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 14struct Results { int diffs, diffs_0x00, diffs_0xff, diffs_by_1; }; 15 16static 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 26template <typename Fn> 27static 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 43DEF_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