[Haskell-beginners] Performance problem with Haskell/OpenGL/GLFW

Jesper Särnesjö sarnesjo at gmail.com
Sun Mar 10 22:23:01 CET 2013

On Mon, Mar 11, 2013 at 7:17 AM, Hollister Herhold <hollister at fafoh.com> wrote:
> Okay, I think I just figured this out. Well, HOW to get it working with the
> accelerated renderer.
> I was wondering a simple way to check renderer info so I ran glxinfo. This
> (automatically) fired up X11, and then on a hunch I re-ran Test2 with X11
> running and got this:
> hhmacbook:~/Development/haskell/OpenGL:57> ./Test2
> hardware
> (2,7,7)
> (3,2,0)
> hhmacbook:~/Development/haskell/OpenGL:58>
> AH HA! I then quit X11 and re-ran Test2, and got this:
> hhmacbook:~/Development/haskell/OpenGL:58> ./Test2
> software
> (2,7,7)
> (3,2,0)
> hhmacbook:~/Development/haskell/OpenGL:59>
> SO- If you want the accelerated renderer, you need to have X11 running.
> Now, I have no idea WHY this is the case, but there you go.
> Hope this helps.

This lead me down an interesting path.

First, I should explain that my machine, like most newish Macs, has
two graphics cards. In my case, a discrete Nvidia GeForce GT 330M, and
an integrated Intel chip. The former is better, but the latter uses
less power, and the system is supposed to switch between them

I used gfxCardStatus [1] to show which card was in use. When I ran
test2.c, the system briefly switched to the discrete card. However,
when I ran Test2.hs, the system kept using the integrated chip the
whole time. Presumably, the Intel chip lacks a hardware implementation
of OpenGL 3.2, which causes the system to fall back to a software
renderer. I then used gfxCardStatus to force the system to *always*
use the discrete card and - boom! - this time Test2.hs received a
hardware renderer!

So it seems that the problem is a) Mac OS X-specific, or possibly
specific to systems with multiple graphics cards, b) related to
triggering the *switch* to the better graphics card. I don't yet
understand why the C program triggers a switch, while the Haskell
program does not, but I'll keep investigating.

Thank you all very much for your help!

Jesper Särnesjö

[1] http://gfx.io

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