I have an older MacBook Pro 17″, and while it can handle Diablo III just fine, it doesn’t do so well when I try and play with an external monitor connected.
The GPU is powering two displays even though I’m only utilizing one during the game.
The obvious solution would be to disable the built-in display and solely use the larger external display. With Mac OS X Lion, that’s not easily done (anymore).
Clamshells and how it was before . . .
“Clamshell mode” is where you are using your MBP connected to an external monitor, keyboard, and mouse, with the lid closed. It temporally disables your built-in screen and lightens the GPU load by only powering the single external display.
Before Lion, while in clamshell mode you could open the lid and the built-in display would still stay off.
Why would you want to open the lid while using clamshell mode? For more ventilation. While Apple’s official stance is that you don’t need the lid open – a lot of people disagree (myself included).
You see, a major source of air intake and exhaust is utilized within the spaces of the built-in keyboard. Anyone who uses a keyboard protector on their MBP/MPA will tell you that the protector get very toasty – because you are blocking ventilation!
So what are you doing to your computer while in lid-CLOSED clamshell mode?
That’s right: blocking ventilation! What’s worse, is that the uni-body MBPs have a rubber seal around the lid that restricts all airflow between the lid (screen) and the keyboard while closed… you are basically toasting your computer’s innards and screen!
Do the research! You will find countless reports of MBP an MBA fans spinning up full speed while in clamshell mode. That’s a thermal response to increased heat (due to lack of full through-keyboard ventilation).
What changed? . . .
With the introduction of Lion, Apple changed things. They “assumed” that after you put the machine into clamshell mode, that if you opened the lid, you want to re-use your built-in screen.
Well, not everyone wants that. I can sorta understand why they did that. I don’t really remember if it was easy or not to re-connect the built in display (besides unplugging the external).
There are however situations where you may want to disable the built-in display…
Slow GPU or over-heating for Diablo III? . . .
So, if I play D3 on my MBP alone, it plays fine. If I connect it to an external setup (no clamshell) the video lags a lot. Thoughts? The GUP is taxed having to support two monitors even though I’m only using one (the external).
Test? Try it in clamshell mode. Sure enough, the game runs smoothly in clamshell mode connected to my external monitor. Problem? Yeah, I don’t want my computer innards or it’s screen toasted!
Solution? After some quick googling, you can find out that there is a magnetic trigger somewhere on your MBP/MBA chassis. If you place a small magnet over that switch, the computer will think that the lid is closed, and thus enter clamshell mode (while the lid is open)!!!
You will have to figure out where the switch is on your model. Some people said above the audio jack, but mine was on the opposite side, above the kensington security slot.
Now back to playing Diablo III, while keeping my computer well ventilated! ;)