// SPDX-FileCopyrightText: fabian "ryg" giesen // SPDX-License-Identifier: MIT // stb_dxt.h - v1.12 - DXT1/DXT5 compressor #include #include #include #if !defined(STBD_FABS) #include #endif #ifndef STBD_FABS #define STBD_FABS(x) fabs(x) #endif static const unsigned char stb__OMatch5[256][2] = { {0, 0}, {0, 0}, {0, 1}, {0, 1}, {1, 0}, {1, 0}, {1, 0}, {1, 1}, {1, 1}, {1, 1}, {1, 2}, {0, 4}, {2, 1}, {2, 1}, {2, 1}, {2, 2}, {2, 2}, {2, 2}, {2, 3}, {1, 5}, {3, 2}, {3, 2}, {4, 0}, {3, 3}, {3, 3}, {3, 3}, {3, 4}, {3, 4}, {3, 4}, {3, 5}, {4, 3}, {4, 3}, {5, 2}, {4, 4}, {4, 4}, {4, 5}, {4, 5}, {5, 4}, {5, 4}, {5, 4}, {6, 3}, {5, 5}, {5, 5}, {5, 6}, {4, 8}, {6, 5}, {6, 5}, {6, 5}, {6, 6}, {6, 6}, {6, 6}, {6, 7}, {5, 9}, {7, 6}, {7, 6}, {8, 4}, {7, 7}, {7, 7}, {7, 7}, {7, 8}, {7, 8}, {7, 8}, {7, 9}, {8, 7}, {8, 7}, {9, 6}, {8, 8}, {8, 8}, {8, 9}, {8, 9}, {9, 8}, {9, 8}, {9, 8}, {10, 7}, {9, 9}, {9, 9}, {9, 10}, {8, 12}, {10, 9}, {10, 9}, {10, 9}, {10, 10}, {10, 10}, {10, 10}, {10, 11}, {9, 13}, {11, 10}, {11, 10}, {12, 8}, {11, 11}, {11, 11}, {11, 11}, {11, 12}, {11, 12}, {11, 12}, {11, 13}, {12, 11}, {12, 11}, {13, 10}, {12, 12}, {12, 12}, {12, 13}, {12, 13}, {13, 12}, {13, 12}, {13, 12}, {14, 11}, {13, 13}, {13, 13}, {13, 14}, {12, 16}, {14, 13}, {14, 13}, {14, 13}, {14, 14}, {14, 14}, {14, 14}, {14, 15}, {13, 17}, {15, 14}, {15, 14}, {16, 12}, {15, 15}, {15, 15}, {15, 15}, {15, 16}, {15, 16}, {15, 16}, {15, 17}, {16, 15}, {16, 15}, {17, 14}, {16, 16}, {16, 16}, {16, 17}, {16, 17}, {17, 16}, {17, 16}, {17, 16}, {18, 15}, {17, 17}, {17, 17}, {17, 18}, {16, 20}, {18, 17}, {18, 17}, {18, 17}, {18, 18}, {18, 18}, {18, 18}, {18, 19}, {17, 21}, {19, 18}, {19, 18}, {20, 16}, {19, 19}, {19, 19}, {19, 19}, {19, 20}, {19, 20}, {19, 20}, {19, 21}, {20, 19}, {20, 19}, {21, 18}, {20, 20}, {20, 20}, {20, 21}, {20, 21}, {21, 20}, {21, 20}, {21, 20}, {22, 19}, {21, 21}, {21, 21}, {21, 22}, {20, 24}, {22, 21}, {22, 21}, {22, 21}, {22, 22}, {22, 22}, {22, 22}, {22, 23}, {21, 25}, {23, 22}, {23, 22}, {24, 20}, {23, 23}, {23, 23}, {23, 23}, {23, 24}, {23, 24}, {23, 24}, {23, 25}, {24, 23}, {24, 23}, {25, 22}, {24, 24}, {24, 24}, {24, 25}, {24, 25}, {25, 24}, {25, 24}, {25, 24}, {26, 23}, {25, 25}, {25, 25}, {25, 26}, {24, 28}, {26, 25}, {26, 25}, {26, 25}, {26, 26}, {26, 26}, {26, 26}, {26, 27}, {25, 29}, {27, 26}, {27, 26}, {28, 24}, {27, 27}, {27, 27}, {27, 27}, {27, 28}, {27, 28}, {27, 28}, {27, 29}, {28, 27}, {28, 27}, {29, 26}, {28, 28}, {28, 28}, {28, 29}, {28, 29}, {29, 28}, {29, 28}, {29, 28}, {30, 27}, {29, 29}, {29, 29}, {29, 30}, {29, 30}, {30, 29}, {30, 29}, {30, 29}, {30, 30}, {30, 30}, {30, 30}, {30, 31}, {30, 31}, {31, 30}, {31, 30}, {31, 30}, {31, 31}, {31, 31}, }; static const unsigned char stb__OMatch6[256][2] = { {0, 0}, {0, 1}, {1, 0}, {1, 1}, {1, 1}, {1, 2}, {2, 1}, {2, 2}, {2, 2}, {2, 