Changes in uspace/lib/softrend/compose.c [b22b449d:6d5e378] in mainline

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;
+        double mul;
+        double mul_cmp;
 
-        uint8_t res_a;
-        uint8_t res_r;
-        uint8_t res_g;
-        uint8_t res_b;
+        double res_a;
+        double res_r;
+        double res_g;
+        double res_b;
 
-        res_a = (ALPHA(fg) * 255 + (255 - ALPHA(fg)) * ALPHA(bg)) / 255;
-        mf = ALPHA(fg);
-        mb = (255 * 255 - ALPHA(fg) * ALPHA(bg)) / 255;
+        if (ALPHA(bg) == 255) {
+                res_a = 1;
+                mul = ((double) ALPHA(fg)) / 255.0;
+                mul_cmp = 1 - mul;
+        } else {
+                double fg_a = ((double) ALPHA(fg)) / 255.0;
+                double bg_a = ((double) ALPHA(bg)) / 255.0;
 
-        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_a = 1 - (1 - fg_a) * (1 - bg_a);
+                mul = fg_a / res_a;
+                mul_cmp = 1 - mul;
+        }
 
-        return PIXEL(res_a, res_r, res_g, res_b);
+        res_r = mul * ((double) RED(fg)) + mul_cmp * ((double) RED(bg));
+        res_g = mul * ((double) GREEN(fg)) + mul_cmp * ((double) GREEN(bg));
+        res_b = mul * ((double) BLUE(fg)) + mul_cmp * ((double) BLUE(bg));
+
+        return PIXEL((unsigned) (res_a * 255),
+            (unsigned) res_r, (unsigned) res_g, (unsigned) res_b);
 }