[Gtk2hs-users] [Haskell-cafe] Anyone know why this always returns invalid texture objects?

[Jefferson Heard]

Ah, that's good to know.  I thought initGL would create the context.
Sorry to be unclear in the code I posted, but part of createGUIObject
is a glDrawingAreaNew.  It creates a drawing area, which is then
stored in a giant UserInterface record.

data UserInterface = MainWindow {
  ...
  , drawing_canvas :: GLDrawingArea
  }

createGUIObject = do
  ...
  config <- glConfigNew ...
  canvas <- glDrawingAreaNew config

  return $ MainWindow { ... drawing_canvas = canvas .. }

It seems that won't create the context?  do I have to show the window
first, or can I just do...

withGLDrawingArea $ glGenObjects n

?

Thanks!

-- Jeff

On Thu, Nov 6, 2008 at 9:15 PM, Bertram Felgenhauer
<bertram.felgenhauer at googlemail.com> wrote:
> [CCing gtk2hs-users]
>
> Jefferson Heard wrote:
>> import Graphics.UI.Gtk
>> import Graphics.UI.Gtk.Glade
>> import Graphics.UI.Gtk.OpenGL
>> import qualified Graphics.Rendering.OpenGL as GL
>> import Graphics.Rendering.OpenGL (($=))
>>
>> main = do
>>   initGUI
>>   initGL
>
> "initGL" may be slightly misleading - it initialises the
> gtkglext gtk+ extension. It does not create a GL context.
>
>>   GL.shadeModel $= GL.Flat
>>   GL.depthFunc $= Just GL.Less
>>   (window1,gui,dlgs) <- constructGUIObject
>>   (sX, sY) <- liftM (mapPair fromIntegral) . widgetGetSize .
>> drawing_canvas $ gui -- get the canvas size for determining the part
>> of the widget to repaint
>>   pb <- pixbufNew ColorspaceRgb False 8 (round pbWidth) (round pbHeight)
>>   pixbufFill pb 0 0 0 255
>>   pxbufs <- initSubpixbufs pb texRows texCols
>>   textures <- GL.genObjectNames (texRows*texCols)
>>   print textures
>
> There is no active GL context at this point. GtkGLExt creates
> new GL contexts for GL enabled widgets when they're realized -
> I think. I'm a bit fuzzy about the exact life time of the GL
> context. [1]
>
> After the context was created, you have to activate it before
> doing any GL operations.
>
> In Gtk2hs you can use the GLDrawingArea widget, which provides
> withGLDrawingArea for easy activation of the GL context.
>
> There's an example in the gtk2hs sources, in examples/opengl.
>
> Enabling GL for other widgets is not supported well at the moment.
> (There are low level bindings (using DrawWindow), but no generic
> binding to the higher level gtk_widget_set_gl_capability() call.
> Such support wouldn't be too hard to add, I think.)
>
> HTH,
>
> Bertram
>
> [1] see http://gtkglext.sourceforge.net/reference/gtkglext/gtkglext-gtkglwidget.html#gtk-widget-get-gl-context
>
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