Godot 4 shader to create icon decorations (bordered and optional circle).

icon_decoration.shader

shader_type canvas_item;

uniform vec3 border_color: source_color = vec3(0);
uniform float border_width: hint_range(0, 10) = 0;
uniform bool circle = false;

void fragment() {
	float center = 0.5;
	float border_width_uv = border_width * min(TEXTURE_PIXEL_SIZE.x, TEXTURE_PIXEL_SIZE.y);
	float border_start = center - border_width_uv;
	
	if (circle) {
		if (step(border_start, length(UV - vec2(center, center))) == 1.0) {
			COLOR.rgb = border_color;
		}
		COLOR.a *= step(length(UV - vec2(center, center)), center);
	} else {
		if (step(border_start, abs(UV.x - center)) == 1.0 ||
			step(border_start, abs(UV.y - center)) == 1.0) {
			COLOR.rgb = border_color;
		}
	}
}