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Unified Diff: src/utils/SkTextureCompressor.cpp

Issue 347673002: Some improvements to LATC compression (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: Use new function name Created 6 years, 6 months ago
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Index: src/utils/SkTextureCompressor.cpp
diff --git a/src/utils/SkTextureCompressor.cpp b/src/utils/SkTextureCompressor.cpp
index fb41928269be4b98e006c83d702d25d6cd291849..3a7fcfb1d296d730491792a707c0f043c3e5be27 100644
--- a/src/utils/SkTextureCompressor.cpp
+++ b/src/utils/SkTextureCompressor.cpp
@@ -29,26 +29,12 @@ template <typename T> inline T abs_diff(const T &a, const T &b) {
//
////////////////////////////////////////////////////////////////////////////////
-// Return the squared minimum error cost of approximating 'pixel' using the
-// provided palette. Return this in the middle 16 bits of the integer. Return
-// the best index in the palette for this pixel in the bottom 8 bits.
-static uint32_t compute_error(uint8_t pixel, uint8_t palette[8]) {
- int minIndex = 0;
- uint8_t error = abs_diff(palette[0], pixel);
- for (int i = 1; i < 8; ++i) {
- uint8_t diff = abs_diff(palette[i], pixel);
- if (diff < error) {
- minIndex = i;
- error = diff;
- }
- }
- uint16_t errSq = static_cast<uint16_t>(error) * static_cast<uint16_t>(error);
- SkASSERT(minIndex >= 0 && minIndex < 8);
- return (static_cast<uint32_t>(errSq) << 8) | static_cast<uint32_t>(minIndex);
-}
+// LATC compressed texels down into square 4x4 blocks
+static const int kPaletteSize = 8;
+static const int kLATCBlockSize = 4;
+static const int kPixelsPerBlock = kLATCBlockSize * kLATCBlockSize;
-// 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. LATC constructs
+// 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
@@ -68,142 +54,281 @@ static uint32_t compute_error(uint8_t pixel, uint8_t palette[8]) {
// ( 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
-//
-// We compute the LATC palette using the following simple algorithm:
-// 1. Choose the minimum and maximum values in the block as LUM0 and LUM1
-// 2. Figure out which of the two possible palettes is better.
-static uint64_t compress_latc_block(uint8_t block[16]) {
- // Just do a simple min/max but choose which of the
- // two palettes is better
- uint8_t maxVal = 0;
+static void generate_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;
+ }
+}
+
+static bool is_extremal(uint8_t pixel) {
+ return 0 == pixel || 255 == pixel;
+}
+
+// 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_block_bb(const uint8_t pixels[]) {
uint8_t minVal = 255;
- for (int i = 0; i < 16; ++i) {
- maxVal = SkMax32(maxVal, block[i]);
- minVal = SkMin32(minVal, block[i]);
+ uint8_t maxVal = 0;
+ for (int i = 0; i < kPixelsPerBlock; ++i) {
+ minVal = SkTMin(pixels[i], minVal);
+ maxVal = SkTMax(pixels[i], maxVal);
}
- // Generate palettes
- uint8_t palettes[2][8];
+ SkASSERT(!is_extremal(minVal));
+ SkASSERT(!is_extremal(maxVal));
+
+ uint8_t palette[kPaletteSize];
+ generate_palette(palette, maxVal, minVal);
- // Straight linear ramp
- palettes[0][0] = maxVal;
- palettes[0][1] = minVal;
- for (int i = 1; i < 7; ++i) {
- palettes[0][i+1] = ((7-i)*maxVal + i*minVal) / 7;
+ uint64_t indices = 0;
+ for (int i = kPixelsPerBlock - 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 < kPaletteSize; ++j) {
+ uint8_t error = abs_diff(pixels[i], palette[j]);
+ if (error < bestError) {
+ bestError = error;
+ idx = j;
+ }
+ }
+
+ indices <<= 3;
+ indices |= idx;
}
- // Smaller linear ramp with min and max byte values at the end.
- palettes[1][0] = minVal;
- palettes[1][1] = maxVal;
- for (int i = 1; i < 5; ++i) {
- palettes[1][i+1] = ((5-i)*maxVal + i*minVal) / 5;
+ 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_block_bb_ignore_extremal(const uint8_t pixels[]) {
+ uint8_t minVal = 255;
+ uint8_t maxVal = 0;
+ for (int i = 0; i < kPixelsPerBlock; ++i) {
+ if (is_extremal(pixels[i])) {
+ continue;
+ }
+
+ minVal = SkTMin(pixels[i], minVal);
+ maxVal = SkTMax(pixels[i], maxVal);
}
- palettes[1][6] = 0;
- palettes[1][7] = 255;
-
- // Figure out which of the two is better:
- // - accumError holds the accumulated error for each pixel from
- // the associated palette
- // - indices holds the best indices for each palette in the
- // bottom 48 (16*3) bits.
