Writing a filter (alias editing the "darken" one)

General Development
#1

I have a nice handheld (rg280m) running retroarch.

Unfortunately I damaged its screen and it now has a significant and annoying light bleed on its right side.

I considered editing the “darken” filter so to actually enable it on the bled pixels so to even the brightness out.

I could not find a guide about how to do that though, and admittedly I couldn’t still find the difference between shaders and filters so I could admittedly be too clueless to hope to achieve that lol.

Any pointers would be really helpful.

Many thanks.

#2

Filters run on the CPU and are compiled into a dynamic library. Shaders run on the GPU and are compiled at runtime, making them easier to work on.

This is where you would edit the ‘darken’ filter: https://github.com/libretro/RetroArch/blob/0ddfbd976c478f154100fababa3aea76270d12be/gfx/video_filters/darken.c

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#3

Thank you! That must be why shaders are not included in that version of RA. I guess the hardware doesn’t have any GPUs.

#4

Geez, there isn’t a single comment in that file. But also if there were any, it’s probably much cheaper to throw the device away and get a new one LOL

Thanks for answering, that did help.

BTW, may combining filters and shaders make any sense? When could that be desirable?

Thanks again, this is enlightening.

#5

Yes, many people combine the port of blargg/NRS’ NTSC filter with CRT shaders for various reasons.

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#6

You only need to edit these lines to apply the filter to your set of pixels: https://github.com/libretro/RetroArch/blob/master/gfx/video_filters/darken.c#L148-L155

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