Crt-rpi shader: Is there a 1360x768 version?

vanfanel · 25 October 2017 12:05

Hi,

There’s the crt-rpi shader here:

libretro/glsl-shaders/blob/master/crt/shaders/crt-pi.glsl

/*
    crt-pi - A Raspberry Pi friendly CRT shader.

    Copyright (C) 2015-2016 davej

    This program is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by the Free
    Software Foundation; either version 2 of the License, or (at your option)
    any later version.


Notes:

This shader is designed to work well on Raspberry Pi GPUs (i.e. 1080P @ 60Hz on a game with a 4:3 aspect ratio). It pushes the Pi's GPU hard and enabling some features will slow it down so that it is no longer able to match 1080P @ 60Hz. You will need to overclock your Pi to the fastest setting in raspi-config to get the best results from this shader: 'Pi2' for Pi2 and 'Turbo' for original Pi and Pi Zero. Note: Pi2s are slower at running the shader than other Pis, this seems to be down to Pi2s lower maximum memory speed. Pi2s don't quite manage 1080P @ 60Hz - they drop about 1 in 1000 frames. You probably won't notice this, but if you do, try enabling FAKE_GAMMA.

SCANLINES enables scanlines. You'll almost certainly want to use it with MULTISAMPLE to reduce moire effects. SCANLINE_WEIGHT defines how wide scanlines are (it is an inverse value so a higher number = thinner lines). SCANLINE_GAP_BRIGHTNESS defines how dark the gaps between the scan lines are. Darker gaps between scan lines make moire effects more likely.

GAMMA enables gamma correction using the values in INPUT_GAMMA and OUTPUT_GAMMA. FAKE_GAMMA causes it to ignore the values in INPUT_GAMMA and OUTPUT_GAMMA and approximate gamma correction in a way which is faster than true gamma whilst still looking better than having none. You must have GAMMA defined to enable FAKE_GAMMA.

CURVATURE distorts the screen by CURVATURE_X and CURVATURE_Y. Curvature slows things down a lot.

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Well, my monitor’s native mode is DMT 39 (1360x768), while this shader seems to be targeted for 1080p (1920x1080), so even if I activate custom aspect ratio and integer scaling, I still get slightly but annoyingly “uneven” scanlines.

So, is there a 1360x768 version of this shader, please? I seem to recall something specific for that resolution but I can’t find it.

Thanks!

dave_j · 25 October 2017 18:39

There isn’t a 768 version. Even using integer scaling, some screens don’t produce even scan lines. You can try to make them less noticeable by increasing the scanline gap brightness setting - although this will make the scanlines less prominent.

vanfanel · 26 October 2017 00:36

Ah! That must be why I don’t see them “uneven” when I use the NES Mini shader, where scanlines are way brighter… Can you give me a line example for “SCANLINE_GAP_BRIGHTNES” to get brighter scanlines? I have tried alterating all the numbers in that line with no results. I don’t know much about shader coding…

dave_j · 26 October 2017 12:22

The default values are specified in the #pragma parameter lines, the #define versions are just for use during development. The best way is to use the shader parameters in the menu - this will put the parameters in the glslp file. If you have threaded video on you’ll need to temporarily disable it - there’s a bug in retroarch which causes it to crash if you try change shader parameters with threaded video on.

crt-pi needs to be run with linear filtering (which is why it should be specified via the glslp file). Even LCD monitors have image adjustment settings so it might be worth checking the values your’s is set to.

vanfanel · 27 October 2017 10:37

Ah! Thanks a lot, dave_j! I found optimal settings by modifying these values on the menu instead of fiddling with the shader files