- uint32_t accumError[2] = { 0, 0 };
- uint64_t indices[2] = { 0, 0 };
- for (int i = 15; i >= 0; --i) {
- // For each palette:
- // 1. Retreive the result of this pixel
- // 2. Store the error in accumError
- // 3. Store the minimum palette index in indices.
- for (int p = 0; p < 2; ++p) {
- uint32_t result = compute_error(block[i], palettes[p]);
- accumError[p] += (result >> 8);
- indices[p] <<= 3;
- indices[p] |= result & 7;
+
+ SkASSERT(!is_extremal(minVal));
+ SkASSERT(!is_extremal(maxVal));
+
+ uint8_t palette[kPaletteSize];
+ generate_palette(palette, minVal, maxVal);
+
+ uint64_t indices = 0;
+ for (int i = kPixelsPerBlock - 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 < kPaletteSize - 2; ++j) {
+ uint8_t error = abs_diff(pixels[i], palette[j]);
+ if (error < bestError) {
+ bestError = error;
+ idx = j;
+ }
+ }
}
+
+ indices <<= 3;
+ indices |= idx;
}
- SkASSERT(indices[0] < (static_cast<uint64_t>(1) << 48));
- SkASSERT(indices[1] < (static_cast<uint64_t>(1) << 48));
+ return
+ SkEndian_SwapLE64(
+ static_cast<uint64_t>(minVal) |
+ (static_cast<uint64_t>(maxVal) << 8) |
+ (indices << 16));
+}
- uint8_t paletteIdx = (accumError[0] > accumError[1]) ? 0 : 1;
- // Assemble the compressed block.
- uint64_t result = 0;
+// 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_block(const uint8_t pixels[]) {
+ // Collect unique pixels
+ int nUniquePixels = 0;
+ uint8_t uniquePixels[kPixelsPerBlock];
+ for (int i = 0; i < kPixelsPerBlock; ++i) {
+ bool foundPixel = false;
+ for (int j = 0; j < nUniquePixels; ++j) {
+ foundPixel = foundPixel || uniquePixels[j] == pixels[i];
+ }
- // Jam the first two palette entries into the bottom 16 bits of
- // a 64 bit integer. Based on the palette that we chose, one will
- // be larger than the other and it will select the proper palette.
- result |= static_cast<uint64_t>(palettes[paletteIdx][0]);
- result |= static_cast<uint64_t>(palettes[paletteIdx][1]) << 8;
+ if (!foundPixel) {
+ uniquePixels[nUniquePixels] = pixels[i];
+ ++nUniquePixels;
+ }
+ }
- // Jam the indices into the top 48 bits.
- result |= indices[paletteIdx] << 16;
+ // 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 = kPixelsPerBlock - 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);
+ }
- // We assume everything is little endian, if it's not then make it so.
- return SkEndian_SwapLE64(result);
-}
+ // Count non-maximal pixel values
+ int nonExtremalPixels = 0;
+ for (int i = 0; i < nUniquePixels; ++i) {
+ if (!is_extremal(uniquePixels[i])) {
+ ++nonExtremalPixels;
+ }
+ }
-static SkData *compress_a8_to_latc(const SkBitmap &bm) {
- // LATC compressed texels down into square 4x4 blocks
- static const int kLATCBlockSize = 4;
+ // 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_block_bb(pixels);
+ } else {
+ return compress_block_bb_ignore_extremal(pixels);
+ }
+}
+static bool compress_a8_to_latc(uint8_t* dst, const uint8_t* src,
+ int width, int height, int rowBytes) {
// Make sure that our data is well-formed enough to be
// considered for LATC compression
- if (bm.width() == 0 || bm.height() == 0 ||
- (bm.width() % kLATCBlockSize) != 0 ||
- (bm.height() % kLATCBlockSize) != 0 ||
- (bm.colorType() != kAlpha_8_SkColorType)) {
- return NULL;
+ if (0 == width || 0 == height ||
+ (width % kLATCBlockSize) != 0 || (height % kLATCBlockSize) != 0) {
+ return false;
}
- // The LATC format is 64 bits per 4x4 block.