3}, {3, 2}, {3, 3}, {3, 3}, {3, 4}, {4, 3}, {4, 4}, {4, 4}, {4, 5}, {5, 4}, {5, 5}, {5, 5}, {5, 6}, {6, 5}, {6, 6}, {6, 6}, {6, 7}, {7, 6}, {7, 7}, {7, 7}, {7, 8}, {8, 7}, {8, 8}, {8, 8}, {8, 9}, {9, 8}, {9, 9}, {9, 9}, {9, 10}, {10, 9}, {10, 10}, {10, 10}, {10, 11}, {11, 10}, {8, 16}, {11, 11}, {11, 12}, {12, 11}, {9, 17}, {12, 12}, {12, 13}, {13, 12}, {11, 16}, {13, 13}, {13, 14}, {14, 13}, {12, 17}, {14, 14}, {14, 15}, {15, 14}, {14, 16}, {15, 15}, {15, 16}, {16, 14}, {16, 15}, {17, 14}, {16, 16}, {16, 17}, {17, 16}, {18, 15}, {17, 17}, {17, 18}, {18, 17}, {20, 14}, {18, 18}, {18, 19}, {19, 18}, {21, 15}, {19, 19}, {19, 20}, {20, 19}, {20, 20}, {20, 20}, {20, 21}, {21, 20}, {21, 21}, {21, 21}, {21, 22}, {22, 21}, {22, 22}, {22, 22}, {22, 23}, {23, 22}, {23, 23}, {23, 23}, {23, 24}, {24, 23}, {24, 24}, {24, 24}, {24, 25}, {25, 24}, {25, 25}, {25, 25}, {25, 26}, {26, 25}, {26, 26}, {26, 26}, {26, 27}, {27, 26}, {24, 32}, {27, 27}, {27, 28}, {28, 27}, {25, 33}, {28, 28}, {28, 29}, {29, 28}, {27, 32}, {29, 29}, {29, 30}, {30, 29}, {28, 33}, {30, 30}, {30, 31}, {31, 30}, {30, 32}, {31, 31}, {31, 32}, {32, 30}, {32, 31}, {33, 30}, {32, 32}, {32, 33}, {33, 32}, {34, 31}, {33, 33}, {33, 34}, {34, 33}, {36, 30}, {34, 34}, {34, 35}, {35, 34}, {37, 31}, {35, 35}, {35, 36}, {36, 35}, {36, 36}, {36, 36}, {36, 37}, {37, 36}, {37, 37}, {37, 37}, {37, 38}, {38, 37}, {38, 38}, {38, 38}, {38, 39}, {39, 38}, {39, 39}, {39, 39}, {39, 40}, {40, 39}, {40, 40}, {40, 40}, {40, 41}, {41, 40}, {41, 41}, {41, 41}, {41, 42}, {42, 41}, {42, 42}, {42, 42}, {42, 43}, {43, 42}, {40, 48}, {43, 43}, {43, 44}, {44, 43}, {41, 49}, {44, 44}, {44, 45}, {45, 44}, {43, 48}, {45, 45}, {45, 46}, {46, 45}, {44, 49}, {46, 46}, {46, 47}, {47, 46}, {46, 48}, {47, 47}, {47, 48}, {48, 46}, {48, 47}, {49, 46}, {48, 48}, {48, 49}, {49, 48}, {50, 47}, {49, 49}, {49, 50}, {50, 49}, {52, 46}, {50, 50}, {50, 51}, {51, 50}, {53, 47}, {51, 51}, {51, 52}, {52, 51}, {52, 52}, {52, 52}, {52, 53}, {53, 52}, {53, 53}, {53, 53}, {53, 54}, {54, 53}, {54, 54}, {54, 54}, {54, 55}, {55, 54}, {55, 55}, {55, 55}, {55, 56}, {56, 55}, {56, 56}, {56, 56}, {56, 57}, {57, 56}, {57, 57}, {57, 57}, {57, 58}, {58, 57}, {58, 58}, {58, 58}, {58, 59}, {59, 58}, {59, 59}, {59, 59}, {59, 60}, {60, 59}, {60, 60}, {60, 60}, {60, 61}, {61, 60}, {61, 61}, {61, 61}, {61, 62}, {62, 61}, {62, 62}, {62, 62}, {62, 63}, {63, 62}, {63, 63}, {63, 63}, }; static int stb__Mul8Bit(int a, int b) { int t = a * b + 128; return (t + (t >> 8)) >> 8; } static void stb__From16Bit(unsigned char* out, unsigned short v) { int rv = (v & 0xf800) >> 11; int gv = (v & 0x07e0) >> 5; int bv = (v & 0x001f) >> 0; // expand to 8 bits via bit replication out[0] = static_cast((rv * 33) >> 2); out[1] = static_cast((gv * 65) >> 4); out[2] = static_cast((bv * 33) >> 2); out[3] = 0; } static