Add Min and Max blend modes

include/SFML/Graphics/BlendMode.hpp

@@ -70,7 +70,9 @@ struct SFML_GRAPHICS_API BlendMode
     {
         Add,             //!< Pixel = Src * SrcFactor + Dst * DstFactor
         Subtract,        //!< Pixel = Src * SrcFactor - Dst * DstFactor
-        ReverseSubtract //!< Pixel = Dst * DstFactor - Src * SrcFactor
+        ReverseSubtract, //!< Pixel = Dst * DstFactor - Src * SrcFactor
+        Min,             //!< Pixel = min(Dst, Src)
+        Max              //!< Pixel = max(Dst, Src)
     };
 
     ////////////////////////////////////////////////////////////
@@ -150,6 +152,8 @@ SFML_GRAPHICS_API bool operator !=(const BlendMode& left, const BlendMode& right
 SFML_GRAPHICS_API extern const BlendMode BlendAlpha;    //!< Blend source and dest according to dest alpha
 SFML_GRAPHICS_API extern const BlendMode BlendAdd;      //!< Add source to dest
 SFML_GRAPHICS_API extern const BlendMode BlendMultiply; //!< Multiply source and dest
+SFML_GRAPHICS_API extern const BlendMode BlendMin;      //!< Take minimum between source and dest
+SFML_GRAPHICS_API extern const BlendMode BlendMax;      //!< Take maximum between source and dest
 SFML_GRAPHICS_API extern const BlendMode BlendNone;     //!< Overwrite dest with source
 
 } // namespace sf

src/SFML/Graphics/BlendMode.cpp

@@ -37,8 +37,10 @@ const BlendMode BlendAlpha(BlendMode::SrcAlpha, BlendMode::OneMinusSrcAlpha, Ble
                            BlendMode::One, BlendMode::OneMinusSrcAlpha, BlendMode::Add);
 const BlendMode BlendAdd(BlendMode::SrcAlpha, BlendMode::One, BlendMode::Add,
                          BlendMode::One, BlendMode::One, BlendMode::Add);
-const BlendMode BlendMultiply(BlendMode::DstColor, BlendMode::Zero);
+const BlendMode BlendMultiply(BlendMode::DstColor, BlendMode::Zero, BlendMode::Add);
-const BlendMode BlendNone(BlendMode::One, BlendMode::Zero);
+const BlendMode BlendMin(BlendMode::One, BlendMode::One, BlendMode::Min);
+const BlendMode BlendMax(BlendMode::One, BlendMode::One, BlendMode::Max);
+const BlendMode BlendNone(BlendMode::One, BlendMode::Zero, BlendMode::Add);
 
 
 ////////////////////////////////////////////////////////////

src/SFML/Graphics/GLExtensions.hpp

@@ -45,7 +45,6 @@
     #define GLEXT_multitexture                        true
     #define GLEXT_texture_edge_clamp                  true
     #define GLEXT_EXT_texture_edge_clamp              true
-    #define GLEXT_blend_minmax                        true
     #define GLEXT_glClientActiveTexture               glClientActiveTexture
     #define GLEXT_glActiveTexture                     glActiveTexture
     #define GLEXT_GL_TEXTURE0                         GL_TEXTURE0
@@ -140,6 +139,11 @@
     #define GLEXT_texture_sRGB                        false
     #define GLEXT_GL_SRGB8_ALPHA8                     0
 
+    // Core since 3.0 - EXT_blend_minmax
+    #define GLEXT_blend_minmax                        SF_GLAD_GL_EXT_blend_minmax
+    #define GLEXT_GL_MIN                              GL_MIN_EXT
+    #define GLEXT_GL_MAX                              GL_MAX_EXT
+
 #else
 
     // SFML requires at a bare minimum OpenGL 1.1 capability
@@ -164,6 +168,8 @@
     #define GLEXT_blend_minmax                        SF_GLAD_GL_EXT_blend_minmax
     #define GLEXT_glBlendEquation                     glBlendEquationEXT
     #define GLEXT_GL_FUNC_ADD                         GL_FUNC_ADD_EXT
+    #define GLEXT_GL_MIN                              GL_MIN_EXT
+    #define GLEXT_GL_MAX                              GL_MAX_EXT
 
     // Core since 1.2 - EXT_blend_subtract
     #define GLEXT_blend_subtract                      SF_GLAD_GL_EXT_blend_subtract

src/SFML/Graphics/RenderTarget.cpp

@@ -110,13 +110,36 @@ namespace
     {
         switch (blendEquation)
         {
-            case sf::BlendMode::Add:             return GLEXT_GL_FUNC_ADD;
+            case sf::BlendMode::Add:
-            case sf::BlendMode::Subtract:        return GLEXT_GL_FUNC_SUBTRACT;
+                return GLEXT_GL_FUNC_ADD;
-            case sf::BlendMode::ReverseSubtract: return GLEXT_GL_FUNC_REVERSE_SUBTRACT;
+            case sf::BlendMode::Subtract:
+                if (GLEXT_blend_subtract)
+                    return GLEXT_GL_FUNC_SUBTRACT;
+                break;
+            case sf::BlendMode::ReverseSubtract:
+                if (GLEXT_blend_subtract)
+                    return GLEXT_GL_FUNC_REVERSE_SUBTRACT;
+                break;
+            case sf::BlendMode::Min:
+                if (GLEXT_blend_minmax)
+                    return GLEXT_GL_MIN;
+                break;
+            case sf::BlendMode::Max:
+                if (GLEXT_blend_minmax)
+                    return GLEXT_GL_MAX;
+                break;
+        }
+
+        static bool warned = false;
+        if (!warned)
+        {
+            sf::err() << "OpenGL extension EXT_blend_minmax or EXT_blend_subtract unavailable" << std::endl;
+            sf::err() << "Some blending equations will fallback to sf::BlendMode::Add" << std::endl;
+            sf::err() << "Ensure that hardware acceleration is enabled if available" << std::endl;
+
+            warned = true;
         }
 
-        sf::err() << "Invalid value for sf::BlendMode::Equation! Fallback to sf::BlendMode::Add." << std::endl;
-        assert(false);
         return GLEXT_GL_FUNC_ADD;
     }
 }
@@ -591,7 +614,7 @@ void RenderTarget::applyBlendMode(const BlendMode& mode)
             factorToGlConstant(mode.colorDstFactor)));
     }
 
-    if (GLEXT_blend_minmax && GLEXT_blend_subtract)
+    if (GLEXT_blend_minmax || GLEXT_blend_subtract)
     {
         if (GLEXT_blend_equation_separate)
         {
@@ -610,7 +633,11 @@ void RenderTarget::applyBlendMode(const BlendMode& mode)
 
         if (!warned)
         {
-            err() << "OpenGL extension EXT_blend_minmax and/or EXT_blend_subtract unavailable" << std::endl;
+#ifdef SFML_OPENGL_ES
+            err() << "OpenGL ES extension OES_blend_subtract unavailable" << std::endl;
+#else
+            err() << "OpenGL extension EXT_blend_minmax and EXT_blend_subtract unavailable" << std::endl;
+#endif
             err() << "Selecting a blend equation not possible" << std::endl;
             err() << "Ensure that hardware acceleration is enabled if available" << std::endl;