Re: [PyOpenGL-Users] gluUnProject Projection Failed

[Eleftherios G. <gar...@gm...>]

Hello,

Thank you again for your response.

- Show quoted text -
On Tue, Apr 13, 2010 at 11:20 AM, Greg Ewing <gre...@ca...>wrote:

> Eleftherios Garyfallidis wrote:
> > to get
>
>> the near plane I believe you need to gluUnProject with z=0. and to get the
>> far plane you need to gluUnProject with z=1
>>
>
> You're quite right, I was misremembering, sorry.
>
>
>  Surprisingly, when I do glu.gluUnProject(x,viewport[3]-y,0.) and
>> glu.gluUnProject(x,viewport[3]-y,1.) in PyOpenGL it seems it works fine but
>> when I am feeding the transformation matrices by myself I am getting this
>> error "Projection Failed".
>>
>
> That sounds like there is something wrong with your matrices.
> How are you getting them? Are you getting them directly from
> OpenGL, or calculating them yourself? If you're calculating them
> yourself, you might be making a mistake somewhere.
>

> What happens if you retrieve the relevant matrices from OpenGL
> and feed them to gluUnProject? If that works, compare them with
> your own matrices to see if there is a difference.
>

  Yes this is what I am doing just calculating these matrices using the
following PyOpenGL functions

  import OpenGL.GL as gl

  modelviewmatrix=gl.glGetDoublev(gl.GL_MODELVIEW_MATRIX)

  projectionmatrix=gl.glGetDoublev(gl.GL_PROJECTION_MATRIX)

  viewport=gl.glGetDoublev(gl.GL_VIEWPORT)

  These matrices are numpy arrays do you think that it might be a problem
when we put these as input in gluUnProject? Should I transform them into
something else perhaps?

  By the way I do confirm that when using gluUnProject without feeding in
the transformation matrices as in glu.gluUnProject(x,viewport[3]
-y,0.) does work correctly :-) I made some tests with picking planes and the
accuracy of picking was excellent!!! The tests involved checking if the
segment AB (where A is near and B is far) intersects with planes. For my
application I need to check against many planes so I made a function for
this in cython. The link for the code is here

http://github.com/Garyfallidis/Fos/blob/master/fos/core/collision.pyx

Best wishes,
Eleftherios