(width, height, newWidth, newHeight,
+                               comps, source, srcRowStride, newSource);
+      source = newSource;
+      width = newWidth;
+      height = newHeight;
+      srcRowStride = comps * newWidth;
+   }
+
+   destRowStride = (destRowStride - width * 2) / 4;
+   for (y = 0; y < height; y += 4) {
+      for (x = 0; x < width; x += 8) {
+         const unsigned char *lines[4];
+         lines[0] = &data[x * comps + (y + 0) * srcRowStride];
+         lines[1] = &data[x * comps + (y + 1) * srcRowStride];
+         lines[2] = &data[x * comps + (y + 2) * srcRowStride];
+         lines[3] = &data[x * comps + (y + 3) * srcRowStride];
+         fxt1_quantize(encoded, lines, comps);
+         /* 128 bits per 8x4 block = 4bpp */
+         encoded += 4;
+      }
+      encoded += destRowStride;
+   }
+
    return 0;
 }
+
+
+/***************************************************************************\
+ * FXT1 decoder
+ *
+ * The decoder is based on GL_3DFX_texture_compression_FXT1
+ * specification and serves as a concept for the encoder.
+\***************************************************************************/
+
+
+/* lookup table for scaling 5 bit colors up to 8 bits */
+static unsigned char _rgb_scale_5[] = {
+   0,   8,   16,  25,  33,  41,  49,  58,
+   66,  74,  82,  90,  99,  107, 115, 123,
+   132, 140, 148, 156, 165, 173, 181, 189,
+   197, 206, 214, 222, 230, 239, 247, 255
+};
+
+/* lookup table for scaling 6 bit colors up to 8 bits */
+static unsigned char _rgb_scale_6[] = {
+   0,   4,   8,   12,  16,  20,  24,  28,
+   32,  36,  40,  45,  49,  53,  57,  61,
+   65,  69,  73,  77,  81,  85,  89,  93,
+   97,  101, 105, 109, 113, 117, 121, 125,
+   130, 134, 138, 142, 146, 150, 154, 158,
+   162, 166, 170, 174, 178, 182, 186, 190,
+   194, 198, 202, 206, 210, 215, 219, 223,
+   227, 231, 235, 239, 243, 247, 251, 255
+};
+
+
+#define CC_SEL(cc, which) ((cc)[(which) / 32] >> ((which) & 31))
+#define UP5(c) _rgb_scale_5[(c) & 31]
+#define UP6(c, b) _rgb_scale_6[(((c) & 31) << 1) | ((b) & 1)]
+#define LERP(n, t, c0, c1) (((n) - (t)) * (c0) + (t) * (c1) + (n) / 2) / (n)
+#define ZERO_4UBV(v) *((unsigned long *)(v)) = 0
+
+
+static void
+fxt1_decode_1HI (unsigned long code, int t, unsigned char *rgba)
+{
+   const unsigned long *cc;
+
+   t *= 3;
+   cc = (unsigned long *)(code + t / 8);
+   t = (cc[0] >> (t & 7)) & 7;
+
+   if (t == 7) {
+      ZERO_4UBV(rgba);
+   } else {
+      cc = (unsigned long *)(code + 12);
+      if (t == 0) {
+         rgba[BCOMP] = UP5(CC_SEL(cc, 0));
+         rgba[GCOMP] = UP5(CC_SEL(cc, 5));
+         rgba[RCOMP] = UP5(CC_SEL(cc, 10));
+      } else if (t == 6) {
+         rgba[BCOMP] = UP5(CC_SEL(cc, 15));
+         rgba[GCOMP] = UP5(CC_SEL(cc, 20));
+         rgba[RCOMP] = UP5(CC_SEL(cc, 25));
+      } else {
+         rgba[BCOMP] = LERP(6, t, UP5(CC_SEL(cc, 0)), UP5(CC_SEL(cc, 15)));
+         rgba[GCOMP] = LERP(6, t, UP5(CC_SEL(cc, 5)), UP5(CC_SEL(cc, 20)));
