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#include "Test.h"
#include "SkColor.h"
#define ASSERT(x) REPORTER_ASSERT(r, x)
// All algorithms we're testing have this interface.
// We want a single channel blend, src over dst, assuming src is premultiplied by srcAlpha.
typedef uint8_t(*Blend)(uint8_t dst, uint8_t src, uint8_t srcAlpha);
// This is our golden algorithm.
static uint8_t blend_double_round(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
SkASSERT(src <= srcAlpha);
return SkToU8(0.5 + src + dst * (255.0 - srcAlpha) / 255.0);
}
static uint8_t abs_diff(uint8_t a, uint8_t b) {
const int diff = a - b;
return diff > 0 ? diff : -diff;
}
static void test(skiatest::Reporter* r, int maxDiff, Blend algorithm,
uint8_t dst, uint8_t src, uint8_t alpha) {
const uint8_t golden = blend_double_round(dst, src, alpha);
const uint8_t blend = algorithm(dst, src, alpha);
if (abs_diff(blend, golden) > maxDiff) {
SkDebugf("dst %02x, src %02x, alpha %02x, |%02x - %02x| > %d\n",
dst, src, alpha, blend, golden, maxDiff);
ASSERT(abs_diff(blend, golden) <= maxDiff);
}
}
// Exhaustively compare an algorithm against our golden, for a given alpha.
static void test_alpha(skiatest::Reporter* r, uint8_t alpha, int maxDiff, Blend algorithm) {
SkASSERT(maxDiff >= 0);
for (unsigned src = 0; src <= alpha; src++) {
for (unsigned dst = 0; dst < 256; dst++) {
test(r, maxDiff, algorithm, dst, src, alpha);
}
}
}
// Exhaustively compare an algorithm against our golden, for a given dst.
static void test_dst(skiatest::Reporter* r, uint8_t dst, int maxDiff, Blend algorithm) {
SkASSERT(maxDiff >= 0);
for (unsigned alpha = 0; alpha < 256; alpha++) {
for (unsigned src = 0; src <= alpha; src++) {
test(r, maxDiff, algorithm, dst, src, alpha);
}
}
}
static uint8_t blend_double_trunc(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
return SkToU8(src + dst * (255.0 - srcAlpha) / 255.0);
}
static uint8_t blend_float_trunc(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
return SkToU8(src + dst * (255.0f - srcAlpha) / 255.0f);
}
static uint8_t blend_float_round(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
return SkToU8(0.5f + src + dst * (255.0f - srcAlpha) / 255.0f);
}
static uint8_t blend_255_trunc(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint16_t invAlpha = 255 - srcAlpha;
const uint16_t product = dst * invAlpha;
return src + (product >> 8);
}
static uint8_t blend_255_round(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint16_t invAlpha = 255 - srcAlpha;
const uint16_t product = dst * invAlpha + 128;
return src + (product >> 8);
}
static uint8_t blend_256_trunc(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint16_t invAlpha = 256 - (srcAlpha + (srcAlpha >> 7));
const uint16_t product = dst * invAlpha;
return src + (product >> 8);
}
static uint8_t blend_256_round(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint16_t invAlpha = 256 - (srcAlpha + (srcAlpha >> 7));
const uint16_t product = dst * invAlpha + 128;
return src + (product >> 8);
}
static uint8_t blend_256_round_alt(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint8_t invAlpha8 = 255 - srcAlpha;
const uint16_t invAlpha = invAlpha8 + (invAlpha8 >> 7);
const uint16_t product = dst * invAlpha + 128;
return src + (product >> 8);
}
static uint8_t blend_256_plus1_trunc(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint16_t invAlpha = 256 - (srcAlpha + 1);
const uint16_t product = dst * invAlpha;
return src + (product >> 8);
}
static uint8_t blend_256_plus1_round(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint16_t invAlpha = 256 - (srcAlpha + 1);
const uint16_t product = dst * invAlpha + 128;
return src + (product >> 8);
}
static uint8_t blend_perfect(uint8_t dst, uint8_t src, uint8_t srcAlpha) {
const uint8_t invAlpha = 255 - srcAlpha;
const uint16_t product = dst * invAlpha + 128;
return src + ((product + (product >> 8)) >> 8);
}
// We want 0 diff whenever src is fully transparent.
DEF_TEST(Blend_alpha_0x00, r) {
const uint8_t alpha = 0x00;
// GOOD
test_alpha(r, alpha, 0, blend_256_round);
test_alpha(r, alpha, 0, blend_256_round_alt);
test_alpha(r, alpha, 0, blend_256_trunc);
test_alpha(r, alpha, 0, blend_double_trunc);
test_alpha(r, alpha, 0, blend_float_round);
test_alpha(r, alpha, 0, blend_float_trunc);
test_alpha(r, alpha, 0, blend_perfect);
// BAD
test_alpha(r, alpha, 1, blend_255_round);
test_alpha(r, alpha, 1, blend_255_trunc);
test_alpha(r, alpha, 1, blend_256_plus1_round);
test_alpha(r, alpha, 1, blend_256_plus1_trunc);
}
// We want 0 diff whenever dst is 0.