- static const int kLATCEncodedBlockSize = 8;
-
- int blocksX = bm.width() / kLATCBlockSize;
- int blocksY = bm.height() / kLATCBlockSize;
-
- int compressedDataSize = blocksX * blocksY * kLATCEncodedBlockSize;
- uint64_t* dst = reinterpret_cast<uint64_t*>(sk_malloc_throw(compressedDataSize));
+ int blocksX = width / kLATCBlockSize;
+ int blocksY = height / kLATCBlockSize;
uint8_t block[16];
- const uint8_t* row = reinterpret_cast<const uint8_t*>(bm.getPixels());
- uint64_t* encPtr = dst;
+ uint64_t* encPtr = reinterpret_cast<uint64_t*>(dst);
for (int y = 0; y < blocksY; ++y) {
for (int x = 0; x < blocksX; ++x) {
- memcpy(block, row + (kLATCBlockSize * x), 4);
- memcpy(block + 4, row + bm.rowBytes() + (kLATCBlockSize * x), 4);
- memcpy(block + 8, row + 2*bm.rowBytes() + (kLATCBlockSize * x), 4);
- memcpy(block + 12, row + 3*bm.rowBytes() + (kLATCBlockSize * x), 4);
-
- *encPtr = compress_latc_block(block);
+ // Load block
+ static const int kBS = kLATCBlockSize;
+ for (int k = 0; k < kBS; ++k) {
+ memcpy(block + k*kBS, src + k*rowBytes + (kBS * x), kBS);
+ }
+
+ // Compress it
+ *encPtr = compress_block(block);
++encPtr;
}
- row += kLATCBlockSize * bm.rowBytes();
+ src += kLATCBlockSize * rowBytes;
}
- return SkData::NewFromMalloc(dst, compressedDataSize);
+ return true;
}
////////////////////////////////////////////////////////////////////////////////
namespace SkTextureCompressor {
-typedef SkData *(*CompressBitmapProc)(const SkBitmap &bitmap);
+static size_t get_compressed_data_size(Format fmt, int width, int height) {
+ switch (fmt) {
+ case kLATC_Format:
+ {
+ // The LATC format is 64 bits per 4x4 block.
+ static const int kLATCEncodedBlockSize = 8;
-SkData *CompressBitmapToFormat(const SkBitmap &bitmap, Format format) {
- SkAutoLockPixels alp(bitmap);
+ int blocksX = width / kLATCBlockSize;
+ int blocksY = height / kLATCBlockSize;
- CompressBitmapProc kProcMap[kLastEnum_SkColorType + 1][kFormatCnt];
- memset(kProcMap, 0, sizeof(kProcMap));
+ return blocksX * blocksY * kLATCEncodedBlockSize;
+ }
+
+ default:
+ SkFAIL("Unknown compressed format!");
+ return 0;
+ }
+}
- // Map available bitmap configs to compression functions
- kProcMap[kAlpha_8_SkColorType][kLATC_Format] = compress_a8_to_latc;
+typedef bool (*CompressBitmapProc)(uint8_t* dst, const uint8_t* src,
+ int width, int height, int rowBytes);
+
+bool CompressBufferToFormat(uint8_t* dst, const uint8_t* src, SkColorType srcColorType,
+ int width, int height, int rowBytes, Format format) {
+
+ CompressBitmapProc kProcMap[kFormatCnt][kLastEnum_SkColorType + 1];
+ memset(kProcMap, 0, sizeof(kProcMap));
- CompressBitmapProc proc = kProcMap[bitmap.colorType()][format];
+ kProcMap[kLATC_Format][kAlpha_8_SkColorType] = compress_a8_to_latc;
+
+ CompressBitmapProc proc = kProcMap[format][srcColorType];
if (NULL != proc) {
- return proc(bitmap);
+ return proc(dst, src, width, height, rowBytes);
+ }
+
+ return false;
+}
+
+SkData *CompressBitmapToFormat(const SkBitmap &bitmap, Format format) {
+ SkAutoLockPixels alp(bitmap);
+
+ int compressedDataSize = get_compressed_data_size(format, bitmap.width(), bitmap.height());
+ const uint8_t* src = reinterpret_cast<const uint8_t*>(bitmap.getPixels());
+ uint8_t* dst = reinterpret_cast<uint8_t*>(sk_malloc_throw(compressedDataSize));
+ if (CompressBufferToFormat(dst, src, bitmap.colorType(), bitmap.width(), bitmap.height(),
+ bitmap.rowBytes(), format)) {
+ return SkData::NewFromMalloc(dst, compressedDataSize);
}
+ sk_free(dst);
return NULL;
}
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