/*
* 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.h"
#include "SkTextureCompressor_Blitter.h"
#include "SkTextureCompressor_Utils.h"
#include "SkBlitter.h"
#include "SkEndian.h"
// #define COMPRESS_R11_EAC_SLOW 1
// #define COMPRESS_R11_EAC_FAST 1
#define COMPRESS_R11_EAC_FASTEST 1
// Blocks compressed into R11 EAC are represented as follows:
// 0000000000000000000000000000000000000000000000000000000000000000
// |base_cw|mod|mul| ----------------- indices -------------------
//
// To reconstruct the value of a given pixel, we use the formula:
// clamp[0, 2047](base_cw * 8 + 4 + mod_val*mul*8)
//
// mod_val is chosen from a palette of values based on the index of the
// given pixel. The palette is chosen by the value stored in mod.
// This formula returns a value between 0 and 2047, which is converted
// to a float from 0 to 1 in OpenGL.
//
// If mul is zero, then we set mul = 1/8, so that the formula becomes
// clamp[0, 2047](base_cw * 8 + 4 + mod_val)
static const int kNumR11EACPalettes = 16;
static const int kR11EACPaletteSize = 8;
static const int kR11EACModifierPalettes[kNumR11EACPalettes][kR11EACPaletteSize] = {
{-3, -6, -9, -15, 2, 5, 8, 14},
{-3, -7, -10, -13, 2, 6, 9, 12},
{-2, -5, -8, -13, 1, 4, 7, 12},
{-2, -4, -6, -13, 1, 3, 5, 12},
{-3, -6, -8, -12, 2, 5, 7, 11},
{-3, -7, -9, -11, 2, 6, 8, 10},
{-4, -7, -8, -11, 3, 6, 7, 10},
{-3, -5, -8, -11, 2, 4, 7, 10},
{-2, -6, -8, -10, 1, 5, 7, 9},
{-2, -5, -8, -10, 1, 4, 7, 9},
{-2, -4, -8, -10, 1, 3, 7, 9},
{-2, -5, -7, -10, 1, 4, 6, 9},
{-3, -4, -7, -10, 2, 3, 6, 9},
{-1, -2, -3, -10, 0, 1, 2, 9},
{-4, -6, -8, -9, 3, 5, 7, 8},
{-3, -5, -7, -9, 2, 4, 6, 8}
};
#if COMPRESS_R11_EAC_SLOW
// Pack the base codeword, palette, and multiplier into the 64 bits necessary
// to decode it.
static uint64_t pack_r11eac_block(uint16_t base_cw, uint16_t palette, uint16_t multiplier,
uint64_t indices) {
SkASSERT(palette < 16);
SkASSERT(multiplier < 16);
SkASSERT(indices < (static_cast<uint64_t>(1) << 48));
const uint64_t b = static_cast<uint64_t>(base_cw) << 56;
const uint64_t m = static_cast<uint64_t>(multiplier) << 52;
const uint64_t p = static_cast<uint64_t>(palette) << 48;
return SkEndian_SwapBE64(b | m | p | indices);
}
// Given a base codeword, a modifier, and a multiplier, compute the proper
// pixel value in the range [0, 2047].
static uint16_t compute_r11eac_pixel(int base_cw, int modifier, int multiplier) {
int ret = (base_cw * 8 + 4) + (modifier * multiplier * 8);
return (ret > 2047)? 2047 : ((ret < 0)? 0 : ret);
}
// Compress a block into R11 EAC format.
// The compression works as follows:
// 1. Find the center of the span of the block's values. Use this as the base codeword.
