1 /*
2 * Copyright 2015 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 "SkColor.h"
10 #include "SkColorPriv.h"
11 #include "SkTaskGroup.h"
12 #include <functional>
13
14 struct Results { int diffs, diffs_0x00, diffs_0xff, diffs_by_1; };
15
acceptable(const Results & r)16 static bool acceptable(const Results& r) {
17 #if 0
18 SkDebugf("%d diffs, %d at 0x00, %d at 0xff, %d off by 1, all out of 65536\n",
19 r.diffs, r.diffs_0x00, r.diffs_0xff, r.diffs_by_1);
20 #endif
21 return r.diffs_by_1 == r.diffs // never off by more than 1
22 && r.diffs_0x00 == 0 // transparent must stay transparent
23 && r.diffs_0xff == 0; // opaque must stay opaque
24 }
25
26 template <typename Fn>
test(Fn && multiply)27 static Results test(Fn&& multiply) {
28 Results r = { 0,0,0,0 };
29 for (int x = 0; x < 256; x++) {
30 for (int y = 0; y < 256; y++) {
31 int p = multiply(x, y),
32 ideal = (x*y+127)/255;
33 if (p != ideal) {
34 r.diffs++;
35 if (x == 0x00 || y == 0x00) { r.diffs_0x00++; }
36 if (x == 0xff || y == 0xff) { r.diffs_0xff++; }
37 if (SkTAbs(ideal - p) == 1) { r.diffs_by_1++; }
38 }
39 }}
40 return r;
41 }
42
DEF_TEST(Blend_byte_multiply,r)43 DEF_TEST(Blend_byte_multiply, r) {
44 // These are all temptingly close but fundamentally broken.
45 int (*broken[])(int, int) = {
46 [](int x, int y) { return (x*y)>>8; },
47 [](int x, int y) { return (x*y+128)>>8; },
48 [](int x, int y) { y += y>>7; return (x*y)>>8; },
49 };
50 for (auto multiply : broken) { REPORTER_ASSERT(r, !acceptable(test(multiply))); }
51
52 // These are fine to use, but not perfect.
53 int (*fine[])(int, int) = {
54 [](int x, int y) { return (x*y+x)>>8; },
55 [](int x, int y) { return (x*y+y)>>8; },
56 [](int x, int y) { return (x*y+255)>>8; },
57 [](int x, int y) { y += y>>7; return (x*y+128)>>8; },
58 };
59 for (auto multiply : fine) { REPORTER_ASSERT(r, acceptable(test(multiply))); }
60
61 // These are pefect.
62 int (*perfect[])(int, int) = {
63 [](int x, int y) { return (x*y+127)/255; }, // Duh.
64 [](int x, int y) { int p = (x*y+128); return (p+(p>>8))>>8; },
65 [](int x, int y) { return ((x*y+128)*257)>>16; },
66 };
67 for (auto multiply : perfect) { REPORTER_ASSERT(r, test(multiply).diffs == 0); }
68 }
69