How to get world-space position in canvas_item shader?

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1

Godot Version

4.6.1

Question

I want to draw an inifity grid with a single quad mesh.

I’m using MeshInstance2D with a rectangle mesh, the mesh is shown successfully, but the position (‘world_pos‘ in shader) looks always the screen space position, it doesn’t move or scale when camera is moving or scaling. Also I can’t find anything like VIEW_MATRIX or CAMERA_MATRIX. What’s the proper way to do so?

code:

shader_type canvas_item;

uniform vec2 grid_size = vec2(64.0, 64.0);
uniform float line_width_px = 2.0;
uniform vec4 grid_color : source_color = vec4(0.5,0.5,0.5,0.5);

void vertex() {
	VERTEX = (MODEL_MATRIX * vec4(VERTEX, 0.0, 1.0)).xy;
}

void fragment() {
    vec2 world_pos = VERTEX;
    vec2 coord = world_pos / grid_size;
    vec2 grid = abs(fract(coord - 0.5) - 0.5);
    vec2 fw = fwidth(coord);
    float line = min(grid.x / fw.x, grid.y / fw.y);
    float alpha = 1.0 - smoothstep(0.0, line_width_px, line);
    COLOR = vec4(grid_color.rgb, grid_color.a * alpha);
}
2

Don’t assign the result back to VERTEX. Use your own varying instead.