store SkAlphaType inside SkBitmap, on road to support unpremul

src/core/SkBitmap.cpp

Index: src/core/SkBitmap.cpp
diff --git a/src/core/SkBitmap.cpp b/src/core/SkBitmap.cpp
index 128726cb63d9198477afd698e377c6ee02cef6ed..4a7f6bf748e910e37232280589004d9e49366f55 100644
--- a/src/core/SkBitmap.cpp
+++ b/src/core/SkBitmap.cpp
@@ -266,33 +266,59 @@ void SkBitmap::getBounds(SkIRect* bounds) const {
 
 ///////////////////////////////////////////////////////////////////////////////
 
-void SkBitmap::setConfig(Config c, int width, int height, size_t rowBytes) {
-    this->freePixels();
-
+bool SkBitmap::setConfig(Config config, int width, int height, size_t rowBytes,
+                         SkAlphaType alphaType) {
     if ((width | height) < 0) {
-        goto err;
+        goto ERROR;
     }
-
     if (rowBytes == 0) {
-        rowBytes = SkBitmap::ComputeRowBytes(c, width);
-        if (0 == rowBytes && kNo_Config != c) {
-            goto err;
+        rowBytes = SkBitmap::ComputeRowBytes(config, width);
+        if (0 == rowBytes && kNo_Config != config) {
+            goto ERROR;
         }
     }
 
-    fConfig     = SkToU8(c);
+    // check for legal/supported config+alphaType combinations
+    //
+    switch (config) {
+        case kNo_Config:
+            alphaType = kIgnore_SkAlphaType;    // canonicalize
+            break;
+        case kA1_Config:
+        case kA8_Config:
+            if (kUnpremul_SkAlphaType == alphaType) {
+                alphaType = kPremul_SkAlphaType;

[scroggo, 2013/09/30 22:20:04]

Why change it to Premul? For historical reasons/so we don't have to add another
type?

+            }
+            // fall-through
+        case kIndex8_Config:
+        case kARGB_4444_Config:
+        case kARGB_8888_Config:
+            if (kIgnore_SkAlphaType == alphaType) {
+                goto ERROR;   // not supported yet
+            }
+            break;
+        case kRGB_565_Config:
+            alphaType = kOpaque_SkAlphaType;    // canonicalize
+            break;
+    }
+
+    this->freePixels();
+
+    fConfig     = SkToU8(config);
+    fAlphaType  = SkToU8(alphaType);
     fWidth      = width;
     fHeight     = height;
     fRowBytes   = SkToU32(rowBytes);
 
-    fBytesPerPixel = (uint8_t)ComputeBytesPerPixel(c);
+    fBytesPerPixel = (uint8_t)ComputeBytesPerPixel(config);
 
     SkDEBUGCODE(this->validate();)
-    return;
+    return true;
 
     // if we got here, we had an error, so we reset the bitmap to empty
-err:
+ERROR:
     this->reset();
+    return false;
 }
 
 void SkBitmap::updatePixelsFromRef() const {