Making a texture render to itself

george7378 · 2014-02-17T13:24:21

Hi everyone, I'm working with post-processing in HLSL, i.e. I pass a texture to my effect file containing the back buffer and I then render a sprite using my shader to create various effects. I am doing Gaussian blur right now which means that I need to use multiple steps: - Render scene to texture - Render a sprite with the texture blurred horizontally - Render a sprite with the texture blurred vertically I've seen a few tutorials which seem to imply that you should render the back buffer to one texture (let's call it t_A), then render the horizontal blur to another separate texture (which I'll call t_B), and then render the final sprite by sampling t_B to perform the vertical blur. However, I decided to try and do it with only one texture, and so my program renders the scene to the texture, then passes the texture straight into the shader to perform the horizontal blur, then immediately passes it straight back in to do the final vertical blur, all without changing the render target (and all within the same BeginScene() and EndScene() pair). So my question is: is it safe to make a texture sample itself in my shader while also rendering onto itself? Of course I pass the texture into the shader before I start drawing again, so I guess it's stored in there, but there must be a reason why the tutorials are using different textures to do different parts of the post-processing. Thanks!

Graphics and GPU Programming Programming

Started by george7378 February 16, 2014 04:44 PM

10 comments, last by george7378 10 years, 2 months ago

JohnnyCode

1,084

February 17, 2014 03:21 AM

You are perhaps not combining the ouput of first horizontal pass, and you only sample original texture in creating vertical pass. Blending them will result in a blur, but not the exact gausian blur, since that demands the vertical dissorted texture to be sampled to generate horizontal one. But if result is satisfying and you are not doing an university assignment you can stick to it, since it is more optimized in terms of memory resources and state changes.

george7378

1,443

Author

February 17, 2014 01:24 PM

I've changed it so that I do the ping-pong rendering between two different textures. It's very little extra effort but it means that I can be guaranteed safe results (and I don't get the warning signs any more). When I render properly I get exactly the same result with the Gaussian blur as I I do with the single texture, so the GPU must be making a separate copy. Thanks for the help!

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Making a texture render to itself

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Making a texture render to itself

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