unsigned short stb__As16Bit(int r, int g, int b) { return (unsigned short)((stb__Mul8Bit(r, 31) << 11) + (stb__Mul8Bit(g, 63) << 5) + stb__Mul8Bit(b, 31)); } // linear interpolation at 1/3 point between a and b, using desired rounding // type static int stb__Lerp13(int a, int b) { #ifdef STB_DXT_USE_ROUNDING_BIAS // with rounding bias return a + stb__Mul8Bit(b - a, 0x55); #else // without rounding bias // replace "/ 3" by "* 0xaaab) >> 17" if your compiler sucks or you really // need every ounce of speed. return (2 * a + b) / 3; #endif } // linear interpolation at 1/2 point between a and b static int stb__Lerp12(int a, int b) { return (a + b) / 2; } // lerp RGB color static void stb__Lerp13RGB(unsigned char* out, unsigned char* p1, unsigned char* p2) { out[0] = (unsigned char)stb__Lerp13(p1[0], p2[0]); out[1] = (unsigned char)stb__Lerp13(p1[1], p2[1]); out[2] = (unsigned char)stb__Lerp13(p1[2], p2[2]); } static void stb__Lerp12RGB(unsigned char* out, unsigned char* p1, unsigned char* p2) { out[0] = (unsigned char)stb__Lerp12(p1[0], p2[0]); out[1] = (unsigned char)stb__Lerp12(p1[1], p2[1]); out[2] = (unsigned char)stb__Lerp12(p1[2], p2[2]); } /****************************************************************************/ static void stb__Eval4Colors(unsigned char* color, unsigned short c0, unsigned short c1) { stb__From16Bit(color + 0, c0); stb__From16Bit(color + 4, c1); stb__Lerp13RGB(color + 8, color + 0, color + 4); stb__Lerp13RGB(color + 12, color + 4, color + 0); } static void stb__Eval3Colors(unsigned char* color, unsigned short c0, unsigned short c1) { stb__From16Bit(color + 0, c0); stb__From16Bit(color + 4, c1); stb__Lerp12RGB(color + 8, color + 0, color + 4); } // The color matching function static unsigned int stb__MatchColorsBlock(unsigned char* block, unsigned char* color) { unsigned int mask = 0; int dirr = color[0 * 4 + 0] - color[1 * 4 + 0]; int dirg = color[0 * 4 + 1] - color[1 * 4 + 1]; int dirb = color[0 * 4 + 2] - color[1 * 4 + 2]; int dots[16]; int stops[4]; int i; int c0Point, halfPoint, c3Point; for (i = 0; i < 16; i++) dots[i] = block[i * 4 + 0] * dirr + block[i * 4 + 1] * dirg + block[i * 4 + 2] * dirb; for (i = 0; i < 4; i++) stops[i] = color[i * 4 + 0] * dirr + color[i * 4 + 1] * dirg + color[i * 4 + 2] * dirb; // think of the colors as arranged on a line; project point onto that line, // then choose next color out of available ones. we compute the crossover // points for "best color in top half"/"best in bottom half" and then the same // inside that subinterval. // // relying on this 1d approximation isn't always optimal in terms of euclidean // distance, but it's very close and a lot faster. // http://cbloomrants.blogspot.com/2008/12/12-08-08-dxtc-summary.html c0Point = (stops[1] + stops[3]); halfPoint = (stops[3] + stops[2]); c3Point = (stops[2] + stops[0]); for (i = 15; i >= 0; i--) { int dot = dots[i] * 2; mask <<= 2; if (dot < halfPoint) mask |= (dot < c0Point) ? 