Two changes:

1. GL_DST_ALPHA and GL_ONE_MINUS_DST_ALPHA were moved from GL3 to GL.
2. I reverted to the previous switch/case statements in
GLRenderer.convertBlendFunc(BlendFunc).

jme3-core/src/main/java/com/jme3/material/RenderState.java

@@ -205,7 +205,6 @@ public class RenderState implements Cloneable, Savable {
         Max
     }
     
-    
     /**
      * <code>BlendFunc</code> defines the blending functions for use with 
      * <code>BlendMode.Custom</code>.
@@ -216,67 +215,49 @@ public class RenderState implements Cloneable, Savable {
         /**
          * RGB Factor (0, 0, 0), Alpha Factor (0)
          */
-        Zero(0),
+        Zero,
         /**
          * RGB Factor (1, 1, 1), Alpha Factor (1)
          */
-        One(1),
+        One,
         /**
          * RGB Factor (R_s0, G_s0, B_s0), Alpha Factor (A_s0)
          */
-        Src_Color(2),
+        Src_Color,
         /**
          * RGB Factor (1-R_s0, 1-G_s0, 1-B_s0), Alpha Factor (1-A_s0)
          */
-        One_Minus_Src_Color(3),
+        One_Minus_Src_Color,
         /**
          * RGB Factor (R_d, G_d, B_d), Alpha Factor (A_d)
          */
-        Dst_Color(4),
+        Dst_Color,
         /**
          * RGB Factor (1-R_d, 1-G_d, 1-B_d), Alpha Factor (1-A_d)
          */
-        One_Minus_Dst_Color(5),
+        One_Minus_Dst_Color,
         /**
          * RGB Factor (A_s0, A_s0, A_s0), Alpha Factor (A_s0)
          */
-        Src_Alpha(6),
+        Src_Alpha,
         /**
          * RGB Factor (1-A_s0, 1-A_s0, 1-A_s0), Alpha Factor (1-A_s0)
          */
-        One_Minus_Src_Alpha(7),
+        One_Minus_Src_Alpha,
         /**
          * RGB Factor (A_d, A_d, A_d), Alpha Factor (A_d)
          */
-        Dst_Alpha(8),
+        Dst_Alpha,
         /**
          * RGB Factor (1-A_d, 1-A_d, 1-A_d), Alpha Factor (1-A_d)
          */
-        One_Minus_Dst_Alpha(9),
+        One_Minus_Dst_Alpha,
         /**
          * RGB Factor (i, i, i), Alpha Factor (1)
          */
-        Src_Alpha_Saturate(10);
-        
-        // Convenience value for easy use by the renderer.
-        private final int value;
-        
-        // Convenience constructor.
-        private BlendFunc(int value) {
-            this.value=value;
-        }
-        
-        /**
-         * Provides a predefined integer value for easy use by the renderer.
-         * 
-         * @return   The predefined integer value.
-         */
-        public int getIntValue() {
-            return value;
-        }
+        Src_Alpha_Saturate;
     }
     
-
     /**
      * <code>BlendMode</code> specifies the blending operation to use.
      *

jme3-core/src/main/java/com/jme3/renderer/opengl/GL.java

@@ -62,6 +62,7 @@ public interface GL {
     public static final int GL_DEPTH_COMPONENT16 = 0x81A5;
     public static final int GL_DEPTH_TEST = 0xB71;
     public static final int GL_DOUBLE = 0x140A;
+    public static final int GL_DST_ALPHA = 0x0304;
     public static final int GL_DST_COLOR = 0x306;
     public static final int GL_DYNAMIC_DRAW = 0x88E8;
     public static final int GL_ELEMENT_ARRAY_BUFFER = 0x8893;
@@ -118,6 +119,7 @@ public interface GL {
     public static final int GL_NONE = 0x0;
     public static final int GL_NOTEQUAL = 0x205;
     public static final int GL_ONE = 0x1;
+    public static final int GL_ONE_MINUS_DST_ALPHA = 0x0305;
     public static final int GL_ONE_MINUS_DST_COLOR = 0x307;
     public static final int GL_ONE_MINUS_SRC_ALPHA = 0x303;
     public static final int GL_ONE_MINUS_SRC_COLOR = 0x301;

jme3-core/src/main/java/com/jme3/renderer/opengl/GL3.java

@@ -41,9 +41,7 @@ import java.nio.IntBuffer;
 public interface GL3 extends GL2 {
 
     public static final int GL_DEPTH_STENCIL_ATTACHMENT = 0x821A;
-    public static final int GL_DST_ALPHA = 0x0304;
     public static final int GL_GEOMETRY_SHADER = 0x8DD9;
-    public static final int GL_ONE_MINUS_DST_ALPHA = 0x0305;
     public static final int GL_NUM_EXTENSIONS = 0x821D;
     public static final int GL_R8 = 0x8229;
     public static final int GL_R16F = 0x822D;

jme3-core/src/main/java/com/jme3/renderer/opengl/GLRenderer.java

@@ -751,10 +751,10 @@ public final class GLRenderer implements Renderer {
                         break;
                     case Custom:
                         gl.glBlendFuncSeparate(
-                            state.getCustomSfactorRGB().getIntValue(),
-                            state.getCustomDfactorRGB().getIntValue(),
-                            state.getCustomSfactorAlpha().getIntValue(),
-                            state.getCustomDfactorAlpha().getIntValue());
+                            convertBlendFunc(state.getCustomSfactorRGB()),
+                            convertBlendFunc(state.getCustomDfactorRGB()),
+                            convertBlendFunc(state.getCustomSfactorAlpha()),
+                            convertBlendFunc(state.getCustomDfactorAlpha()));
                         break;
                     default:
                         throw new UnsupportedOperationException("Unrecognized blend mode: "
@@ -857,6 +857,35 @@ public final class GLRenderer implements Renderer {
                 throw new UnsupportedOperationException("Unrecognized alpha blend operation: " + blendEquationAlpha);
         }
     }
+    
+    private int convertBlendFunc(BlendFunc blendFunc) {
+        switch (blendFunc) {
+            case Zero:
+                return GL.GL_ZERO;
+            case One:
+                return GL.GL_ONE;
+            case Src_Color:
+                return GL.GL_SRC_COLOR;
+            case One_Minus_Src_Color:
+                return GL.GL_ONE_MINUS_SRC_COLOR;
+            case Dst_Color:
+                return GL.GL_DST_COLOR;
+            case One_Minus_Dst_Color:
+                return GL.GL_ONE_MINUS_DST_COLOR;
+            case Src_Alpha:
+                return GL.GL_SRC_ALPHA;
+            case One_Minus_Src_Alpha:
+                return GL.GL_ONE_MINUS_SRC_ALPHA;
+            case Dst_Alpha:
+                return GL.GL_DST_ALPHA;
+            case One_Minus_Dst_Alpha:
+                return GL.GL_ONE_MINUS_DST_ALPHA;
+            case Src_Alpha_Saturate:        
+                return GL.GL_SRC_ALPHA_SATURATE;
+            default:
+                throw new UnsupportedOperationException("Unrecognized blend function operation: " + blendFunc);
+         }
+    }
 
     private int convertStencilOperation(StencilOperation stencilOp) {
         switch (stencilOp) {