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Migi0027

Speed - Texture Lookups and Structured Buffers

10 posts in this topic

Hi guys,

 

so currently I'm following the deferred pipeline, storing the normals/depths/etc.. in different render targets.

 

Now I'm not proud of it, but each single time I render a, e.g., point light, I reconstruct the position and normals per pixel, and then do some lighting calculations, a single pass of a point light takes around 500 us.

 

Now for performance I though it would be better if I packed the gbuffer into a structured buffer, so I did. I construct the gbuffer from the textures in the compute shader bound as a UAV, then access it in the pixel shader for lighting as a SRV. I was expecting an increase in performance, as texture lookups are expensive, but instead rendering a point light took around 1000 us.

 

For the unpacked gbuffer, I have 3 float4 textures, and in the packed gbuffer, the structured buffer consists of 2 float4 and 1 float3.

 

Now my question is how are the speeds when comparing texture lookups and structured buffers, is it supposed to be like this? Or am I doing something wrong?

 

I apologize that I do not have the source code, but at the moment I do not have access to the machine where the source code is on. When I get access, I'll post it, should be within a few hours.

 

Thank you for your time

-MIGI0027

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Buffer reads have the same problem, so you're going to avoid it by switching to buffers

 

It's probably just me, but please elaborate unsure.png .

 

By buffer reads do you mean just reading from a buffer or structured buffers?

Edited by Migi0027
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I would guess that MJP just accidentally omitted the word "not" there.

 

Indeed, sorry about that. 

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So I learned that some developers manage to get a point light to render in about 0.5 us, which I find amazing.

 

So out of curiosity, what are your measures, of a single point light, directional or something close?

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So I managed to compress my gbuffer into 2 float2s, which is good, I hope. smile.png

struct GB
{
	float4 ColorXYZ_RoughW;
	float4 NormXY_PostZ_DepthW;
};

So, as millions of people say, I store the view space position depth, and then reconstruct it later on, but, there's a problem. The position isn't being reconstructed correctly, and I'm following MJP's article on the reconstruction part 3.

 

What I'm currently doing:

Forward GBuffer Rendering:
output.depth = length(input.positionView.xyz);

Directional Light Shading:
   Vertex Shader;;
	float3 positionWS = mul(Output.Pos, mul(viewInv, projInv)); // not the fastest, I know...
	Output.ViewRay = positionWS - cameraPosition;

   Pixel Shader;;
	float depth = gb.NormXY_PostZ_DepthW.w;
	float3 viewRay = normalize(input.ViewRay);
	float3 positionWS = cameraPosition + viewRay * depth;
	return float4(positionWS, 1); // debugging purposes

And this is the result:

 

wb40h2.png

 

So I'm not expecting a rescue mission, but maybe you could spot the issue? happy.png  ( If it's that simple )

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Maybe I'm doing something wrong, as usual.

 

In the vertex shader I have the Output.Pos, which is the screen space pos of the full screen quad.

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