1 : 3; else mask |= (dot < c3Point) ? 2 : 0; } return mask; } static unsigned int stb__MatchColorsAlphaBlock(unsigned char* block, unsigned char* color) { unsigned int mask = 0; int dirr = color[0 * 4 + 0] - color[1 * 4 + 0]; int dirg = color[0 * 4 + 1] - color[1 * 4 + 1]; int dirb = color[0 * 4 + 2] - color[1 * 4 + 2]; int dots[16]; int stops[3]; int i; int c0Point, c2Point; for (i = 0; i < 16; i++) dots[i] = block[i * 4 + 0] * dirr + block[i * 4 + 1] * dirg + block[i * 4 + 2] * dirb; for (i = 0; i < 3; i++) stops[i] = color[i * 4 + 0] * dirr + color[i * 4 + 1] * dirg + color[i * 4 + 2] * dirb; c0Point = (stops[1] + stops[2]); c2Point = (stops[2] + stops[0]); for (i = 15; i >= 0; i--) { int dot = dots[i] * 2; mask <<= 2; if (block[i * 4 + 3] == 0) mask |= 3; else if (dot < c2Point) mask |= (dot < c0Point) ? 0 : 2; else mask |= (dot < c0Point) ? 1 : 0; } return mask; } static void stb__ReorderColors(unsigned short* pmax16, unsigned short* pmin16) { if (*pmin16 < *pmax16) { unsigned short t = *pmin16; *pmin16 = *pmax16; *pmax16 = t; } } static void stb__FinalizeColors(unsigned short* pmax16, unsigned short* pmin16, unsigned int* pmask) { if (*pmax16 < *pmin16) { unsigned short t = *pmin16; *pmin16 = *pmax16; *pmax16 = t; *pmask ^= 0x55555555; } } // The color optimization function. (Clever code, part 1) static void stb__OptimizeColorsBlock(unsigned char* block, unsigned short* pmax16, unsigned short* pmin16) { int mind, maxd; unsigned char *minp, *maxp; double magn; int v_r, v_g, v_b; static const int nIterPower = 4; float covf[6], vfr, vfg, vfb; // determine color distribution int cov[6]; int mu[3], min[3], max[3]; int ch, i, iter; for (ch = 0; ch < 3; ch++) { const unsigned char* bp = ((const unsigned char*)block) + ch; int muv, minv, maxv; muv = minv = maxv = bp[0]; for (i = 4; i < 64; i += 4) { muv += bp[i]; if (bp[i] < minv) minv = bp[i]; else if (bp[i] > maxv) maxv = bp[i]; } mu[ch] = (muv + 8) >> 4; min[ch] = minv; max[ch] = maxv; } // determine covariance matrix for (i = 0; i < 6; i++) cov[i] = 0; for (i = 0; i < 16; i++) { int r = block[i * 4 + 0] - mu[0]; int g = block[i * 4 + 1] - mu[1]; int b = block[i * 4 + 2] - mu[2]; cov[0] += r * r; cov[1] += r * g; cov[2] += r * b; cov[3] += g * g; cov[4] += g * b; cov[5] += b * b; } // convert covariance matrix to float, find principal axis via power iter for (i = 0; i < 6; i++) covf[i] = static_cast(cov[i]) / 255.0f; vfr = (float)(max[0] - min[0]); vfg = (float)(max[1] - min[1]); vfb = (float)(max[2] - min[2]); for (iter = 0; iter < nIterPower; iter++) { float r = vfr * covf[0] + vfg * covf[1] + vfb * covf[2]; float g = vfr * covf[1] + vfg * covf[3] + vfb * covf[4]; float b = vfr * covf[2] + vfg * covf[4] + vfb * covf[5]; vfr = r; vfg = g; vfb = b; } magn = STBD_FABS(vfr); if (STBD_FABS(vfg) > magn) magn = STBD_FABS(vfg); if (STBD_FABS(vfb) > magn) magn = STBD_FABS(vfb); if (magn < 4.0f) { // too small, default to luminance v_r = 299; // JPEG YCbCr luma coefs, scaled by 1000. v_g = 587; v_b = 114; } else { magn = 512.0 / magn; v_r = (int)(vfr * magn); v_g = (int)(vfg * magn); v_b = (int)(vfb * magn); } minp = maxp = block; mind = maxd = block[0] * v_r + block[1] * v_g + block[2] * v_b; // Pick colors at extreme points for (i = 1; i < 16; i++) { int dot = block[i * 4 + 0] * v_r + block[i * 4 + 1] * v_g + block[i * 4 + 2] * v_b; if (dot < mind) { mind = dot; minp = block + i * 4; } if (dot > maxd) { maxd = dot; maxp = block + i * 4; } } *pmax16 = stb__As16Bit(maxp[0], maxp[1], maxp[2]); *pmin16 = stb__As16Bit(minp[0], minp[1], minp[2]); stb__ReorderColors(pmax16, pmin16); } static void stb__OptimizeColorsAlphaBlock(unsigned char* block, unsigned short* pmax16, unsigned short* pmin16) { int mind, maxd; unsigned char *minp, *maxp; double magn; int v_r, v_g, v_b; static const int nIterPower = 4; float covf[6], vfr, vfg, vfb; // determine color distribution int cov[6]; int mu[3], min[3], max[3]; int ch, i, iter; for (ch = 0; ch < 3; ch++) { const unsigned char* bp = ((const unsigned char*)block) + ch; int muv = 0, minv = 256, maxv = -1; int num = 0; for (i = 0; i < 64; i += 4) { if (bp[3 - ch] == 0) { continue; } muv += bp[i]; if (bp[i] < minv) minv = bp[i]; else if (bp[i] > maxv) maxv = bp[i]; num++; } mu[ch] = num > 0 ? (muv + 8) / num : 0; min[ch] = minv; max[ch] = maxv; } // determine covariance matrix for (i = 0; i < 6; i++) cov[i] = 0; for (i = 0; i < 16; i++) { if (block[i * 4 + 3] == 0) { continue; } int r = block[i * 4 + 0] - mu[0]; int g = block[i * 4 + 1] - mu[1]; int b = block[i * 4 + 2] - mu[2]; cov[0] += r * r; cov[1] += r * g; cov[2] += r * b; cov[3] += g * g; cov[4] += g * b; cov[5] += b * b; } // convert covariance matrix to float, find principal axis via power iter for (i = 0; i < 6; i++) covf[i] = static_cast(cov[i]) / 255.0f; vfr = (float)(max[0] - min[0]); vfg = (float)(max[1] - min[1]); vfb = (float)(max[2] - min[2]); for (iter = 0; iter < nIterPower; iter++) { float r = vfr * covf[0] + vfg * covf[1] + vfb * covf[2]; float g = vfr * covf[1] + vfg * covf[3] + vfb * covf[4]; float b = vfr * covf[2] + vfg * covf[4] + vfb * covf[5]; vfr = r; vfg = g; vfb = b; } magn = STBD_FABS(vfr); if (STBD_FABS(vfg) > magn) magn = STBD_FABS(vfg); if (STBD_FABS(vfb) > magn) magn = STBD_FABS(vfb); if (magn < 4.0f) { // too small, default to luminance v_r = 299; // JPEG YCbCr luma coefs, scaled by 1000. v_g = 587; v_b = 114; } else { magn = 512.0 / magn; v_r = (int)(vfr * magn); v_g = (int)(vfg * magn); v_b = (int)(vfb * magn); } minp = maxp = NULL; mind = 0x7fffffff; maxd = -0x80000000; // Pick