From 4eeab6a30510d806b366609792a143de3ee9dd7e Mon Sep 17 00:00:00 2001
From: Ben Morris <ben@bendmorris.com>
Date: Wed, 18 Feb 2015 09:29:25 -0800
Subject: [PATCH] Adding TILE_BLEND_SUBTRACT flag for subtract blend mode using
 drawTiles.

---
 legacy/project/include/Graphics.h               | 1 +
 legacy/project/src/common/ExternalInterface.cpp | 4 ++++
 legacy/project/src/common/GraphicsData.cpp      | 3 +++
 legacy/project/src/common/Hardware.cpp          | 2 ++
 legacy/project/src/opengl/OpenGLContext.cpp     | 8 ++++++++
 5 files changed, 18 insertions(+)

diff --git a/legacy/project/include/Graphics.h b/legacy/project/include/Graphics.h
index b0e7571c3..4020d6a9a 100644
--- a/legacy/project/include/Graphics.h
+++ b/legacy/project/include/Graphics.h
@@ -263,6 +263,7 @@ enum PathCommand
    pcBlendModeAdd   = 0x20,
    pcBlendModeMultiply   = 0x21,
    pcBlendModeScreen   = 0x22,
+   pcBlendModeSubtract   = 0x23,
 };
 
 enum WindingRule { wrOddEven, wrNonZero };
diff --git a/legacy/project/src/common/ExternalInterface.cpp b/legacy/project/src/common/ExternalInterface.cpp
index 6acc72ab2..79f445ba5 100644
--- a/legacy/project/src/common/ExternalInterface.cpp
+++ b/legacy/project/src/common/ExternalInterface.cpp
@@ -2792,6 +2792,7 @@ value nme_gfx_draw_tiles(value inGfx,value inSheet, value inXYIDs,value inFlags,
         TILE_BLEND_ADD   = 0x10000,
         TILE_BLEND_MULTIPLY   = 0x20000,
         TILE_BLEND_SCREEN   = 0x40000,
+        TILE_BLEND_SUBTRACT   = 0x80000,
         TILE_BLEND_MASK  = 0xf0000,
       };
 
@@ -2808,6 +2809,9 @@ value nme_gfx_draw_tiles(value inGfx,value inSheet, value inXYIDs,value inFlags,
          case TILE_BLEND_SCREEN:
             blend = bmScreen;
             break;
+         case TILE_BLEND_SUBTRACT:
+            blend = bmSubtract;
+            break;
       }
 
       bool smooth = flags & TILE_SMOOTH;
diff --git a/legacy/project/src/common/GraphicsData.cpp b/legacy/project/src/common/GraphicsData.cpp
index 3352b3882..bb4d088bd 100644
--- a/legacy/project/src/common/GraphicsData.cpp
+++ b/legacy/project/src/common/GraphicsData.cpp
@@ -51,6 +51,9 @@ void GraphicsPath::elementBlendMode(int inMode)
       case bmScreen:
          commands.push_back(pcBlendModeScreen);
          break;
+      case bmSubtract:
+         commands.push_back(pcBlendModeSubtract);
+         break;
    }
 }
 
diff --git a/legacy/project/src/common/Hardware.cpp b/legacy/project/src/common/Hardware.cpp
index 85d01f74f..f075bd68d 100644
--- a/legacy/project/src/common/Hardware.cpp
+++ b/legacy/project/src/common/Hardware.cpp
@@ -216,6 +216,8 @@ public:
                mElement.mBlendMode = bmMultiply;
             else if (cmd[i] == pcBlendModeScreen)
                mElement.mBlendMode = bmScreen;
+            else if (cmd[i] == pcBlendModeSubtract)
+               mElement.mBlendMode = bmSubtract;
          }
 
          if (has_colour)
diff --git a/legacy/project/src/opengl/OpenGLContext.cpp b/legacy/project/src/opengl/OpenGLContext.cpp
index b01274a62..65d15d92b 100644
--- a/legacy/project/src/opengl/OpenGLContext.cpp
+++ b/legacy/project/src/opengl/OpenGLContext.cpp
@@ -481,15 +481,23 @@ public:
          {
             case bmAdd:
                glBlendFunc( GL_SRC_ALPHA, GL_ONE );
+               glBlendEquation( GL_FUNC_ADD);
                break;
             case bmMultiply:
                glBlendFunc( GL_DST_COLOR, GL_ONE_MINUS_SRC_ALPHA);
+               glBlendEquation( GL_FUNC_ADD);
                break;
             case bmScreen:
                glBlendFunc( GL_ONE, GL_ONE_MINUS_SRC_COLOR);
+               glBlendEquation( GL_FUNC_ADD);
+               break;
+            case bmSubtract:
+               glBlendFunc( GL_SRC_ALPHA, GL_ONE);
+               glBlendEquation( GL_FUNC_REVERSE_SUBTRACT);
                break;
             default:
                glBlendFunc(premAlpha ? GL_ONE : GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
+               glBlendEquation( GL_FUNC_ADD);
          }