DM: find max component difference
So far unused except to back BitmapsEqual, but I want to play with it in CLs I'm working on.
BUG=skia:
R=reed@google.com, mtklein@google.com
Author: mtklein@chromium.org
Review URL: https://codereview.chromium.org/290043005
git-svn-id: http://skia.googlecode.com/svn/trunk@14759 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/dm/DMUtil.cpp b/dm/DMUtil.cpp
index bef903d..d7d6691 100644
--- a/dm/DMUtil.cpp
+++ b/dm/DMUtil.cpp
@@ -1,5 +1,6 @@
#include "DMUtil.h"
+#include "SkColorPriv.h"
#include "SkPicture.h"
#include "SkPictureRecorder.h"
@@ -38,9 +39,52 @@
canvas.flush();
}
-bool BitmapsEqual(const SkBitmap& a, const SkBitmap& b) {
+static void unpack_565(uint16_t pixel, unsigned* r, unsigned* g, unsigned* b) {
+ *r = SkGetPackedR16(pixel);
+ *g = SkGetPackedG16(pixel);
+ *b = SkGetPackedB16(pixel);
+}
+
+// Returns |a-b|.
+static unsigned abs_diff(unsigned a, unsigned b) {
+ return a > b ? a - b : b - a;
+}
+
+unsigned MaxComponentDifference(const SkBitmap& a, const SkBitmap& b) {
+ if (a.info() != b.info()) {
+ SkFAIL("Can't compare bitmaps of different shapes.");
+ }
+
+ unsigned max = 0;
+
const SkAutoLockPixels lockA(a), lockB(b);
- return a.getSize() == b.getSize() && 0 == memcmp(a.getPixels(), b.getPixels(), b.getSize());
+ if (a.info().colorType() == kRGB_565_SkColorType) {
+ // 565 is special/annoying because its 3 components straddle 2 bytes.
+ const uint16_t* aPixels = (const uint16_t*)a.getPixels();
+ const uint16_t* bPixels = (const uint16_t*)b.getPixels();
+ for (size_t i = 0; i < a.getSize() / 2; i++) {
+ unsigned ar, ag, ab,
+ br, bg, bb;
+ unpack_565(aPixels[i], &ar, &ag, &ab);
+ unpack_565(bPixels[i], &br, &bg, &bb);
+ max = SkTMax(max, abs_diff(ar, br));
+ max = SkTMax(max, abs_diff(ag, bg));
+ max = SkTMax(max, abs_diff(ab, bb));
+ }
+ } else {
+ // Everything else we produce is byte aligned, so max component diff == max byte diff.
+ const uint8_t* aBytes = (const uint8_t*)a.getPixels();
+ const uint8_t* bBytes = (const uint8_t*)b.getPixels();
+ for (size_t i = 0; i < a.getSize(); i++) {
+ max = SkTMax(max, abs_diff(aBytes[i], bBytes[i]));
+ }
+ }
+
+ return max;
+}
+
+bool BitmapsEqual(const SkBitmap& a, const SkBitmap& b) {
+ return a.info() == b.info() && 0 == MaxComponentDifference(a, b);
}
} // namespace DM
diff --git a/dm/DMUtil.h b/dm/DMUtil.h
index 535d9f2..b5b5e32 100644
--- a/dm/DMUtil.h
+++ b/dm/DMUtil.h
@@ -28,6 +28,9 @@
// Draw picture to bitmap.
void DrawPicture(SkPicture* picture, SkBitmap* bitmap);
+// What is the maximum component difference in these bitmaps?
+unsigned MaxComponentDifference(const SkBitmap& a, const SkBitmap& b);
+
// Are these identical bitmaps?
bool BitmapsEqual(const SkBitmap& a, const SkBitmap& b);