Changeset d723a80 in mainline

Timestamp:

2018-10-18T18:55:40Z (6 years ago)

Author:

Maurizio Lombardi <mlombard@…>

Children:

14ad75c

Parents:

8a1afd2

Message:

compositor: fix the over operator

If a vterm is on top of a vcalc and you decrease the opacity of the
first (or rotate/resize it), the result composite image is obviously wrong
(the vcalc's buttons become black…).

This is because of some mistakes in the over operator's implementation.
This patch fixes the problem by reimplementing it.

File:

• uspace/lib/softrend/compose.c (modified) (1 diff)

uspace/lib/softrend/compose.c

@@ -53 +53 @@
 pixel_t compose_over(pixel_t fg, pixel_t bg)
 {
-        uint16_t mf;
-        uint16_t mb;
-
         uint8_t res_a;
         uint8_t res_r;
         uint8_t res_g;
         uint8_t res_b;
+        uint32_t res_a_inv;
 
-        res_a = (ALPHA(fg) * 255 + (255 - ALPHA(fg)) * ALPHA(bg)) / 255;
-        mf = ALPHA(fg);
-        mb = (255 * 255 - ALPHA(fg) * ALPHA(bg)) / 255;
+        res_a_inv = ALPHA(bg) * (255 - ALPHA(fg));
+        res_a = ALPHA(fg) + (res_a_inv / 255);
 
-        res_r = (mf * RED(fg) + mb * RED(bg)) / 255;
-        res_g = (mf * GREEN(fg) + mb * GREEN(bg)) / 255;
-        res_b = (mf * BLUE(fg) + mb * BLUE(bg)) / 255;
+        res_r = (RED(fg) * ALPHA(fg) / 255) + (RED(bg) * res_a_inv) / (255 * 255);
+        res_g = (GREEN(fg) * ALPHA(fg) / 255) + (GREEN(bg) * res_a_inv) / (255 * 255);
+        res_b = (BLUE(fg) * ALPHA(fg) / 255) + (BLUE(bg) * res_a_inv) / (255 * 255);
 
         return PIXEL(res_a, res_r, res_g, res_b);