// 2. Choose a multiplier based roughly on the size of the span of block values
// 3. Iterate through each palette and choose the one with the most accurate
// modifiers.
static inline uint64_t compress_heterogeneous_r11eac_block(const uint8_t block[16]) {
// Find the center of the data...
uint16_t bmin = block[0];
uint16_t bmax = block[0];
for (int i = 1; i < 16; ++i) {
bmin = SkTMin<uint16_t>(bmin, block[i]);
bmax = SkTMax<uint16_t>(bmax, block[i]);
}
uint16_t center = (bmax + bmin) >> 1;
SkASSERT(center <= 255);
// Based on the min and max, we can guesstimate a proper multiplier
// This is kind of a magic choice to start with.
uint16_t multiplier = (bmax - center) / 10;
// Now convert the block to 11 bits and transpose it to match
// the proper layout
uint16_t cblock[16];
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
int srcIdx = i*4+j;
int dstIdx = j*4+i;
cblock[dstIdx] = (block[srcIdx] << 3) | (block[srcIdx] >> 5);
}
}
// Finally, choose the proper palette and indices
uint32_t bestError = 0xFFFFFFFF;
uint64_t bestIndices = 0;
uint16_t bestPalette = 0;
for (uint16_t paletteIdx = 0; paletteIdx < kNumR11EACPalettes; ++paletteIdx) {
const int *palette = kR11EACModifierPalettes[paletteIdx];
// Iterate through each pixel to find the best palette index
// and update the indices with the choice. Also store the error
// for this palette to be compared against the best error...
uint32_t error = 0;
uint64_t indices = 0;
for (int pixelIdx = 0; pixelIdx < 16; ++pixelIdx) {
const uint16_t pixel = cblock[pixelIdx];
// Iterate through each palette value to find the best index
// for this particular pixel for this particular palette.
uint16_t bestPixelError =
abs_diff(pixel, compute_r11eac_pixel(center, palette[0], multiplier));
int bestIndex = 0;
for (int i = 1; i < kR11EACPaletteSize; ++i) {
const uint16_t p = compute_r11eac_pixel(center, palette[i], multiplier);
const uint16_t perror = abs_diff(pixel, p);
// Is this index better?
if (perror < bestPixelError) {
bestIndex = i;
bestPixelError = perror;
}
}
SkASSERT(bestIndex < 8);
error += bestPixelError;
indices <<= 3;
indices |= bestIndex;
}
SkASSERT(indices < (static_cast<uint64_t>(1) << 48));
// Is this palette better?
if (error < bestError) {
bestPalette = paletteIdx;
bestIndices = indices;
bestError = error;
}
}
// Finally, pack everything together...
return pack_r11eac_block(center, bestPalette, multiplier, bestIndices);
}
#endif // COMPRESS_R11_EAC_SLOW
#if COMPRESS_R11_EAC_FAST
// This function takes into account that most blocks that we compress have a gradation from
// fully opaque to fully transparent. The compression scheme works by selecting the
// palette and multiplier that has the tightest fit to the 0-255 range. This is encoded
// as the block header (0x8490). The indices are then selected by considering the top
// three bits of each alpha value. For alpha masks, this reduces the dynamic range from
// 17 to 8, but the quality is still acceptable.
//
// There are a few caveats that need to be taken care of...
//
// 1. The block is read in as scanlines, so the indices are stored as:
// 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
// However, the decomrpession routine reads them in column-major order, so they
// need to be packed as:
// 0 4 8 12 1 5 9 13 2 6 10 14 3 7 11 15
// So when reading, they must be transposed.
//
// 2. We cannot use the top three bits as an index directly, since the R11 EAC palettes
// above store the modulation values first decreasing and then increasing:
// e.g. {-3, -6, -9, -15, 2, 5, 8, 14}
// Hence, we need to convert the indices with the following mapping:
// From: 0 1 2 3 4 5 6 7
// To: 3 2 1 0 4 5 6 7
static inline uint64_t compress_heterogeneous_r11eac_block(const uint8_t block[16]) {
uint64_t retVal = static_cast<uint64_t>(0x8490) << 48;
for(int i = 0; i < 4; ++i) {
for(int j = 0; j < 4; ++j) {
const int shift = 45-3*(j*4+i);
SkASSERT(shift <= 45);
const uint64_t idx = block[i*4+j] >> 5;
SkASSERT(idx < 8);
// !SPEED! This is slightly faster than having an if-statement.
switch(idx) {
case 0:
case 1:
case 2:
case 3:
retVal |= (3-idx) << shift;
break;
default:
retVal |= idx << shift;
break;
}
}
}
return SkEndian_SwapBE64(retVal);
}
#endif // COMPRESS_R11_EAC_FAST
#if (COMPRESS_R11_EAC_SLOW) || (COMPRESS_R11_EAC_FAST)
static uint64_t compress_r11eac_block(const uint8_t block[16]) {
// Are all blocks a solid color?
