Fading without artifacts

[Laurent]

Would that work?

I'm sorry, I don't have the time to investigate and find a good solution to your problem, so you'd better try your ideas directly and see if they work

[Foaly]

Well it was more a general question to everybody. I not an expert in GLSL so I was wondering if someone could tell me if my idea is even possible, before I waist my time with trying something that won't work. Main question is how can I pass the Rendertexture to the shader. (so that I can retrieve the color using texture2D())

Or is there another way to apply a global shader to a rendertexture?

What about the other questions in my previous post?

[Laurent]

Main question is how can I pass the Rendertexture to the shader

sf::Shader has a setParameter(name, sf::Texture) function.

Or is there another way to apply a global shader to a rendertexture?

Other than what?

[Foaly]

Other than what?

Other than drawing a rectangle over the texture after everything else is drawn with blendmode set to None and apply a shader to the rectangle. The rendertextures texture is passed to the shader so you can modify it there.

I get a error saying "parameter "texture" not found in shader" when I call shader.setParameter("texture", rendertexture.getTexture()); although I declared uniform sampler2D texture; in the shader.

[Laurent]

Other than drawing a rectangle over the texture after everything else is drawn with blendmode set to None and apply a shader to the rectangle. The rendertextures texture is passed to the shader so you can modify it there.

So you want to draw the render-texture on the render-texture? It doesn't work, you can't have the render-texture as both the source and the destination.

I get a error saying "parameter "texture" not found in shader" when I call shader.setParameter("texture", rendertexture.getTexture()); although I declared uniform sampler2D texture; in the shader.

The GLSL compiler optimizes out unused variables (unused = not part of the code that produces the final pixel), so make sure that you use it in your shader.

[Foaly]

Ah thanks for the explanation. I was wondering what the problem was.

So if I can't use a render-texture as the source and the destination, is there any other way to apply a "global" shader to a render-texture?

[Laurent]

If you want to draw a texture on itself, you have to use two render-textures: one is the source, one is the destination, and you swap them every frame so that the previous destination becomes the new source etc.

[Foaly]

So that is the only way how i can fade out a render-texture? Using two textures and a shader. There is no way the problem with the artifacts will be resolved?

By the way: what exactly do you me by a render-texture can't be source and destination. If I apply the shader to the rectangle and draw it onto the render-texture, the rectangle is the source and the render-texture the destination. the shader simply uses information from the render-texture to compute it's color.

[Laurent]

So that is the only way how i can fade out a render-texture? Using two textures and a shader

Nobody said that, this is just your idea. But since nobody seems to have the time to investigate this issue, you're on your own

By the way: what exactly do you me by a render-texture can't be source and destination. If I apply the shader to the rectangle and draw it onto the render-texture, the rectangle is the source and the render-texture the destination. the shader simply uses information from the render-texture to compute it's color.

If you use the texture in your shader, it is a source. You can't read and write to the same texture at the same time.

[Foaly]

Alright I found this article: http://www.pixelnerve.com/v/2010/07/20/pingpong-technique/ I think the technique described is what I need. Or does anybody else know a different technique on how I could achieve this effect?

@Laurent: Are still convinced that adding a subtract blendmode is still not an option? I think it would be really helpful. Especially with this issue or issues like this. You could simply use the subtract blendmode instead of solving it with two textures and a shader that subtracts the colors