Working on 'et' (my escape-time #fractal program) this morning.

I added #supersampling presets from 1x1 through 8x8, selectable by keypress. It already did supersampling but you had to enter 3 numbers in a modal dialog.

The calculations of the array used for progressive image rendering were annoyingly slow, so I'm now caching them on disk using the xdg-basedir and vector-mmap packages (et is written in #Haskell). I also need the directory and filepath packages for this part.

The arrays get quite big, almost 700MB total for all supersampling sizes with a base resolution of 1024x576 pixels (it takes up 6 bytes per pixel). Changing the base resolution size means recalculating and storing another set of arrays. Cache will bloat!

So I'm thinking there might be a better procedural way to do what the arrays do, which is #Adam7 style interlacing (coarse pixels getting gradually finer in a multipass rendering) with the pixels in each pass ordered so that the center gets rendered first and it spreads out towards the edges.

So in short I need a cheap function from (ImageWidth, ImageHeight, PixelIndex) to (PixelX, PixelY, PixelWidth, PixelHeight), because using anything other than #atomics to increment PixelIndex is much too slow in #concurrent #multicore Haskell.