bool solid = true;
for (int i = 1; i < 16; ++i) {
if (block[i] != block[0]) {
solid = false;
break;
}
}
if (solid) {
switch(block[0]) {
// Fully transparent? We know the encoding...
case 0:
// (0x0020 << 48) produces the following:
// basw_cw: 0
// mod: 0, palette: {-3, -6, -9, -15, 2, 5, 8, 14}
// multiplier: 2
// mod_val: -3
//
// this gives the following formula:
// clamp[0, 2047](0*8+4+(-3)*2*8) = 0
//
// Furthermore, it is impervious to endianness:
// 0x0020000000002000ULL
// Will produce one pixel with index 2, which gives:
// clamp[0, 2047](0*8+4+(-9)*2*8) = 0
return 0x0020000000002000ULL;
// Fully opaque? We know this encoding too...
case 255:
// -1 produces the following:
// basw_cw: 255
// mod: 15, palette: {-3, -5, -7, -9, 2, 4, 6, 8}
// mod_val: 8
//
// this gives the following formula:
// clamp[0, 2047](255*8+4+8*8*8) = clamp[0, 2047](2556) = 2047
return 0xFFFFFFFFFFFFFFFFULL;
default:
// !TODO! krajcevski:
// This will probably never happen, since we're using this format
// primarily for compressing alpha maps. Usually the only
// non-fullly opaque or fully transparent blocks are not a solid
// intermediate color. If we notice that they are, then we can
// add another optimization...
break;
}
}
return compress_heterogeneous_r11eac_block(block);
}
// This function is used by R11 EAC to compress 4x4 blocks
// of 8-bit alpha into 64-bit values that comprise the compressed data.
// 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.
typedef uint64_t (*A84x4To64BitProc)(const uint8_t block[]);
static bool compress_4x4_a8_to_64bit(uint8_t* dst, const uint8_t* src,
int width, int height, size_t 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;
}
#endif // (COMPRESS_R11_EAC_SLOW) || (COMPRESS_R11_EAC_FAST)
// This function converts an integer containing four bytes of alpha
// values into an integer containing four bytes of indices into R11 EAC.
// Note, there needs to be a mapping of indices:
// 0 1 2 3 4 5 6 7
// 3 2 1 0 4 5 6 7
//
// To compute this, we first negate each byte, and then add three, which
// gives the mapping
// 3 2 1 0 -1 -2 -3 -4
//
// Then we mask out the negative values, take their absolute value, and
// add three.
//
// Most of the voodoo in this function comes from Hacker's Delight, section 2-18
static inline uint32_t convert_indices(uint32_t x) {
// Take the top three bits...
x = SkTextureCompressor::ConvertToThreeBitIndex(x);
// Negate...
x = ~((0x80808080 - x) ^ 0x7F7F7F7F);
// Add three
const uint32_t s = (x & 0x7F7F7F7F) + 0x03030303;
x = ((x ^ 0x03030303) & 0x80808080) ^ s;
// Absolute value
const uint32_t a = x & 0x80808080;
const uint32_t b = a >> 7;
// Aside: mask negatives (m is three if the byte was negative)
const uint32_t m = (a >> 6) | b;
// .. continue absolute value
x = (x ^ ((a - b) | a)) + b;
// Add three
return x + m;
}
#if COMPRESS_R11_EAC_FASTEST
template<unsigned shift>
static inline uint64_t swap_shift(uint64_t x, uint64_t mask) {
const uint64_t t = (x ^ (x >> shift)) & mask;
return x ^ t ^ (t << shift);
}
static inline uint64_t interleave6(uint64_t topRows, uint64_t bottomRows) {
// If our 3-bit block indices are laid out as:
// a b c d
// e f g h
// i j k l
// m n o p
//
// This function expects topRows and bottomRows to contain the first two rows
// of indices interleaved in the least significant bits of a and b. In other words...
