1 /*
2 * Copyright 2011 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #include "SkColorPriv.h"
9 #include "Test.h"
10
11 // our std SkAlpha255To256
test_srcover0(unsigned dst,unsigned alpha)12 static int test_srcover0(unsigned dst, unsigned alpha) {
13 return alpha + SkAlphaMul(dst, SkAlpha255To256(255 - alpha));
14 }
15
16 // faster hack +1
test_srcover1(unsigned dst,unsigned alpha)17 static int test_srcover1(unsigned dst, unsigned alpha) {
18 return alpha + SkAlphaMul(dst, 256 - alpha);
19 }
20
21 // slower "correct"
test_srcover2(unsigned dst,unsigned alpha)22 static int test_srcover2(unsigned dst, unsigned alpha) {
23 return alpha + SkMulDiv255Round(dst, 255 - alpha);
24 }
25
DEF_TEST(SrcOver,reporter)26 DEF_TEST(SrcOver, reporter) {
27 /* Here's the idea. Can we ensure that when we blend on top of an opaque
28 dst, that the result always stay's opaque (i.e. exactly 255)?
29 */
30
31 unsigned i;
32 int opaqueCounter0 = 0;
33 int opaqueCounter1 = 0;
34 int opaqueCounter2 = 0;
35 for (i = 0; i <= 255; i++) {
36 unsigned result0 = test_srcover0(0xFF, i);
37 unsigned result1 = test_srcover1(0xFF, i);
38 unsigned result2 = test_srcover2(0xFF, i);
39 opaqueCounter0 += (result0 == 0xFF);
40 opaqueCounter1 += (result1 == 0xFF);
41 opaqueCounter2 += (result2 == 0xFF);
42 }
43 #if 0
44 INFOF(reporter, "---- opaque test: [%d %d %d]\n",
45 opaqueCounter0, opaqueCounter1, opaqueCounter2);
46 #endif
47 // we acknowledge that technique0 does not always return opaque
48 REPORTER_ASSERT(reporter, opaqueCounter0 == 256);
49 REPORTER_ASSERT(reporter, opaqueCounter1 == 256);
50 REPORTER_ASSERT(reporter, opaqueCounter2 == 256);
51
52 // Now ensure that we never over/underflow a byte
53 for (i = 0; i <= 255; i++) {
54 for (unsigned dst = 0; dst <= 255; dst++) {
55 unsigned r0 = test_srcover0(dst, i);
56 unsigned r1 = test_srcover1(dst, i);
57 unsigned r2 = test_srcover2(dst, i);
58 unsigned max = SkMax32(dst, i);
59 // ignore the known failure
60 if (dst != 255) {
61 REPORTER_ASSERT(reporter, r0 <= 255 && r0 >= max);
62 }
63 REPORTER_ASSERT(reporter, r1 <= 255 && r1 >= max);
64 REPORTER_ASSERT(reporter, r2 <= 255 && r2 >= max);
65
66 #if 0
67 // this shows where r1 (faster) differs from r2 (more exact)
68 if (r1 != r2) {
69 INFOF(reporter, "--- dst=%d i=%d r1=%d r2=%d exact=%g\n",
70 dst, i, r1, r2, i + dst - dst*i/255.0f);
71 }
72 #endif
73 }
74 }
75 }
76