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How to make HLSL antialias filter

Started by novatin Apr 7, 2009 at 2:18 AM 5 replies 9k views

Original Post

Apr 7, 2009 at 2:18 AM

Hi, I have been wondering how to antialias this little DirectX 9 program of mine. I have three vertices defined like this to make a simple triangle: LPDIRECT3DVERTEXBUFFER9 p_dx_VertexBuffer; cv_Vertices[0].x = 5.0f; cv_Vertices[0].y = 10.0f; cv_Vertices[0].z = 0.0f; cv_Vertices[0].color = 0xffffffff; cv_Vertices[1].x = 10.0f; cv_Vertices[1].y = 0.0f; cv_Vertices[1].z = 0.0f; cv_Vertices[1].color = 0xffffffff; cv_Vertices[2].x = 0.0f; cv_Vertices[2].y = 0.0f; cv_Vertices[2].z = 0.0f; cv_Vertices[2].color = 0xffffffff; And then I draw them to a windowed DirectX scene using p_dx_Device->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 1); Is it possible to make an antialias filter (pref. supersampling) using HLSL to smooth the edges that are visible when this triangle rotates? Thank you very much in advance :)

SiS-Shadowman

Apr 7, 2009 at 5:24 AM

I'm not sure if it's the only method, but I thought anti aliasing had to be enabled through the driver. From my understanding, it works on the final image, taking the depthbuffer into account to smooth the edges, and not on a 'per-object' basis.
However you should be able to implement this using a post-processing effect (as AA cannot be enabled when doing a render-to-texture). The effect works on the final color- and depthbuffer and checks the distance between the pixels in world/camera space and blurs them over if the distance is bigger than a certain threshold (the algorithm is probably more sophisticated).

MJP

Apr 7, 2009 at 10:57 AM

Quote:
Original post by SiS-Shadowman
I'm not sure if it's the only method, but I thought anti aliasing had to be enabled through the driver. From my understanding, it works on the final image, taking the depthbuffer into account to smooth the edges, and not on a 'per-object' basis.

Well it's not really a "driver" thing, but multisample anti-aliasing is definitely what you want to use here. Any form of super-sampling is going to be expensive. To enable it just specify D3DMULTISAMPLE_2_SAMPLES or D3DMULTISAMPLE_4_SAMPLES as the MultiSampleType parameter of the D3DPRESENT_PARAMETERS struct you pass to IDirect3D9::CreateDevice.

Quote:
Original post by SiS-Shadowman
(as AA cannot be enabled when doing a render-to-texture)

Negative, Ghost Rider. You use IDirect3DDevice9::StretchRect to resolve a multisampled render target surface (created with CreateRenderTarget) to a render target texture.

novatin

Apr 7, 2009 at 12:09 PM

Thank you!

I don't know what I was trying earlier as I tried to implement other tutorials' methods which included setting to D3DMULTISAMPLE_4_SAMPLES but didn't quite work but this worked like a charm.

Now that it's clear that it can be done, is there a way to implement the antialias-filtering in HLSL pixel shader? My goal is to get a little bit into the HLSL programmable pipelines.

novatin

Apr 9, 2009 at 2:44 AM

Let me elaborate a little.

With what code (in HLSL) I could make a pixel shader that would count an average of its surrounding pixels with a defined pattern such as this:

1 0 1
0 0 0
1 0 1

where the current pixel value in processing is (x,y), so we get:
outpixel = ( (x-1, y-1) + (x+1,y-1) + (x-1,y+1) + (x+1,y+1) ) / 4.

Or is there a way to predefine that I would like to use a grid algorithm, or lets say jitter.

SiS-Shadowman

Apr 9, 2009 at 8:25 AM

Quote:
Original post by MJP
Quote:
Original post by SiS-Shadowman
(as AA cannot be enabled when doing a render-to-texture)

Negative, Ghost Rider. You use IDirect3DDevice9::StretchRect to resolve a multisampled render target surface (created with CreateRenderTarget) to a render target texture.

Oops, I forgot that, I stumbled accros a tutorial from nvidia several months ago that used that technique. I'll try to keep it in mind this time ;)

novatin

Apr 12, 2009 at 1:10 PM

Quote:
Original post by MJP
Any form of super-sampling is going to be expensive.

I would like to learn how to do an antialias filter (supersampling with different patterns) written in HLSL, regardless of the performance hit..

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