feat: Implement the "Stop N Go" arena with new assets, scenes, and associated game logic and UI.

assets/shaders/outline3d.gdshader

@@ -1,21 +1,24 @@
 shader_type spatial;
 render_mode cull_front, unshaded;
 
-// Controls the width of the outline
-uniform float outline_thickness : hint_range(0.0, 0.5) = 0.03;
-
-// Controls the color of the outline
 uniform vec4 outline_color : source_color = vec4(0.0, 0.0, 0.0, 1.0);
+uniform float thickness : hint_range(0.0, 10.0) = 5.0; // Thickness in pixels
 
 void vertex() {
-	// The core of the inverted hull method:
-	// We push the vertices outward along their normal vectors.
-	// Since front faces are culled, this creates the outline border.
-	VERTEX += NORMAL * outline_thickness;
+	// Calculate the vertex position and normal in projection space
+	vec4 clip_position = PROJECTION_MATRIX * (MODELVIEW_MATRIX * vec4(VERTEX, 1.0));
+	vec3 clip_normal = mat3(PROJECTION_MATRIX) * (mat3(MODELVIEW_MATRIX) * NORMAL);
+	
+	// Normalize the normal vector and convert to pixel space
+	vec2 clip_norm = normalize(clip_normal.xy);
+	vec2 pixel_size = 1.0 / VIEWPORT_SIZE;
+	
+	// Multiply by W to keep pixel size constant across distances
+	clip_position.xy += clip_norm * pixel_size * thickness * clip_position.w;
+	
+	POSITION = clip_position;
 }
 
 void fragment() {
-	// Apply the solid outline color
 	ALBEDO = outline_color.rgb;
-	ALPHA = outline_color.a;
 }