+         rgba[RCOMP] = LERP(6, t, UP5(CC_SEL(cc, 10)), UP5(CC_SEL(cc, 25)));
+      }
+      rgba[ACOMP] = 255;
+   }
+}
+
+
+static void
+fxt1_decode_1CHROMA (unsigned long code, int t, unsigned char *rgba)
+{
+   const unsigned long *cc;
+   unsigned long kk;
+
+   cc = (unsigned long *)code;
+   if (t & 16) {
+      cc++;
+      t &= 15;
+   }
+   t = (cc[0] >> (t * 2)) & 3;
+
+   t *= 15;
+   cc = (unsigned long *)(code + 8 + t / 8);
+   kk = cc[0] >> (t & 7);
+   rgba[BCOMP] = UP5(kk);
+   rgba[GCOMP] = UP5(kk >> 5);
+   rgba[RCOMP] = UP5(kk >> 10);
+   rgba[ACOMP] = 255;
+}
+
+
+static void
+fxt1_decode_1MIXED (unsigned long code, int t, unsigned char *rgba)
+{
+   const unsigned long *cc;
+   unsigned int col[2][3];
+   int glsb, selb;
+
+   cc = (unsigned long *)code;
+   if (t & 16) {
+      t &= 15;
+      t = (cc[1] >> (t * 2)) & 3;
+      /* col 2 */
+      col[0][BCOMP] = (*(unsigned long *)(code + 11)) >> 6;
+      col[0][GCOMP] = CC_SEL(cc, 99);
+      col[0][RCOMP] = CC_SEL(cc, 104);
+      /* col 3 */
+      col[1][BCOMP] = CC_SEL(cc, 109);
+      col[1][GCOMP] = CC_SEL(cc, 114);
+      col[1][RCOMP] = CC_SEL(cc, 119);
+      glsb = CC_SEL(cc, 126);
+      selb = CC_SEL(cc, 33);
+   } else {
+      t = (cc[0] >> (t * 2)) & 3;
+      /* col 0 */
+      col[0][BCOMP] = CC_SEL(cc, 64);
+      col[0][GCOMP] = CC_SEL(cc, 69);
+      col[0][RCOMP] = CC_SEL(cc, 74);
+      /* col 1 */
+      col[1][BCOMP] = CC_SEL(cc, 79);
+      col[1][GCOMP] = CC_SEL(cc, 84);
+      col[1][RCOMP] = CC_SEL(cc, 89);
+      glsb = CC_SEL(cc, 125);
+      selb = CC_SEL(cc, 1);
+   }
+
+   if (CC_SEL(cc, 124) & 1) {
+      /* alpha[0] == 1 */
+
+      if (t == 3) {
+         ZERO_4UBV(rgba);
+      } else {
+         if (t == 0) {
+            rgba[BCOMP] = UP5(col[0][BCOMP]);
+            rgba[GCOMP] = UP5(col[0][GCOMP]);
+            rgba[RCOMP] = UP5(col[0][RCOMP]);
+         } else if (t == 2) {
+            rgba[BCOMP] = UP5(col[1][BCOMP]);
+            rgba[GCOMP] = UP6(col[1][GCOMP], glsb);
+            rgba[RCOMP] = UP5(col[1][RCOMP]);
+         } else {
+            rgba[BCOMP] = (UP5(col[0][BCOMP]) + UP5(col[1][BCOMP])) / 2;
+            rgba[GCOMP] = (UP5(col[0][GCOMP]) + UP6(col[1][GCOMP], glsb)) / 2;
+            rgba[RCOMP] = (UP5(col[0][RCOMP]) + UP5(col[1][RCOMP])) / 2;
+         }
+         rgba[ACOMP] = 255;
+      }
+   } else {
+      /* alpha[0] == 0 */
+
+      if (t == 0) {
+         rgba[BCOMP] = UP5(col[0][BCOMP]);
+         rgba[GCOMP] = UP6(col[0][GCOMP], glsb ^ selb);
+         rgba[RCOMP] = UP5(col[0][RCOMP]);
+      } else if (t == 3) {
+         rgba[BCOMP] = UP5(col[1][BCOMP]);
+         rgba[GCOMP] = UP6(col[1][GCOMP], glsb);
+         rgba[RCOMP] = UP5(col[1][RCOMP]);
+      } else {
+         rgba[BCOMP] = LERP(3, t, UP5(col[0][BCOMP]), UP5(col[1][BCOMP]));
+         rgba[GCOMP] = LERP(3, t, UP6(col[0][GCOMP], glsb ^ selb),
+                                  UP6(col[1][GCOMP], glsb));
+         rgba[RCOMP] = LERP(3, t, UP5(col[0][RCOMP]), UP5(col[1][RCOMP]));
