Add initial pipeline for decompressors

src/utils/SkTextureCompressor_R11EAC.cpp

Index: src/utils/SkTextureCompressor_R11EAC.cpp
diff --git a/src/utils/SkTextureCompressor_R11EAC.cpp b/src/utils/SkTextureCompressor_R11EAC.cpp
index 982fb012ef3cf9b3b6249b96eb1a6cb788789958..7baa219a28de88d05e2a6966b85b9d45ab2534e6 100644
--- a/src/utils/SkTextureCompressor_R11EAC.cpp
+++ b/src/utils/SkTextureCompressor_R11EAC.cpp
@@ -29,8 +29,6 @@
 // If mul is zero, then we set mul = 1/8, so that the formula becomes
 // clamp[0, 2047](base_cw * 8 + 4 + mod_val)
 
-#if COMPRESS_R11_EAC_SLOW
-
 static const int kNumR11EACPalettes = 16;
 static const int kR11EACPaletteSize = 8;
 static const int kR11EACModifierPalettes[kNumR11EACPalettes][kR11EACPaletteSize] = {
@@ -52,6 +50,8 @@ static const int kR11EACModifierPalettes[kNumR11EACPalettes][kR11EACPaletteSize]
     {-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,
@@ -557,6 +557,38 @@ inline void compress_block_vertical(uint8_t* dstPtr, const uint8_t *block) {
                              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;
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 namespace SkTextureCompressor {
@@ -582,4 +614,14 @@ SkBlitter* CreateR11EACBlitter(int width, int height, void* outputBuffer) {
         (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