clear [ColorBuffer]

[H.]

Hello,

The program:

import Graphics.Rendering.OpenGL
import Graphics.UI.GLUT

main = do
  _ <- getArgsAndInitialize
  createWindow "Hello World"
  displayCallback $= clear [ ColorBuffer ]
  mainLoop

and the problem:
The ColorBuffer is not cleared, the window shows what was there before it was
created.
Creating windows, drawing points,... works all well, but "clear [
ColorBuffer ]" seems not to work.
(I'm using the ghc 6.6 on Windows)

Thanks in advance for your help.


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[jamin1001]

Looks like you need to flush the graphics commands.


try this:

// displayCallback $= clear [ ColorBuffer ]
displayCallback $= display

display = do
  clear [ ColorBuffer ]
  flush


Did that work?



Jamin


--- "h." <h._h._h._@...> wrote:

> Hello,
>
> The program:
>
> import Graphics.Rendering.OpenGL
> import Graphics.UI.GLUT
>
> main = do
>   _ <- getArgsAndInitialize
>   createWindow "Hello World"
>   displayCallback $= clear [ ColorBuffer ]
>   mainLoop
>
> and the problem:
> The ColorBuffer is not cleared, the window shows
> what was there before it was
> created.
> Creating windows, drawing points,... works all well,
> but "clear [
> ColorBuffer ]" seems not to work.
> (I'm using the ghc 6.6 on Windows)
>
> Thanks in advance for your help.
>
>
> _______________________________________________
> HOpenGL mailing list
> HOpenGL@...
> http://www.haskell.org/mailman/listinfo/hopengl
>

 
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[Sven Panne]

On Friday 16 February 2007 19:35, h. wrote:
>  [...] and the problem:
> The ColorBuffer is not cleared, the window shows what was there before it
> was created. [...]

Just a small addition: As was already pointed out, rendering in OpenGL is not
synchronous, which is a very good design decision given the capabilities and
architectures of today's graphic cards. If you use single-buffering (as in
your example), a 'flush' or 'finish' is needed, see:

http://www.haskell.org/ghc/docs/latest/html/libraries/OpenGL/Graphics-Rendering-OpenGL-GL-FlushFinish.html

If double-buffering is used, GLUT's 'swapBuffers' is your friend:

http://www.haskell.org/ghc/docs/latest/html/libraries/GLUT/Graphics-UI-GLUT-Window.html#v%3AswapBuffers

Example:

--------------------------------------------------------------------------
import Graphics.UI.GLUT

main :: IO ()
main = do
   _ <- getArgsAndInitialize
   initialDisplayMode $= [ DoubleBuffered ]
   createWindow "Hello World"
   displayCallback $= do clear [ ColorBuffer ]; swapBuffers
   mainLoop
--------------------------------------------------------------------------

Other UI toolkits with an OpenGL canvas will have something similar
to 'swapBuffers', e.g. 'glDrawableSwapBuffers' in Gtk2Hs, IIRC.

Cheers,
   S.
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[jamin1001]

Regarding Chris' post -

I ran into a lot of problems too since there are old
versions of HOpenGL and corresponding examples
floating around out there with differing advice, such
as at http://www.haskell.org/HOpenGL/.  I'm not sure
why it hasn't been updated since it's off of the main
haskell.org.

There are some sites that include a lot of Red Book
examples that should just compile and work with the
method I gave (such as ghc --make Planet.hs).  Anyone
know a reason why some tutorials use the -package GLUT
option?


Try some of these links:

This should have the newer examples (can anyone tell
me if there are any better sites than this?)
http://cvs.haskell.org/cgi-bin/cvsweb.cgi/~checkout~/fptools/libraries/GLUT/examples/RedBook/

This is a newer tutorial (blog):
http://blog.mikael.johanssons.org/archive/2006/09/opengl-programming-in-haskell-a-tutorial-part-2/

This is older:
http://www.haskell.org/~pairwise/HOpenGL/HOpenGL.html


-Jamin




 
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[Sven Panne]

On Thursday 22 February 2007 13:02, Jamin A. Ohmoto-Frederick wrote:
> Regarding Chris' post -
>
> I ran into a lot of problems too since there are old
> versions of HOpenGL and corresponding examples
> floating around out there with differing advice, such
> as at http://www.haskell.org/HOpenGL/.  I'm not sure
> why it hasn't been updated since it's off of the main
> haskell.org.

