input: printable, comment on what magic indexes mean

src/input/key.zig

@@ -243,4 +243,77 @@ pub const Key = enum(c_int) {
             else => null,
         };
     }
+
+    /// True if this key represents a printable character.
+    pub fn printable(self: Key) bool {
+        return switch (self) {
+            .a,
+            .b,
+            .c,
+            .d,
+            .e,
+            .f,
+            .g,
+            .h,
+            .i,
+            .j,
+            .k,
+            .l,
+            .m,
+            .n,
+            .o,
+            .p,
+            .q,
+            .r,
+            .s,
+            .t,
+            .u,
+            .v,
+            .w,
+            .x,
+            .y,
+            .z,
+            .zero,
+            .one,
+            .two,
+            .three,
+            .four,
+            .five,
+            .six,
+            .seven,
+            .eight,
+            .nine,
+            .semicolon,
+            .space,
+            .apostrophe,
+            .comma,
+            .grave_accent,
+            .period,
+            .slash,
+            .minus,
+            .equal,
+            .left_bracket,
+            .right_bracket,
+            .backslash,
+            .kp_0,
+            .kp_1,
+            .kp_2,
+            .kp_3,
+            .kp_4,
+            .kp_5,
+            .kp_6,
+            .kp_7,
+            .kp_8,
+            .kp_9,
+            .kp_decimal,
+            .kp_divide,
+            .kp_multiply,
+            .kp_subtract,
+            .kp_add,
+            .kp_equal,
+            => true,
+
+            else => false,
+        };
+    }
 };

src/input/keycodes.zig

@@ -8,14 +8,12 @@ const Key = @import("key.zig").Key;
 
 /// The full list of entries for the current platform.
 pub const entries: []const Entry = entries: {
-    const native_idx = if (builtin.target.isDarwin())
+    const native_idx = switch (builtin.os.tag) {
-        4
+        .macos => 4, // mac
-    else if (builtin.target.isWindows())
+        .windows => 3, // win
-        3
+        .linux => 2, // xkb
-    else if (builtin.target.isLinux())
+        else => @compileError("unsupported platform"),
-        2
+    };
-    else
-        @compileError("unsupported platform");
 
     var result: [raw_entries.len]Entry = undefined;
     for (raw_entries, 0..) |raw, i| {