So, I’ve Googled my way to a very simple example to test how this’d work. However, the example below basically doesn’t have any effect. (Setting pixColor[1] = 1.0; makes everything green so the shader is loaded correctly).

precision highp float;
varying vec2 v_texcoord;
uniform sampler2D tex;

void main() {
	// get the pixel color
       vec4 pixColor = texture2D(tex, v_texcoord);

	// change the alpha
	pixColor[3] = 0.75;

	// set the pixel color
	gl_FragColor = pixColor;
}

Since I don’t know anything about shaders, before I open an issue on Hyprland, is this how you’d set the alpha of each pixel on a screen?

I suspect this might not be possible in Hyprland after all as it doesn’t natively support per-window shaders. IIUC, Hyprland applies the shader after it composits so there’s technically nothing behind the window I’m trying to make transparent.