colors at extreme points for (i = 0; i < 16; i++) { if (block[i * 4 + 3] == 0) { continue; } int dot = block[i * 4 + 0] * v_r + block[i * 4 + 1] * v_g + block[i * 4 + 2] * v_b; if (dot < mind) { mind = dot; minp = block + i * 4; } if (dot > maxd) { maxd = dot; maxp = block + i * 4; } } if (!maxp) { // all alpha, no color *pmin16 = 0xffff; *pmax16 = 0; } else { // endpoint colors found *pmax16 = stb__As16Bit(maxp[0], maxp[1], maxp[2]); *pmin16 = stb__As16Bit(minp[0], minp[1], minp[2]); if (*pmax16 == *pmin16) { // modify the endpoints to indicate presence of an alpha block if (*pmax16 > 0) { (*pmax16)--; } else { (*pmin16)++; } } stb__ReorderColors(pmax16, pmin16); } } static const float stb__midpoints5[32] = { 0.015686f, 0.047059f, 0.078431f, 0.111765f, 0.145098f, 0.176471f, 0.207843f, 0.241176f, 0.274510f, 0.305882f, 0.337255f, 0.370588f, 0.403922f, 0.435294f, 0.466667f, 0.5f, 0.533333f, 0.564706f, 0.596078f, 0.629412f, 0.662745f, 0.694118f, 0.725490f, 0.758824f, 0.792157f, 0.823529f, 0.854902f, 0.888235f, 0.921569f, 0.952941f, 0.984314f, 1.0f}; static const float stb__midpoints6[64] = { 0.007843f, 0.023529f, 0.039216f, 0.054902f, 0.070588f, 0.086275f, 0.101961f, 0.117647f, 0.133333f, 0.149020f, 0.164706f, 0.180392f, 0.196078f, 0.211765f, 0.227451f, 0.245098f, 0.262745f, 0.278431f, 0.294118f, 0.309804f, 0.325490f, 0.341176f, 0.356863f, 0.372549f, 0.388235f, 0.403922f, 0.419608f, 0.435294f, 0.450980f, 0.466667f, 0.482353f, 0.500000f, 0.517647f, 0.533333f, 0.549020f, 0.564706f, 0.580392f, 0.596078f, 0.611765f, 0.627451f, 0.643137f, 0.658824f, 0.674510f, 0.690196f, 0.705882f, 0.721569f, 0.737255f, 0.754902f, 0.772549f, 0.788235f, 0.803922f, 0.819608f, 0.835294f, 0.850980f, 0.866667f, 0.882353f, 0.898039f, 0.913725f, 0.929412f, 0.945098f, 0.960784f, 0.976471f, 0.992157f, 1.0f}; static unsigned short stb__Quantize5(float x) { unsigned short q; x = x < 0 ? 0 : x > 1 ? 1 : x; // saturate q = (unsigned short)(x * 31); q += (x > stb__midpoints5[q]); return q; } static unsigned short stb__Quantize6(float x) { unsigned short q; x = x < 0 ? 0 : x > 1 ? 1 : x; // saturate q = (unsigned short)(x * 63); q += (x > stb__midpoints6[q]); return q; } // The refinement function. (Clever code, part 2) // Tries to optimize colors to suit block contents better. // (By solving a least squares system via normal equations+Cramer's rule) static int stb__RefineBlock(unsigned char* block, unsigned short* pmax16, unsigned short* pmin16, unsigned int mask) { static const int w1Tab[4] = {3, 0, 2, 1}; static const int prods[4] = {0x090000, 0x000900, 0x040102, 0x010402}; // ^some magic to save a lot of multiplies in the accumulating loop... // (precomputed products of weights for least squares system, accumulated // inside one 32-bit register) float f; unsigned short oldMin, oldMax, min16, max16; int i, akku = 