Re: [PyOpenGL-Users] gluUnProject Projection Failed

[Gary H. <gh...@di...>]

Eleftherios Garyfallidis wrote:
> Hello,
>
> Thank you again for your response.
>
> - Show quoted text -
> On Tue, Apr 13, 2010 at 11:20 AM, Greg Ewing 
> <gre...@ca... <mailto: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)


I have not followed this thread at all -- so I don't know the history.  
Nevertheless, I see a potential problem.

The call to gluUnProject expects the viewport to be passed in as 
integers (GLint*) so you should be using glGetIntegerv not glGetDoublev 
to get the viewport as an array of integers.

Here's gluUnProject's spec:
  GLint gluUnProject(    GLdouble winX,
       GLdouble winY,
       GLdouble winZ,
       const GLdouble * model,
       const GLdouble * proj,
       const GLint * view,           // !!!!!
       GLdouble* objX,
       GLdouble* objY,
      GLdouble* objZ);

Using glGetDoublev for the two matricies and glGetIntegerv for the 
viewport as input to gluUnProject has always worked well for me.

>
>   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
>  
>
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-- 
Gary Herron, PhD.
Department of Computer Science
DigiPen Institute of Technology
(425) 895-4418