Refactor texture compressors into separate files
R=robertphillips@google.com
Author: krajcevski@google.com
Review URL: https://codereview.chromium.org/403383003
diff --git a/src/utils/SkTextureCompressor_LATC.cpp b/src/utils/SkTextureCompressor_LATC.cpp
new file mode 100644
index 0000000..d042a84
--- /dev/null
+++ b/src/utils/SkTextureCompressor_LATC.cpp
@@ -0,0 +1,294 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkTextureCompressor_LATC.h"
+
+#include "SkEndian.h"
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Utility Functions
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// Absolute difference between two values. More correct than SkTAbs(a - b)
+// because it works on unsigned values.
+template <typename T> inline T abs_diff(const T &a, const T &b) {
+ return (a > b) ? (a - b) : (b - a);
+}
+
+static bool is_extremal(uint8_t pixel) {
+ return 0 == pixel || 255 == pixel;
+}
+
+typedef uint64_t (*A84x4To64BitProc)(const uint8_t block[]);
+
+// This function is used by both R11 EAC and LATC to compress 4x4 blocks
+// of 8-bit alpha into 64-bit values that comprise the compressed data.
+// For both formats, we need to make sure that the dimensions of the
+// src pixels are divisible by 4, and copy 4x4 blocks one at a time
+// for compression.
+static bool compress_4x4_a8_to_64bit(uint8_t* dst, const uint8_t* src,
+ int width, int height, int rowBytes,
+ A84x4To64BitProc proc) {
+ // Make sure that our data is well-formed enough to be considered for compression
+ if (0 == width || 0 == height || (width % 4) != 0 || (height % 4) != 0) {
+ return false;
+ }
+
+ int blocksX = width >> 2;
+ int blocksY = height >> 2;
+
+ uint8_t block[16];
+ uint64_t* encPtr = reinterpret_cast<uint64_t*>(dst);
+ for (int y = 0; y < blocksY; ++y) {
+ for (int x = 0; x < blocksX; ++x) {
+ // Load block
+ for (int k = 0; k < 4; ++k) {
+ memcpy(block + k*4, src + k*rowBytes + 4*x, 4);
+ }
+
+ // Compress it
+ *encPtr = proc(block);
+ ++encPtr;
+ }
+ src += 4 * rowBytes;
+ }
+
+ return true;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// LATC compressor
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// LATC compressed texels down into square 4x4 blocks
+static const int kLATCPaletteSize = 8;
+static const int kLATCBlockSize = 4;
+static const int kLATCPixelsPerBlock = kLATCBlockSize * kLATCBlockSize;
+
+// Generates an LATC palette. LATC constructs
+// a palette of eight colors from LUM0 and LUM1 using the algorithm:
+//
+// LUM0, if lum0 > lum1 and code(x,y) == 0
+// LUM1, if lum0 > lum1 and code(x,y) == 1
+// (6*LUM0+ LUM1)/7, if lum0 > lum1 and code(x,y) == 2
+// (5*LUM0+2*LUM1)/7, if lum0 > lum1 and code(x,y) == 3
+// (4*LUM0+3*LUM1)/7, if lum0 > lum1 and code(x,y) == 4
+// (3*LUM0+4*LUM1)/7, if lum0 > lum1 and code(x,y) == 5
+// (2*LUM0+5*LUM1)/7, if lum0 > lum1 and code(x,y) == 6
+// ( LUM0+6*LUM1)/7, if lum0 > lum1 and code(x,y) == 7
+//
+// LUM0, if lum0 <= lum1 and code(x,y) == 0
+// LUM1, if lum0 <= lum1 and code(x,y) == 1
+// (4*LUM0+ LUM1)/5, if lum0 <= lum1 and code(x,y) == 2
+// (3*LUM0+2*LUM1)/5, if lum0 <= lum1 and code(x,y) == 3
+// (2*LUM0+3*LUM1)/5, if lum0 <= lum1 and code(x,y) == 4
+// ( LUM0+4*LUM1)/5, if lum0 <= lum1 and code(x,y) == 5
+// 0, if lum0 <= lum1 and code(x,y) == 6
+// 255, if lum0 <= lum1 and code(x,y) == 7
+
+static void generate_latc_palette(uint8_t palette[], uint8_t lum0, uint8_t lum1) {
+ palette[0] = lum0;
+ palette[1] = lum1;
+ if (lum0 > lum1) {
+ for (int i = 1; i < 7; i++) {
+ palette[i+1] = ((7-i)*lum0 + i*lum1) / 7;
+ }
+ } else {
+ for (int i = 1; i < 5; i++) {
+ palette[i+1] = ((5-i)*lum0 + i*lum1) / 5;
+ }
+ palette[6] = 0;
+ palette[7] = 255;
+ }
+}
+
+// Compress a block by using the bounding box of the pixels. It is assumed that
+// there are no extremal pixels in this block otherwise we would have used
+// compressBlockBBIgnoreExtremal.
+static uint64_t compress_latc_block_bb(const uint8_t pixels[]) {
+ uint8_t minVal = 255;
+ uint8_t maxVal = 0;
+ for (int i = 0; i < kLATCPixelsPerBlock; ++i) {
+ minVal = SkTMin(pixels[i], minVal);
+ maxVal = SkTMax(pixels[i], maxVal);
+ }
+
+ SkASSERT(!is_extremal(minVal));
+ SkASSERT(!is_extremal(maxVal));
+
+ uint8_t palette[kLATCPaletteSize];
+ generate_latc_palette(palette, maxVal, minVal);
+
+ uint64_t indices = 0;
+ for (int i = kLATCPixelsPerBlock - 1; i >= 0; --i) {
+
+ // Find the best palette index
+ uint8_t bestError = abs_diff(pixels[i], palette[0]);
+ uint8_t idx = 0;
+ for (int j = 1; j < kLATCPaletteSize; ++j) {
+ uint8_t error = abs_diff(pixels[i], palette[j]);
+ if (error < bestError) {
+ bestError = error;
+ idx = j;
+ }
+ }
+
+ indices <<= 3;
+ indices |= idx;
+ }
+
+ return
+ SkEndian_SwapLE64(
+ static_cast<uint64_t>(maxVal) |
+ (static_cast<uint64_t>(minVal) << 8) |
+ (indices << 16));
+}
+
+// Compress a block by using the bounding box of the pixels without taking into
+// account the extremal values. The generated palette will contain extremal values
+// and fewer points along the line segment to interpolate.
