2 * Copyright 2011 Google Inc.
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
8 #include "SkColorPriv.h"
9 #include "SkXfermode.h"
12 // our std SkAlpha255To256
13 static int test_srcover0(unsigned dst, unsigned alpha) {
14 return alpha + SkAlphaMul(dst, SkAlpha255To256(255 - alpha));
18 static int test_srcover1(unsigned dst, unsigned alpha) {
19 return alpha + SkAlphaMul(dst, 256 - alpha);
23 static int test_srcover2(unsigned dst, unsigned alpha) {
24 return alpha + SkMulDiv255Round(dst, 255 - alpha);
27 DEF_TEST(SrcOver, reporter) {
28 /* Here's the idea. Can we ensure that when we blend on top of an opaque
29 dst, that the result always stay's opaque (i.e. exactly 255)?
33 int opaqueCounter0 = 0;
34 int opaqueCounter1 = 0;
35 int opaqueCounter2 = 0;
36 for (i = 0; i <= 255; i++) {
37 unsigned result0 = test_srcover0(0xFF, i);
38 unsigned result1 = test_srcover1(0xFF, i);
39 unsigned result2 = test_srcover2(0xFF, i);
40 opaqueCounter0 += (result0 == 0xFF);
41 opaqueCounter1 += (result1 == 0xFF);
42 opaqueCounter2 += (result2 == 0xFF);
45 SkDebugf("---- opaque test: [%d %d %d]\n",
46 opaqueCounter0, opaqueCounter1, opaqueCounter2);
48 // we acknowledge that technique0 does not always return opaque
49 REPORTER_ASSERT(reporter, opaqueCounter0 == 256);
50 REPORTER_ASSERT(reporter, opaqueCounter1 == 256);
51 REPORTER_ASSERT(reporter, opaqueCounter2 == 256);
53 // Now ensure that we never over/underflow a byte
54 for (i = 0; i <= 255; i++) {
55 for (unsigned dst = 0; dst <= 255; dst++) {
56 unsigned r0 = test_srcover0(dst, i);
57 unsigned r1 = test_srcover1(dst, i);
58 unsigned r2 = test_srcover2(dst, i);
59 unsigned max = SkMax32(dst, i);
60 // ignore the known failure
62 REPORTER_ASSERT(reporter, r0 <= 255 && r0 >= max);
64 REPORTER_ASSERT(reporter, r1 <= 255 && r1 >= max);
65 REPORTER_ASSERT(reporter, r2 <= 255 && r2 >= max);
68 // this shows where r1 (faster) differs from r2 (more exact)
70 SkDebugf("--- dst=%d i=%d r1=%d r2=%d exact=%g\n",
71 dst, i, r1, r2, i + dst - dst*i/255.0f);