core: darwin: Add ability to detect and fire magnify event which is triggered by pinch to zoom on a trackpad

src/Core.zig

@@ -522,6 +522,10 @@ pub const Event = union(enum) {
     window_open: struct {
         window_id: mach.ObjectID,
     },
+    magnify: struct {
+        window_id: mach.ObjectID,
+        magnification: f32,
+    },
     focus_gained: struct {
         window_id: mach.ObjectID,
     },

src/core/Darwin.zig

@@ -209,6 +209,14 @@ fn initWindow(
             );
             view.setBlock_flagsChanged(flagsChanged.asBlock().copy());
 
+            var magnify = objc.foundation.stackBlockLiteral(
+                ViewCallbacks.magnify,
+                context,
+                null,
+                null,
+            );
+            view.setBlock_magnify(magnify.asBlock().copy());
+
             var mouseMoved = objc.foundation.stackBlockLiteral(
                 ViewCallbacks.mouseMoved,
                 context,
@@ -405,6 +413,17 @@ const ViewCallbacks = struct {
         } });
     }
 
+    // This is currently only supported on macOS using a trackpad
+    pub fn magnify(block: *objc.foundation.BlockLiteral(*Context), event: *objc.app_kit.Event) callconv(.C) void {
+        const core: *Core = block.context.core;
+        const window_id = block.context.window_id;
+
+        core.pushEvent(.{ .magnify = .{
+            .window_id = window_id,
+            .magnification = @floatCast(event.magnification()),
+        } });
+    }
+
     pub fn keyDown(block: *objc.foundation.BlockLiteral(*Context), event: *objc.app_kit.Event) callconv(.C) void {
         const core: *Core = block.context.core;
         const window_id = block.context.window_id;