Re: [pygame] opengl from python - drawing wireframe shape colours and contour in the same time

[Casey Duncan <casey@xxxxxxxxxxx>]

You can draw wireframes instead of fills by setting:

glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)

Then draw your geometry as desired.

Note this has the same limitations and drawbacks as GL_LINE, but for  
simulating old-school vector graphics it works pretty good. You can  
control whether or not a particular edge is drawn using edge flags.  
That way interior edges that exist just for tessellation, don't  
clutter up the rendering.

What typically looks good is to do a first pass at low alpha with a  
wide glLineWidth, then render again with a higher alpha and a lower  
width. Last draw with line width set to 1 (or whatever) and full  
alpha. Gives a decent glowing vector line effect. Also be sure to  
enable multisampling to combat aliasing.

I attached a screenshot of a model rendered using this technique. The  
code that produced it can be found here:

http://code.google.com/p/caseman/source/browse/trunk/eos/tools/show_obj.py

The libraries it uses to load the model and draw it are there as well.

hth,

-Casey


On Jul 27, 2009, at 2:06 PM, Paulo Silva wrote:

> no, my idea is doing simple poly games, a bit like those 3d games from
> Amiga time (such as Robocop3 and many others) - very flatcoloured -
> but i really wanted so have the meshes wireframed - thanks for all
> useful info! :)
>
> On 7/27/09, Ian Mallett <geometrian@xxxxxxxxx> wrote:
> > Yes, unfortunately.  That may be a problem, especially if the  
> > object is high
> > poly.  There are more complex methods that use shaders.  One of the  
> > better
> > ones I've found is:
> >
> > Render the scene to two textures, one RGB and the other depth
> > Apply an edge-detection filter to the depth texture (no edge =  
> > white, edge =
> > black)
> > Multiply the two textures together on a fullscreen quad.
> >
> > The problem here is you'd need shaders if you want to only have one  
> > pass,
> > which may be overkill.  (MRT to render to both textures  
> > simultaneously or
> > storing the depth in the alpha channel of the texture).  If you  
> > want to use
> > fixed function, you'd need two render-to-textures; one for each  
> > texture--and
> > so there wouldn't really be an advantage to this method over the  
> > original
> > one.
> >
> > There's also normal-based edge detection, which I have tried as  
> > well.  It's
> > simpler, though you'll probably need a shader here too.  This  
> > unfortunately
> > suffers from line-thickness, which may or may not be a problem.   
> > You'd only
> > need one pass though.
> >
> > HTH,
> > Ian