pyopengl-users

[PyOpenGL-Users] OpenGl + Mouse Selection

[Jasper P. <ja...@pe...>]

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I want to be able to "select" different entities rendered in OpenGL w/
a mouse -- essentially asking which shape the mouse pointer is over.
Ideally this could be used to select game pieces to move, etc.

This is fairly easy to compute when rending in an orthographic view, as you
can simply translate mouse coordinates to viewpane coordinates.  However,
this doesn't work well for perspective views!

It would be nice to simply ask opengl what lies behind a certain screen
coordinate, but I haven't been able to find anything amongst the "glut"
(rimshot!) of opengl documentation about this.

Has anyone here had any experience with something like this?  I suspect
there must be an easy way to do it, as obviously the information is
available inside of opengl.

- -Jasper

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Re: [PyOpenGL-Users] OpenGl + Mouse Selection

[Mike C. F. <mcf...@ro...>]

There are a number of ways to do this, but the most common way I've 
encountered is to use the glSelectBuffer-based selection mechanisms 
which come with OpenGL.  You can find sample code for the glSelectBuffer 
stuff in OpenGLContext or just about any OpenGL reference or programming 
Web site (such as NeHe).

The basic approach is to re-render the scene in "select" mode, pushing 
"names" (integers) onto the selection stack as you render to a frustum 
which is the projection of your picking point to infinity.  When you 
exit the select rendering mode you receive a list of records indicating 
which names were active when items were rendered to the frustum.

Hope this helps,
Mike

Jasper Phillips wrote:

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>
>I want to be able to "select" different entities rendered in OpenGL w/
>a mouse -- essentially asking which shape the mouse pointer is over.
>Ideally this could be used to select game pieces to move, etc.
>
>This is fairly easy to compute when rending in an orthographic view, as you
>can simply translate mouse coordinates to viewpane coordinates.  However,
>this doesn't work well for perspective views!
>
>It would be nice to simply ask opengl what lies behind a certain screen
>coordinate, but I haven't been able to find anything amongst the "glut"
>(rimshot!) of opengl documentation about this.
>
>Has anyone here had any experience with something like this?  I suspect
>there must be an easy way to do it, as obviously the information is
>available inside of opengl.
>
>- -Jasper
>
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>Version: GnuPG v1.0.6 (GNU/Linux)
>Comment: For info see http://www.gnupg.org
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>iD8DBQE+pEJN8EpjZ7/X9bIRAilwAKDWUmh9ltlv1HiYRh7G5WO0TlJwWQCg1F3N
>v9HHh5Eip+cBteBTCcPFMbE=
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>
>
>-------------------------------------------------------
>This sf.net email is sponsored by:ThinkGeek
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>

-- 
_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/

Re: [PyOpenGL-Users] OpenGl + Mouse Selection

[Jasper P. <ja...@pe...>]

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That sounds like what I want.  Thanks for the search reference!
- -Jasper

On Mon, 21 Apr 2003, Mike C. Fletcher wrote:
> There are a number of ways to do this, but the most common way I've 
> encountered is to use the glSelectBuffer-based selection mechanisms 
> which come with OpenGL.  You can find sample code for the glSelectBuffer 
> stuff in OpenGLContext or just about any OpenGL reference or programming 
> Web site (such as NeHe).
> 
> The basic approach is to re-render the scene in "select" mode, pushing 
> "names" (integers) onto the selection stack as you render to a frustum 
> which is the projection of your picking point to infinity.  When you 
> exit the select rendering mode you receive a list of records indicating 
> which names were active when items were rendered to the frustum.
> 
> Hope this helps,
> Mike

[snip my original question]
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Re: [newsletters] Re: [PyOpenGL-Users] OpenGl + Mouse Selection

[sebastien H. <2l...@2l...>]

I use this method with good success.

I just have a little problem. My program paint some line on the OpenGL 
panel and when i try to select one, I need to be very close to select 
it. Is it a way to make the select area more large ?

Thanks in advance.

SEB

Jasper Phillips a écrit:

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>
>That sounds like what I want.  Thanks for the search reference!
>- -Jasper
>
>On Mon, 21 Apr 2003, Mike C. Fletcher wrote:
>  
>
>>There are a number of ways to do this, but the most common way I've 
>>encountered is to use the glSelectBuffer-based selection mechanisms 
>>which come with OpenGL.  You can find sample code for the glSelectBuffer 
>>stuff in OpenGLContext or just about any OpenGL reference or programming 
>>Web site (such as NeHe).
>>
>>The basic approach is to re-render the scene in "select" mode, pushing 
>>"names" (integers) onto the selection stack as you render to a frustum 
>>which is the projection of your picking point to infinity.  When you 
>>exit the select rendering mode you receive a list of records indicating 
>>which names were active when items were rendered to the frustum.
>>
>>Hope this helps,
>>Mike
>>    
>>
>
>[snip my original question]
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>ic7GD51sUgA+UrrgT+jii2M=
>=04I+
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>
>
>
>-------------------------------------------------------
>This sf.net email is sponsored by:ThinkGeek
>Welcome to geek heaven.
>http://thinkgeek.com/sf
>_______________________________________________
>PyOpenGL Homepage
>http://pyopengl.sourceforge.net
>_______________________________________________
>PyOpenGL-Users mailing list
>PyO...@li...
>https://lists.sourceforge.net/lists/listinfo/pyopengl-users
>
>
>  
>

