ngl: Small shader improvements

Add a variant of gskSetOutputColor that saves a
few multiplications, and use it where possible.

gsk/ngl/resources/blend.glsl

@@ -310,5 +310,5 @@ void main() {
   else
     discard;
 
-  gskSetOutputColor(result * u_alpha);
+  gskSetScaledOutputColor(result, u_alpha);
 }

gsk/ngl/resources/blit.glsl

@@ -13,5 +13,5 @@ void main() {
 void main() {
   vec4 diffuse = GskTexture(u_source, vUv);
 
-  gskSetOutputColor(diffuse * u_alpha);
+  gskSetScaledOutputColor(diffuse, u_alpha);
 }

gsk/ngl/resources/border.glsl

@@ -39,5 +39,5 @@ void main() {
                       gsk_rounded_rect_coverage(gsk_decode_rect(transformed_inside_outline), frag),
                       0.0, 1.0);
 
-  gskSetOutputColor(final_color * alpha);
+  gskSetScaledOutputColor(final_color, alpha);
 }

gsk/ngl/resources/conic_gradient.glsl

@@ -75,7 +75,7 @@ void main() {
       vec4 curr_color = gsk_premultiply(get_color(i));
       vec4 next_color = gsk_premultiply(get_color(i + 1));
       vec4 color = mix(curr_color, next_color, f);
-      gskSetOutputColor(color * u_alpha);
+      gskSetScaledOutputColor(color, u_alpha);
       return;
     }
   }

gsk/ngl/resources/inset_shadow.glsl

@@ -40,5 +40,5 @@ void main() {
                       gsk_rounded_rect_coverage(gsk_decode_rect(transformed_inside_outline), frag),
                       0.0, 1.0);
 
-  gskSetOutputColor(final_color * alpha);
+  gskSetScaledOutputColor(final_color, alpha);
 }

gsk/ngl/resources/linear_gradient.glsl

@@ -97,7 +97,7 @@ void main() {
       vec4 curr_color = gsk_premultiply(get_color(i));
       vec4 next_color = gsk_premultiply(get_color(i + 1));
       vec4 color = mix(curr_color, next_color, f);
-      gskSetOutputColor(color * u_alpha);
+      gskSetScaledOutputColor(color, u_alpha);
       return;
     }
   }

gsk/ngl/resources/outset_shadow.glsl

@@ -30,7 +30,5 @@ void main() {
 
   alpha *= (1.0 -  clamp(gsk_rounded_rect_coverage(gsk_decode_rect(transformed_outline), frag), 0.0, 1.0));
 
-  vec4 color = final_color * alpha;
+  gskSetScaledOutputColor(final_color, alpha);
-
-  gskSetOutputColor(color);
 }

gsk/ngl/resources/preamble.fs.glsl

@@ -123,11 +123,35 @@ void gskSetOutputColor(vec4 color) {
 #if defined(NO_CLIP)
   result = color;
 #elif defined(RECT_CLIP)
-  result = color * gsk_rect_coverage(gsk_get_bounds(u_clip_rect),
+  float coverage = gsk_rect_coverage(gsk_get_bounds(u_clip_rect),
                                      gsk_get_frag_coord());
+  result = color * coverage;
 #else
-  result = color * gsk_rounded_rect_coverage(gsk_create_rect(u_clip_rect),
+  float coverage = gsk_rounded_rect_coverage(gsk_create_rect(u_clip_rect),
                                              gsk_get_frag_coord());
+  result = color * coverage;
+#endif
+
+#if defined(GSK_GLES) || defined(GSK_LEGACY)
+  gl_FragColor = result;
+#else
+  outputColor = result;
+#endif
+}
+
+void gskSetScaledOutputColor(vec4 color, float alpha) {
+  vec4 result;
+
+#if defined(NO_CLIP)
+  result = color * alpha;
+#elif defined(RECT_CLIP)
+  float coverage = gsk_rect_coverage(gsk_get_bounds(u_clip_rect),
+                                     gsk_get_frag_coord());
+  result = color * (alpha * coverage);
+#else
+  float coverage = gsk_rounded_rect_coverage(gsk_create_rect(u_clip_rect),
+                                             gsk_get_frag_coord());
+  result = color * (alpha * coverage);
 #endif
 
 #if defined(GSK_GLES) || defined(GSK_LEGACY)

gsk/ngl/resources/radial_gradient.glsl

@@ -77,7 +77,7 @@ void main() {
       vec4 curr_color = gsk_premultiply(get_color(i));
       vec4 next_color = gsk_premultiply(get_color(i + 1));
       vec4 color = mix(curr_color, next_color, f);
-      gskSetOutputColor(color * u_alpha);
+      gskSetScaledOutputColor(color, u_alpha);
       return;
     }
   }

gsk/ngl/resources/repeat.glsl

@@ -40,5 +40,5 @@ void main() {
 
   vec4 diffuse = GskTexture(u_source, tp);
 
-  gskSetOutputColor(diffuse * u_alpha);
+  gskSetScaledOutputColor(diffuse, u_alpha);
 }

gsk/ngl/resources/unblurred_outset_shadow.glsl

@@ -39,6 +39,6 @@ void main() {
                       gsk_rounded_rect_coverage(gsk_decode_rect(transformed_inside_outline), frag),
                       0.0, 1.0);
 
-  gskSetOutputColor(final_color * alpha);
+  gskSetScaledOutputColor(final_color, alpha);
 }