Add downsample from 8888 to 4444.

src/core/SkBitmap.cpp

Index: src/core/SkBitmap.cpp
diff --git a/src/core/SkBitmap.cpp b/src/core/SkBitmap.cpp
index 9a116dfc2ed511a90f35bb63f35377fdb824fd7b..9000a3669ff64bff76d9c2e1bd41704bebd222fe 100644
--- a/src/core/SkBitmap.cpp
+++ b/src/core/SkBitmap.cpp
@@ -1017,11 +1017,12 @@ bool SkBitmap::canCopyTo(Config dstConfig) const {
             break;
         case kA1_Config:
         case kIndex8_Config:
-        case kARGB_4444_Config:
             if (!sameConfigs) {
                 return false;
             }
             break;
+        case kARGB_4444_Config:
+            return sameConfigs || kARGB_8888_Config == this->config();
         default:
             return false;
     }
@@ -1109,6 +1110,21 @@ bool SkBitmap::copyTo(SkBitmap* dst, Config dstConfig, Allocator* alloc) const {
                 dstP += tmpDst.rowBytes();
             }
         }
+    } else if (SkBitmap::kARGB_4444_Config == dstConfig
+               && SkBitmap::kARGB_8888_Config == src->config()) {
+        SkASSERT(src->height() == tmpDst.height());
+        SkASSERT(src->width() == tmpDst.width());
+        for (int y = 0; y < src->height(); ++y) {
+            SkPMColor16* SK_RESTRICT dstRow = (SkPMColor16*) tmpDst.getAddr16(0, y);
+            SkPMColor* SK_RESTRICT srcRow = (SkPMColor*) src->getAddr32(0, y);
+            DITHER_4444_SCAN(y);
+            for (int x = 0; x < src->width(); ++x) {
+                SkColor c = SkUnPreMultiply::PMColorToColor(srcRow[x]);

[reed1, 2013/08/07 18:30:03]

Why the unpremultiply step? I think you can call this guy directly:

static inline SkPMColor16 SkDitherARGB32To4444(SkPMColor c, unsigned dither)

[scroggo, 2013/08/07 19:04:19]

Overlooked that one. New patch calls the version that takes an SkPMColor.

+                dstRow[x] = SkDitherARGB32To4444(SkColorGetA(c), SkColorGetR(c),
+                                                 SkColorGetG(c), SkColorGetB(c),
+                                                 DITHER_VALUE(x));
+            }
+        }
     } else {
         // if the src has alpha, we have to clear the dst first
         if (!src->isOpaque()) {