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Fix mask gamma rounding issues on x87.

Browse Source 
https://codereview.appspot.com/6497091/

May require rebaselines.


git-svn-id: http://skia.googlecode.com/svn/trunk@5446 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
bungeman@google.com 2012-09-07 21:45:19 +00:00
parent 50a035ddbb
commit d92f336ac7
1 changed files with 13 additions and 7 deletions
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20
src/core/SkMaskGamma.cpp
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@ -49,8 +49,8 @@ static float apply_contrast(float srca, float contrast) {
}
void SkTMaskGamma_build_correcting_lut(uint8_t table[256], U8CPU srcI, SkScalar contrast,
const SkColorSpaceLuminance& srcConvert,
const SkColorSpaceLuminance& dstConvert) {
const SkColorSpaceLuminance& srcConvert,
const SkColorSpaceLuminance& dstConvert) {
const float src = (float)srcI / 255.0f;
const float linSrc = srcConvert.toLuma(src);
//Guess at the dst. The perceptual inverse provides smaller visual
@ -62,19 +62,25 @@ void SkTMaskGamma_build_correcting_lut(uint8_t table[256], U8CPU srcI, SkScalar
//Contrast value tapers off to 0 as the src luminance becomes white
const float adjustedContrast = SkScalarToFloat(contrast) * linDst;
const float step = 1.0f / 255.0f;
//Remove discontinuity and instability when src is close to dst.
//The value 1/256 is arbitrary and appears to contain the instability.
if (fabs(src - dst) < (1.0f / 256.0f)) {
float rawSrca = 0.0f;
for (int i = 0; i < 256; ++i, rawSrca += step) {
float ii = 0.0f;
for (int i = 0; i < 256; ++i, ii += 1.0f) {
float rawSrca = ii / 255.0f;
float srca = apply_contrast(rawSrca, adjustedContrast);
table[i] = SkToU8(sk_float_round2int(255.0f * srca));
}
} else {
float rawSrca = 0.0f;
for (int i = 0; i < 256; ++i, rawSrca += step) {
// Avoid slow int to float conversion.
float ii = 0.0f;
for (int i = 0; i < 256; ++i, ii += 1.0f) {
// 'rawSrca += 1.0f / 255.0f' and even
// 'rawSrca = i * (1.0f / 255.0f)' can add up to more than 1.0f.
// When this happens the table[255] == 0x0 instead of 0xff.
// See http://code.google.com/p/chromium/issues/detail?id=146466
float rawSrca = ii / 255.0f;
float srca = apply_contrast(rawSrca, adjustedContrast);
SkASSERT(srca <= 1.0f);
float dsta = 1.0f - srca;