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/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "Test.h"
#include "SkColor.h"
#include "SkColorPriv.h"
#include "SkTaskGroup.h"
#include <functional>
struct Results { int diffs, diffs_0x00, diffs_0xff, diffs_by_1; };
static bool acceptable(const Results& r) {
#if 0
SkDebugf("%d diffs, %d at 0x00, %d at 0xff, %d off by 1, all out of 65536\n",
r.diffs, r.diffs_0x00, r.diffs_0xff, r.diffs_by_1);
#endif
return r.diffs_by_1 == r.diffs // never off by more than 1
&& r.diffs_0x00 == 0 // transparent must stay transparent
&& r.diffs_0xff == 0; // opaque must stay opaque
}
template <typename Fn>
static Results test(Fn&& multiply) {
Results r = { 0,0,0,0 };
for (int x = 0; x < 256; x++) {
for (int y = 0; y < 256; y++) {
int p = multiply(x, y),
ideal = (x*y+127)/255;
if (p != ideal) {
r.diffs++;
if (x == 0x00 || y == 0x00) { r.diffs_0x00++; }
if (x == 0xff || y == 0xff) { r.diffs_0xff++; }
if (SkTAbs(ideal - p) == 1) { r.diffs_by_1++; }
}
}}
return r;
}
DEF_TEST(Blend_byte_multiply, r) {
// These are all temptingly close but fundamentally broken.
int (*broken[])(int, int) = {
[](int x, int y) { return (x*y)>>8; },
[](int x, int y) { return (x*y+128)>>8; },
[](int x, int y) { y += y>>7; return (x*y)>>8; },
};
for (auto multiply : broken) { REPORTER_ASSERT(r, !acceptable(test(multiply))); }
// These are fine to use, but not perfect.
int (*fine[])(int, int) = {
[](int x, int y) { return (x*y+x)>>8; },
[](int x, int y) { return (x*y+y)>>8; },
[](int x, int y) { return (x*y+255)>>8; },
[](int x, int y) { y += y>>7; return (x*y+128)>>8; },
};
for (auto multiply : fine) { REPORTER_ASSERT(r, acceptable(test(multiply))); }
// These are pefect.
int (*perfect[])(int, int) = {
[](int x, int y) { return (x*y+127)/255; }, // Duh.
[](int x, int y) { int p = (x*y+128); return (p+(p>>8))>>8; },
[](int x, int y) { return ((x*y+128)*257)>>16; },
};
for (auto multiply : perfect) { REPORTER_ASSERT(r, test(multiply).diffs == 0); }
}
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