Hi all, apologies for the delay in getting this up here but a mystery illness since last Thursday has kept me at bay - I managed to get this working a week ago but I'm only just getting round to sorting it out. I'll try to sort a screenshot at some point. A few notes:
This is adapted from code originally done and kindly shared by Martins Upitis http://devlog-martinsh.blogspot.fi/2013/05/image-imperfections-and-film-grain-post.html with the exception that I have removed the element that crates coloured noise. I did this because I didn't personally feel the extra processing is necessary, and film grain should be kept subtle. I've always preferrred mono noise/grain. It wouldn't be difficult to add this back in, however - this is the first time I've ever looked at a shader and I was just keeping things simple.
I also borrowed a little bit of code from the implementation here http://www.html5gamedevs.com/topic/8393-phaser-filterkit-vignette-and-filmgrain/ which was ported from the same source but adapted slightly. I can't remember exactly what the additions were but I think there was a slightly different function for randomising/rotating some coordinates - I left it in as I was experimenting with the various methods. There were some issues while testing where the noise would create repeating distracting patterns and I thought this might have been the cause - it likely wasn't, so it might just be adding unnecessary processing.
Another slight change I made was altering the luminence coefficients to Rec 709 - the original is still commented out in the code, as are a few other things, if you want to experiment. Hope you find it useful.
Default settings for params are 0.05 for grain amount (0 to 0.10 is a logical range for intensity), 2.5 for grain size (1.5 to 4.0 and beyond if you like, bigger would probably suit a nightvision effect) and luminance stays at 1.0, but can be tweaked - experiment.
Also many thanks to Gigatron for the effort put into converting despite me having already finished it, apologies for not responding sooner - see above And to chrisbrobs
Link to zip containing fx and xml file
If anyone has any optimisations or ideas, please feel free to improve and share with the community.