add readPixels to SkImage

src/core/SkImageInfo.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageInfo.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
@@ skipping 58 matching lines @@
             alphaType = kOpaque_SkAlphaType;
             break;
         default:
             return false;
     }
     if (canonical) {
         *canonical = alphaType;
     }
     return true;
 }
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+#include "SkReadPixelsRec.h"
+
+bool SkReadPixelsRec::trim(int srcWidth, int srcHeight) {
+    switch (fInfo.colorType()) {
+        case kUnknown_SkColorType:
+        case kIndex_8_SkColorType:
+            return false;
+        default:
+            break;
+    }
+    if (NULL == fPixels || fRowBytes < fInfo.minRowBytes()) {
+        return false;
+    }
+    if (0 == fInfo.width() || 0 == fInfo.height()) {
+        return false;
+    }
+
+    int x = fX;
+    int y = fY;
+    SkIRect srcR = SkIRect::MakeXYWH(x, y, fInfo.width(), fInfo.height());
+    if (!srcR.intersect(0, 0, srcWidth, srcHeight)) {
+        return false;
+    }
+
+    // if x or y are negative, then we have to adjust pixels
+    if (x > 0) {
+        x = 0;
+    }
+    if (y > 0) {
+        y = 0;
+    }
+    // here x,y are either 0 or negative
+    fPixels = ((char*)fPixels - y * fRowBytes - x * fInfo.bytesPerPixel());
+    // the intersect may have shrunk info's logical size
+    fInfo = fInfo.makeWH(srcR.width(), srcR.height());
+    fX = srcR.x();
+    fY = srcR.y();
+
+    return true;
+}
+