@Bonnie Hi yes this doesn't work well, the drew line get softer and softer with more zoom, and it gets bigger when zoomed out. I have to revert back to the wheelEvent controlled zoom. Oh and I just observed that the lagging issue are also presented on Photoshop too. When the zoom factor get to about 7x, zoom will get less responsive. So I'm all good now, if even Photoshop is having the same problem, that's nothing more I can do about it. I'll call this a day. Thanks for the help.

Hi and welcome to devnet, Can you show the code you are using ? What exactly do you expect ? What exactly do you get ?