How to zoom image using GtkImage Widget?

["raymond-xu" <raymond-xu 126 com>]

Hi everyone!
 
 I'm trying to write a program using GtkImage widget to show image, I want to zoom image in the widget. My 
solution is :
1 create a GtkImage 
2 add handler for "size-allocate" signal of GtkImage widget
3 use gdk functions to scale the image
 
The main problem is on the step 2, in the callback of the "size-allocate" signal, I always get width of the 
request width, it seems not the actual width allocated for GtkImage. Is it a bug?
 
If anyone has some solution or can fix problem, let me know.
 
Thanks advance