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Update blending logic

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- Unpremultiply properly
- No longer uses floats
This commit is contained in:
ZachNagengast 2023-11-03 15:05:31 -07:00
parent f97570f523
commit bb0eff44cd
1 changed files with 25 additions and 16 deletions
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41
src/_imagingft.c
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@ -1049,6 +1049,7 @@ font_render(FontObject *self, PyObject *args) {
int k;
unsigned char v;
unsigned char *target;
unsigned int tmp;
if (color) {
/* target[RGB] returns the color, target[A] returns the mask */
/* target bands get split again in ImageDraw.text */
@ -1059,25 +1060,33 @@ font_render(FontObject *self, PyObject *args) {
if (color && bitmap.pixel_mode == FT_PIXEL_MODE_BGRA) {
/* paste color glyph */
for (k = x0; k < x1; k++) {
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 src_alpha = source[k * 4 + 3];
int dst_blu = target[k * 4 + 0];
int dst_grn = target[k * 4 + 1];
int dst_red = target[k * 4 + 2];
/* paste only if source has data */
if (src_alpha > 0) {
/* unpremultiply RGBA */
int src_red = CLIP8((255 * (int)source[k * 4 + 0]) / src_alpha);
int src_grn = CLIP8((255 * (int)source[k * 4 + 1]) / src_alpha);
int src_blu = CLIP8((255 * (int)source[k * 4 + 2]) / src_alpha);
/* 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);
/* blend required if target has data */
if (target[k * 4 + 3] > 0) {
/* blend colors to BGRa */
target[k * 4 + 0] = BLEND(src_alpha, target[k * 4 + 0], src_blu, tmp);
target[k * 4 + 1] = BLEND(src_alpha, target[k * 4 + 1], src_grn, tmp);
target[k * 4 + 2] = BLEND(src_alpha, target[k * 4 + 2], src_red, tmp);
target[k * 4 + 3] = CLIP8(out_alpha * 255.0);
/* blend alpha */
int out_alpha = CLIP8(src_alpha + MULDIV255(target[k * 4 + 3], (255 - src_alpha), tmp));
target[k * 4 + 3] = out_alpha;
} else {
/* paste source directly to BGRa */
target[k * 4 + 0] = src_blu;
target[k * 4 + 1] = src_grn;
target[k * 4 + 2] = src_red;
target[k * 4 + 3] = src_alpha;
}
}
}
} else if (bitmap.pixel_mode == FT_PIXEL_MODE_GRAY) {
if (color) {