// Adapted from Leafshade Interactive's outline shader
// explained and shown in https://youtu.be/yh1Kdr37RmI.

shader_type canvas_item;

uniform vec4 line_color : source_color = vec4(1.0);
uniform float line_thickness : hint_range(0.0, 10.0) = 2.0;

void fragment() {
	vec2 size = TEXTURE_PIXEL_SIZE * line_thickness;
	
	float outline =
		texture(TEXTURE, UV + vec2( size.x, 0)).a +
		texture(TEXTURE, UV + vec2(-size.x, 0)).a +
		texture(TEXTURE, UV + vec2(0,  size.y)).a +
		texture(TEXTURE, UV + vec2(0, -size.y)).a +
		texture(TEXTURE, UV + vec2( size.x,  size.y)).a +
		texture(TEXTURE, UV + vec2(-size.x,  size.y)).a +
		texture(TEXTURE, UV + vec2(-size.x, -size.y)).a +
		texture(TEXTURE, UV + vec2( size.x, -size.y)).a;
	
	float alpha = min(outline, 1.0) - texture(TEXTURE, UV).a;
	COLOR = vec4(line_color.rgb, line_color.a * alpha);
}