//
// If the architecture is big endian, then topRows and bottomRows will contain the following:
// Bits 31-0:
// a: 00 a e 00 b f 00 c g 00 d h
// b: 00 i m 00 j n 00 k o 00 l p
//
// If the architecture is little endian, then topRows and bottomRows will contain
// the following:
// Bits 31-0:
// a: 00 d h 00 c g 00 b f 00 a e
// b: 00 l p 00 k o 00 j n 00 i m
//
// This function returns a 48-bit packing of the form:
// a e i m b f j n c g k o d h l p
//
// !SPEED! this function might be even faster if certain SIMD intrinsics are
// used..
// For both architectures, we can figure out a packing of the bits by
// using a shuffle and a few shift-rotates...
uint64_t x = (static_cast<uint64_t>(topRows) << 32) | static_cast<uint64_t>(bottomRows);
// x: 00 a e 00 b f 00 c g 00 d h 00 i m 00 j n 00 k o 00 l p
x = swap_shift<10>(x, 0x3FC0003FC00000ULL);
// x: b f 00 00 00 a e c g i m 00 00 00 d h j n 00 k o 00 l p
x = (x | ((x << 52) & (0x3FULL << 52)) | ((x << 20) & (0x3FULL << 28))) >> 16;
// x: 00 00 00 00 00 00 00 00 b f l p a e c g i m k o d h j n
x = swap_shift<6>(x, 0xFC0000ULL);
#if defined (SK_CPU_BENDIAN)
// x: 00 00 00 00 00 00 00 00 b f l p a e i m c g k o d h j n
x = swap_shift<36>(x, 0x3FULL);
// x: 00 00 00 00 00 00 00 00 b f j n a e i m c g k o d h l p
x = swap_shift<12>(x, 0xFFF000000ULL);
#else
// If our CPU is little endian, then the above logic will
// produce the following indices:
// x: 00 00 00 00 00 00 00 00 c g i m d h l p b f j n a e k o
x = swap_shift<36>(x, 0xFC0ULL);
// x: 00 00 00 00 00 00 00 00 a e i m d h l p b f j n c g k o
x = (x & (0xFFFULL << 36)) | ((x & 0xFFFFFFULL) << 12) | ((x >> 24) & 0xFFFULL);
#endif
// x: 00 00 00 00 00 00 00 00 a e i m b f j n c g k o d h l p
return x;
}
// This function follows the same basic procedure as compress_heterogeneous_r11eac_block
// above when COMPRESS_R11_EAC_FAST is defined, but it avoids a few loads/stores and
// tries to optimize where it can using SIMD.
static uint64_t compress_r11eac_block_fast(const uint8_t* src, size_t rowBytes) {
// Store each row of alpha values in an integer
const uint32_t alphaRow1 = *(reinterpret_cast<const uint32_t*>(src));
const uint32_t alphaRow2 = *(reinterpret_cast<const uint32_t*>(src + rowBytes));
const uint32_t alphaRow3 = *(reinterpret_cast<const uint32_t*>(src + 2*rowBytes));
const uint32_t alphaRow4 = *(reinterpret_cast<const uint32_t*>(src + 3*rowBytes));
// Check for solid blocks. The explanations for these values
// can be found in the comments of compress_r11eac_block above
if (alphaRow1 == alphaRow2 && alphaRow1 == alphaRow3 && alphaRow1 == alphaRow4) {
if (0 == alphaRow1) {
// Fully transparent block
return 0x0020000000002000ULL;
} else if (0xFFFFFFFF == alphaRow1) {
// Fully opaque block
return 0xFFFFFFFFFFFFFFFFULL;
}
}
// Convert each integer of alpha values into an integer of indices
const uint32_t indexRow1 = convert_indices(alphaRow1);
const uint32_t indexRow2 = convert_indices(alphaRow2);
const uint32_t indexRow3 = convert_indices(alphaRow3);
const uint32_t indexRow4 = convert_indices(alphaRow4);
// Interleave the indices from the top two rows and bottom two rows
// prior to passing them to interleave6. Since each index is at most
// three bits, then each byte can hold two indices... The way that the
// compression scheme expects the packing allows us to efficiently pack
// the top two rows and bottom two rows. Interleaving each 6-bit sequence
// and tightly packing it into a uint64_t is a little trickier, which is
// taken care of in interleave6.
