ARGB image encoder for checksums.

src/utils/SkBitmapHasher.cpp

Index: src/utils/SkBitmapHasher.cpp
===================================================================
--- src/utils/SkBitmapHasher.cpp	(revision 8777)
+++ src/utils/SkBitmapHasher.cpp	(working copy)
@@ -1,4 +1,3 @@
-
 /*
  * Copyright 2012 Google Inc.
  *
@@ -8,37 +7,38 @@
 
 #include "SkBitmap.h"
 #include "SkBitmapHasher.h"
-#include "SkBitmapTransformer.h"
 #include "SkCityHash.h"
 #include "SkEndian.h"
+#include "SkImageEncoder.h"
+#include "SkStream.h"
 
 /**
  * Write an integer value into a bytebuffer in little-endian order.

[epoger, 2013/04/19 21:13:02]

"into a bytebuffer" -> "to a stream"

[bungeman-skia, 2013/04/22 18:31:14]

Done.

  */
-static void write_int_to_buffer(int val, char* buf) {
+static void write_int_to_buffer(int val, SkWStream* out) {
     val = SkEndian_SwapLE32(val);
-    for (int byte=0; byte<4; byte++) {
-        *buf++ = (char)(val & 0xff);
+    for (size_t byte = 0; byte < sizeof(int); ++byte) {
+        out->write8((uint8_t)(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
+/*static*/ bool SkBitmapHasher::ComputeDigestInternal(const SkBitmap& bitmap,
+                                                      SkHashDigest *result) {
+    size_t pixelBufferSize = bitmap.width() * bitmap.height() * 4;
+    size_t totalBufferSize = pixelBufferSize + 2 * sizeof(int);
 
     SkAutoMalloc bufferManager(totalBufferSize);
     char *bufferStart = static_cast<char *>(bufferManager.get());
-    char *bufPtr = bufferStart;
+    SkWStream* out = new SkMemoryWStream(bufferStart, totalBufferSize);
+
     // start with the x/y dimensions
-    write_int_to_buffer(bitmap.width(), bufPtr);
-    bufPtr += 4;
-    write_int_to_buffer(bitmap.height(), bufPtr);
-    bufPtr += 4;
+    write_int_to_buffer(bitmap.width(), out);
+    write_int_to_buffer(bitmap.height(), out);
 
     // add all the pixel data
-    if (!transformer.copyBitmapToPixelBuffer(bufPtr, pixelBufferSize)) {
+    SkAutoTDelete<SkImageEncoder> enc(CreateARGBImageEncoder());

[epoger, 2013/04/19 21:13:02]

Is there a significant performance penalty for creating an SkARGBImageEncoder
every time we call ComputeDigestInternal()?  If not, this should be fine...

+    if (!enc->encodeStream(out, bitmap, 100)) {

[epoger, 2013/04/19 21:13:02]

Where does the magic "100" come from?  Can we refer to a constant variable
instead?

[bungeman-skia, 2013/04/22 18:31:14]

Ah, you need a good editor which will show documentation as you
type/hover/navigate.

"at quality level 'quality' (which can be in range 0-100)"

However, changed to use SkImageEncoder::kDefaultQuality.

         return false;
     }
     *result = SkCityHash::Compute64(bufferStart, totalBufferSize);
@@ -46,25 +46,13 @@
 }
 
 /*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);
+    if (ComputeDigestInternal(bitmap, result)) {
+        return true;
     }
 
     // Hmm, that didn't work. Maybe if we create a new

[epoger, 2013/04/19 21:13:02]

I don't know why we would encounter this anymore, now that the transformer can
handle lots of different input configs.  But I guess there's no harm...

[bungeman-skia, 2013/04/22 18:31:14]

Well, this doesn't support A8 or A1, since I didn't know what to do with them.
On the other hand, bitmap.copyTo doesn't handle A1, and seems a bit fuzzy about
A8 itself.

     // 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;
-    }
+    return ComputeDigestInternal(copyBitmap, result);
 }