Add downsample from 8888 to 4444.

Extend SkBitmap::copyTo to copy from a source with
SkARGB_8888_Config to a destination bitmap with
SkARGB_4444_Config.

BUG=http://code.google.com/p/chromium/issues/detail?id=245774
R=reed@google.com

Review URL: https://codereview.chromium.org/22350003

git-svn-id: http://skia.googlecode.com/svn/trunk@10621 2bbb7eff-a529-9590-31e7-b0007b416f81

gm/copyTo4444.cpp

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkCanvas.h"
+#include "SkImageDecoder.h"
+#include "SkOSFile.h"
+
+namespace skiagm {
+
+/**
+ *  Test copying an image from 8888 to 4444.
+ */
+class CopyTo4444GM : public GM {
+public:
+    CopyTo4444GM() {}
+
+protected:
+    virtual SkString onShortName() {
+        return SkString("copyTo4444");
+    }
+
+    virtual SkISize onISize() {
+        return make_isize(1024, 512);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) {
+        SkBitmap bm, bm4444;
+        SkString filename = SkOSPath::SkPathJoin(
+                INHERITED::gResourcePath.c_str(), "mandrill_512.png");
+        if (!SkImageDecoder::DecodeFile(filename.c_str(), &bm,
+                                        SkBitmap::kARGB_8888_Config,
+                                        SkImageDecoder::kDecodePixels_Mode)) {
+            SkDebugf("Could not decode the file. Did you forget to set the "
+                     "resourcePath?\n");
+            return;
+        }
+        canvas->drawBitmap(bm, 0, 0);
+        SkAssertResult(bm.copyTo(&bm4444, SkBitmap::kARGB_4444_Config));
+        canvas->drawBitmap(bm4444, bm.width(), 0);
+    }
+
+private:
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static GM* MyFactory(void*) { return new CopyTo4444GM; }
+static GMRegistry reg(MyFactory);
+
+}

gyp/gmslides.gypi

@@ -28,6 +28,7 @@
     '../gm/composeshader.cpp',
     #'../gm/conicpaths.cpp',
     '../gm/convexpaths.cpp',
+    '../gm/copyTo4444.cpp',
     '../gm/cubicpaths.cpp',
     '../gm/cmykjpeg.cpp',
     '../gm/degeneratesegments.cpp',

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 +1110,19 @@ 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) {
+                dstRow[x] = SkDitherARGB32To4444(srcRow[x],
+                                                 DITHER_VALUE(x));
+            }
+        }
     } else {
         // if the src has alpha, we have to clear the dst first
         if (!src->isOpaque()) {