72 lines
2.4 KiB
C++
72 lines
2.4 KiB
C++
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#include "Test.h"
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#include "SkColorPriv.h"
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#include "SkXfermode.h"
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// our std SkAlpha255To256
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static int test_srcover0(unsigned dst, unsigned alpha) {
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return alpha + SkAlphaMul(dst, SkAlpha255To256(255 - alpha));
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}
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// faster hack +1
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static int test_srcover1(unsigned dst, unsigned alpha) {
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return alpha + SkAlphaMul(dst, 256 - alpha);
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}
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// slower "correct"
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static int test_srcover2(unsigned dst, unsigned alpha) {
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return alpha + SkMulDiv255Round(dst, 255 - alpha);
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}
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static void test_srcover_hack(skiatest::Reporter* reporter) {
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/* Here's the idea. Can we ensure that when we blend on top of an opaque
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dst, that the result always stay's opaque (i.e. exactly 255)?
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*/
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unsigned i;
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int opaqueCounter0 = 0;
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int opaqueCounter1 = 0;
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int opaqueCounter2 = 0;
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for (i = 0; i <= 255; i++) {
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unsigned result0 = test_srcover0(0xFF, i);
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unsigned result1 = test_srcover1(0xFF, i);
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unsigned result2 = test_srcover2(0xFF, i);
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opaqueCounter0 += (result0 == 0xFF);
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opaqueCounter1 += (result1 == 0xFF);
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opaqueCounter2 += (result2 == 0xFF);
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}
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#if 0
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SkDebugf("---- opaque test: [%d %d %d]\n",
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opaqueCounter0, opaqueCounter1, opaqueCounter2);
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#endif
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// we acknowledge that technique0 does not always return opaque
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REPORTER_ASSERT(reporter, opaqueCounter0 == 129);
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REPORTER_ASSERT(reporter, opaqueCounter1 == 256);
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REPORTER_ASSERT(reporter, opaqueCounter2 == 256);
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// Now ensure that we never over/underflow a byte
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for (i = 0; i <= 255; i++) {
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for (unsigned dst = 0; dst <= 255; dst++) {
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unsigned r0 = test_srcover0(dst, i);
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unsigned r1 = test_srcover1(dst, i);
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unsigned r2 = test_srcover2(dst, i);
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unsigned max = SkMax32(dst, i);
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// ignore the known failure
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if (dst != 255) {
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REPORTER_ASSERT(reporter, r0 <= 255 && r0 >= max);
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}
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REPORTER_ASSERT(reporter, r1 <= 255 && r1 >= max);
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REPORTER_ASSERT(reporter, r2 <= 255 && r2 >= max);
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#if 0
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// this shows where r1 (faster) differs from r2 (more exact)
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if (r1 != r2) {
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SkDebugf("--- dst=%d i=%d r1=%d r2=%d exact=%g\n", dst, i, r1, r2, i + dst - dst*i/255.0f);
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}
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#endif
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}
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}
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}
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#include "TestClassDef.h"
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DEFINE_TESTCLASS("SrcOver", SrcOverTestClass, test_srcover_hack)
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