07764cefbb
BUG=skia: GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=5133 Change-Id: I6e8596dcb17cd7e8efa67859bb682bf9bfcac4db Reviewed-on: https://skia-review.googlesource.com/5133 Reviewed-by: Mike Reed <reed@google.com> Commit-Queue: Mike Reed <reed@google.com>
69 lines
2.3 KiB
C++
69 lines
2.3 KiB
C++
/*
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* Copyright 2015 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#include "Test.h"
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#include "SkColor.h"
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#include "SkColorPriv.h"
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#include "SkTaskGroup.h"
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#include <functional>
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struct Results { int diffs, diffs_0x00, diffs_0xff, diffs_by_1; };
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static bool acceptable(const Results& r) {
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#if 0
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SkDebugf("%d diffs, %d at 0x00, %d at 0xff, %d off by 1, all out of 65536\n",
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r.diffs, r.diffs_0x00, r.diffs_0xff, r.diffs_by_1);
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#endif
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return r.diffs_by_1 == r.diffs // never off by more than 1
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&& r.diffs_0x00 == 0 // transparent must stay transparent
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&& r.diffs_0xff == 0; // opaque must stay opaque
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}
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template <typename Fn>
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static Results test(Fn&& multiply) {
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Results r = { 0,0,0,0 };
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for (int x = 0; x < 256; x++) {
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for (int y = 0; y < 256; y++) {
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int p = multiply(x, y),
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ideal = (x*y+127)/255;
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if (p != ideal) {
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r.diffs++;
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if (x == 0x00 || y == 0x00) { r.diffs_0x00++; }
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if (x == 0xff || y == 0xff) { r.diffs_0xff++; }
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if (SkTAbs(ideal - p) == 1) { r.diffs_by_1++; }
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}
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}}
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return r;
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}
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DEF_TEST(Blend_byte_multiply, r) {
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// These are all temptingly close but fundamentally broken.
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int (*broken[])(int, int) = {
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[](int x, int y) { return (x*y)>>8; },
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[](int x, int y) { return (x*y+128)>>8; },
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[](int x, int y) { y += y>>7; return (x*y)>>8; },
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};
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for (auto multiply : broken) { REPORTER_ASSERT(r, !acceptable(test(multiply))); }
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// These are fine to use, but not perfect.
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int (*fine[])(int, int) = {
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[](int x, int y) { return (x*y+x)>>8; },
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[](int x, int y) { return (x*y+y)>>8; },
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[](int x, int y) { return (x*y+255)>>8; },
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[](int x, int y) { y += y>>7; return (x*y+128)>>8; },
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};
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for (auto multiply : fine) { REPORTER_ASSERT(r, acceptable(test(multiply))); }
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// These are pefect.
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int (*perfect[])(int, int) = {
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[](int x, int y) { return (x*y+127)/255; }, // Duh.
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[](int x, int y) { int p = (x*y+128); return (p+(p>>8))>>8; },
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[](int x, int y) { return ((x*y+128)*257)>>16; },
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};
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for (auto multiply : perfect) { REPORTER_ASSERT(r, test(multiply).diffs == 0); }
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}
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