Universal Outline2D Shader (with fix for Godot 4.x)

godot/Shaders/outline2D.shader

@@ -0,0 +1,69 @@
+shader_type canvas_item;
+
+const int Inner = 1;
+const int Outer = 2;
+
+// TODO: Add support for struct uniforms in shaders: https://github.com/godotengine/godot/pull/93603
+//struct Outline {
+	//bool inner;
+	//bool outer;
+//};
+//uniform Outline outline_type;
+
+/**
+	1 = Inner Outline
+	2 = Outer Outline
+	3 = Inner + Outer Outline
+*/
+uniform int outline_type: hint_range(1, 3) = 3;
+uniform bool enabled = true;
+uniform vec4 line_color : source_color = vec4(1);
+uniform float line_thickness : hint_range(0, 10) = 1.0;
+
+const vec2 OFFSETS[8] = {
+	vec2(-1, -1), vec2(-1, 0), vec2(-1, 1), vec2(0, -1), vec2(0, 1), 
+	vec2(1, -1), vec2(1, 0), vec2(1, 1)
+};
+
+vec4 apply_shader(sampler2D txtr, vec2 txtr_pixel_size, vec4 color, vec2 uv) {
+	bool apply_inner = bool(outline_type & Inner);
+	bool apply_outer = bool(outline_type & Outer);
+
+	vec2 size = txtr_pixel_size * line_thickness / 2.0;
+
+	float inline = 1.0;
+	float outline = apply_inner && !apply_outer ? 1.0 : 0.0;
+	for (int i = 0; i < OFFSETS.length(); i++) {
+		float sample = texture(txtr, uv + size * OFFSETS[i]).a;
+
+		// outer and inner_outer outline
+		if (apply_outer) outline += sample;
+		else if (apply_inner) outline *= sample;
+
+		if (apply_inner && apply_outer) inline *= sample;
+	}
+
+	if (apply_inner && apply_outer) {
+		outline = min(1.0, outline) - color.a;
+		inline = (1.0 - inline) * color.a;
+	}
+	else if (apply_outer) outline = min(outline, 1.0);
+	else if (apply_inner) outline = 1.0 - outline;
+
+	float mix_value;
+	if (apply_inner && apply_outer) mix_value = outline + inline;
+	else if (apply_inner) mix_value = outline * color.a;
+	else if (apply_outer) mix_value = outline - color.a;
+
+	vec4 outlined_result = mix(color, line_color, mix_value);
+	// inner and inner_outer outline
+	if (apply_inner) {
+		outlined_result = mix(color, outlined_result, outlined_result.a);
+	}	
+	return outlined_result;
+}
+
+void fragment() {
+	if (enabled) COLOR = apply_shader(TEXTURE, TEXTURE_PIXEL_SIZE, COLOR, UV);
+	else COLOR = COLOR;
+}