From eb72df73408cd0fed31b0251ccaf9cbf65147bd7 Mon Sep 17 00:00:00 2001
From: codeanticode <andres.colubri@gmail.com>
Date: Thu, 3 Oct 2013 18:23:04 -0400
Subject: [PATCH] correctly implements SUBTRACT blend mode

---
 core/src/processing/opengl/PGraphicsOpenGL.java | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/core/src/processing/opengl/PGraphicsOpenGL.java b/core/src/processing/opengl/PGraphicsOpenGL.java
index c71b4cf7c..6ad53ce7b 100644
--- a/core/src/processing/opengl/PGraphicsOpenGL.java
+++ b/core/src/processing/opengl/PGraphicsOpenGL.java
@@ -5690,9 +5690,11 @@ public class PGraphicsOpenGL extends PGraphics {
 
     } else if (blendMode == SUBTRACT) {
       if (blendEqSupported) {
-        pgl.blendEquation(PGL.FUNC_ADD);
+        pgl.blendEquation(PGL.FUNC_REVERSE_SUBTRACT);
+        pgl.blendFunc(PGL.ONE, PGL.SRC_ALPHA);
+      } else {
+        PGraphics.showWarning(BLEND_DRIVER_ERROR, "SUBTRACT");
       }
-      pgl.blendFunc(PGL.ONE_MINUS_DST_COLOR, PGL.ZERO);
 
     } else if (blendMode == LIGHTEST) {
       if (blendEqSupported) {
@@ -5712,11 +5714,9 @@ public class PGraphicsOpenGL extends PGraphics {
 
     } else if (blendMode == DIFFERENCE) {
       if (blendEqSupported) {
-        pgl.blendEquation(PGL.FUNC_REVERSE_SUBTRACT);
-        pgl.blendFunc(PGL.ONE, PGL.ONE);
-      } else {
-        PGraphics.showWarning(BLEND_DRIVER_ERROR, "DIFFERENCE");
+        pgl.blendEquation(PGL.FUNC_ADD);
       }
+      pgl.blendFunc(PGL.ONE_MINUS_DST_COLOR, PGL.ZERO);
 
     } else if (blendMode == EXCLUSION) {
       if (blendEqSupported) {