From fa5ab64c94d2c381c4cdef909637a0e7fd6eb786 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Fri, 28 Oct 2005 13:18:09 +0000
Subject: [PATCH] From Ravi Mathur, "Here is an update to BlendEquation that
 adds checking for the SGIX_blend_alpha_minmax and EXT_blend_logic_op
 extensions.  It is tested with the osgblendequation example.  If the
 extensions are not supported, a WARN level notification is generated."

---
 include/osg/BlendEquation |  4 ++++
 src/osg/BlendEquation.cpp | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/osg/BlendEquation b/include/osg/BlendEquation
index 136e2a59d..0625d89fd 100644
--- a/include/osg/BlendEquation
+++ b/include/osg/BlendEquation
@@ -107,6 +107,8 @@ class OSG_EXPORT BlendEquation : public StateAttribute
 
                 void setBlendEquationSupported(bool flag) { _isBlendEquationSupported=flag; }
                 bool isBlendEquationSupported() const { return _isBlendEquationSupported; }
+                bool isSGIXMinMaxSupported() const { return _isSGIXMinMaxSupported; }
+                bool isLogicOpSupported() const { return _isLogicOpSupported; }
                 
                 void setBlendEquationProc(void* ptr) { _glBlendEquation = ptr; }
                 void glBlendEquation(GLenum mode) const;
@@ -116,6 +118,8 @@ class OSG_EXPORT BlendEquation : public StateAttribute
                 ~Extensions() {}
                 
                 bool    _isBlendEquationSupported;
+                bool    _isSGIXMinMaxSupported;
+                bool    _isLogicOpSupported;
 
                 void*   _glBlendEquation;
 
diff --git a/src/osg/BlendEquation.cpp b/src/osg/BlendEquation.cpp
index 2ad2ab072..7e7cc052f 100644
--- a/src/osg/BlendEquation.cpp
+++ b/src/osg/BlendEquation.cpp
@@ -48,6 +48,21 @@ void BlendEquation::apply(State& state) const
         return;
     }
 
+    GLenum eqn = static_cast<GLenum>(_equation);
+
+    if((eqn == ALPHA_MIN || eqn == ALPHA_MAX) && 
+       !extensions->isSGIXMinMaxSupported())
+    {
+    notify(WARN)<<"Warning: BlendEquation::apply(..) failed, SGIX_blend_alpha_minmax extension is not supported by OpenGL driver." << std::endl;
+    return;
+    }
+
+    if(eqn == LOGIC_OP && !extensions->isLogicOpSupported())
+    {
+    notify(WARN)<<"Warning: BlendEquation::apply(..) failed, EXT_blend_logic_op extension is not supported by OpenGL driver." << std::endl;
+    return;
+    }
+    
     extensions->glBlendEquation(static_cast<GLenum>(_equation));
     
 }
@@ -77,6 +92,9 @@ BlendEquation::Extensions::Extensions(const Extensions& rhs):
     Referenced()
 {
     _isBlendEquationSupported = rhs._isBlendEquationSupported;
+    _isSGIXMinMaxSupported = rhs._isSGIXMinMaxSupported;
+    _isLogicOpSupported = rhs._isLogicOpSupported;
+    _glBlendEquation = rhs._glBlendEquation;
 }
 
 void BlendEquation::Extensions::lowestCommonDenominator(const Extensions& rhs)
@@ -89,6 +107,9 @@ void BlendEquation::Extensions::setupGLExtenions(unsigned int contextID)
 {
     _isBlendEquationSupported = isGLExtensionSupported(contextID,"GL_EXT_blend_equation") ||
                              strncmp((const char*)glGetString(GL_VERSION),"1.2",3)>=0;
+    
+    _isSGIXMinMaxSupported = isGLExtensionSupported(contextID, "SGIX_blend_alpha_minmax");
+    _isLogicOpSupported = isGLExtensionSupported(contextID, "EXT_blend_logic_op");
 
     _glBlendEquation = getGLExtensionFuncPtr("glBlendEquation", "glBlendEquationEXT");
 }