Ogre Forums

Hi, I am trying to write a template shader for my custom hlms which will have multiple "sections". Basically I want to write couple of pieces and based on the Renderable's properties, only once piece will be inserted to the shader:

@piece(PropertyA) @insertpiece(ShaderA) @end
@piece(PropertyB) @insertpiece(ShaderB) @end
@piece(PropertyC) @insertpiece(ShaderC) @end
@piece(!PropertyA && !PropertyB && !PropertyC) @insertpiece(DefaultShader) @end

This of course work, but I would like to write last part in more general way that if I insert new PropertyD, that I don't have to update the condition there. Something like this (but it doesn't work):

@piece(PropertyA) @insertpiece(ShaderA) @set(ShaderSet, 1) @end
@piece(PropertyB) @insertpiece(ShaderB) @set(ShaderSet, 1) @end
@piece(PropertyC) @insertpiece(ShaderC) @set(ShaderSet, 1) @end
@piece(!ShaderSet) @insertpiece(DefaultShader) @end

From what I read in the documentation for HLMS I think I understand why it is not working - the @set is evaluated after the pieces are inserted, which is just too late. I tried it also with @pset, but this one is evaluated before any piece is inserted. Is there something more dynamic? There was description of something similar and recommended that it is possible to use HLSL/GLSL preprocessor macros with their own cons and pros. I would like to stick purely to HLMS preprocessing so if there is nothing else what I can do, I will stick to my original template code (with last part naming all properties).

Since the Hlms parses files as individual units and in alphabetical order, you can workaround this by using two files:

// 01.Script_piece_all.any
@property(PropertyA) @insertpiece(ShaderA) @set(ShaderSet, 1) @end
@property(PropertyB) @insertpiece(ShaderB) @set(ShaderSet, 1) @end
@property(PropertyC) @insertpiece(ShaderC) @set(ShaderSet, 1) @end

// 02.Script_piece_all.any
@property(!ShaderSet) @insertpiece(DefaultShader) @end

This way 01.Script_piece_all.any will be parsed, the piece inserted and the property set.
Then 02.Script_piece_all.any gets parsed with ShaderSet already set.

Alternatively in C++, Hlms::notifyPropertiesMergedPreGenerationStep (or HlmsListener::propertiesMergedPreGenerationStep) can do the same evaluation, where you can check if Prop A, B or C have been set, then set/unset ShaderSet:

void MyListener::propertiesMergedPreGenerationStep(
	Hlms *hlms, const HlmsCache &passCache, const HlmsPropertyVec &renderableCacheProperties,
	const PiecesMap renderableCachePieces[NumShaderTypes], const HlmsPropertyVec &properties,
	const QueuedRenderable &queuedRenderable, const size_t tid )
{
	if( hlms->_getProperty( tid, "A" ) != 0 ||
	    hlms->_getProperty( tid, "B" ) != 0 ||
    	    hlms->_getProperty( tid, "C" ) != 0 )
	{
	    hlms->_setProperty( tid, "ShaderSet", 1 );
	}
}

The approach with 2 files sounds better for me. However I need to wrap the "implementation" in a piece. So something like this:

// 01.Script_piece_all.any
@piece(mainShaderBody)
@property(PropertyA) @insertpiece(ShaderA) @set(ShaderSet, 1) @end
@property(PropertyB) @insertpiece(ShaderB) @set(ShaderSet, 1) @end
@property(PropertyC) @insertpiece(ShaderC) @set(ShaderSet, 1) @end
@end

And in the second file:

// 02.Script_piece_all.any
@insertpiece(mainShaderBody)
@property(!ShaderSet) @insertpiece(DefaultShader) @end

Without trying it, do you think it could work? I will experiment with it later as I am in the middle of shader implementation and I went for now with the solution of using all the conditions as mentioned in my first post.