very starty setup

root.gdshader

@@ -1,5 +1,7 @@
 shader_type canvas_item;
 
+uniform sampler2D trail_tex;
+
 uniform float sensor_distance = 2.0;
 uniform float sensor_angle = 15.0;
 uniform float rotation_angle = 23.0;
@@ -7,10 +9,11 @@ uniform float move_distance = 2.67;
 uniform float decay_factor = 0.75;
 
 void fragment() {
-	COLOR = vec4(0.05, 0.05, 0.05, 1.0);
-}
-
-//void light() {
-//	// Called for every pixel for every light affecting the CanvasItem.
-//	// Uncomment to replace the default light processing function with this one.
-//}
+    vec2 uv = UV;
+    // Read current trail value
+    vec4 trail = texture(trail_tex, uv);
+    // Apply decay
+    trail *= decay_factor;
+    
+    COLOR = trail;
+}