Add window.gldrawablesize

src/sdl.zig

@@ -86,6 +86,13 @@ pub const Window = struct {
         };
         return Renderer{ .renderer = renderer };
     }
+
+    pub fn glDrawableSize(self: Window) struct { w: i32, h: i32 } {
+        var width: c_int = 0;
+        var height: c_int = 0;
+        c.SDL_GL_GetDrawableSize(self.window, &width, &height);
+        return .{ .w = width, .h = height };
+    }
 };
 
 pub const RendererFlags = struct {