From 61507b525f1687abcbe5a35ae2c4809c4f24f3f6 Mon Sep 17 00:00:00 2001
From: Edwin Jakobs <edwin@rndr.studio>
Date: Sun, 9 Feb 2020 16:10:59 +0100
Subject: [PATCH] Fix opacity handling for blend filters in orx-fx

---
 .../org/openrndr/extra/fx/gl3/blend/add.frag  | 21 ++------------
 .../extra/fx/gl3/blend/color-burn.frag        | 29 +++++--------------
 .../extra/fx/gl3/blend/color-dodge.frag       | 23 ++++-----------
 .../openrndr/extra/fx/gl3/blend/darken.frag   | 23 ++++-----------
 .../extra/fx/gl3/blend/destination-in.frag    |  4 +--
 .../extra/fx/gl3/blend/destination-out.frag   |  4 +--
 .../extra/fx/gl3/blend/hard-light.frag        | 23 ++++-----------
 .../openrndr/extra/fx/gl3/blend/lighten.frag  | 23 ++++-----------
 .../openrndr/extra/fx/gl3/blend/multiply.frag | 21 ++------------
 .../openrndr/extra/fx/gl3/blend/normal.frag   |  2 +-
 .../openrndr/extra/fx/gl3/blend/overlay.frag  | 23 +++++++++++----
 .../openrndr/extra/fx/gl3/blend/screen.frag   | 22 ++++----------
 .../extra/fx/gl3/blend/source-in.frag         |  4 +--
 .../extra/fx/gl3/blend/source-out.frag        |  4 +--
 .../openrndr/extra/fx/gl3/blend/subtract.frag | 21 ++------------
 .../org/openrndr/extra/fx/gl3/blend/xor.frag  |  6 ++--
 16 files changed, 74 insertions(+), 179 deletions(-)

diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/add.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/add.frag
index fbafb892..e7b50217 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/add.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/add.frag
@@ -8,22 +8,7 @@ out vec4 o_color;
 void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
-
-    vec3 na = a.a == 0.0 ? a.rgb: a.rgb / a.a;
-    vec3 nb = b.a == 0.0 ? b.rgb: b.rgb / b.a;
-
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
-
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(vec3(0.0), nb.rgb, b.a);
-
-    vec4 m = vec4(ka+kb, 1.0) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
-
+    vec3 na = a.a > 0 ? a.rgb/a.a : vec3(0.0);
+    vec3 addColor = b.rgb; //mix(vec3(0.0), nb, b.a);
+    o_color = vec4((na + addColor), 1) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-burn.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-burn.frag
index e6835d00..506b18ae 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-burn.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-burn.frag
@@ -5,35 +5,22 @@ uniform sampler2D tex0;
 uniform sampler2D tex1;
 
 float blendColorBurn(float base, float blend) {
-	return (blend==0.0)?blend:max((1.0-((1.0-base)/blend)),0.0);
+	return (blend==0.0) ? blend : max((1.0 - ((1.0 - base) / blend)), 0.0);
 }
 
-
 out vec4 o_color;
 void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
 
     vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
-    vec3 nb = b.a == 0.0 ? b.rgb: b.rgb / b.a;
+    vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
 
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
+    vec3 m = vec3(
+        blendColorBurn(na.r, nb.r),
+        blendColorBurn(na.g, nb.g),
+        blendColorBurn(na.b, nb.b)
+        );
 
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(vec3(1.0), nb.rgb, b.a);
-
-    vec4 m = vec4(
-        blendColorBurn(ka.r, kb.r),
-        blendColorBurn(ka.g, kb.g),
-        blendColorBurn(ka.b, kb.b),
-
-        1.0
-        ) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
+    o_color = vec4(na * (1.0 - b.a) + b.a * m, 1.0) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-dodge.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-dodge.frag
index 492ec947..17c9edf0 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-dodge.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/color-dodge.frag
@@ -16,22 +16,11 @@ void main() {
     vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
     vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
 
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
+    vec3 m = vec3(
+        dodge(na.r, nb.r),
+        dodge(na.g, nb.g),
+        dodge(na.b, nb.b)
+        );
 
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(vec3(0.0), nb.rgb, b.a);
-
-    vec4 m = vec4(
-        dodge(ka.r, kb.r),
-        dodge(ka.g, kb.g),
-        dodge(ka.b, kb.b),
-        1.0
-        ) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
+    o_color = vec4(na * (1.0 - b.a) + b.a * m, 1.0) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/darken.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/darken.frag
index d9d70cc1..39e0d942 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/darken.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/darken.frag
@@ -12,23 +12,10 @@ void main() {
     vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
     vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
 
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
+    vec3 m = vec3(
+        nb.r <= na.r? nb.r : na.r,
+        nb.g <= na.g? nb.g : na.g,
+        nb.b <= na.b? nb.b : na.b);
 
