add color burn, fragment early discard

data/layout.xml

@@ -343,7 +343,7 @@
               </node>
             </node>
             <node height="30" width="100%" pad="1" dir="row" margin="0 0 5 0">
-              <combobox id="pattern-blend-mode" width="100%" height="28" combo-list="Normal,-,Multiply,Subtract,Darken,Overlay,Color Dodge,Linear Burn,Hard Mix,-,Linear Height,Height"/>
+              <combobox id="pattern-blend-mode" width="100%" height="28" combo-list="Normal,-,Multiply,Subtract,Darken,Overlay,Color Dodge,Color Burn,Linear Burn,Hard Mix,-,Linear Height,Height"/>
             </node>
             <!--
             <node height="30" width="100%" pad="1" dir="row" margin="0 0 5 0">
@@ -433,7 +433,7 @@
               </node>
             </node>
             <node height="30" width="100%" pad="1" dir="row" margin="0 0 5 0">
-              <combobox id="dual-blend-mode" width="100%" height="28" combo-list="Normal,-,Multiply,Subtract,Darken,Overlay,Color Dodge,Linear Burn,Hard Mix,-,Linear Height,Height"/>
+              <combobox id="dual-blend-mode" width="100%" height="28" combo-list="Normal,-,Multiply,Subtract,Darken,Overlay,Color Dodge,Color Burn,Linear Burn,Hard Mix,-,Linear Height,Height"/>
             </node>
             <node align="center" dir="row">
               <checkbox id="dual-randflip" height="20" width="20"/>

data/shaders/comp-draw.glsl

@@ -52,6 +52,11 @@ void main()
 {
     mediump vec4 base = texture(tex, uv);
     mediump vec4 stroke = texture(tex_stroke, uv);
+    if (stroke.a == 0)
+    {
+        frag = base;
+        return;
+    }
 
     if (use_pattern)
     {

data/shaders/include/blend-stroke.glsl

@@ -1,19 +1,19 @@
 mediump float blend_stroke_screen(mediump float base, mediump float stroke)
 {
-    return clamp(base + stroke - (base * stroke), 0.0, 1.0);
+    return base + stroke - (base * stroke);
 }
 
 mediump float blend_stroke_hard_light(mediump float base, mediump float stroke)
 {
     if (stroke < 0.5)
-        return max(1.0, base * (stroke * 2.0)); // multiply
+        return base * (stroke * 2.0); // multiply
     else
         return blend_stroke_screen(base, 2.0 * stroke - 1.0);
 }
 
 mediump float blend_stroke_hard_mix(mediump float base, mediump float stroke)
 {
-    return base + stroke > 0.5 ? 1.0 : 0.0;
+    return base + stroke < 0.5 ? 0.0 : base + stroke;
 }
 
 mediump float blend_stroke_color_dodge(mediump float base, mediump float stroke)
@@ -23,20 +23,30 @@ mediump float blend_stroke_color_dodge(mediump float base, mediump float stroke)
     else if (stroke == 1.0)
         return 1.0;
     else
-        return min(1.0, base / (1.0 - stroke));
+        return base / (1.0 - stroke);
+}
+
+mediump float blend_stroke_color_burn(mediump float base, mediump float stroke)
+{
+    if (base == 0.0)
+        return 0.0;
+    else if (stroke == 1.0)
+        return 1.0;
+    else
+        return 1.0 - (1.0 - base) / stroke;
 }
 
 mediump float blend_stroke_linear_height(mediump float base, mediump float stroke, mediump float depth)
 {
     mediump float partial = (1.0 - stroke) * pow(depth, 0.25) + (base * depth * 10.0);
-    return stroke * partial;
+    return base * partial;
 }
 
 mediump float blend_stroke_height(mediump float base, mediump float stroke, mediump float depth)
 {
     mediump float A = pow((1.0 - stroke), max(1.0, (1.0 - depth) * 10.0)) * pow(depth, 0.25);
     mediump float B = (base * depth * 5.0);
-    return stroke * (A + B);
+    return base * (A + B);
 }
 
 mediump float blend_stroke(mediump float base, mediump float stroke, mediump float depth, int mode)
@@ -46,10 +56,11 @@ mediump float blend_stroke(mediump float base, mediump float stroke, mediump flo
    else if (mode == 2) /* subtract    */ return mix(base, max(0.0, base - stroke), depth);
    else if (mode == 3) /* darken      */ return mix(base, min(base, stroke), depth);
    else if (mode == 4) /* overlay     */ return mix(base, blend_stroke_hard_light(stroke, base), depth);
-   else if (mode == 5) /* col-dodge   */ return mix(base, blend_stroke_color_dodge(stroke, base), depth);
+   else if (mode == 5) /* col-dodge   */ return mix(base, blend_stroke_color_dodge(base, stroke), depth);
-   else if (mode == 6) /* lin-burn    */ return mix(base, clamp(stroke + base - 1.0, 0.0, 1.0), depth);
+   else if (mode == 6) /* col-burn    */ return mix(base, blend_stroke_color_burn(base, stroke), depth);
-   else if (mode == 7) /* hard-mix    */ return mix(base, blend_stroke_hard_mix(base, stroke), depth);
+   else if (mode == 7) /* lin-burn    */ return mix(base, clamp(base + stroke - 1.0, 0.0, 1.0), depth);
-   else if (mode == 8) /* lin-height  */ return blend_stroke_linear_height(base, stroke, depth);
+   else if (mode == 8) /* hard-mix    */ return mix(base, blend_stroke_hard_mix(base, stroke), depth);
-   else if (mode == 9) /* height      */ return blend_stroke_height(base, stroke, depth);
+   else if (mode == 9) /* lin-height  */ return blend_stroke_linear_height(base, stroke, depth);
+   else if (mode ==10) /* height      */ return blend_stroke_height(base, stroke, depth);
    else return 1.0;
 }

data/shaders/stroke.glsl

@@ -59,6 +59,10 @@ void main()
     mediump float brush_alpha = ( 1.0 - texture(tex, uv/q).r ) * alpha;
     mediump vec4 fg = vec4(col.rgb, brush_alpha);
 
+    // early discard
+    if (fg.a == 0.0)
+        discard;
+
     if (use_pattern)
     {
         mediump vec2 rscale = resolution / vec2(512.0);
@@ -84,7 +88,7 @@ void main()
     fg.a *= 1.0-rand(uv2+uv)*noise;
 
     // no need to go further
-    if (fg.a == 0.0)
+    if (fg.a <= 0.0)
         discard;
 
     if (mix_alpha > 0.0)