Split SkBmpCodec into three separate classes

src/codec/SkCodecPriv.h

 /*
  * Copyright 2015 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCodecPriv_DEFINED
 #define SkCodecPriv_DEFINED
 
+#include "SkBmpCodec.h"
 #include "SkColorTable.h"
 #include "SkImageInfo.h"
 #include "SkSwizzler.h"
 #include "SkTypes.h"
 #include "SkUtils.h"
 
 /*
  *
  * Helper routine for alpha result codes
  *
  */
 #define INIT_RESULT_ALPHA                       \
     uint8_t zeroAlpha = 0;                      \
     uint8_t maxAlpha = 0xFF;
 
 #define UPDATE_RESULT_ALPHA(alpha)              \
     zeroAlpha |= (alpha);                       \
     maxAlpha  &= (alpha);
 
 #define COMPUTE_RESULT_ALPHA                    \
     SkSwizzler::GetResult(zeroAlpha, maxAlpha);
 
+static inline bool valid_alpha(SkAlphaType dstAlpha, SkAlphaType srcAlpha) {
+    // Check for supported alpha types
+    if (srcAlpha != dstAlpha) {
+        if (kOpaque_SkAlphaType == srcAlpha) {
+            // If the source is opaque, we must decode to opaque
+            return false;
+        }
+
+        // The source is not opaque
+        switch (dstAlpha) {
+            case kPremul_SkAlphaType:
+            case kUnpremul_SkAlphaType:
+                // The source is not opaque, so either of these is okay
+                break;
+            default:
+                // We cannot decode a non-opaque image to opaque (or unknown)
+                return false;
+        }
+    }
+    return true;
+}
+
 /*
- *
  * Copy the codec color table back to the client when kIndex8 color type is requested
- *
  */
 static inline void copy_color_table(const SkImageInfo& dstInfo, SkColorTable* colorTable,
         SkPMColor* inputColorPtr, int* inputColorCount) {
     if (kIndex_8_SkColorType == dstInfo.colorType()) {
         SkASSERT(NULL != inputColorPtr);
         SkASSERT(NULL != inputColorCount);
         SkASSERT(NULL != colorTable);
         memcpy(inputColorPtr, colorTable->readColors(), *inputColorCount * 4);
     }
 }
 
 /*
- *
  * Compute row bytes for an image using pixels per byte
- *
  */
 static inline size_t compute_row_bytes_ppb(int width, uint32_t pixelsPerByte) {
     return (width + pixelsPerByte - 1) / pixelsPerByte;
 }
 
 /*
- *
  * Compute row bytes for an image using bytes per pixel
- *
  */
 static inline size_t compute_row_bytes_bpp(int width, uint32_t bytesPerPixel) {
     return width * bytesPerPixel;
 }
 
 /*
- *
  * Compute row bytes for an image
- *
  */
 static inline size_t compute_row_bytes(int width, uint32_t bitsPerPixel) {
     if (bitsPerPixel < 16) {
         SkASSERT(0 == 8 % bitsPerPixel);
         const uint32_t pixelsPerByte = 8 / bitsPerPixel;
         return compute_row_bytes_ppb(width, pixelsPerByte);
     } else {
         SkASSERT(0 == bitsPerPixel % 8);
         const uint32_t bytesPerPixel = bitsPerPixel / 8;
         return compute_row_bytes_bpp(width, bytesPerPixel);
     }
 }
 
 /*
- *
  * Get a byte from a buffer
  * This method is unsafe, the caller is responsible for performing a check
- *
  */
 static inline uint8_t get_byte(uint8_t* buffer, uint32_t i) {
     return buffer[i];
 }
 
 /*
- *
  * Get a short from a buffer
  * This method is unsafe, the caller is responsible for performing a check
- *
  */
 static inline uint16_t get_short(uint8_t* buffer, uint32_t i) {
     uint16_t result;
     memcpy(&result, &(buffer[i]), 2);
 #ifdef SK_CPU_BENDIAN
     return SkEndianSwap16(result);
 #else
     return result;
 #endif
 }
 
 /*
- *
  * Get an int from a buffer
  * This method is unsafe, the caller is responsible for performing a check
- *
  */
 static inline uint32_t get_int(uint8_t* buffer, uint32_t i) {
     uint32_t result;
     memcpy(&result, &(buffer[i]), 4);
 #ifdef SK_CPU_BENDIAN
     return SkEndianSwap32(result);
 #else
     return result;
 #endif
 }
 
 #ifdef SK_PRINT_CODEC_MESSAGES
     #define SkCodecPrintf SkDebugf
 #else
     #define SkCodecPrintf(...)
 #endif
 
 #endif // SkCodecPriv_DEFINED