Cursor uniforms for custom shaders

[KroneCorylus]

Hi,

After reading issue #4199, I thought this feature could be implemented using custom shaders if Ghostty passes some additional uniforms. This would not only enable the requested functionality but also allow for more interactive and dynamic shader effects.

I have never worked with Zig before, so my implementation might not be ideal, but I hope it serves as inspiration. My changes should maintain compatibility with ShaderToy, as they only introduce new uniforms without altering existing behavior.

Currently, I have implemented these changes for OpenGL. Below are two example shaders demonstrating what’s possible with this approach:

blaze_trail.mp4

simple_trail.mp4

You can find the changes here: https://github.com/KroneCorylus/ghostty/tree/custom-shaders-cursor-uniforms

I’d love to hear your thoughts on this approach. Thanks

[rhodes-b]

May be worth posting in the #development channel on discord that you are looking for feedback!
(less likely to get missed)

[pluiedev]

Hey that looks super cool! The diff looks clean as well (with some minor changes needed). Would you be interested in opening a PR?

[KroneCorylus]

Thanks @pluiedev! I’ve opened PR #6912, and I’ll be ready to make any requested changes

[mitchellh]

I like this! Super clean diff. I think exposing cursor times to a custom shader is a no-brainer. I'll review your PR and port it to Metal and there's no need to block that.

Separately, you've nerd sniped me so I think I may add generalized cursor trail support to the core of Ghostty. I didn't realize it could be this simple, really. By doing it in core we can be slightly more power efficient because we can avoid frame redraws if we know the cursor hasn't moved over a certain period of time. For custom shaders, we redraw on every frame (vsync) because we can't know if animations exist or not (there's a config to disable this but then custom shaders are only drawn on terminal state change, and only one frame).

Do you have the shaders that you used to make these animations, and would you be open to them being contributed?

[mitchellh]

Ah, I noticed that these shaders aren't ready to be dropped in to the custom-shader arg. I'll read the source in more detail and try to convert them later but do you have examples for that? Appreciate it.

[KroneCorylus]

I’ve uploaded the exact version of the shader I’m using here.

I also noticed that if I don’t include another shader, it doesn’t work. I’ve included the other shader I’m using so you can test it as well. I didn’t notice this issue before, so I assume it’s a problem with my implementation.

As for why the shaders I shared with you aren’t working, I’m not sure. I’ll take a look and let you know.

I’m currently at work, but I’ll check it later

[KroneCorylus]

I know what the problem is; I'm not sampling iChannel0 because the other shader does it for me.

[KroneCorylus]

I’ve updated my shaders, and everything should work now except for blaze_cursor.glsl

[mitchellh]

Thanks, these work. I'll take a look at that PR soon.

[Jacfger]

Hi, I'm super interested in your stuff, so I cloned your pr branch and compiled it myself. While there were no issue loading the shader, it seems like it's not actually showing anything on my computer. Is that a MacOS issue?

[chardskarth]

@00-kat this means this PR doesnt support mac yet? Thats a bummer.

Looking forward to make this work for mac too

[00-kat]

To quote Mitchell from right above:

I'll review your PR and port it to Metal […]

— #6901 (comment)

[Jacfger]

Yes but iirc apple do have a very minimal support of openGL up to 4.1. While ghostty did say it need 4.2, but that was for Linux, so I wonder if it could somehow still work with Mac

[Jacfger]

But I tried it a little bit, the shader compiles. Didn't work.

[chardskarth]

The long awaited dependency of this is finally merged (#7620).

They said the changes on top should be trivial, but I don't know zig enough to port the changes from the PR (#6912).

[qwerasd205]

Implemented in #7648. Thank you!

[gj1118]

@qwerasd205 Thanks for all the hard work. Much appreciated. That said, I had a question to ask please - How can I add the custom shader for those cursor effects? I have already downloaded the shaders from @KroneCorylus's repo and updated my config to use those shaders, but its not working for me. I have also updated Ghostty to the latest version which was released today. Also I dont know any Zig. Kindly help.

Thanks

[Jacobus-afk]

thanks @chardskarth this worked for me in ubuntu 24

[hugows]

That also worked for me, cheers.

[Jacfger]

@chardskarth Thanks my dude. Had been wondering why it's bugging. 🤦🏼‍♂️