DEF_TEST(Blend_dst_0x00, r) {
const uint8_t dst = 0x00;
// GOOD
test_dst(r, dst, 0, blend_255_round);
test_dst(r, dst, 0, blend_255_trunc);
test_dst(r, dst, 0, blend_256_plus1_round);
test_dst(r, dst, 0, blend_256_plus1_trunc);
test_dst(r, dst, 0, blend_256_round);
test_dst(r, dst, 0, blend_256_round_alt);
test_dst(r, dst, 0, blend_256_trunc);
test_dst(r, dst, 0, blend_double_trunc);
test_dst(r, dst, 0, blend_float_round);
test_dst(r, dst, 0, blend_float_trunc);
test_dst(r, dst, 0, blend_perfect);
// BAD
}
// We want 0 diff whenever src is fully opaque.
DEF_TEST(Blend_alpha_0xFF, r) {
const uint8_t alpha = 0xFF;
// GOOD
test_alpha(r, alpha, 0, blend_255_round);
test_alpha(r, alpha, 0, blend_255_trunc);
test_alpha(r, alpha, 0, blend_256_plus1_round);
test_alpha(r, alpha, 0, blend_256_plus1_trunc);
test_alpha(r, alpha, 0, blend_256_round);
test_alpha(r, alpha, 0, blend_256_round_alt);
test_alpha(r, alpha, 0, blend_256_trunc);
test_alpha(r, alpha, 0, blend_double_trunc);
test_alpha(r, alpha, 0, blend_float_round);
test_alpha(r, alpha, 0, blend_float_trunc);
test_alpha(r, alpha, 0, blend_perfect);
// BAD
}
// We want 0 diff whenever dst is 0xFF.
DEF_TEST(Blend_dst_0xFF, r) {
const uint8_t dst = 0xFF;
// GOOD
test_dst(r, dst, 0, blend_256_round);
test_dst(r, dst, 0, blend_256_round_alt);
test_dst(r, dst, 0, blend_double_trunc);
test_dst(r, dst, 0, blend_float_round);
test_dst(r, dst, 0, blend_float_trunc);
test_dst(r, dst, 0, blend_perfect);
// BAD
test_dst(r, dst, 1, blend_255_round);
test_dst(r, dst, 1, blend_255_trunc);
test_dst(r, dst, 1, blend_256_plus1_round);
test_dst(r, dst, 1, blend_256_plus1_trunc);
test_dst(r, dst, 1, blend_256_trunc);
}
// We'd like diff <= 1 everywhere.
DEF_TEST(Blend_alpha_Exhaustive, r) {
for (unsigned alpha = 0; alpha < 256; alpha++) {
// PERFECT
test_alpha(r, alpha, 0, blend_float_round);
test_alpha(r, alpha, 0, blend_perfect);
// GOOD
test_alpha(r, alpha, 1, blend_255_round);
test_alpha(r, alpha, 1, blend_256_plus1_round);
test_alpha(r, alpha, 1, blend_256_round);
test_alpha(r, alpha, 1, blend_256_round_alt);
test_alpha(r, alpha, 1, blend_256_trunc);
test_alpha(r, alpha, 1, blend_double_trunc);
test_alpha(r, alpha, 1, blend_float_trunc);
// BAD
test_alpha(r, alpha, 2, blend_255_trunc);
test_alpha(r, alpha, 2, blend_256_plus1_trunc);
}
}
// We'd like diff <= 1 everywhere.
DEF_TEST(Blend_dst_Exhaustive, r) {
for (unsigned dst = 0; dst < 256; dst++) {
// PERFECT
test_dst(r, dst, 0, blend_float_round);
test_dst(r, dst, 0, blend_perfect);
// GOOD
test_dst(r, dst, 1, blend_255_round);
test_dst(r, dst, 1, blend_256_plus1_round);
test_dst(r, dst, 1, blend_256_round);
test_dst(r, dst, 1, blend_256_round_alt);
test_dst(r, dst, 1, blend_256_trunc);
test_dst(r, dst, 1, blend_double_trunc);
test_dst(r, dst, 1, blend_float_trunc);
// BAD
test_dst(r, dst, 2, blend_255_trunc);
test_dst(r, dst, 2, blend_256_plus1_trunc);
}
}
// Overall summary:
// PERFECT
// blend_double_round
// blend_float_round
// blend_perfect
// GOOD ENOUGH
// blend_double_trunc
// blend_float_trunc
// blend_256_round
// blend_256_round_alt
// NOT GOOD ENOUGH
// all others
//
// Algorithms that make sense to use in Skia: blend_256_round, blend_256_round_alt, blend_perfect
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