building a pure graphics pipeline version of this

shaders/trail_shader.gdshader

@@ -0,0 +1,8 @@
+shader_type canvas_item;
+
+void fragment() {
+	vec3 c1 = vec3(0.0, 0.4, 0.4);
+	vec3 c2 = vec3(0.4, 0.0, 0.4);
+	vec3 cout = mix(c1, c2, UV.x);
+	COLOR = vec4(cout, 1.0);
+}