0, xx, xy, yy; int At1_r, At1_g, At1_b; int At2_r, At2_g, At2_b; unsigned int cm = mask; oldMin = *pmin16; oldMax = *pmax16; if ((mask ^ (mask << 2)) < 4) // all pixels have the same index? { // yes, linear system would be singular; solve using optimal // single-color match on average color int r = 8, g = 8, b = 8; for (i = 0; i < 16; ++i) { r += block[i * 4 + 0]; g += block[i * 4 + 1]; b += block[i * 4 + 2]; } r >>= 4; g >>= 4; b >>= 4; max16 = static_cast((stb__OMatch5[r][0] << 11) | (stb__OMatch6[g][0] << 5) | stb__OMatch5[b][0]); min16 = static_cast((stb__OMatch5[r][1] << 11) | (stb__OMatch6[g][1] << 5) | stb__OMatch5[b][1]); } else { At1_r = At1_g = At1_b = 0; At2_r = At2_g = At2_b = 0; for (i = 0; i < 16; ++i, cm >>= 2) { int step = cm & 3; int w1 = w1Tab[step]; int r = block[i * 4 + 0]; int g = block[i * 4 + 1]; int b = block[i * 4 + 2]; akku += prods[step]; At1_r += w1 * r; At1_g += w1 * g; At1_b += w1 * b; At2_r += r; At2_g += g; At2_b += b; } At2_r = 3 * At2_r - At1_r; At2_g = 3 * At2_g - At1_g; At2_b = 3 * At2_b - At1_b; // extract solutions and decide solvability xx = akku >> 16; yy = (akku >> 8) & 0xff; xy = (akku >> 0) & 0xff; f = 3.0f / 255.0f / static_cast(xx * yy - xy * xy); max16 = static_cast( stb__Quantize5(static_cast(At1_r * yy - At2_r * xy) * f) << 11); max16 |= static_cast( stb__Quantize6(static_cast(At1_g * yy - At2_g * xy) * f) << 5); max16 |= static_cast( stb__Quantize5(static_cast(At1_b * yy - At2_b * xy) * f) << 0); min16 = static_cast( stb__Quantize5(static_cast(At2_r * xx - At1_r * xy) * f) << 11); min16 |= static_cast( stb__Quantize6(static_cast(At2_g * xx - At1_g * xy) * f) << 5); min16 |= static_cast( stb__Quantize5(static_cast(At2_b * xx - At1_b * xy) * f) << 0); } *pmin16 = min16; *pmax16 = max16; stb__ReorderColors(pmax16, pmin16); return oldMin != min16 || oldMax != max16; } // Color block compression static void stb__CompressColorBlock(unsigned char* dest, unsigned char* block, int alpha, int mode) { unsigned int mask; int i; int refinecount; unsigned short max16, min16; unsigned char color[4 * 4]; refinecount = (mode & STB_DXT_HIGHQUAL) ? 2 : 1; // check if block is constant for (i = 1; i < 16; i++) if (((unsigned int*)block)[i] != ((unsigned int*)block)[0]) break; if (i == 16 && block[3] == 0 && alpha) { // constant alpha mask = 0xffffffff; max16 = 0; min16 = 0xffff; } else if (i == 16) { // constant color int r = block[0], g = block[1], b = block[2]; mask = 0xaaaaaaaa; max16 = static_cast((stb__OMatch5[r][0] << 11) | (stb__OMatch6[g][0] << 5) | stb__OMatch5[b][0]); min16 = static_cast((stb__OMatch5[r][1] << 11) | (stb__OMatch6[g][1] << 5) | stb__OMatch5[b][1]); } else if (alpha) { stb__OptimizeColorsAlphaBlock(block, &max16, &min16); stb__Eval3Colors(color, max16, min16); mask = stb__MatchColorsAlphaBlock(block, color); } else { // first