Add new function dw_render_redraw() which will trigger expose event on render widgets. This is to help optimize drawing on GTK4 and GTK3 with Wayland. To make existing code function on GTK4 and GTK3 with Wayland, drawing outside of a callback will mark widgets dirty and dw_flush() will trigger draw/expose callbacks on them. This may result in double drawing the widgets. dw_render_redraw() will allow you to just trigger the draw event without actually attempting to draw, allowing one draw pass in the expose callback. Only tested on Windows, may require fixes on other platforms.

--- a/os2/dw.c	Mon Mar 08 19:24:21 2021 +0000
+++ b/os2/dw.c	Mon Mar 08 19:53:55 2021 +0000
@@ -4975,6 +4975,16 @@
 }
 
 /*
+ * Invalidate the render widget triggering an expose event.
+ * Parameters:
+ *       handle: A handle to a render widget to be redrawn.
+ */
+void API dw_render_redraw(HWND handle)
+{
+   WinInvalidateRect(handle, NULL, FALSE);
+}
+
+/*
  * Changes a window's parent to newparent.
  * Parameters:
  *           handle: The window handle to destroy.