How can i get the pixel position in a light shader?

[canslp]

Godot Version

4.2.1

Question

In spatial shaders, I’ve been using VERTEX and some matrix multiplications to get the position of the fragment pixel. In the light function, I don’t have access to VERTEX. How can I get the worldspace coordinate in the ‘light’ function?

[pennyloafers]

There is a light vertex in the unreleased Godot 4.3

Add `LIGHT_VERTEX` to fragment shader

[canslp]

oh, that’s perfect. though i guess that means there’s no way to access it until 4.3 then, right?

[pennyloafers]

You can download the dev release.

Godot download archive - Godot Engine

[pennyloafers]

btw there is also the varying keyword if you want to try and pass the vertex down to the light function.

shader_type spatial;

varying vec3 some_color;

void vertex() {
    some_color = NORMAL; // Make the normal the color.
}

void fragment() {
    ALBEDO = some_color;
}

void light() {
    DIFFUSE_LIGHT = some_color * 100; // optionally
}

[canslp]

oh that’s interesting, does the ‘varying’ key word just create a persistent variable?

[pennyloafers]

I think so, there is a concept on GPUs called work groups. So in theory that variable should be shared only within the workgroup. And it should all align to a single pixel, or group of pixels? Don’t quote me on that I’m still learning.

I saw it in the docs here.

Shading language

I guess pixels and fragments.

[canslp]

okay this totally worked thanks