Transparency not working when custom-shader is defined

[ryanfelder]

It seems that when I enable a custom-shader, my terminal is no longer transparent.
I can toggle this behavior with a single # character.
I am on Fedora 41, with Nvidia proprietary drivers and a Geforce RTX 3060.

Here is my ghostty config

window-decoration=true  
gtk-titlebar=false  
window-padding-x=8  
window-padding-y=8  
background=#22190B  
foreground=#E1CBA6  
background-opacity=0.7  
#custom-shader=/home/ryan/Programs/ghostty/shaders/bloom075.glsl  

[rhodes-b]

The shader needs to support transparency, shaders draw on top of the background and if they override the background then it will no longer be transparent

[ryanfelder]

Hmm, I wonder if any shader can be used with a transparent background then... I mean, if a shader doesn't draw on the background has it done anything at all? I think I need to learn a bit more about shaders.

Thanks for the reply!

[xav-ie]

Is it possible to get a simple example of a shader that supports transparency? My shader that works fine on macos and supports transparency does not work on linux:
https://github.com/xav-ie/dots/blob/32d32f41754c00d86f993f4778b9d8bbd521315f/home-manager/dotfiles/ghostty/watersubtle.glsl
I think this is bug.

[00-KAMIDUKI]

I have the same problem on linux. Can we open an issue for this bug?

[rhodes-b]

I dont think it is a bug the supporting transparency might only work with macos.

GTK doesnt know whats under your window it just sets the background to nothing

[GlitchedCode]

void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
    fragColor = vec4(texture(iChannel0, fragCoord / iResolution.xy).a);
}

This simple shader outputs a fully white image on Arch Linux with Hyprland and NVIDIA drivers. Setting fragColor = vec4(.0); outputs a fully transparent image instead, and manually setting the alpha channel to 0.1 gives a gradually brightened image that eventually becomes white. I have the following config

theme = "Duotone Dark"
custom-shader = "test.glsl"
window-decoration = false
background-opacity = 0.85
background-blur-radius = 20

Transparency works fine without enabling shaders. Looks to me like an issue with getting a consistent alpha channel into the shader and consistently applying that transparency like the application does when shaders are disabled.