2 replies to this topic

[he3117]

Hi

I want to start writing forward rendering pipeline for my deferred engine and I'm looking for efficient way to pass light information to shader.

I have an idea about it.I don't want to pass light info as constant or array so I'm thinking about sending them as textures.

for point lights I need:

 

struct PointLight

{

   COLOR LightColor;

   Vector3 LightPosition;

   float LightRadius;

}

 

It seems I can store this structure in 2 pixel of a texture:

RGB=LightColor;

alpha=LightRadius;

 

RGB=xyz of light position

 

struct SpotLight

{

   COLOR LightColor;

   Vector3 LightPosition;

   float LightRadius;

   float CosAngel;

}

RGB=LightColor;

alpha=LightRadius;

 

RGB=xyz of light position

alpha=CosAngel;

 

so with a texture 128*2 I can pass 128 point light to the shader.

But what is the best way to fill this texture?Should I make a vertex buffer with light info and pass it to a shader to writing in texture or use LockRect and fill the texture on CPU?

 

also I can pack all light info in one texture and use another texture to pass ligh Ids to shader

[Schrompf]

Try standard passing by constant registers first. Textures can store a lot more data than constant registers, but access to textures is pretty slow, and updating them is even slower. In contrast: reading from constant registers is "free" by nearly any measurement, and updating constant registers is quite cheap in my experience. And with 4096 x float4 constant registers you can still store a lot of lights.

[Jason Z]

Try standard passing by constant registers first. Textures can store a lot more data than constant registers, but access to textures is pretty slow, and updating them is even slower. In contrast: reading from constant registers is "free" by nearly any measurement, and updating constant registers is quite cheap in my experience. And with 4096 x float4 constant registers you can still store a lot of lights.

 

I completely agree with this - you could try using a texture as an experiment, but you are nearly certain to switch back to using constants afterwards...