Blurry drop shadow, godot canvas shader

blurry_drop_shadow.gdshader

shader_type canvas_item;

uniform float blur_radius : hint_range(0.0, 1.0) = 0.25;
uniform vec4 shadow_color : source_color = vec4(0.0, 0.0, 0.0, 1.0);

void fragment() {
	vec4 original_texture_color = texture(TEXTURE, UV);

    float shadow_alpha = 0.0;
	if (original_texture_color.a < 1.0) {
	    for (float x = -blur_radius; x <= blur_radius; x+=0.01) {
	        for (float y = -blur_radius; y <= blur_radius; y+=0.01) {
	            shadow_alpha += texture(TEXTURE, UV + vec2(x, y)).a * 0.01;
	        }
	    }
	}

	vec4 sc = shadow_color;
	sc.a = shadow_alpha;

	COLOR = mix(sc, original_texture_color, original_texture_color.a);

}

This is wildly inefficient, you probably shouldn't use it!