move readPixels from bitmap -> pixmap

src/core/SkPixmap.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
+#include "SkConfig8888.h"
 #include "SkPixmap.h"
 
 void SkAutoPixmapUnlock::reset(const SkPixmap& pm, void (*unlock)(void*), void* ctx) {
     SkASSERT(pm.addr() != NULL);
 
     this->unlock();
     fPixmap = pm;
     fUnlockProc = unlock;
     fUnlockContext = ctx;
     fIsLocked = true;
 }
+
+/////////////////////////////////////////////////////////////////////////////////////////////////
+
+bool SkPixmap::readPixels(const SkImageInfo& requestedDstInfo, void* dstPixels, size_t dstRB,
+                          int x, int y) const {
+    if (kUnknown_SkColorType == requestedDstInfo.colorType()) {
+        return false;
+    }
+    if (NULL == dstPixels || dstRB < requestedDstInfo.minRowBytes()) {
+        return false;
+    }
+    if (0 == requestedDstInfo.width() || 0 == requestedDstInfo.height()) {
+        return false;
+    }
+    
+    SkIRect srcR = SkIRect::MakeXYWH(x, y, requestedDstInfo.width(), requestedDstInfo.height());
+    if (!srcR.intersect(0, 0, this->width(), this->height())) {
+        return false;
+    }
+    
+    // the intersect may have shrunk info's logical size
+    const SkImageInfo dstInfo = requestedDstInfo.makeWH(srcR.width(), srcR.height());
+    
+    // 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
+    dstPixels = ((char*)dstPixels - y * dstRB - x * dstInfo.bytesPerPixel());
+
+    const SkImageInfo srcInfo = this->info().makeWH(dstInfo.width(), dstInfo.height());
+    const void* srcPixels = this->addr(srcR.x(), srcR.y());
+    return SkPixelInfo::CopyPixels(dstInfo, dstPixels, dstRB,
+                                   srcInfo, srcPixels, this->rowBytes(), this->ctable());
+}