1 /* 2 * Copyright 2011 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 "SkColorData.h" 9 #include "Test.h" 10 11 // our std SkAlpha255To256 12 static int test_srcover0(unsigned dst, unsigned alpha) { 13 return alpha + SkAlphaMul(dst, SkAlpha255To256(255 - alpha)); 14 } 15 16 // faster hack +1 17 static int test_srcover1(unsigned dst, unsigned alpha) { 18 return alpha + SkAlphaMul(dst, 256 - alpha); 19 } 20 21 // slower "correct" 22 static int test_srcover2(unsigned dst, unsigned alpha) { 23 return alpha + SkMulDiv255Round(dst, 255 - alpha); 24 } 25 26 DEF_TEST(SrcOver, reporter) { 27 /* Here's the idea. Can we ensure that when we blend on top of an opaque 28 dst, that the result always stay's opaque (i.e. exactly 255)? 29 */ 30 31 unsigned i; 32 int opaqueCounter0 = 0; 33 int opaqueCounter1 = 0; 34 int opaqueCounter2 = 0; 35 for (i = 0; i <= 255; i++) { 36 unsigned result0 = test_srcover0(0xFF, i); 37 unsigned result1 = test_srcover1(0xFF, i); 38 unsigned result2 = test_srcover2(0xFF, i); 39 opaqueCounter0 += (result0 == 0xFF); 40 opaqueCounter1 += (result1 == 0xFF); 41 opaqueCounter2 += (result2 == 0xFF); 42 } 43 #if 0 44 INFOF(reporter, "---- opaque test: [%d %d %d]\n", 45 opaqueCounter0, opaqueCounter1, opaqueCounter2); 46 #endif 47 // we acknowledge that technique0 does not always return opaque 48 REPORTER_ASSERT(reporter, opaqueCounter0 == 256); 49 REPORTER_ASSERT(reporter, opaqueCounter1 == 256); 50 REPORTER_ASSERT(reporter, opaqueCounter2 == 256); 51 52 // Now ensure that we never over/underflow a byte 53 for (i = 0; i <= 255; i++) { 54 for (unsigned dst = 0; dst <= 255; dst++) { 55 unsigned r0 = test_srcover0(dst, i); 56 unsigned r1 = test_srcover1(dst, i); 57 unsigned r2 = test_srcover2(dst, i); 58 unsigned max = SkMax32(dst, i); 59 // ignore the known failure 60 if (dst != 255) { 61 REPORTER_ASSERT(reporter, r0 <= 255 && r0 >= max); 62 } 63 REPORTER_ASSERT(reporter, r1 <= 255 && r1 >= max); 64 REPORTER_ASSERT(reporter, r2 <= 255 && r2 >= max); 65 66 #if 0 67 // this shows where r1 (faster) differs from r2 (more exact) 68 if (r1 != r2) { 69 INFOF(reporter, "--- dst=%d i=%d r1=%d r2=%d exact=%g\n", 70 dst, i, r1, r2, i + dst - dst*i/255.0f); 71 } 72 #endif 73 } 74 } 75 } 76
