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Blend colors with alpha when pasting

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- Previously took the highest alpha as threshold
This commit is contained in:
ZachNagengast 2023-10-26 21:40:41 -07:00
parent 57c72b6e00
commit f97570f523
1 changed files with 19 additions and 10 deletions
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29
src/_imagingft.c
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@ -1059,16 +1059,25 @@ font_render(FontObject *self, PyObject *args) {
if (color && bitmap.pixel_mode == FT_PIXEL_MODE_BGRA) {
/* paste color glyph */
for (k = x0; k < x1; k++) {
if (target[k * 4 + 3] < source[k * 4 + 3]) {
/* unpremultiply BGRa to RGBA */
target[k * 4 + 0] = CLIP8(
(255 * (int)source[k * 4 + 2]) / source[k * 4 + 3]);
target[k * 4 + 1] = CLIP8(
(255 * (int)source[k * 4 + 1]) / source[k * 4 + 3]);
target[k * 4 + 2] = CLIP8(
(255 * (int)source[k * 4 + 0]) / source[k * 4 + 3]);
target[k * 4 + 3] = source[k * 4 + 3];
}
float src_alpha = (float) source[k * 4 + 3] / 255.0;
float dst_alpha = (float) target[k * 4 + 3] / 255.0;
float out_alpha = src_alpha + dst_alpha * (1.0 - src_alpha);
/* unpremultiply BGRa to RGBA */
int src_red = source[k * 4 + 0];
int src_grn = source[k * 4 + 1];
int src_blu = source[k * 4 + 2];
int dst_blu = target[k * 4 + 0];
int dst_grn = target[k * 4 + 1];
int dst_red = target[k * 4 + 2];
/* blend color values */
target[k * 4 + 0] = CLIP8((src_blu * src_alpha + dst_blu * dst_alpha * (1.0 - src_alpha)) / out_alpha);
target[k * 4 + 1] = CLIP8((src_grn * src_alpha + dst_grn * dst_alpha * (1.0 - src_alpha)) / out_alpha);
target[k * 4 + 2] = CLIP8((src_red * src_alpha + dst_red * dst_alpha * (1.0 - src_alpha)) / out_alpha);
target[k * 4 + 3] = CLIP8(out_alpha * 255.0);
}
} else if (bitmap.pixel_mode == FT_PIXEL_MODE_GRAY) {
if (color) {