Create SkBitmapChecksummer and associated SkBitmapTransformer
As needed to start capturing gm image checksums.
Review URL: https://codereview.appspot.com/6920050
git-svn-id: http://skia.googlecode.com/svn/trunk@6759 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/SkBitmapTransformer.h b/src/utils/SkBitmapTransformer.h
new file mode 100644
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+++ b/src/utils/SkBitmapTransformer.h
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+
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkBitmapTransformer_DEFINED
+#define SkBitmapTransformer_DEFINED
+
+#include "SkBitmap.h"
+
+/**
+ * Class that can copy pixel data out of an SkBitmap, transforming it
+ * into the appropriate PixelFormat.
+ *
+ * As noted in https://codereview.appspot.com/6849119/#msg6 and
+ * https://codereview.appspot.com/6900047 , at some point we might want
+ * to make this more general purpose:
+ * - support more PixelFormats
+ * - use existing SkCanvas::Config8888 enum instead of new PixelFormat enum
+ * - add method to copy pixel data for a single row, instead of the whole bitmap
+ * - add methods to copy pixel data INTO an SkBitmap
+ *
+ * That would allow us to replace SkCopyConfig8888ToBitmap() in
+ * src/core/SkConfig8888.h , as well as the transformations used by
+ * src/images/SkImageDecoder_libpng.cpp , with this common code.
+ *
+ * But for now, we want something more narrowly targeted, just
+ * supplying what is needed by SkBitmapChecksummer.
+ */
+class SkBitmapTransformer {
+public:
+ enum PixelFormat {
+ // 32 bits per pixel, ARGB byte order, with the alpha-channel
+ // value premultiplied into the R/G/B channel values.
+ kARGB_8888_Premul_PixelFormat,
+
+ // marks the end of the list
+ kLast_PixelFormat = kARGB_8888_Premul_PixelFormat,
+ };
+
+ /**
+ * Creates an SkBitmapTransformer instance that can transform between
+ * the given bitmap and a pixel buffer with given pixelFormat.
+ *
+ * Call IsValid() before using, to confirm that this particular
+ * bitmap/pixelFormat combination is supported!
+ */
+ SkBitmapTransformer(const SkBitmap& bitmap, PixelFormat pixelFormat) :
+ fBitmap(bitmap), fPixelFormat(pixelFormat) {}
+
+ /**
+ * Returns true iff we can convert between fBitmap and fPixelFormat.
+ * If this returns false, the return values of any other methods will
+ * be meaningless!
+ *
+ * @param logReason whether to log the reason why this combination
+ * is unsupported (only applies in debug mode)
+ */
+ bool isValid(bool logReason=false) const;
+
+ /**
+ * Returns the number of bytes needed to store a single row of the
+ * bitmap's pixels if converted to pixelFormat.
+ */
+ size_t bytesNeededPerRow() const {
+ // This is hard-coded for the single supported PixelFormat.
+ return fBitmap.width() * 4;
+ }
+
+ /**
+ * Returns the number of bytes needed to store the entire bitmap
+ * if converted to pixelFormat, ASSUMING that it is written
+ * out as a single contiguous blob of pixels (no leftover bytes
+ * at the end of each row).
+ */
+ size_t bytesNeededTotal() const {
+ return this->bytesNeededPerRow() * fBitmap.height();
+ }
+
+ /**
+ * Writes the entire bitmap into dstBuffer, using the already-specified
+ * pixelFormat. Returns true if successful.
+ *
+ * dstBufferSize is the maximum allowable bytes to write into dstBuffer;
+ * if that is not large enough to hold the entire bitmap, then this
+ * will fail immediately and return false.
+ * We force the caller to pass this in to avoid buffer overruns in
+ * unanticipated cases.
+ *
+ * All pixels for all rows will be written into dstBuffer as a
+ * single contiguous blob (no skipped pixels at the end of each
+ * row).
+ */
+ bool copyBitmapToPixelBuffer (void *dstBuffer, size_t dstBufferSize) const;
+
+private:
+ const SkBitmap& fBitmap;
+ const PixelFormat fPixelFormat;
+};
+
+#endif