Retrieve pixel RGB data without resorting to Texture2D.ReadPixels()

Hi I know this is a common problem but still was hoping someone has found an answer.

I'm trying to retrieve the pixel RGB values as seen by the current live camera. In my OnRenderImage (or OnPostrender) I have

tex2D.ReadPixels(rect, 0, 0);

where tex2D is a Texture2D instance and rect is a Rect instance.

ReadPixels is the bottleneck!

I'm posting in the Shader sub forum because I'm actually trying to capture a 'pixellate' shader effect in terms of rgb or brightness values.

 

I'm not entirely sure what your final goal is, but ReadPixels world by copying the screen texture back to the CPU from the GPU, then sending the new texture back. If you're doing this as part of your rendering it is essentially stalling the GPU until it's done.

It's better to try to do everything with render to texture, shaders, and blit commands. Pretty much anything else requires and copy back from the GPU (which is the slow part) and possibly stalling the GPU (also slow).

 

Your goal : capture a 'pixellate' shader effect output.
Steps:
=> First create a camera, setup it's render texture.
=> Render your scene color to this render texture.
=> Then use Graphics.Blit with your 'pixellate' shader on this render texture.
=> Now you retrieve the pixelate result, use it as any shader input program as you want.

 

Thanks for the great replies. My next step is to do everything as suggested but for now am using ReadPixels on a very small (160 x90) webcamtexture which both reduces impact on performance and removes the need for any pixellate shader.