Re: [newsletters] Re: [PyOpenGL-Users] OpenGl + Mouse Selection

[Mike C. F. <mcf...@ro...>]

Setup the projection matrix to be slightly larger than a single point 
(OpenGLContext gives you a 2x2 area).  Here's the code from 
OpenGLContext/renderpass's SelectRenderPass class (matrixSize is just a 
tuple of (2,2) in this case):

    def PickProjection( self ):
        """Setup the constrained picking matrix and result buffer

        We set up the view frustum to be a
        box centered around the picking point of size
        self.matrixSize, projecting back into the screen
        from our current viewpoint.

        We then set up the selection buffer into which
        our results will be saved, and then switch to
        selection-mode rendering.
        """
        glMatrixMode(GL_PROJECTION)
        glLoadIdentity()
        glInitNames()
        x,y = self.pickPoint
        gluPickMatrix(
            x,y,
            self.matrixSize [0], self.matrixSize [1],
            self.getViewport()
        )
        glSelectBuffer(self.bufferSize)
        glRenderMode(GL_SELECT)

You can find documentation on gluPickMatrix here:
http://pyopengl.sourceforge.net/documentation/manual/gluPickMatrix.3G.html

HTH,
Mike

sebastien HEITZMANN wrote:

> I use this method with good success.
>
> I just have a little problem. My program paint some line on the OpenGL 
> panel and when i try to select one, I need to be very close to select 
> it. Is it a way to make the select area more large ?
>
> Thanks in advance.
>
> SEB
>
> Jasper Phillips a écrit:
>
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>>
>> That sounds like what I want.  Thanks for the search reference!
>> - -Jasper
>>
>> On Mon, 21 Apr 2003, Mike C. Fletcher wrote:
>>  
>>
>>> There are a number of ways to do this, but the most common way I've 
>>> encountered is to use the glSelectBuffer-based selection mechanisms 
>>> which come with OpenGL.  You can find sample code for the 
>>> glSelectBuffer stuff in OpenGLContext or just about any OpenGL 
>>> reference or programming Web site (such as NeHe).
>>>
>>> The basic approach is to re-render the scene in "select" mode, 
>>> pushing "names" (integers) onto the selection stack as you render to 
>>> a frustum which is the projection of your picking point to 
>>> infinity.  When you exit the select rendering mode you receive a 
>>> list of records indicating which names were active when items were 
>>> rendered to the frustum.
>>>
>>> Hope this helps,
>>> Mike
>>>   
>>
>>
>> [snip my original question]
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>> Comment: For info see http://www.gnupg.org
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>> iD8DBQE+pFYa8EpjZ7/X9bIRAj6zAJ9Qd3y0PFhixkxbplYA+dxw4vCnYQCgwnGY
>> ic7GD51sUgA+UrrgT+jii2M=
>> =04I+
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>>
>>
>>
>> -------------------------------------------------------
>> This sf.net email is sponsored by:ThinkGeek
>> Welcome to geek heaven.
>> http://thinkgeek.com/sf
>> _______________________________________________
>> PyOpenGL Homepage
>> http://pyopengl.sourceforge.net
>> _______________________________________________
>> PyOpenGL-Users mailing list
>> PyO...@li...
>> https://lists.sourceforge.net/lists/listinfo/pyopengl-users
>>
>>
>>  
>>
>
>
>
> -------------------------------------------------------
> This sf.net email is sponsored by:ThinkGeek
> Welcome to geek heaven.
> http://thinkgeek.com/sf
> _______________________________________________
> PyOpenGL Homepage
> http://pyopengl.sourceforge.net
> _______________________________________________
> PyOpenGL-Users mailing list
> PyO...@li...
> https://lists.sourceforge.net/lists/listinfo/pyopengl-users
>

-- 
_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/

Re: [PyOpenGL-Users] OpenGl + Mouse Selection

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

On Monday 21 April 2003 12:11 pm, Jasper Phillips wrote:
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> Hash: SHA1
>
> I want to be able to "select" different entities rendered in OpenGL w/
> a mouse -- essentially asking which shape the mouse pointer is over.
> Ideally this could be used to select game pieces to move, etc.
>
> This is fairly easy to compute when rending in an orthographic view, as you
> can simply translate mouse coordinates to viewpane coordinates.  However,
> this doesn't work well for perspective views!
>
> It would be nice to simply ask opengl what lies behind a certain screen
> coordinate, but I haven't been able to find anything amongst the "glut"
> (rimshot!) of opengl documentation about this.
>
> Has anyone here had any experience with something like this?  I suspect
> there must be an easy way to do it, as obviously the information is
> available inside of opengl.


OpenGL has a way to do this.  Look at glSelectBuffer, and also
glInitNames, glLoadName, glPushName, and gluPickMaatrix.

Like most things in OpenGL, these are low level tools which provide
much power, but will take a little time to learn to use.

Good Luck,
Gary Herron