From 7ff9478061e369d31228c2f98f8ec91f02de49d5 Mon Sep 17 00:00:00 2001
From: Krozark <maxime.barbier1991@gmail.com>
Date: Thu, 13 Aug 2015 14:40:20 +0200
Subject: [PATCH] add a new BlendMode::Equation : ReverseSubtract

---
 include/SFML/Graphics/BlendMode.hpp | 5 +++--
 src/SFML/Graphics/GLExtensions.hpp  | 2 ++
 src/SFML/Graphics/RenderTarget.cpp  | 1 +
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/SFML/Graphics/BlendMode.hpp b/include/SFML/Graphics/BlendMode.hpp
index 7f5803be..08f049dd 100644
--- a/include/SFML/Graphics/BlendMode.hpp
+++ b/include/SFML/Graphics/BlendMode.hpp
@@ -68,8 +68,9 @@ struct SFML_GRAPHICS_API BlendMode
     ////////////////////////////////////////////////////////
     enum Equation
     {
-        Add,     ///< Pixel = Src * SrcFactor + Dst * DstFactor
-        Subtract ///< Pixel = Src * SrcFactor - Dst * DstFactor
+        Add,            ///< Pixel = Src * SrcFactor + Dst * DstFactor
+        Subtract,       ///< Pixel = Src * SrcFactor - Dst * DstFactor
+        ReverseSubtract ///< Pixel = Dst * DstFactor - Src * SrcFactor
     };
 
     ////////////////////////////////////////////////////////////
diff --git a/src/SFML/Graphics/GLExtensions.hpp b/src/SFML/Graphics/GLExtensions.hpp
index 7f76de9e..bcc5d7e6 100644
--- a/src/SFML/Graphics/GLExtensions.hpp
+++ b/src/SFML/Graphics/GLExtensions.hpp
@@ -64,6 +64,7 @@
     #define GLEXT_glBlendEquation                     glBlendEquationOES
     #define GLEXT_GL_FUNC_ADD                         GL_FUNC_ADD_OES
     #define GLEXT_GL_FUNC_SUBTRACT                    GL_FUNC_SUBTRACT_OES
+    #define GLEXT_GL_FUNC_REVERSE_SUBTRACT            GL_FUNC_REVERSE_SUBTRACT_OES
 
     // The following extensions are optional.
 
@@ -142,6 +143,7 @@
     // Core since 1.2 - EXT_blend_subtract
     #define GLEXT_blend_subtract                      sfogl_ext_EXT_blend_subtract
     #define GLEXT_GL_FUNC_SUBTRACT                    GL_FUNC_SUBTRACT_EXT
+    #define GLEXT_GL_FUNC_REVERSE_SUBTRACT            GL_FUNC_REVERSE_SUBTRACT_EXT
 
     // Core since 1.3 - ARB_multitexture
     #define GLEXT_multitexture                        sfogl_ext_ARB_multitexture
diff --git a/src/SFML/Graphics/RenderTarget.cpp b/src/SFML/Graphics/RenderTarget.cpp
index 28b35e45..ded377c1 100644
--- a/src/SFML/Graphics/RenderTarget.cpp
+++ b/src/SFML/Graphics/RenderTarget.cpp
@@ -67,6 +67,7 @@ namespace
         {
             case sf::BlendMode::Add:             return GLEXT_GL_FUNC_ADD;
             case sf::BlendMode::Subtract:        return GLEXT_GL_FUNC_SUBTRACT;
+            case sf::BlendMode::ReverseSubtract: return GLEXT_GL_FUNC_REVERSE_SUBTRACT;
         }
 
         sf::err() << "Invalid value for sf::BlendMode::Equation! Fallback to sf::BlendMode::Add." << std::endl;