const uint32_t r1r2 = (indexRow1 << 3) | indexRow2;
const uint32_t r3r4 = (indexRow3 << 3) | indexRow4;
const uint64_t indices = interleave6(r1r2, r3r4);
// Return the packed incdices in the least significant bits with the magic header
return SkEndian_SwapBE64(0x8490000000000000ULL | indices);
}
static bool compress_a8_to_r11eac_fast(uint8_t* dst, const uint8_t* src,
int width, int height, size_t rowBytes) {
// 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;
}
const int blocksX = width >> 2;
const int blocksY = height >> 2;
uint64_t* encPtr = reinterpret_cast<uint64_t*>(dst);
for (int y = 0; y < blocksY; ++y) {
for (int x = 0; x < blocksX; ++x) {
// Compress it
*encPtr = compress_r11eac_block_fast(src + 4*x, rowBytes);
++encPtr;
}
src += 4 * rowBytes;
}
return true;
}
#endif // COMPRESS_R11_EAC_FASTEST
////////////////////////////////////////////////////////////////////////////////
//
// Utility functions used by the blitter
//
////////////////////////////////////////////////////////////////////////////////
// The R11 EAC format expects that indices are given in column-major order. Since
// we receive alpha values in raster order, this usually means that we have to use
// pack6 above to properly pack our indices. However, if our indices come from the
// blitter, then each integer will be a column of indices, and hence can be efficiently
// packed. This function takes the bottom three bits of each byte and places them in
// the least significant 12 bits of the resulting integer.
static inline uint32_t pack_indices_vertical(uint32_t x) {
#if defined (SK_CPU_BENDIAN)
return
(x & 7) |
((x >> 5) & (7 << 3)) |
((x >> 10) & (7 << 6)) |
((x >> 15) & (7 << 9));
#else
return
((x >> 24) & 7) |
((x >> 13) & (7 << 3)) |
((x >> 2) & (7 << 6)) |
((x << 9) & (7 << 9));
#endif
}
// This function returns the compressed format of a block given as four columns of
// alpha values. Each column is assumed to be loaded from top to bottom, and hence
// must first be converted to indices and then packed into the resulting 64-bit
// integer.
inline void compress_block_vertical(uint8_t* dstPtr, const uint8_t *block) {
const uint32_t* src = reinterpret_cast<const uint32_t*>(block);
uint64_t* dst = reinterpret_cast<uint64_t*>(dstPtr);
const uint32_t alphaColumn0 = src[0];
const uint32_t alphaColumn1 = src[1];
const uint32_t alphaColumn2 = src[2];
const uint32_t alphaColumn3 = src[3];
if (alphaColumn0 == alphaColumn1 &&
alphaColumn2 == alphaColumn3 &&
alphaColumn0 == alphaColumn2) {
if (0 == alphaColumn0) {
// Transparent
*dst = 0x0020000000002000ULL;
return;
}
else if (0xFFFFFFFF == alphaColumn0) {
// Opaque
*dst = 0xFFFFFFFFFFFFFFFFULL;
return;
}
}
const uint32_t indexColumn0 = convert_indices(alphaColumn0);
const uint32_t indexColumn1 = convert_indices(alphaColumn1);
const uint32_t indexColumn2 = convert_indices(alphaColumn2);
const uint32_t indexColumn3 = convert_indices(alphaColumn3);
const uint32_t packedIndexColumn0 = pack_indices_vertical(indexColumn0);
const uint32_t packedIndexColumn1 = pack_indices_vertical(indexColumn1);
const uint32_t packedIndexColumn2 = pack_indices_vertical(indexColumn2);
const uint32_t packedIndexColumn3 = pack_indices_vertical(indexColumn3);
*dst = SkEndian_SwapBE64(0x8490000000000000ULL |
(static_cast<uint64_t>(packedIndexColumn0) << 36) |
(static_cast<uint64_t>(packedIndexColumn1) << 24) |
static_cast<uint64_t>(packedIndexColumn2 << 12) |
