From: Yoram Shahak (yoram++at++dreamteam-ltd.com)
Date: 10/17/2000 23:12:40
Thanks!
Works fine !
:O)
Yoram Shahak
DreamTeam ltd.
Angus Dorbie wrote:
> Oops, got it slightly wrong on the followup, it's flickering because the
> position is getting clipped (not a fragment test) randomly on each frame
> after transformation through modelview, proximity to the corner is also
> a risk. Same solution except you might want to bring the corner in in
> eye space x, y by a small ammount.
>
> also in the last email I meant to suggest multiplying the WHOLE vector
> not just the Z term.
> Because of the vertex edge clip I'd do this:
>
> farPlaneLL[0] * .99998 <- note slightly smaller
> farPlaneLL[1] * .99998 <- note slightly smaller
> farPlaneLL[2] * .99999
>
> Cheers,Angus.
>
> Angus Dorbie wrote:
> >
> > It has been pointed out to me by a benevolent list lurker that this is
> > not the only explanation and may not be the right answer.
> >
> > The alternative and perhaps more likely explanation is that the draw
> > pixels if flickering because it is drawn EXACTLY at the far clip plane
> > is being z fragment clipped at the far plane due to rounding errors. The
> > solution is to position the image nearer the eye by multiplying
> > farPlaneLL[2] by 0.99999 or so.
> >
> > Cheers,ANgus.
> >
> > Angus Dorbie wrote:
> > >
> > > No clear in pfDraw, you are expected to clear if you have a draw
> > > callback on a channel.
> > >
> > > You may not need to clear if you set your depth test to always when you
> > > draw the image.
> > > Same thing goes for stencil test and write when drawing.
> > >
> > > In general your code should work I as far as I can tell. Are you sure
> > > you are double buffered?
> > >
> > > Cheers,Angus.
> > >
> > > Yoram Shahak wrote:
> > > >
> > > > Hi,
> > > >
> > > > I am trying to implement background texturing using glDrawPixels in my
> > > > draw call back.
> > > > my code looks something like this :
> > > >
> > > > void drawCallBack(pfChannel *chan, void *data)
> > > > {
> > > > preDraw(chan, data);
> > > > pfDraw();
> > > > }
> > > >
> > > > void preDraw()
> > > > {
> > > > chan->clear();
> > > > glClearStencil(0x0);
> > > > glClear(GL_STENCIL_BUFFER_BIT);
> > > >
> > > > pfVec3 farPlaneLL, dummy;
> > > > chan->getFar(farPlaneLL, dummy, dummy, dummy);
> > > >
> > > > glRasterPos3f(farPlaneLL[0], farPlaeLL[1], farPlaneLL[2]);
> > > > glDrawPixels(winWidth, winHeight, imageFormat,GL_UNSIGNED_INT,
> > > > imageBuffer);
> > > >
> > > > }
> > > >
> > > > As a result I get the background image flickering if at all seen.
> > > > Does performer clear the gl buffer in pfDraw ?
> > > > Am I going totally the wrong way about implementing this ?
> > > >
> > > > Please help .
> > > > Thanx.
> > > >
> > > > :o)
> > > >
> > > > Yoram Shahak
> > > > DreamTeam ltd.
> > > >
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> >
> > "In the middle of difficulty lies opportunity."
> > --Albert Einstein
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>
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> For Performer+OpenGL tutorials http://www.dorbie.com/
>
> "In the middle of difficulty lies opportunity."
> --Albert Einstein
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