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