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 "Test.h"
9#include "TestClassDef.h"
10#include "SkColorPriv.h"
11#include "SkXfermode.h"
12
13// our std SkAlpha255To256
14static int test_srcover0(unsigned dst, unsigned alpha) {
15    return alpha + SkAlphaMul(dst, SkAlpha255To256(255 - alpha));
16}
17
18// faster hack +1
19static int test_srcover1(unsigned dst, unsigned alpha) {
20    return alpha + SkAlphaMul(dst, 256 - alpha);
21}
22
23// slower "correct"
24static int test_srcover2(unsigned dst, unsigned alpha) {
25    return alpha + SkMulDiv255Round(dst, 255 - alpha);
26}
27
28DEF_TEST(SrcOver, reporter) {
29    /*  Here's the idea. Can we ensure that when we blend on top of an opaque
30        dst, that the result always stay's opaque (i.e. exactly 255)?
31     */
32
33    unsigned i;
34    int opaqueCounter0 = 0;
35    int opaqueCounter1 = 0;
36    int opaqueCounter2 = 0;
37    for (i = 0; i <= 255; i++) {
38        unsigned result0 = test_srcover0(0xFF, i);
39        unsigned result1 = test_srcover1(0xFF, i);
40        unsigned result2 = test_srcover2(0xFF, i);
41        opaqueCounter0 += (result0 == 0xFF);
42        opaqueCounter1 += (result1 == 0xFF);
43        opaqueCounter2 += (result2 == 0xFF);
44    }
45#if 0
46    SkDebugf("---- opaque test: [%d %d %d]\n",
47             opaqueCounter0, opaqueCounter1, opaqueCounter2);
48#endif
49    // we acknowledge that technique0 does not always return opaque
50    REPORTER_ASSERT(reporter, opaqueCounter0 == 256);
51    REPORTER_ASSERT(reporter, opaqueCounter1 == 256);
52    REPORTER_ASSERT(reporter, opaqueCounter2 == 256);
53
54    // Now ensure that we never over/underflow a byte
55    for (i = 0; i <= 255; i++) {
56        for (unsigned dst = 0; dst <= 255; dst++) {
57            unsigned r0 = test_srcover0(dst, i);
58            unsigned r1 = test_srcover1(dst, i);
59            unsigned r2 = test_srcover2(dst, i);
60            unsigned max = SkMax32(dst, i);
61            // ignore the known failure
62            if (dst != 255) {
63                REPORTER_ASSERT(reporter, r0 <= 255 && r0 >= max);
64            }
65            REPORTER_ASSERT(reporter, r1 <= 255 && r1 >= max);
66            REPORTER_ASSERT(reporter, r2 <= 255 && r2 >= max);
67
68#if 0
69            // this shows where r1 (faster) differs from r2 (more exact)
70            if (r1 != r2) {
71                SkDebugf("--- dst=%d i=%d r1=%d r2=%d exact=%g\n",
72                         dst, i, r1, r2, i + dst - dst*i/255.0f);
73            }
74#endif
75        }
76    }
77}
78