Point Sprites

This post suggests that they arent supported in Unity.

http://answers.unity3d.com/questions/199032/cg-shaders-in-unity-and-point-sprites.html

Is this true and does anyone know why?

 

Point sprites are a thing of the past. A relic from the fixed-function pipeline days. They are not supported by modern hardware.

 

Really? So what if I wanted to produce a purely GPU based particle system (as I have done many times in the past) how would you go about doing it without point sprites or hardware instancing?

 

Wow, nice particle systems you got there. Ok, let me clarify how it works. Modern hardware doesn't natively support point sprites or fixed-function pipeline in general. Modern API like DirectX11 doesn't support them either. But you can still use them with older APIs. Just like you can use fixed function pipeline. Even on modern HW. What will happen in that case is that the graphics driver will replace the fixed-function pipeline things with shaders. The driver will emulate it for you behind the scene.

Now for your question. There are several ways how you can handle particles on DX11 class hardware.

1. Emit a quad for every vertex in geometry shader (textbook solution, not necessarily best/fastest)
2. Create quads from points in tesselator
3. HW Instancing
4. The old fashion way. Works on every hw. Create 4 identical vertices with different uvs for every particle. You also have to store "offset vector" in second uv set for every vertex. That offset will tell you where to move that vertex in vertex shader so that all 4 vertices will form a quad. First vertex will move to lower left corner, second one to upper left corner of the quad etc. You will simply use something like this in vertex shader
   
   Code (CSharp):

   1. position += cameraRightVector * offset.x * particleSize;
   2. position += cameraUpVector * offset.y * particleSize;

Hope it make sense.

Edit: I found a nice comparison.

 

Cool, thanks for that detailed reply! So I would like this to run on mobile too, so I dont want to reply upon DX11 features.

So im thinking 4 is probably the best but perhaps 2, not sure how well supported tessellation is on mobile GPUs..

Mike

 

Yeah, very few mobile devices support tessellation or geometry shaders. 4 is your best bet.