[Haskell-cafe] OpenGL Speed!

[Vo Minh Thu]

2010/7/29 Eitan Goldshtrom <thesourceofx at gmail.com>:
> I'm having an unusual problem with OpenGL. To be honest I probably shouldn't
> be using OpenGL for this, as I'm just doing 2D and only drawing Points, but
> I don't know about any other display packages, so I'm making due. If this is
> a problem because of OpenGL however, then I'll have to learn another
> package. The problem is speed. I have a list of points representing the
> color of 800x600 pixels. All I'm trying to do is display the pixels on the
> screen. I use the following:
>
> renderPrimitive Points $ mapM_ display list
> flush
> where
>   display [] = return ()
>   display ((x,y,i):n) = do
>     color $ Color3 i i i
>     vertex $ Vertex2 x y
>     display n
>
> But, for some reason this takes FOREVER. I don't know how to use debugging
> hooks yet without an IDE -- and I don't use an IDE -- but I used a cleverly
> placed putStrLn to see that it was actually working, just really really
> slowly. Is there a solution to this speed problem or should I use a package
> that's more suited to 2D applications like this? Also, if I should use
> another package, are there any suggestions for which to use? Thanks for any
> help.

Hi,

Although you can use Vertex* to put a single Point on the screen, it
is not meant to be used as some kind of setPixel function.

If your goal is simply to set pixels' value of a raster, you can still
use OpenGL but should use a single textured quad (and thus manipulate
the texture's pixels).

There other possibilities to deal with raster graphics:
- Use gtk; i.e. something like
http://hackage.haskell.org/package/AC-EasyRaster-GTK
- Output the data in some image format (if you want to do it yourself,
the most simple is PPM)
- Use X11 directly (if you're on unix)
- ...

HTH,
Thu