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(na.rgb, nb.rgb, b.a);
-
-
-    vec4 m = vec4(
-        kb.r <= ka.r? kb.r : ka.r,
-        kb.g <= ka.g? kb.g : ka.g,
-        kb.b <= ka.b? kb.b : ka.b,
-        1.0
-        ) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
+    o_color = vec4(na * (1.0 - b.a) + b.a * m, 1.0) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-in.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-in.frag
index 77f80163..17783e68 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-in.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-in.frag
@@ -10,6 +10,6 @@ void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
 
-    o_color.rgb = a.rgb;
-    o_color.a = b.a;
+    vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
+    o_color = vec4(na, 1.0) * b.a * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-out.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-out.frag
index 0284d9d7..7060fac8 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-out.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/destination-out.frag
@@ -9,6 +9,6 @@ void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
 
-    o_color.rgb = a.rgb;
-    o_color.a = max(a.a - b.a, 0.0);
+    vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
+    o_color = vec4(na, 1.0) * max(a.a - b.a, 0.0);
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/hard-light.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/hard-light.frag
index 247bafe9..ad05e06d 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/hard-light.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/hard-light.frag
@@ -12,22 +12,11 @@ void main() {
     vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
     vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
 
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
+    vec3 m = vec3(
+        nb.r <= 0.5? 2*na.r * nb.r : 1.0 - 2.0*(1.0 - na.r)*(1.0 - nb.r),
+        nb.g <= 0.5? 2*na.g * nb.g : 1.0 - 2.0*(1.0 - na.g)*(1.0 - nb.g),
+        nb.b <= 0.5? 2*na.b * nb.b : 1.0 - 2.0*(1.0 - na.b)*(1.0 - nb.b)
+        );
+    o_color = vec4(na * (1.0 - b.a) + b.a * m, 1.0) * a.a;
 
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(vec3(0.5), nb.rgb, b.a);
-
-    vec4 m = vec4(
-        kb.r <= 0.5? 2*ka.r * kb.r : 1.0 - 2.0*(1.0 - ka.r)*(1.0 - kb.r),
-        kb.g <= 0.5? 2*ka.g * kb.g : 1.0 - 2.0*(1.0 - ka.g)*(1.0 - kb.g),
-        kb.b <= 0.5? 2*ka.b * kb.b : 1.0 - 2.0*(1.0 - ka.b)*(1.0 - kb.b),
-        1.0
-        ) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/lighten.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/lighten.frag
index b1cad6cb..e5f91610 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/lighten.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/lighten.frag
@@ -12,23 +12,10 @@ void main() {
     vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
     vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
 
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
+    vec3 m = vec3(
+        nb.r >= na.r? nb.r : na.r,
+        nb.g >= na.g? nb.g : na.g,
+        nb.b >= na.b? nb.b : na.b);
 
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(na.rgb, nb.rgb, b.a);
-
-    vec4 m = vec4(
-        kb.r >= ka.r? kb.r : ka.r,
-        kb.g >= ka.g? kb.g : ka.g,
-        kb.b >= ka.b? kb.b : ka.b,
-        1.0
-        ) * maxAlpha;
-
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
+    o_color = vec4(na * (1.0 - b.a) + b.a * m, 1.0) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/multiply.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/multiply.frag
index 39f61573..d4c3e43e 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/multiply.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/multiply.frag
@@ -8,23 +8,8 @@ out vec4 o_color;
 void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
-
-    vec3 na = a.a == 0.0 ? a.rgb: a.rgb / a.a;
-    vec3 nb = b.a == 0.0 ? b.rgb: b.rgb / b.a;
-
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
-
-    vec3 ka = mix(vec3(1.0), na.rgb, a.a);
-    vec3 kb = mix(vec3(1.0), nb.rgb, b.a);
-
-    vec4 m = vec4(ka*kb, 1.0) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-
-    o_color = l;
-    o_color.a = maxAlpha;
+    vec3 nb = b.a > 0 ? b.rgb/b.a : vec3(0.0);
+    vec3 mulColor = mix(vec3(1.0), nb, b.a);
+    o_color = vec4(a.rgb * mulColor, a.a);
 }
 
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/normal.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/normal.frag
index 29e075b9..5a7403a4 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/normal.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/normal.frag
@@ -11,5 +11,5 @@ void main() {
     float alpha = min(1,max(0, b.a));
 
     o_color = a * (1.0-alpha) + b;
-    o_color.a = 1.0;
+    o_color.a = clamp(o_color.a, 0.0, 1.0);
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/overlay.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/overlay.frag
index c7cb3e65..9690ce2d 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/overlay.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/overlay.frag
@@ -6,18 +6,29 @@ uniform sampler2D tex0;
 uniform sampler2D tex1;
 
 out vec4 o_color;
+
+vec3 demul(vec4 c) {
+    if (c.a == 0) {
+        return vec3(0.0);
+    } else {
+        return c.rgb / c.a;
+    }
+}
+
 void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
 
