Add project files

core/DynamicPolygon.tscn

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+[gd_scene load_steps=2 format=3 uid="uid://cbynoofsjcl45"]
+
+[ext_resource type="Script" path="res://core/dynamic_polygon.gd" id="1_2pai0"]
+
+[node name="DynamicPolygon" type="CollisionPolygon2D"]
+script = ExtResource("1_2pai0")
+update = null
+
+[node name="Polygon2D" type="Polygon2D" parent="."]
+color = Color(0, 0, 0, 1)

core/dynamic_polygon.gd

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+@tool
+extends CollisionPolygon2D
+
+@export var color: Color = Color.WHITE:
+	set(v):
+		color = v
+		update_polygon()
+	get():
+		return color
+
+@export var update: bool:
+	set(v):
+		update_polygon()
+
+func update_polygon():
+	$Polygon2D.polygon = polygon
+	$Polygon2D.color = color
+
+func _ready() -> void:
+	update_polygon()

core/shaders/screen_effects.gdshader

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+shader_type canvas_item;
+render_mode unshaded;
+
+uniform sampler2D screen_texture : hint_screen_texture, repeat_disable, filter_linear_mipmap;
+
+// simple edge detection
+bool is_edge(int radius, vec2 screen_uv, vec2 screen_pixel_size) {
+	bool ed_found_black = false;
+	bool ed_found_color = false;
+	// check neighbor pixels
+	for (int x = -radius; x < radius+1; x++) {
+		for (int y = -radius; y < radius+1; y++) {
+			vec4 p = texture(screen_texture, screen_uv + (vec2(float(x), float(y)) * screen_pixel_size));
+			if (p.rgb == vec3(0.0)) {
+				ed_found_black = true;
+			} else {
+				ed_found_color = true;
+			}
+		}
+	}
+	return ed_found_black && ed_found_color;
+}
+
+void fragment() {
+	// get screen texture
+	vec4 screen = texture(screen_texture, SCREEN_UV);
+	// apply edge detection
+	int radius = max(int(0.003 * (1.0/SCREEN_PIXEL_SIZE.y)), 1); // with a relative radius
+	if (is_edge(radius, SCREEN_UV, SCREEN_PIXEL_SIZE)) {
+		COLOR = screen;
+	} else {
+		COLOR = vec4(0, 0, 0, 1);
+	}
+	// apply glow
+	// blur a relative radius -> x * log(1.0/SCREEN_PIXEL_SIZE.y)
+	// using log, because the LOD value seems to affect the blur radius exponentially
+	vec4 glow = textureLod(screen_texture, SCREEN_UV, 0.5 * log(1.0/SCREEN_PIXEL_SIZE.y));
+	if (screen.rgb == vec3(0.0)) {
+		COLOR = mix(COLOR, glow, 0.4) + (glow * 0.3);
+	}
+}