static_cast<uint64_t>(packedIndexColumn3));
}
static inline int get_r11_eac_index(uint64_t block, int x, int y) {
SkASSERT(x >= 0 && x < 4);
SkASSERT(y >= 0 && y < 4);
const int idx = x*4 + y;
return (block >> ((15-idx)*3)) & 0x7;
}
static void decompress_r11_eac_block(uint8_t* dst, int dstRowBytes, const uint8_t* src) {
const uint64_t block = SkEndian_SwapBE64(*(reinterpret_cast<const uint64_t *>(src)));
const int base_cw = (block >> 56) & 0xFF;
const int mod = (block >> 52) & 0xF;
const int palette_idx = (block >> 48) & 0xF;
const int* palette = kR11EACModifierPalettes[palette_idx];
for (int j = 0; j < 4; ++j) {
for (int i = 0; i < 4; ++i) {
const int idx = get_r11_eac_index(block, i, j);
const int val = base_cw*8 + 4 + palette[idx]*mod*8;
if (val < 0) {
dst[i] = 0;
} else if (val > 2047) {
dst[i] = 0xFF;
} else {
dst[i] = (val >> 3) & 0xFF;
}
}
dst += dstRowBytes;
}
}
// This is the type passed as the CompressorType argument of the compressed
// blitter for the R11 EAC format. The static functions required to be in this
// struct are documented in SkTextureCompressor_Blitter.h
struct CompressorR11EAC {
static inline void CompressA8Vertical(uint8_t* dst, const uint8_t* src) {
compress_block_vertical(dst, src);
}
static inline void CompressA8Horizontal(uint8_t* dst, const uint8_t* src,
int srcRowBytes) {
*(reinterpret_cast<uint64_t*>(dst)) = compress_r11eac_block_fast(src, srcRowBytes);
}
#if PEDANTIC_BLIT_RECT
static inline void UpdateBlock(uint8_t* dst, const uint8_t* src, int srcRowBytes,
const uint8_t* mask) {
// TODO: krajcevski
// The implementation of this function should be similar to that of LATC, since
// the R11EAC indices directly correspond to pixel values.
SkFAIL("Implement me!");
}
#endif
};
////////////////////////////////////////////////////////////////////////////////
namespace SkTextureCompressor {
bool CompressA8ToR11EAC(uint8_t* dst, const uint8_t* src, int width, int height, size_t rowBytes) {
#if (COMPRESS_R11_EAC_SLOW) || (COMPRESS_R11_EAC_FAST)
return compress_4x4_a8_to_64bit(dst, src, width, height, rowBytes, compress_r11eac_block);
#elif COMPRESS_R11_EAC_FASTEST
return compress_a8_to_r11eac_fast(dst, src, width, height, rowBytes);
#else
#error "Must choose R11 EAC algorithm"
#endif
}
SkBlitter* CreateR11EACBlitter(int width, int height, void* outputBuffer,
SkTBlitterAllocator* allocator) {
if ((width % 4) != 0 || (height % 4) != 0) {
return NULL;
}
// Memset the output buffer to an encoding that decodes to zero. We must do this
// in order to avoid having uninitialized values in the buffer if the blitter
// decides not to write certain scanlines (and skip entire rows of blocks).
// In the case of R11, we use the encoding from recognizing all zero pixels from above.
const int nBlocks = (width * height / 16); // 4x4 pixel blocks.
uint64_t *dst = reinterpret_cast<uint64_t *>(outputBuffer);
for (int i = 0; i < nBlocks; ++i) {
*dst = 0x0020000000002000ULL;
++dst;
}
return allocator->createT<
SkTCompressedAlphaBlitter<4, 8, CompressorR11EAC>, int, int, void*>
(width, height, outputBuffer);
}
void DecompressR11EAC(uint8_t* dst, int dstRowBytes, const uint8_t* src, int width, int height) {
for (int j = 0; j < height; j += 4) {
for (int i = 0; i < width; i += 4) {
decompress_r11_eac_block(dst + i, dstRowBytes, src);
src += 8;
}
dst += 4 * dstRowBytes;
}
}
} // namespace SkTextureCompressor