CODEWITHSUNDEEP
compareopengl-es-2.0texturesalpha
Shamrock
Shamrock

Reputation: 446

Comparing textures in OpenGL ES 2.0

I am working on a painting app using the LibGDX framework, though this should be primarily OpenGL related.

Basically, I am looking for a way to prevent the sprites I use to draw from overlapping each other when they aren't fully opaque, as this creates a lot of unpleasant effects. Drawing the sprites at 1.0 alpha onto a texture and then drawing that texture back at the desired alpha gives the effect I want, but that method would involve constantly recreating the texture as the user is drawing, which is far too intensive to be viable.

From what I can see, the best option for me, in basic terms, is to sort of subtract one of these sprites from the other in the fragment shader. I am quite certain this route would work, but I cannot figure out how to get to the point where I can actually compare them in the fragment shader. Both will always use the same single texture, but they will be positioned in different spots. Is it at all possible to actually compare them like that, or is there a suitable alternative?

Upvotes: 1

Views: 176

Answers (1)

ClayMontgomery
ClayMontgomery

Reputation: 2832

It's not actually possible to compare 2 textures that are applied to different geometry (sprites) in the fragment or vertex shader that way, because they will be rendered on different iterations of the shaders, at different points in time.

You could have two or more texture units to sample and subtract multiple textures, but they would have to be applied to the same vertices (sprites), which I think is not what you want.

A better approach would be to compute the proximity of the sprites before they are rendered. You could then either change their positions, or pass the proxmity as a uniform value into the shaders, which could then be used to change the alpha of the fragment pixels for the sprites.

Upvotes: 1

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