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Modifying material colour/transparency with a shader
http://horde3d.org/forums/viewtopic.php?f=2&t=504		 Page 1 of 1
Author:  jazza [ 17.09.2008, 15:30 ]
Post subject:  Modifying material colour/transparency with a shader
Hey guys,

I'm a bit stuck with a little project that I'm working on. I need to be able to change the transparency and colour of a material that I have applied to a scene node. After reading through a few related posts on this forum, I've come to the conclusion that I might have to create my own shader and declare a "uniform" variable to hold the colour and transparency that I want to render.

How do I go about doing this? I've written shaders before but I'm not sure I understand Horde's XML format for shaders. Also how do I ensure that a uniform variable that I've declared in the material.xml file is being passed to the shader?

Any help/advice is greatly appreciated.

Cheers,

Jarryd
Author:  AcidFaucet [ 17.09.2008, 16:06 ]
Post subject:  Re: Modifying material colour/transparency with a shader
A material.xml file looks like:

Code:
<Material class="theClassofTheMaterial">
          <Shader source="nameOfTheShader" />
          <TexUnit unit="#" map="imageFile" />
          <Uniform name="myUniform" a="float" b="float" c="float" d="float />
</Material>


Your shader contexts then access the uniform by declaring it at as normal:

uniform vec4f myUniform;

The Data Format reference in the Horde3D manual covers this material in greater detail.

You can take a look at a palette recoloration technique I put up in the wiki under "Community Tutorials."
Author:  jazza [ 19.09.2008, 10:44 ]
Post subject:  Re: Modifying material colour/transparency with a shader
Thanks for the help! Managed to get my shader working!
Author:  jazza [ 20.09.2008, 10:32 ]
Post subject:  Re: Modifying material colour/transparency with a shader
Alright. Perhaps I spoke to soon.... :(. Let me clarify my problem first. I'm loading a resource as follows:


ResHandle modelRes = Horde3D::addResource( ResourceTypes::SceneGraph, "model.scene.xml", 0 );
NodeHandle modelNode = Horde3D::addNodes( RootNode, modelRes );

The model then loads and displays correctly using a custom shader that I've specified in the material.xml file. The shader is also properly accessing the values of the uniforms declared in the xml file.

My question is, how do I then modify these uniforms at runtime? The API seems to have commands that allow you to modify the material resource for a "mesh node" but not for a "scene graph" node.
Author:  jazza [ 20.09.2008, 10:45 ]
Post subject:  Re: Modifying material colour/transparency with a shader
Just a quick update. I've managed to use setMaterialUniform(materialRes,"particleColour",1.0,0.0,0.0,1.0) but that seems to change the uniforms for all scene nodes that use this material. Is there some way to set these uniforms on a "per mesh/node" basis?

I'm guessing I'll have to clone the material resource in order to do that :S.
Author:  AcidFaucet [ 20.09.2008, 18:21 ]
Post subject:  Re: Modifying material colour/transparency with a shader
You have to clone. A varying uniform is on my own to-do list, if you'd like me to bounce you some code that does the trick (though it's a quirky proof of concept that will look nothing like a final write) then PM me your email address.
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