pyopengl-users

[PyOpenGL-Users] gluPerspective arguments ?

[Anders W. <and...@he...>]

Hi Group, I am a newbie playing around with python and opengl.

I am a bit confused by how gluPerspective works. My book tells me the 
arguments are
gluPerspective( fovy, aspect, near, far)

but I only get a black window whenever near<far, and it seems to work 
much better with something like:
gluPerspective(50, 1, 20.0, 1.0)

i.e. could it be that the python wrapper has the near/far arguments 
reversed ?

-- 
Anders Wallin

Re: [PyOpenGL-Users] gluPerspective arguments ?

[Greg E. <gre...@ca...>]

Anders Wallin wrote:

> i.e. could it be that the python wrapper has the near/far arguments 
> reversed ?

I'm using it with near < far without any problems.
Maybe there's something weird about the coordinate
system you're using?

--
Greg

Re: [PyOpenGL-Users] gluPerspective arguments ?

[Anders W. <and...@he...>]

Greg Ewing wrote:
>
>> i.e. could it be that the python wrapper has the near/far arguments 
>> reversed ?
> I'm using it with near < far without any problems.
> Maybe there's something weird about the coordinate
> system you're using?

My OnDraw() looks something like this:
            glMatrixMode(GL_PROJECTION)
            glLoadIdentity()
            gluPerspective(20, 1, 20.0, 1.0)           # why 20 > 1 ?
            gluLookAt(x , y, z, 0, 0, 0, 0, 0, 1)

            glMatrixMode(GL_MODELVIEW)
            glEnable(GL_DEPTH_TEST)
            glEnable(GL_LIGHTING)
            glEnable(GL_LIGHT0)
            # Draw cube
            glLoadIdentity()
            glBegin(GL_QUADS)
            ....
            glEnd()
            self.SwapBuffers()



If anyone has any good ideas on why my gluPerspective works funnily then 
let me know!
for example, does it make a difference in which order Perspective and 
LookAt are called ?

-- 
Anders Wallin

Re: [PyOpenGL-Users] gluPerspective arguments ?

[Black <py...@bl...>]

It doesn't matter which order gluPerspective() and gluLookAt() are  
called in...

However, what _does_ matter is that gluLookAt() is supposed to be the  
"view" part of the modelview matrix so you want your OnDraw to look  
more like

             glMatrixMode(GL_PROJECTION)
             glLoadIdentity()
             gluPerspective( some more reasonable arguments )
             glMatrixMode(GL_MODELVIEW)
	    glLoadIdentity()
   	    gluLookAt(x , y, z, 0, 0, 0, 0, 0, 1)
             glEnable(GL_DEPTH_TEST)
             glEnable(GL_LIGHTING)
             glEnable(GL_LIGHT0)
             # Draw cube

             glBegin(GL_QUADS)
             ....
             glEnd()
             self.SwapBuffers()


As a side note, you probably want the last three arguments to  
gluLookAt() to be 0,1,0 so you aren't lying on your side...

This is probably enough to give you something to look at, but I do  
urge you to spend some more time figuring out what the projection and  
modelview matrices are and what they do before you get too much  
farther. You might also want to look at some more examples of how to  
organize your code - a lot of the stiff you put in your draw()  
function really shouldn't be there.


On Jul 4, 2006, at 12:26 AM, Anders Wallin wrote:

> Greg Ewing wrote:
>>
>>> i.e. could it be that the python wrapper has the near/far arguments
>>> reversed ?
>> I'm using it with near < far without any problems.
>> Maybe there's something weird about the coordinate
>> system you're using?
>
> My OnDraw() looks something like this:
>             glMatrixMode(GL_PROJECTION)
>             glLoadIdentity()
>             gluPerspective(20, 1, 20.0, 1.0)           # why 20 > 1 ?
>             gluLookAt(x , y, z, 0, 0, 0, 0, 0, 1)
>
>             glMatrixMode(GL_MODELVIEW)
>             glEnable(GL_DEPTH_TEST)
>             glEnable(GL_LIGHTING)
>             glEnable(GL_LIGHT0)
>             # Draw cube
>             glLoadIdentity()
>             glBegin(GL_QUADS)
>             ....
>             glEnd()
>             self.SwapBuffers()
>
>
>
> If anyone has any good ideas on why my gluPerspective works funnily  
> then
> let me know!
> for example, does it make a difference in which order Perspective and
> LookAt are called ?
>
> -- 
> Anders Wallin
>
>
> Using Tomcat but need to do more? Need to support web services,  
> security?
> Get stuff done quickly with pre-integrated technology to make your  
> job easier
> Download IBM WebSphere Application Server v.1.0.1 based on Apache  
> Geronimo
> http://sel.as-us.falkag.net/sel? 
> cmd=lnk&kid=120709&bid=263057&dat=121642
> _______________________________________________
> PyOpenGL Homepage
> http://pyopengl.sourceforge.net
> _______________________________________________
> PyOpenGL-Users mailing list
> PyO...@li...
> https://lists.sourceforge.net/lists/listinfo/pyopengl-users