Retina performance, dual monitors

[Forkjulle]

Using a HDMI cable I have a second screen plugged into my Macbook Pro Retina 15". It's a Dell 27".

I've read a lot of discussions about the choppy performance on the Retina and it's true. The performance is choppy on the Retina.

But it's smooth on the second monitor.

If Mountain Lion is the cause of the choppy performance of the Retina, then why is my second screen smooth (since it's also in Mountain Lion from my rMBP)?

This leads me to believe that the pixel density of the rMBP is simply too much for the hardware. If the issue was with Mountain Lion, then surely the second screen would be choppy too.

 

[bill-p]

Because one screen needs scaling, whereas the other one (your external monitor) doesn't.

Scaling is done in software in Mountain Lion. That's why it's slow.

Mavericks has fixed this somewhat by offloading more tasks to GPU.

 

[maatae]

I actually have the same situation happening with my dell u2412m and rmbp 13. Is your main screen the external by any chance? I think most lag issues on the rmbp have to do with the dock..if i set my dock to the left or right of the screen (as opposed to the bottom, which renders reflections) switching between spaces is extremely smooth. Can anyone else confirm or am i imagining things?