From 7ae200a1dcc370a1f51c387c9261be6ac09a0cd6 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Wed, 22 Mar 2023 13:51:08 -0700
Subject: [PATCH] renderer/metal: fix color bug on macOS 13 Intel.

See the associated test.
---
 src/renderer/Metal.zig | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/renderer/Metal.zig b/src/renderer/Metal.zig
index a7aaaeee9..13fc7ab8c 100644
--- a/src/renderer/Metal.zig
+++ b/src/renderer/Metal.zig
@@ -83,13 +83,28 @@ texture_color: objc.Object, // MTLTexture
 const GPUCell = extern struct {
     mode: GPUCellMode,
     grid_pos: [2]f32,
-    cell_width: u8,
-    color: [4]u8,
     glyph_pos: [2]u32 = .{ 0, 0 },
     glyph_size: [2]u32 = .{ 0, 0 },
     glyph_offset: [2]i32 = .{ 0, 0 },
+    color: [4]u8,
+    cell_width: u8,
 };
 
+// Intel macOS 13 doesn't like it when any field in a vertex buffer is not
+// aligned on the alignment of the struct. I don't understand it, I think
+// this must be some macOS 13 Metal GPU driver bug because it doesn't matter
+// on macOS 12 or Apple Silicon macOS 13.
+//
+// To be safe, we put this test in here.
+test "GPUCell offsets" {
+    const testing = std.testing;
+    const alignment = @alignOf(GPUCell);
+    inline for (@typeInfo(GPUCell).Struct.fields) |field| {
+        const offset = @offsetOf(GPUCell, field.name);
+        try testing.expectEqual(0, @mod(offset, alignment));
+    }
+}
+
 const GPUUniforms = extern struct {
     /// The projection matrix for turning world coordinates to normalized.
     /// This is calculated based on the size of the screen.