pyopengl-users

[PyOpenGL-Users] Aliasing changes when I have a white background

[Rick M. <rpm...@gm...>]

I maintain a chemical graphics program called Vimes
(http://vimes.sf.net) that uses PyOpenGL for it's OpenGL rendering.
I've been very happy with how well PyOpenGL has worked for me over the
years, and I'm particularly thrilled with how easy the new
installation in version 3 is.

I have a more basic problem, though. When I draw a molecule on a black
background, everything looks great:
http://farm2.static.flickr.com/1037/1074160261_a963714943_o.png
If this isn't publication quality, it's close enough that I don't care
about the difference.

However, when I draw a molecule with a white background, the aliasing looks bad:
http://farm2.static.flickr.com/1314/1074160459_5baa206cc4_o.png
I'm not a real OpenGL expert, so I'm probably doing something wrong.
One of the great things about PyOpenGL is that it makes OpenGL
possible for people like me.

Can anyone give me pointers to making this look better? Thanks in advance,

-- 
Rick Muller
rpm...@gm...

Re: [PyOpenGL-Users] Aliasing changes when I have a white background

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

Rick Muller wrote:
> However, when I draw a molecule with a white background, the aliasing looks bad:

You could try turning on FSAA (Full Scene
Anti-Aliasing). There will be an option for this
when you create the OpenGL context, although the
details are platform-dependent.

This causes the scene to be rendered at a higher
resolution and then smoothed. It takes longer to
render, but if you're not trying to get enormous
frame rates, that probably won't be a problem.

--
Greg

Re: [PyOpenGL-Users] Aliasing changes when I have a white background

[Rick M. <rpm...@gm...>]

This is indeed what it looks like, which is why I think I'm doing
something wrong. I thought I was drawing the image on white, but
perhaps I'm not doing what I think I'm doing. Could double buffering
be messing me up here?

The basic way I'm updating my screen is:

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

        #anti-aliasing code
        glEnable(GL_BLEND)
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
        glHint(GL_LINE_SMOOTH_HINT, GL_DONT_CARE)

        glPushMatrix()
        glCallList(self.dlist)
        glPopMatrix()

        self.SwapBuffers()

However, I only set the color when I setup the canvas, so maybe I'm
not updating it in the second buffer. Does anyone have any thoughts on
this?

On 8/11/07, vwf <vw...@vu...> wrote:
> On Fri, Aug 10, 2007 at 02:38:21PM -0600, Rick Muller wrote:
> > http://farm2.static.flickr.com/1037/1074160261_a963714943_o.png
> > If this isn't publication quality, it's close enough that I don't care
> > about the difference.
> > However, when I draw a molecule with a white background, the aliasing looks bad:
> > http://farm2.static.flickr.com/1314/1074160459_5baa206cc4_o.png
> > I'm not a real OpenGL expert, so I'm probably doing something wrong.
>
> I am not an OpenGL anti-aliasing expert either, but did you really draw
> the second image on white? It looks like you drew it on black, and
> placed it on a white background afterwards.
>
>


-- 
Rick Muller
rpm...@gm...

Re: [PyOpenGL-Users] Aliasing changes when I have a white background

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

Rick Muller wrote:
> The basic way I'm updating my screen is:
> 
>         #anti-aliasing code
>         glEnable(GL_BLEND)
>         glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
>         glHint(GL_LINE_SMOOTH_HINT, GL_DONT_CARE)

You're turning on smoothing for lines here, but your
images look like they're made up of filled polygons.
Line smoothing has no effect on polygon rendering.

So I think you're not getting any anti-aliasing at
all, and the black/white difference is just because
the eye doesn't notice it so much against a black
background.

There is an option for smoothing polygons, but using
it correctly is viciously difficult. Unless you're
pushing the limits of rendering speed, FSAA is by
far the better way to go.

--
Greg