mach: expose window size (pixel units, vs. framebuffer subpixel units)

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/Engine.zig

@@ -34,10 +34,20 @@ pub const Core = struct {
         core.internal.setShouldClose(value);
     }
 
+    // Returns the framebuffer size, in subpixel units.
+    //
+    // e.g. returns 1280x960 on macOS for a window that is 640x480
     pub fn getFramebufferSize(core: *Core) !structs.Size {
         return core.internal.getFramebufferSize();
     }
 
+    // Returns the widow size, in pixel units.
+    //
+    // e.g. returns 1280x960 on macOS for a window that is 640x480
+    pub fn getWindowSize(core: *Core) !structs.Size {
+        return core.internal.getWindowSize();
+    }
+
     pub fn setSizeLimits(core: *Core, min: structs.SizeOptional, max: structs.SizeOptional) !void {
         return core.internal.setSizeLimits(min, max);
     }

src/native.zig

@@ -93,6 +93,11 @@ pub const CoreGlfw = struct {
         return @bitCast(structs.Size, size);
     }
 
+    pub fn getWindowSize(self: *CoreGlfw) !structs.Size {
+        const size = try self.window.getSize();
+        return @bitCast(structs.Size, size);
+    }
+
     pub fn setSizeLimits(self: *CoreGlfw, min: structs.SizeOptional, max: structs.SizeOptional) !void {
         try self.window.setSizeLimits(
             @bitCast(glfw.Window.SizeOptional, min),