generic S3TC DXT1 and DXT3 decoding functions

Originally committed as revision 8925 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/s3tc.c

+/*
+ * S3 Texture Compression (S3TC) decoding functions
+ * Copyright (c) 2007 by Ivo van Poorten
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * See also: http://wiki.multimedia.cx/index.php?title=S3TC
+ */
+
+#include "avcodec.h"
+#include "s3tc.h"
+
+static inline void dxt1_decode_pixels(const uint8_t *s, uint32_t *d,
+                                      unsigned int qstride, unsigned int flag,
+                                      uint64_t alpha) {
+    unsigned int x, y, c0, c1, a = (!flag * 255) << 24;
+    unsigned int rb0, rb1, rb2, rb3, g0, g1, g2, g3;
+    uint32_t colors[4], pixels;
+
+    c0 = le2me_16(*(uint16_t *)(s));
+    c1 = le2me_16(*(uint16_t *)(s+2));
+
+    rb0  = (c0<<3 | c0<<8) & 0xf800f8;
+    rb1  = (c1<<3 | c1<<8) & 0xf800f8;
+    rb0 +=        (rb0>>5) & 0x070007;
+    rb1 +=        (rb1>>5) & 0x070007;
+    g0   =        (c0 <<5) & 0x00fc00;
+    g1   =        (c1 <<5) & 0x00fc00;
+    g0  +=        (g0 >>6) & 0x000300;
+    g1  +=        (g1 >>6) & 0x000300;
+
+    colors[0] = rb0 + g0 + a;
+    colors[1] = rb1 + g1 + a;
+
+    if (c0 > c1 || flag) {
+        rb2 = (((2*rb0+rb1) * 21) >> 6) & 0xff00ff;
+        rb3 = (((2*rb1+rb0) * 21) >> 6) & 0xff00ff;
+        g2  = (((2*g0 +g1 ) * 21) >> 6) & 0x00ff00;
+        g3  = (((2*g1 +g0 ) * 21) >> 6) & 0x00ff00;
+        colors[3] = rb3 + g3 + a;
+    } else {
+        rb2 = ((rb0+rb1) >> 1) & 0xff00ff;
+        g2  = ((g0 +g1 ) >> 1) & 0x00ff00;
+        colors[3] = 0;
+    }
+
+    colors[2] = rb2 + g2 + a;
+
+    pixels = le2me_32(*(uint32_t *)(s+4));
+    for (y=0; y<4; y++) {
+        for (x=0; x<4; x++) {
+            a        = (alpha & 0x0f) << 28;
+            a       += a >> 4;
+            d[x]     = a + colors[pixels&3];
+            pixels >>= 2;
+            alpha  >>= 4;
+        }
+        d += qstride;
+    }
+}
+
+void ff_decode_dxt1(const uint8_t *s, uint8_t *dst,
+                    const unsigned int w, const unsigned int h,
+                    const unsigned int stride) {
+    unsigned int bx, by, qstride = stride/4;
+    uint32_t *d = (uint32_t *) dst;
+
+    for (by=0; by < h/4; by++, d += stride-w)
+        for (bx=0; bx < w/4; bx++, s+=8, d+=4)
+            dxt1_decode_pixels(s, d, qstride, 0, 0LL);
+}
+
+void ff_decode_dxt3(const uint8_t *s, uint8_t *dst,
+                    const unsigned int w, const unsigned int h,
+                    const unsigned int stride) {
+    unsigned int bx, by, qstride = stride/4;
+    uint32_t *d = (uint32_t *) dst;
+
+    for (by=0; by < h/4; by++, d += stride-w)
+        for (bx=0; bx < w/4; bx++, s+=16, d+=4)
+            dxt1_decode_pixels(s+8, d, qstride, 1, AV_RL64(s));
+}

libavcodec/s3tc.h

+/*
+ * S3 Texture Compression (S3TC) decoding functions
+ * Copyright (c) 2007 by Ivo van Poorten
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ */
+
+#ifndef FF_S3TC_H
+#define FF_S3TC_H
+
+#define FF_S3TC_DXT1    0x31545844
+#define FF_S3TC_DXT3    0x33545844
+
+void ff_decode_dxt1(const uint8_t *src, uint8_t *dst,
+                    const unsigned int w, const unsigned int h,
+                    const unsigned int stride);
+void ff_decode_dxt3(const uint8_t *src, uint8_t *dst,
+                    const unsigned int w, const unsigned int h,
+                    const unsigned int stride);
+
+#endif