Initial metal abstraction (noop)

src/renderer.zig

@@ -7,11 +7,21 @@
 //! APIs. The renderers in this package assume that the renderer is already
 //! setup (OpenGL has a context, Vulkan has a surface, etc.)
 
+const builtin = @import("builtin");
+
 pub usingnamespace @import("renderer/size.zig");
+pub const Metal = @import("renderer/Metal.zig");
 pub const OpenGL = @import("renderer/OpenGL.zig");
 pub const Thread = @import("renderer/Thread.zig");
 pub const State = @import("renderer/State.zig");
 
+/// The implementation to use for the renderer. This is comptime chosen
+/// so that every build has exactly one renderer implementation.
+pub const Renderer = switch (builtin.os.tag) {
+    .macos => Metal,
+    else => OpenGL,
+};
+
 test {
     @import("std").testing.refAllDecls(@This());
 }