compile metal in cmake

Sources/Voxelotl/shader.metal

@@ -0,0 +1,45 @@
+#ifndef SHADERTYPES_H
+#define SHADERTYPES_H
+
+#ifdef __METAL_VERSION__
+# define NS_ENUM(TYPE, NAME) enum NAME : TYPE NAME; enum NAME : TYPE
+# define NSInteger metal::int32_t
+#else
+# import <Foundation/Foundation.h>
+#endif
+
+#include <simd/simd.h>
+
+typedef NS_ENUM(NSInteger, ShaderInputIdx) {
+  ShaderInputIdxVertices = 0
+};
+
+typedef struct {
+  vector_float4 position;
+  vector_float4 color;
+} ShaderVertex;
+
+#endif//SHADERTYPES_H
+
+#include <metal_stdlib>
+
+using namespace metal;
+
+struct FragmentInput {
+  float4 position [[position]];
+  float4 color;
+};
+
+vertex FragmentInput vertexMain(
+  uint vertexID [[vertex_id]],
+  device const ShaderVertex* vtx [[buffer(ShaderInputIdxVertices)]]
+) {
+  FragmentInput out;
+  out.position = vtx[vertexID].position;
+  out.color    = vtx[vertexID].color;
+  return out;
+}
+
+fragment float4 fragmentMain(FragmentInput in [[stage_in]]) {
+  return in.color;
+}