step: PCA+map along principal axis stb__OptimizeColorsBlock(block, &max16, &min16); if (max16 != min16) { stb__Eval4Colors(color, max16, min16); mask = stb__MatchColorsBlock(block, color); } else mask = 0; // third step: refine (multiple times if requested) for (i = 0; i < refinecount; i++) { unsigned int lastmask = mask; if (stb__RefineBlock(block, &max16, &min16, mask)) { if (max16 != min16) { stb__Eval4Colors(color, max16, min16); mask = stb__MatchColorsBlock(block, color); } else { mask = 0; break; } } if (mask == lastmask) break; } } // write the color block if (!alpha) stb__FinalizeColors(&max16, &min16, &mask); dest[0] = (unsigned char)(max16); dest[1] = (unsigned char)(max16 >> 8); dest[2] = (unsigned char)(min16); dest[3] = (unsigned char)(min16 >> 8); dest[4] = (unsigned char)(mask); dest[5] = (unsigned char)(mask >> 8); dest[6] = (unsigned char)(mask >> 16); dest[7] = (unsigned char)(mask >> 24); } // Alpha block compression (this is easy for a change) static void stb__CompressAlphaBlock(unsigned char* dest, unsigned char* src, int stride) { int i, dist, bias, dist4, dist2, bits, mask; // find min/max color int mn, mx; mn = mx = src[0]; for (i = 1; i < 16; i++) { if (src[i * stride] < mn) mn = src[i * stride]; else if (src[i * stride] > mx) mx = src[i * stride]; } // encode them dest[0] = (unsigned char)mx; dest[1] = (unsigned char)mn; dest += 2; // determine bias and emit color indices // given the choice of mx/mn, these indices are optimal: // http://fgiesen.wordpress.com/2009/12/15/dxt5-alpha-block-index-determination/ dist = mx - mn; dist4 = dist * 4; dist2 = dist * 2; bias = (dist < 8) ? (dist - 1) : (dist / 2 + 2); bias -= mn * 7; bits = 0, mask = 0; for (i = 0; i < 16; i++) { int a = src[i * stride] * 7 + bias; int ind, t; // select index. this is a "linear scale" lerp factor between 0 (val=min) // and 7 (val=max). t = (a >= dist4) ? -1 : 0; ind = t & 4; a -= dist4 & t; t = (a >= dist2) ? -1 : 0; ind += t & 2; a -= dist2 & t; ind += (a >= dist); // turn linear scale into DXT index (0/1 are extremal pts) ind = -ind & 7; ind ^= (2 > ind); // write index mask |= ind << bits; if ((bits += 3) >= 8) { *dest++ = (unsigned char)mask; mask >>= 8; bits -= 8; } } } void stb_compress_bc1_block(unsigned char* dest, const unsigned char* src, int alpha, int mode) { stb__CompressColorBlock(dest, (unsigned char*)src, alpha, mode); } void stb_compress_bc3_block(unsigned char* dest, const unsigned char* src, int mode) { unsigned char data[16][4]; int i; stb__CompressAlphaBlock(dest, (unsigned char*)src + 3, 4); dest += 8; // make a new copy of the data in which alpha is opaque, // because code uses a fast test for color constancy memcpy(data, src, 4 * 16); for (i = 0; i < 16; ++i) data[i][3] = 255; src = &data[0][0]; stb__CompressColorBlock(dest, (unsigned char*)src, 0, mode); }