XNA rendertarget semantics

re: XNA rendertarget semantics

JoelMartinez — Mon, 05 Feb 2007 03:55:32 GMT

ahh, good deal ... I was curious about using this for some post processing, but couldn't really find any coherent data in one place (as you alluded to). thanks Shawn

re: XNA rendertarget semantics

CatalinZima — Mon, 05 Feb 2007 21:46:03 GMT

Thanks! This clears up some things.

I was especially curios about the cost of resolving the render target.

re: XNA rendertarget semantics

Jamezilla — Tue, 06 Feb 2007 07:35:22 GMT

This blog post is kind of troublesome, because I got some post-processing effects going in what I think is the very same way that you say should destroy the textures on the Xbox360, yet they work fine!

I render the scene to target A, resolve A, switch to target B, render A to B with an effect, resolve B, switch to C, render A to C with an effect, resolve C, then render A, B, and C to the backbuffer.

This should be destroying everything, but it's not. Works flawlessly on Windows and Xbox360. What gives? Should I repost this on the XNA forum for the general edification of the masses?

Thanks, love your blog!

re: XNA rendertarget semantics

ShawnHargreaves — Tue, 06 Feb 2007 10:41:21 GMT

Sorry, unclear wording on my part there! Your approach seems fine. The thing that is lost when you call resolve is the contents of the buffer that is being rendered onto: the texture that it resolves into (which is returned by GetTexture) will never be lost.

This is fine:

- Render to A

- Resolve A

- Render to B

- Resolve B

- Render A.GetTexture and B.GetTexture to C

But this is not:

- Render to A

- Resolve A

- Carry on rendering more stuff to A

No good because the resolve cleared the current contents of the rendertarget!

re: XNA rendertarget semantics

Jamezilla — Wed, 07 Feb 2007 01:11:05 GMT

Now all is clear!

I like simple diagrams, preferably with lots of pictures, arrows, and colors, and anything beyond that is difficult to fit into my brain...

Thank you very much!

I love your blog doubly now!

re: XNA rendertarget semantics

hr0nix — Sun, 18 Mar 2007 20:58:59 GMT

btw, there is no simple way to do such a save/restore for the RenderTargetCube. What should we do in that case?

re: XNA rendertarget semantics

ShawnHargreaves — Mon, 19 Mar 2007 17:44:04 GMT

You should be able to render any individual face of the cubemap texture to the backbuffer, in just the same way you would for a 2D rendertarget. You need a custom pixel shader to do that, but it should be simple enough to write a shader that just grabs pixels from one face of the cubemap.

Remember that only the texture portion of the RenderTargetCube is truly a cubemap: the current rendertarget is still just a 2D surface, so you are only ever rendering to (and thus only need to worry about restoring) one face of that cubemap at a time.

re: XNA rendertarget semantics

hr0nix — Wed, 21 Mar 2007 20:12:05 GMT

Probably XNA should have more useful RenderTargets and support features like 'RT stacking'. I hope that feature will appear in future releases.

BTW, what is the lifetime of the resolved texture? I do some rendering into RT, than resolve it, than do some other rendering into another RT, set the previous RT and try to get resolved texture, but i has InvalidOperationException at this time. That was my simple attemp to implement RT stacking myself, and it fails =). Can you give some explanation, please?