renderer: make GraphicsAPI.swap_chain_count required

src/renderer/Metal.zig

@@ -34,6 +34,9 @@ pub const imagepkg = @import("metal/image.zig");
 
 pub const custom_shader_target: shadertoy.Target = .msl;
 
+/// Triple buffering.
+pub const swap_chain_count = 3;
+
 const log = std.log.scoped(.metal);
 
 // Get native API access on certain platforms so we can do more customization.

src/renderer/generic.zig

@@ -204,15 +204,7 @@ pub fn Renderer(comptime GraphicsAPI: type) type {
             // If this is one then we don't do any double+ buffering at all.
             // This is comptime because there isn't a good reason to change
             // this at runtime and there is a lot of complexity to support it.
-            const buf_count = count: {
-                if (@hasDecl(GraphicsAPI, "swap_chain_count")) {
-                    break :count GraphicsAPI.swap_chain_count;
-                }
-
-                // Default to triple buffering if
-                // graphics API has no preference.
-                break :count 3;
-            };
+            const buf_count = GraphicsAPI.swap_chain_count;
 
             /// `buf_count` structs that can hold the
             /// data needed by the GPU to draw a frame.