shader_type canvas_item;

uniform vec4 border_color : hint_color = vec4(0.0, 0.0, 0.0, 1.0);
uniform bool border_corners = false;

bool is_border(sampler2D tex, vec2 uv, vec2 pixel_size) {
	float check = texture(tex, uv + vec2(pixel_size.x, 0.0)).a;
	check += texture(tex, uv + vec2(-pixel_size.x, 0.0)).a;
	check += texture(tex, uv + vec2(0.0, pixel_size.y)).a;
	check += texture(tex, uv + vec2(0.0, -pixel_size.y)).a;
	
	if (border_corners) {
		check += texture(tex, uv + pixel_size).a;
		check += texture(tex, uv - pixel_size).a;
		check += texture(tex, uv + vec2(pixel_size.x, -pixel_size.y)).a;
		check += texture(tex, uv + vec2(-pixel_size.x, pixel_size.y)).a;
	}
	
	return check > 0.0;
}

void fragment() {
	COLOR = texture(TEXTURE, UV);
	
	if (COLOR.a == 0.0 && is_border(TEXTURE, UV, TEXTURE_PIXEL_SIZE)) {
		COLOR = border_color;
	}
}