How to make a 200 X 300 drawable region using Graphics-View-Framework classes ?

I'm trying to build a software that can help user design animations, by importing images but the issue is i don't want to use entire window as my canvas, but rather a specific constant size, say 200 X 300 for each frame. User can import images and place them in this 200 X 300 Rectangular view , if any image is out of this view, it should simply be ignored , and otherwise if some portion of image is inside the 200X300 rectangular region, only that amount of portion should be rendered while exporting a frame as an image. How can i implement this , I have read documentation however it would be better if i could get some visual representation or diagram/illustrations that can help me understand QGraphicsView and QGraphicsScene intuitively.