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png_loaders: fix the wrong premultiplying operations.

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It should not modify the alpha channel value while premultiplying
that turned out with the wrong visual result.

@Issue: https://github.com/Samsung/thorvg/issues/655
This commit is contained in:
Hermet Park 2021-12-14 16:33:17 +09:00 • committed by JunsuChoi
parent 62c9feb80a
commit 36da47af80
3 changed files with 14 additions and 8 deletions
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6
src/examples/PicturePng.cpp
View file

@ -31,6 +31,12 @@ void tvgDrawCmds(tvg::Canvas* canvas)
{
if (!canvas) return;
//Background
auto bg = tvg::Shape::gen();
bg->appendRect(0, 0, WIDTH, HEIGHT, 0, 0); //x, y, w, h, rx, ry
bg->fill(255, 255, 255, 255); //r, g, b, a
canvas->push(move(bg));
//Load png file from path
auto opacity = 51;

8
src/loaders/external_png/tvgPngLoader.cpp
View file

@ -23,10 +23,10 @@
#include "tvgLoader.h"
#include "tvgPngLoader.h"
static inline uint32_t ALPHA_BLEND(uint32_t c, uint32_t a)
static inline uint32_t PREMULTIPLY(uint32_t c)
{
return (((((c >> 8) & 0x00ff00ff) * a + 0x00ff00ff) & 0xff00ff00) +
((((c & 0x00ff00ff) * a + 0x00ff00ff) >> 8) & 0x00ff00ff));
auto a = (c >> 24);
return (c & 0xff000000) + ((((c >> 8) & 0xff) * a) & 0xff00) + ((((c & 0x00ff00ff) * a) >> 8) & 0x00ff00ff);
}
@ -36,7 +36,7 @@ static void _premultiply(uint32_t* data, uint32_t w, uint32_t h)
for (uint32_t y = 0; y < h; ++y, buffer += w) {
auto src = buffer;
for (uint32_t x = 0; x < w; ++x, ++src) {
*src = ALPHA_BLEND(*src, (*src >> 24));
*src = PREMULTIPLY(*src);
}
}
}

8
src/loaders/png/tvgPngLoader.cpp
View file

@ -29,10 +29,10 @@
/************************************************************************/
static inline uint32_t ALPHA_BLEND(uint32_t c, uint32_t a)
static inline uint32_t PREMULTIPLY(uint32_t c)
{
return (((((c >> 8) & 0x00ff00ff) * a + 0x00ff00ff) & 0xff00ff00) +
((((c & 0x00ff00ff) * a + 0x00ff00ff) >> 8) & 0x00ff00ff));
auto a = (c >> 24);
return (c & 0xff000000) + ((((c >> 8) & 0xff) * a) & 0xff00) + ((((c & 0x00ff00ff) * a) >> 8) & 0x00ff00ff);
}
@ -42,7 +42,7 @@ static void _premultiply(uint32_t* data, uint32_t w, uint32_t h)
for (uint32_t y = 0; y < h; ++y, buffer += w) {
auto src = buffer;
for (uint32_t x = 0; x < w; ++x, ++src) {
*src = ALPHA_BLEND(*src, (*src >> 24));
*src = PREMULTIPLY(*src);
}
}
}