+static uint64_t compress_latc_block_bb_ignore_extremal(const uint8_t pixels[]) {
+ uint8_t minVal = 255;
+ uint8_t maxVal = 0;
+ for (int i = 0; i < kLATCPixelsPerBlock; ++i) {
+ if (is_extremal(pixels[i])) {
+ continue;
+ }
+
+ minVal = SkTMin(pixels[i], minVal);
+ maxVal = SkTMax(pixels[i], maxVal);
+ }
+
+ SkASSERT(!is_extremal(minVal));
+ SkASSERT(!is_extremal(maxVal));
+
+ uint8_t palette[kLATCPaletteSize];
+ generate_latc_palette(palette, minVal, maxVal);
+
+ uint64_t indices = 0;
+ for (int i = kLATCPixelsPerBlock - 1; i >= 0; --i) {
+
+ // Find the best palette index
+ uint8_t idx = 0;
+ if (is_extremal(pixels[i])) {
+ if (0xFF == pixels[i]) {
+ idx = 7;
+ } else if (0 == pixels[i]) {
+ idx = 6;
+ } else {
+ SkFAIL("Pixel is extremal but not really?!");
+ }
+ } else {
+ uint8_t bestError = abs_diff(pixels[i], palette[0]);
+ for (int j = 1; j < kLATCPaletteSize - 2; ++j) {
+ uint8_t error = abs_diff(pixels[i], palette[j]);
+ if (error < bestError) {
+ bestError = error;
+ idx = j;
+ }
+ }
+ }
+
+ indices <<= 3;
+ indices |= idx;
+ }
+
+ return
+ SkEndian_SwapLE64(
+ static_cast<uint64_t>(minVal) |
+ (static_cast<uint64_t>(maxVal) << 8) |
+ (indices << 16));
+}
+
+
+// Compress LATC block. Each 4x4 block of pixels is decompressed by LATC from two
+// values LUM0 and LUM1, and an index into the generated palette. Details of how
+// the palette is generated can be found in the comments of generatePalette above.
+//
+// We choose which palette type to use based on whether or not 'pixels' contains
+// any extremal values (0 or 255). If there are extremal values, then we use the
+// palette that has the extremal values built in. Otherwise, we use the full bounding
+// box.
+
+static uint64_t compress_latc_block(const uint8_t pixels[]) {
+ // Collect unique pixels
+ int nUniquePixels = 0;
+ uint8_t uniquePixels[kLATCPixelsPerBlock];
+ for (int i = 0; i < kLATCPixelsPerBlock; ++i) {
+ bool foundPixel = false;
+ for (int j = 0; j < nUniquePixels; ++j) {
+ foundPixel = foundPixel || uniquePixels[j] == pixels[i];
+ }
+
+ if (!foundPixel) {
+ uniquePixels[nUniquePixels] = pixels[i];
+ ++nUniquePixels;
+ }
+ }
+
+ // If there's only one unique pixel, then our compression is easy.
+ if (1 == nUniquePixels) {
+ return SkEndian_SwapLE64(pixels[0] | (pixels[0] << 8));
+
+ // Similarly, if there are only two unique pixels, then our compression is
+ // easy again: place the pixels in the block header, and assign the indices
+ // with one or zero depending on which pixel they belong to.
+ } else if (2 == nUniquePixels) {
+ uint64_t outBlock = 0;
+ for (int i = kLATCPixelsPerBlock - 1; i >= 0; --i) {
+ int idx = 0;
+ if (pixels[i] == uniquePixels[1]) {
+ idx = 1;
+ }
+
+ outBlock <<= 3;
+ outBlock |= idx;
+ }
+ outBlock <<= 16;
+ outBlock |= (uniquePixels[0] | (uniquePixels[1] << 8));
+ return SkEndian_SwapLE64(outBlock);
+ }
+
+ // Count non-maximal pixel values
+ int nonExtremalPixels = 0;
+ for (int i = 0; i < nUniquePixels; ++i) {
+ if (!is_extremal(uniquePixels[i])) {
+ ++nonExtremalPixels;
+ }
+ }
+
+ // If all the pixels are nonmaximal then compute the palette using
+ // the bounding box of all the pixels.
+ if (nonExtremalPixels == nUniquePixels) {
+ // This is really just for correctness, in all of my tests we
+ // never take this step. We don't lose too much perf here because
+ // most of the processing in this function is worth it for the
+ // 1 == nUniquePixels optimization.
+ return compress_latc_block_bb(pixels);
+ } else {
+ return compress_latc_block_bb_ignore_extremal(pixels);
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+namespace SkTextureCompressor {
+
+bool CompressA8ToLATC(uint8_t* dst, const uint8_t* src, int width, int height, int rowBytes) {
+ return compress_4x4_a8_to_64bit(dst, src, width, height, rowBytes, compress_latc_block);
+}
+
+SkBlitter* CreateLATCBlitter(int width, int height, void* outputBuffer) {
+ // TODO (krajcevski)
+ return NULL;
+}
+
+} // SkTextureCompressor