Use BlendFactor only when MaterialType != EMT_ONETEXTURE_BLEND

The way this was implemented BlendFactor and MaterialTypeParam could conflict otherwise as they both send the blend functions.

We could probably rewrite all places which use EMT_ONETEXTURE_BLEND+MaterialTypeParam to additionally check for BlendFactor, but it would still set the blend-functions twice. 
I'm not sure if BlendFactor works with 2D materials currently? (but we can't set those to shaders yet anyway except in the gles branch...).

I've also started documenting a few things about how I suppose it's working, I hope I got it all right.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6034 dfc29bdd-3216-0410-991c-e03cc46cb475

include/EMaterialTypes.h

@@ -187,7 +187,9 @@ namespace video
 		EMT_PARALLAX_MAP_TRANSPARENT_VERTEX_ALPHA,
 
 		//! BlendFunc = source * sourceFactor + dest * destFactor ( E_BLEND_FUNC )
-		/** Using only first texture. Generic blending method. */
+		/** Using only first texture. Generic blending method. 
+		The blend function is set to SMaterial::MaterialTypeParam with 
+		pack_textureBlendFunc (for 2D) or pack_textureBlendFuncSeparate (for 3D). */
 		EMT_ONETEXTURE_BLEND,
 
 		//! This value is not used. It only forces this enumeration to compile to 32 bit.

include/SMaterial.h

@@ -19,7 +19,8 @@ namespace video
 {
 	class ITexture;
 
-	//! Flag for EMT_ONETEXTURE_BLEND, ( BlendFactor ) BlendFunc = source * sourceFactor + dest * destFactor
+	//! Flag for MaterialTypeParam (in combination with EMT_ONETEXTURE_BLEND) or for BlendFactor
+	//! BlendFunc = source * sourceFactor + dest * destFactor
 	enum E_BLEND_FACTOR
 	{
 		EBF_ZERO	= 0,		//!< src & dest	(0, 0, 0, 0)
@@ -431,8 +432,8 @@ namespace video
 		f32 Shininess;
 
 		//! Free parameter, dependent on the material type.
-		/** Mostly ignored, used for example in EMT_PARALLAX_MAP_SOLID
+		/** Mostly ignored, used for example in EMT_PARALLAX_MAP_SOLID,
-		and EMT_TRANSPARENT_ALPHA_CHANNEL. */
+		EMT_TRANSPARENT_ALPHA_CHANNEL and EMT_ONETEXTURE_BLEND. */
 		f32 MaterialTypeParam;
 
 		//! Second free parameter, dependent on the material type.
@@ -474,8 +475,14 @@ namespace video
 
 		//! Store the blend factors
 		/** textureBlendFunc/textureBlendFuncSeparate functions should be used to write
-		properly blending factors to this parameter. If you use EMT_ONETEXTURE_BLEND
+		properly blending factors to this parameter. 
-		type for this material, this field should be equal to MaterialTypeParams. */
+		Due to historical reasons this parameter is not used for material type 
+		EMT_ONETEXTURE_BLEND which uses MaterialTypeParam instead for the blend factor.
+		It's generally used only for materials without any blending otherwise (like EMT_SOLID).
+		It's main use is to allow having shader materials which can enable/disable 
+		blending after they have been created. 
+		When you set this you usually also have to set BlendOperation to a value != EBO_NONE
+		(setting it to EBO_ADD is probably the most common one value). */
 		f32 BlendFactor;
 
 		//! DEPRECATED. Will be removed after Irrlicht 1.9. Please use PolygonOffsetDepthBias instead.

source/Irrlicht/CD3D9Driver.cpp

@@ -2219,7 +2219,9 @@ void CD3D9Driver::setBasicRenderStates(const SMaterial& material, const SMateria
 	}
 
     // Blend Factor
-	if (IR(material.BlendFactor) & 0xFFFFFFFF)
+	if (IR(material.BlendFactor) & 0xFFFFFFFF	// TODO: why the & 0xFFFFFFFF?
+		&& material.MaterialType != EMT_ONETEXTURE_BLEND
+		)
 	{
         E_BLEND_FACTOR srcRGBFact = EBF_ZERO;
         E_BLEND_FACTOR dstRGBFact = EBF_ZERO;

source/Irrlicht/CNullDriver.cpp

@@ -2759,7 +2759,9 @@ bool CNullDriver::needsTransparentRenderPass(const irr::video::SMaterial& materi
 	//      zwrite disabled and getWriteZBuffer calls this function.
 
 	video::IMaterialRenderer* rnd = getMaterialRenderer(material.MaterialType);
-	if (rnd && rnd->isTransparent())
+	// TODO: I suspect IMaterialRenderer::isTransparent also often could use SMaterial as parameter 
+	//       We could for example then get rid of IsTransparent function in SMaterial and move that to the software material renderer.
+	if (rnd && rnd->isTransparent())	
 		return true;
 
 	return false;

source/Irrlicht/COpenGLDriver.cpp

@@ -2585,7 +2585,9 @@ void COpenGLDriver::setBasicRenderStates(const SMaterial& material, const SMater
 	}
 
     // Blend Factor
-	if (IR(material.BlendFactor) & 0xFFFFFFFF)
+	if (IR(material.BlendFactor) & 0xFFFFFFFF	// TODO: why the & 0xFFFFFFFF?
+		&& material.MaterialType != EMT_ONETEXTURE_BLEND
+		)
 	{
         E_BLEND_FACTOR srcRGBFact = EBF_ZERO;
         E_BLEND_FACTOR dstRGBFact = EBF_ZERO;

source/Irrlicht/COpenGLShaderMaterialRenderer.h

@@ -21,7 +21,7 @@ namespace video
 class COpenGLDriver;
 class IShaderConstantSetCallBack;
 
-//! Class for using vertex and pixel shaders with OpenGL
+//! Class for using vertex and pixel shaders with OpenGL (asm not glsl!)
 class COpenGLShaderMaterialRenderer : public IMaterialRenderer
 {
 public:

tests/tests-last-passed-at.txt

@@ -1,4 +1,4 @@
 Tests finished. 72 tests of 72 passed.
 Compiled as DEBUG
-Test suite pass at GMT Fri Jan 03 10:49:15 2020
+Test suite pass at GMT Fri Jan 03 14:40:24 2020