Add downsample from 8888 to 4444.

src/core/SkBitmap.cpp

 
 /*
  * Copyright 2008 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.
  */
 
 
 #include "SkBitmap.h"
@@ skipping 999 matching lines @@
     }
 
     bool sameConfigs = (this->config() == dstConfig);
     switch (dstConfig) {
         case kA8_Config:
         case kRGB_565_Config:
         case kARGB_8888_Config:
             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;
     }
 
     // do not copy src if srcConfig == kA1_Config while dstConfig != kA1_Config
     if (this->getConfig() == kA1_Config && !sameConfigs) {
         return false;
     }
 
     return true;
@@ skipping 67 matching lines @@
             const char* srcP = reinterpret_cast<const char*>(src->getPixels());
             char* dstP = reinterpret_cast<char*>(tmpDst.getPixels());
             // to be sure we don't read too much, only copy our logical pixels
             size_t bytesToCopy = tmpDst.width() * tmpDst.bytesPerPixel();
             for (int y = 0; y < tmpDst.height(); y++) {
                 memcpy(dstP, srcP, bytesToCopy);
                 srcP += src->rowBytes();
                 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()) {
             tmpDst.eraseColor(SK_ColorTRANSPARENT);
         }
 
         SkCanvas canvas(tmpDst);
         SkPaint  paint;
 
         paint.setDither(true);
@@ skipping 564 matching lines @@
         if (NULL != uri) {
             str->appendf(" uri:\"%s\"", uri);
         } else {
             str->appendf(" pixelref:%p", pr);
         }
     }
 
     str->append(")");
 }
 #endif