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DarkBASIC Professional Discussion / Alter the Colour of a Shader Affected Object

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Sasuke
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Posted: 29th Oct 2011 21:34
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Basically I need to change the colour and alpha of an object that's affected by a shader, but not through the shader. I've gotten stuck on how to do this affectively and efficiently. So I ask you guys. Any ideas?

Cheers in advance
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Diggsey
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Posted: 30th Oct 2011 01:21
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Well you'd have to do it "through the shader" at some level since the shader completely determines the output colour of an object.

Why not make a variable in the shader which is the desired colour and then change that on the fly from DBPro with "set effect constant vector".

[b]
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Sasuke
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Posted: 30th Oct 2011 02:32
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I need to use a single shader for multiple objects, like over a 1000 objects. Hence why I said not through the shader. Similar to Point Sprites where the color is set up via a memblock. I'm guessing there's a way to set up a shader to used whatever the vertex diffuse is. Or other methods I haven't thought of...
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Chris Tate
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Posted: 30th Oct 2011 03:21 Edited at: 30th Oct 2011 03:22
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What about creating a diffuse texture to blend with the shader?

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Sasuke
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Posted: 30th Oct 2011 11:08
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Then it's a question of how would you get every colour and alpha? Other than creating a 1 x 1 px render target to generate the diffuse texture using something like image kit to update the texture's color. It would work but to do it for every single active object required would be expensive.
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Diggsey
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Posted: 30th Oct 2011 13:18
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Ah, I see what you mean now. Well one way is to generate a 1x1px image of the desired colour for each object using memblocks and texture that object with it. You can access the texture from a shader easily enough.

You could also do it through vertex diffuse but that would be even more wasteful, since you wouldn't be able to share vertexdata between objects and changing the colour would require you to go through every vertex on an object.

There may also be some way to get the current diffuse colour, but I'm not sure exactly how much information DBPro gives the shader.

[b]
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IanM
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Posted: 30th Oct 2011 14:40
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Isn't this the kind of thing where having multiple techniques in the shader can help?

Have two techniques - one that calls a pixel shader without the colouring, and one that calls a pixel shader with the colouring. Then you can colour your object just by switching techique. The second pixel shader can use an extra texture to provide the extra colouring if you need different colours on several objects.

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Green Gandalf
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Posted: 30th Oct 2011 15:02
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Quote: "Other than creating a 1 x 1 px render target to generate the diffuse texture using something like image kit to update the texture's color. It would work but to do it for every single active object required would be expensive."


Would a 1x1 texture for each object really be that expensive?
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