[HOpenGL] hopengl 2.4.0.1 slowdown

[Sven Panne]

Am Sonntag, 13. September 2009 18:03:30 schrieb Csaba Hruska:
> Hi! I've upgraded my haskell programs to opengl 2.4.0.1 and I've noticed
> massive (3X) slowdown.
> I did only type fixes on code.
> Is it normal?

I could reproduce this, but the slowdown was related to the OpenGL package 
only indirectly, the real cause were your type fixes. I had a look at your 
code, and you can quickly get back your previous performance by an evil 2-line 
hack:

-----------------------------------------------------------------------------------------------
panne at spock:~/build/lambdacube> diff 
lambdacube.orig/Graphics/LambdaCube/Render.hs 
lambdacude/Graphics/LambdaCube/Render.hs
11a12
> import Unsafe.Coerce
42c43
<     m <- (newMatrix ColumnMajor $ map realToFrac $ toListsMat44 t) :: IO 
(GLmatrix GLfloat)
---
>     m <- (newMatrix ColumnMajor $ unsafeCoerce $ toListsMat44 t) :: IO 
(GLmatrix GLfloat)
-----------------------------------------------------------------------------------------------

As I said, this is evil and probably not the right way to fix you code. Your 
FloatType and OpenGL's GLfloat have the same runtime representation, so 
'realToFrac' is a no-op at runtime, *but* 'map realToFrac' is not a no-op, at 
least not with GHC's current optimizer. To avoid creating the transformation 
matrices over and over again, you could e.g. use a GLmatrix for your 
Transformation type or use GLfloat directly in your Math module.

In a nutshell: "map realToFrac" considered harmful. ;-)

Cheers,
   S.