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

[Jesper Särnesjö]

On Fri, Mar 8, 2013 at 11:25 PM, Jesper Särnesjö <sarnesjo at gmail.com> wrote:
> The program's CPU usage is quite high in general, and increases with
> the number of pixels redrawn per frame. It uses OpenGL 3.2, does most
> of its work on the GPU, and should do a constant amount of work per
> frame on the CPU, so this makes little sense.
>
> I've created a smaller program (still 91 lines, though), which renders
> a single triangle, but still reproduces this problem. If I make the
> triangle smaller (by editing vertexData), CPU usage goes down, and if
> I make it bigger, CPU usage goes up. [1]
>
> I've also created a C program which does the same thing (as far as
> possible), but which does not exhibit this problem. CPU usage is far
> lower, and stays constant regardless of the number of pixels redrawns
> per frame. [2]

I've figured out what the problem is: the Haskell program is using a
software implementation of OpenGL, so rendering *does* in fact happen
on the CPU.

This seems to happen because I request a renderer conforming to the
OpenGL 3.2 Core profile, while running on Mac OS X 10.8.2 [3]. If I
remove those lines from displayOptions, the program receives a
hardware-accelerated renderer. Of course, then I can't use features
from OpenGL 3.2, so that's hardly a solution.

It would appear that there is in fact some relevant difference between
the Haskell [1] and C [2] versions of my program, or possibly some way
in which the bindings from the GLFW-b package are different from the C
library.

I've updated my programs to check for hardware acceleration and also
print the GLFW and OpenGL versions. [4]

-- 
Jesper Särnesjö
http://jesper.sarnesjo.org/

[1] https://gist.github.com/sarnesjo/5116084#file-test-hs
[2] https://gist.github.com/sarnesjo/5116084#file-test-c
[3] http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Conceptual/OpenGL-MacProgGuide/opengl_pixelformats/opengl_pixelformats.html
[4] https://gist.github.com/sarnesjo/5116084/revisions