+    vec3 na = demul(a);
+    vec3 nb = demul(b);
+
     vec4 c = vec4(
-        a.r <= 0.5? 2.0*a.r * b.r : 1.0 - 2.0*(1.0-a.r)*(1.0-b.r),
-        a.g <= 0.5? 2.0*a.g * b.g : 1.0 - 2.0*(1.0-a.g)*(1.0-b.g),
-        a.b <= 0.5? 2.0*a.b * b.b : 1.0 - 2.0*(1.0-a.b)*(1.0-b.b),
+        na.r <= 0.5? 2.0 * na.r * nb.r : (1.0 - 2.0 * (1.0 - na.r) * (1.0 - nb.r)),
+        na.g <= 0.5? 2.0 * na.g * nb.g : (1.0 - 2.0 * (1.0 - na.g) * (1.0 - nb.g)),
+        na.b <= 0.5? 2.0 * na.b * nb.b : (1.0 - 2.0 * (1.0 - na.b) * (1.0 - nb.b)),
         1.0
         );
 
-    vec4 d = a *  (1.0 - b.a) + c * b.a;
-    o_color = max(vec4(0), min(vec4(1), d));
-    o_color.a = 1.0;
+    vec3 fc = na * (1.0 - b.a) + c.rgb * b.a;
+    o_color = vec4(fc, 1.0) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/screen.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/screen.frag
index 1d3e7976..ecb3c187 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/screen.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/screen.frag
@@ -12,22 +12,10 @@ void main() {
     vec3 na = a.a == 0.0 ? vec3(0.0): a.rgb / a.a;
     vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
 
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
+    vec3 m = vec3(
+        1.0-((1.0-na.r)*(1.0-nb.r)),
+        1.0-((1.0-na.g)*(1.0-nb.g)),
+        1.0-((1.0-na.b)*(1.0-nb.b)));
 
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(na.rgb, nb.rgb, b.a);
-
-    vec4 m = vec4(
-        1.0-((1.0-ka.r)*(1.0-kb.r)),
-        1.0-((1.0-ka.g)*(1.0-kb.g)),
-        1.0-((1.0-ka.b)*(1.0-kb.b)),
-        1.0
-    ) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
+    o_color = vec4(na * (1.0 - b.a) + b.a * m, 1.0) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-in.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-in.frag
index a9e92c5f..112b13bb 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-in.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-in.frag
@@ -9,6 +9,6 @@ void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
 
-    o_color.rgb = b.rgb;
-    o_color.a = a.a;
+    vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
+    o_color = vec4(nb, 1.0) * a.a * b.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-out.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-out.frag
index 96a8a077..86c9e2f1 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-out.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/source-out.frag
@@ -9,6 +9,6 @@ void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
 
-    o_color.rgb = b.rgb;
-    o_color.a = max(b.a - a.a, 0.0);
+    vec3 nb = b.a == 0.0 ? vec3(0.0): b.rgb / b.a;
+    o_color = vec4(nb, 1.0) * max(b.a - a.a, 0.0);
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/subtract.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/subtract.frag
index e9a9ef06..f19a5c69 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/subtract.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/subtract.frag
@@ -8,22 +8,7 @@ out vec4 o_color;
 void main() {
     vec4 a = texture(tex0, v_texCoord0);
     vec4 b = texture(tex1, v_texCoord0);
-
-    vec3 na = a.a == 0.0 ? a.rgb: a.rgb / a.a;
-    vec3 nb = b.a == 0.0 ? b.rgb: b.rgb / b.a;
-
-    float minAlpha = min(a.a, b.a);
-    float maxAlpha = max(a.a, b.a);
-
-    vec3 ka = mix(vec3(0.0), na.rgb, a.a);
-    vec3 kb = mix(vec3(0.0), nb.rgb, b.a);
-
-    vec4 m = vec4(na-kb, 1.0) * maxAlpha;
-
-    vec4 l = a;
-    l = l * (1.0 - b.a) + b;
-    l = l * (1.0 - m.a) + m;
-    o_color = l;
-    o_color.a = maxAlpha;
-
+    vec3 na = a.a > 0 ? a.rgb/a.a : vec3(0.0);
+    vec3 subColor = b.rgb;
+    o_color = vec4(max(na - subColor, vec3(0.0)), 1) * a.a;
 }
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/xor.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/xor.frag
index 7419da5d..c0ead762 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/xor.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/blend/xor.frag
@@ -10,12 +10,14 @@ void main() {
     vec4 b = texture(tex1, v_texCoord0);
     vec4 color = vec4(0.0);
 
+    vec3 na = a.a == 0.0 ? vec3(0.0) : a.rgb/a.a;
+    vec3 nb = b.a == 0.0 ? vec3(0.0) : b.rgb/b.a;
     if (a.a > b.a) {
-        color = a;
+        color = vec4(na, 1.0) * (b.a == 0.0? a.a : (1.0-b.a));
     }
 
     if (b.a > a.a) {
-        color = b;
+        color = vec4(nb, 1.0) * (a.a == 0.0? b.a : (1.0-a.a));
     }
 
     o_color = color;