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/*
* Copyright 2011 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 "SkColorPriv.h"
#include "SkXfermode.h"
// our std SkAlpha255To256
static int test_srcover0(unsigned dst, unsigned alpha) {
return alpha + SkAlphaMul(dst, SkAlpha255To256(255 - alpha));
}
// faster hack +1
static int test_srcover1(unsigned dst, unsigned alpha) {
return alpha + SkAlphaMul(dst, 256 - alpha);
}
// slower "correct"
static int test_srcover2(unsigned dst, unsigned alpha) {
return alpha + SkMulDiv255Round(dst, 255 - alpha);
}
static void test_srcover_hack(skiatest::Reporter* reporter) {
/* Here's the idea. Can we ensure that when we blend on top of an opaque
dst, that the result always stay's opaque (i.e. exactly 255)?
*/
unsigned i;
int opaqueCounter0 = 0;
int opaqueCounter1 = 0;
int opaqueCounter2 = 0;
for (i = 0; i <= 255; i++) {
unsigned result0 = test_srcover0(0xFF, i);
unsigned result1 = test_srcover1(0xFF, i);
unsigned result2 = test_srcover2(0xFF, i);
opaqueCounter0 += (result0 == 0xFF);
opaqueCounter1 += (result1 == 0xFF);
opaqueCounter2 += (result2 == 0xFF);
}
#if 0
SkDebugf("---- opaque test: [%d %d %d]\n",
opaqueCounter0, opaqueCounter1, opaqueCounter2);
#endif
// we acknowledge that technique0 does not always return opaque
REPORTER_ASSERT(reporter, opaqueCounter0 == 256);
REPORTER_ASSERT(reporter, opaqueCounter1 == 256);
REPORTER_ASSERT(reporter, opaqueCounter2 == 256);
// Now ensure that we never over/underflow a byte
for (i = 0; i <= 255; i++) {
for (unsigned dst = 0; dst <= 255; dst++) {
unsigned r0 = test_srcover0(dst, i);
unsigned r1 = test_srcover1(dst, i);
unsigned r2 = test_srcover2(dst, i);
unsigned max = SkMax32(dst, i);
// ignore the known failure
if (dst != 255) {
REPORTER_ASSERT(reporter, r0 <= 255 && r0 >= max);
}
REPORTER_ASSERT(reporter, r1 <= 255 && r1 >= max);
REPORTER_ASSERT(reporter, r2 <= 255 && r2 >= max);
#if 0
// this shows where r1 (faster) differs from r2 (more exact)
if (r1 != r2) {
SkDebugf("--- dst=%d i=%d r1=%d r2=%d exact=%g\n",
dst, i, r1, r2, i + dst - dst*i/255.0f);
}
#endif
}
}
}
#include "TestClassDef.h"
DEFINE_TESTCLASS("SrcOver", SrcOverTestClass, test_srcover_hack)
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