I admit being guilty here of not upating that site for a very long time. My
amount of time I can work on HOpenGL varies quite a bit depending on my Real
Life (tm) ;-), I think it might be a good idea to move the stuff to the
Haskell Wiki, so it is easier to keep things up-to-date, integrate more
examples/tutorials/etc.  I'll think about that...

> There are some sites that include a lot of Red Book
> examples that should just compile and work with the
> method I gave (such as ghc --make Planet.hs).  Anyone
> know a reason why some tutorials use the -package GLUT
> option?

The OpenGL/GLUT packages are exposed by default, so there is no need to
specify them explicitly, unless you are manually compiling and linking. This
is explained in detail at:

http://www.haskell.org/ghc/docs/latest/html/users_guide/packages.html#using-packages

So the easiest way to use all OpenGL/GLUT stuff is importing Graphics.UI.GLUT
and using "ghc --make". A single import, no special options...

> Try some of these links:
>
> This should have the newer examples (can anyone tell
> me if there are any better sites than this?)
> http://cvs.haskell.org/cgi-bin/cvsweb.cgi/~checkout~/fptools/libraries/GLUT
>/examples/RedBook/ [...]

The OpenGL/GLUT packages are now under darcs control instead of CVS, so the
latest and greatest examples are available at:

   http://darcs.haskell.org/packages/GLUT/examples/

If you use Hugs, it may already ship with all the examples, e.g. at:

   /usr/lib/hugs/demos/GLUT

Cheers,
   S.
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[H.]

Thanks a lot, it does work!

I just read a hOpenGL tutorial, and nowhere was used the flush command in
connection to clear the ColorBuffer


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[Chris Perez]

Thanks Alot! I found the new updated redbook in the source code for GHC 6.6 with tons of examples. I have finally gotten the samples to compile and run, looks like clear sailing from here.

On 2/22/07, Sven Panne <sven.panne@...> wrote:

On Thursday 22 February 2007 13:02, Jamin A. Ohmoto-Frederick wrote:
> Regarding Chris' post -
>
> I ran into a lot of problems too since there are old
> versions of HOpenGL and corresponding examples
> floating around out there with differing advice, such
> as at http://www.haskell.org/HOpenGL/.  I'm not sure
> why it hasn't been updated since it's off of the main
> haskell.org.

I admit being guilty here of not upating that site for a very long time. My
amount of time I can work on HOpenGL varies quite a bit depending on my Real
Life (tm) ;-), I think it might be a good idea to move the stuff to the
Haskell Wiki, so it is easier to keep things up-to-date, integrate more
examples/tutorials/etc.  I'll think about that...

> There are some sites that include a lot of Red Book
> examples that should just compile and work with the
> method I gave (such as ghc --make Planet.hs).  Anyone
> know a reason why some tutorials use the -package GLUT
> option?

The OpenGL/GLUT packages are exposed by default, so there is no need to
specify them explicitly, unless you are manually compiling and linking. This
is explained in detail at:

http://www.haskell.org/ghc/docs/latest/html/users_guide/packages.html#using-packages

So the easiest way to use all OpenGL/GLUT stuff is importing Graphics.UI.GLUT
and using "ghc --make". A single import, no special options...

> Try some of these links:
>
> This should have the newer examples (can anyone tell
> me if there are any better sites than this?)
> http://cvs.haskell.org/cgi-bin/cvsweb.cgi/~checkout~/fptools/libraries/GLUT
>/examples/RedBook/ [...]

The OpenGL/GLUT packages are now under darcs control instead of CVS, so the
latest and greatest examples are available at:

   http://darcs.haskell.org/packages/GLUT/examples/

If you use Hugs, it may already ship with all the examples, e.g. at:

   /usr/lib/hugs/demos/GLUT

Cheers,
   S.
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--
Without Wax,
        Chris
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[Sven Panne]

On Thursday 22 February 2007 16:38, h. wrote:
> Thanks a lot, it does work!
>
> I just read a hOpenGL tutorial, and nowhere was used the flush command in
> connection to clear the ColorBuffer

The reason that leaving out 'flush' seems to work sometimes is that some
OpenGL implementations (e.g. Mesa in SW rendering mode) do not have the
highly asynchronous behaviour allowed by the OpenGL spec. OTOH, e.g. NVIDIA's
driver definitely needs a 'flush'/'swapBuffers'. So as a general rule, use
one of these functions at the end of your display callback.

Cheers,
   S.
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