+      }
+      rgba[ACOMP] = 255;
+   }
+}
+
+
+static void
+fxt1_decode_1ALPHA (unsigned long code, int t, unsigned char *rgba)
+{
+   const unsigned long *cc;
+
+   cc = (unsigned long *)code;
+   if (CC_SEL(cc, 124) & 1) {
+      /* lerp == 1 */
+      unsigned int col0[4];
+
+      if (t & 16) {
+         t &= 15;
+         t = (cc[1] >> (t * 2)) & 3;
+         /* col 2 */
+         col0[BCOMP] = (*(unsigned long *)(code + 11)) >> 6;
+         col0[GCOMP] = CC_SEL(cc, 99);
+         col0[RCOMP] = CC_SEL(cc, 104);
+         col0[ACOMP] = CC_SEL(cc, 119);
+      } else {
+         t = (cc[0] >> (t * 2)) & 3;
+         /* col 0 */
+         col0[BCOMP] = CC_SEL(cc, 64);
+         col0[GCOMP] = CC_SEL(cc, 69);
+         col0[RCOMP] = CC_SEL(cc, 74);
+         col0[ACOMP] = CC_SEL(cc, 109);
+      }
+
+      if (t == 0) {
+         rgba[BCOMP] = UP5(col0[BCOMP]);
+         rgba[GCOMP] = UP5(col0[GCOMP]);
+         rgba[RCOMP] = UP5(col0[RCOMP]);
+         rgba[ACOMP] = UP5(col0[ACOMP]);
+      } else if (t == 3) {
+         rgba[BCOMP] = UP5(CC_SEL(cc, 79));
+         rgba[GCOMP] = UP5(CC_SEL(cc, 84));
+         rgba[RCOMP] = UP5(CC_SEL(cc, 89));
+         rgba[ACOMP] = UP5(CC_SEL(cc, 114));
+      } else {
+         rgba[BCOMP] = LERP(3, t, UP5(col0[BCOMP]), UP5(CC_SEL(cc, 79)));
+         rgba[GCOMP] = LERP(3, t, UP5(col0[GCOMP]), UP5(CC_SEL(cc, 84)));
+         rgba[RCOMP] = LERP(3, t, UP5(col0[RCOMP]), UP5(CC_SEL(cc, 89)));
+         rgba[ACOMP] = LERP(3, t, UP5(col0[ACOMP]), UP5(CC_SEL(cc, 114)));
+      }
+   } else {
+      /* lerp == 0 */
+
+      if (t & 16) {
+         cc++;
+         t &= 15;
+      }
+      t = (cc[0] >> (t * 2)) & 3;
+
+      if (t == 3) {
+         ZERO_4UBV(rgba);
+      } else {
+         unsigned long kk;
+         cc = (unsigned long *)code;
+         rgba[ACOMP] = UP5(cc[3] >> (t * 5 + 13));
+         t *= 15;
+         cc = (unsigned long *)(code + 8 + t / 8);
+         kk = cc[0] >> (t & 7);
+         rgba[BCOMP] = UP5(kk);
+         rgba[GCOMP] = UP5(kk >> 5);
+         rgba[RCOMP] = UP5(kk >> 10);
+      }
+   }
+}
+
+
+void
+fxt1_decode_1 (const void *texture, int width,
+               int i, int j, unsigned char *rgba)
+{
+   static void (*decode_1[]) (unsigned long, int, unsigned char *) = {
+      fxt1_decode_1HI,     /* cc-high   = "00?" */
+      fxt1_decode_1HI,     /* cc-high   = "00?" */
+      fxt1_decode_1CHROMA, /* cc-chroma = "010" */
+      fxt1_decode_1ALPHA,  /* alpha     = "011" */
+      fxt1_decode_1MIXED,  /* mixed     = "1??" */
+      fxt1_decode_1MIXED,  /* mixed     = "1??" */
+      fxt1_decode_1MIXED,  /* mixed     = "1??" */
+      fxt1_decode_1MIXED   /* mixed     = "1??" */
+   };
+
+   unsigned long code = (unsigned long)texture +
+                        ((j / 4) * (width / 8) + (i / 8)) * 16;
+   int mode = CC_SEL((unsigned long *)code, 125);
+   int t = i & 7;
+
+   if (t & 4) {
+      t += 12;
+   }
+   t += (j & 3) * 4;
+
+   decode_1[mode](code, t, rgba);
+}