UV checker : fix calculated uv in checker shader

h3d/shader/Checker.hx

@@ -9,6 +9,12 @@ class Checker extends hxsl.Shader {
 		@param var height : Float;
 
 		var calculatedUV : Vec2;
+
+		@input var input : { var uv : Vec2; }
+		function vertex() {
+			calculatedUV = input.uv;
+		}
+
 		function fragment() {
 			if ( ((calculatedUV.fract().x - 0.5) * (calculatedUV.fract().y - 0.5)) > 0.0 ) {
 				pixelColor.rgb = vec3(1.0);