commit 908f5836626d792c5e33ad93f44c6a418a0cc8f5
author epoger@google.com <epoger@google.com@2bbb7eff-a529-9590-31e7-b0007b416f81> Fri Apr 12 02:23:55 2013 +0000
committer epoger@google.com <epoger@google.com@2bbb7eff-a529-9590-31e7-b0007b416f81> Fri Apr 12 02:23:55 2013 +0000
tree 2387bc49caeabbd315b34d9973327a5fa310335e
parent bcbf5aa77ddce07c95efc51c567ce737da7f267d

rename SkBitmapChecksummer as SkBitmapHasher, and prepare for it to possibly use
some algorithm other than CityHash
Review URL: https://codereview.chromium.org/14170010

git-svn-id: http://skia.googlecode.com/svn/trunk@8639 2bbb7eff-a529-9590-31e7-b0007b416f81

src/utils/SkBitmapHasher.cpp

diff --git a/src/utils/SkBitmapHasher.cpp b/src/utils/SkBitmapHasher.cpp
new file mode 100644
index 0000000..6df3ab9
--- /dev/null
+++ b/src/utils/SkBitmapHasher.cpp
@@ -0,0 +1,70 @@
+
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBitmap.h"
+#include "SkBitmapHasher.h"
+#include "SkBitmapTransformer.h"
+#include "SkCityHash.h"
+#include "SkEndian.h"
+
+/**
+ * Write an integer value into a bytebuffer in little-endian order.
+ */
+static void write_int_to_buffer(int val, char* buf) {
+    val = SkEndian_SwapLE32(val);
+    for (int byte=0; byte<4; byte++) {
+        *buf++ = (char)(val & 0xff);
+        val = val >> 8;
+    }
+}
+
+/*static*/ bool SkBitmapHasher::ComputeDigestInternal(
+        const SkBitmap& bitmap, const SkBitmapTransformer& transformer, SkHashDigest *result) {
+    size_t pixelBufferSize = transformer.bytesNeededTotal();
+    size_t totalBufferSize = pixelBufferSize + 8; // leave room for x/y dimensions
+
+    SkAutoMalloc bufferManager(totalBufferSize);
+    char *bufferStart = static_cast<char *>(bufferManager.get());
+    char *bufPtr = bufferStart;
+    // start with the x/y dimensions
+    write_int_to_buffer(bitmap.width(), bufPtr);
+    bufPtr += 4;
+    write_int_to_buffer(bitmap.height(), bufPtr);
+    bufPtr += 4;
+
+    // add all the pixel data
+    if (!transformer.copyBitmapToPixelBuffer(bufPtr, pixelBufferSize)) {
+        return false;
+    }
+    *result = SkCityHash::Compute64(bufferStart, totalBufferSize);
+    return true;
+}
+
+/*static*/ bool SkBitmapHasher::ComputeDigest(const SkBitmap& bitmap, SkHashDigest *result) {
+    const SkBitmapTransformer::PixelFormat kPixelFormat =
+        SkBitmapTransformer::kARGB_8888_Premul_PixelFormat;
+
+    // First, try to transform the existing bitmap.
+    const SkBitmapTransformer transformer =
+        SkBitmapTransformer(bitmap, kPixelFormat);
+    if (transformer.isValid(false)) {
+        return ComputeDigestInternal(bitmap, transformer, result);
+    }
+
+    // Hmm, that didn't work. Maybe if we create a new
+    // kARGB_8888_Config version of the bitmap it will work better?
+    SkBitmap copyBitmap;
+    bitmap.copyTo(&copyBitmap, SkBitmap::kARGB_8888_Config);
+    const SkBitmapTransformer copyTransformer =
+        SkBitmapTransformer(copyBitmap, kPixelFormat);
+    if (copyTransformer.isValid(true)) {
+        return ComputeDigestInternal(copyBitmap, copyTransformer, result);
+    } else {
+        return false;
+    }
+}