Progressive rendering

[tryptophan]

I'm wondering if someone could explain how progressive rendering is working. I understand the concept but not exactly sure how it is working in Fragmentarium. I noticed in the 2dProgressive.frag that it defines (not includes?) another .frag called BufferShader.frag. Also I've noticed the 2dProgressive has a backbuffer sampler and the BufferShader has a frontbuffer. Now I'm pretty sure one or both is taking the output of one or the other and feeding in back into itself but I'm not sure of how its setup. Any comments?

thanks
Keith

[Syntopia]

Hi Keith,

Whenever you enable dual-buffering, by using something like:

Code:

#buffer RGBA32F
#buffershader "BufferShader.frag"

Fragmentarium will create two buffers, with the requested datatype (32-bit floats for each of the 4 color channels - from now I will call these 'HDR' buffers - in the example above).

When the shader is executed, it will write to the front-buffer, but it is allowed to sample from the backbuffer.
After it has rendered a frame, the backbuffer and frontbuffer is swapped - so the backbuffer always contains the previous output from the main shader.

The 'BufferShader.frag' is different. It reads from the frontbuffer, and is responsible for rendering the HDR buffer to the screen, which is always 8-bit RGBA. Typically it will contain code for tonemapping and post-processing the HDR buffers. The buffershader is not required - if is omitted colors will simply output whatever is in the HDR buffers, clamped from 0 to 1. You may also use the HDR buffers for other purposes than colors - e.g. the Reaction-Diffusion example use channels for different chemical species, and use the buffershader to convert this into an image.

Hope this helps, Mikael.

[tryptophan]

Cheers thanks I understand. The backbuffer is always a step behind and is sampling the frontbuffer which gets its input from the shader. I guess the backbuffer counter is the number of times this process happens for each final frame rendered.

thanks
Keith