Changeset 4fff3c7 in mainline for uspace/lib/softrend/compose.c

Timestamp:

2018-10-19T07:51:31Z (6 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

2cea4c58

Parents:

bae43dc

git-author:

Maurizio Lombardi <mlombard@…> (2018-10-18 18:55:40)

git-committer:

Jakub Jermar <jakub@…> (2018-10-19 07:51:31)

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);