Re: transparency
Angus Dorbie (angus++at++division.demon.co.uk)
Mon, 23 Jan 1995 09:59:49 +0000
On Jan 20, 4:04pm, Lance R. Marrou wrote:
> Subject: transparency
> I get a different result from using this:
>
> pfGStateMode( exp_gstate, PFSTATE_TRANSPARENCY,
> PFTR_ON|PFTR_NO_OCCLUDE );
>
> as opposed to:
>
> long exp_trans_state;
> long PreDraw(pfTraverser *trav, void *data)
> {
> exp_trans_state = pfGetTransparency();
> pfTransparency(PFTR_ON|PFTR_NO_OCCLUDE);
> return PFTRAV_CONT;
> }
>
> long PostDraw(pfTraverser *trav, void *data)
> {
> pfTransparency(exp_trans_state);
> return PFTRAV_CONT;
> }
>
> The pre-draw and post-draw function callback technique provides
> the correct transparent geoset (of course the alpha values are
> set correctly). However, setting the state mode works for
> allowing transparency, but it makes the geoset occlude other
> transparent geometry. I have attempted just about every combination
> of state mode to get it to work the same, but no luck. Obviously,
> I could just stick to the function callbacks, but I want to know
> why setting the state doesn't work.
>
> I have images which show the results of both methods for those
> interested to see them.
>
>
>-- End of excerpt from Lance R. Marrou
Hi Lance,
your problem may be that when you set the geostate transparency on
performer sorts associated geometry but when you simply add callbacks performer
cannot know what youre doing in there and so doesn't sort. The apparent result
is very different because of the drawing order, although geometry is still
being drawn in exactly the same way.
--
Angus Dorbie Division Ltd,
Software Engineer 19 Apex Court,
Tel: (01454)615554 Woodlands,
Fax: (01454)615532 Bristol BS12 4JT,
angus++at++division.demon.co.uk UK
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on Mon Aug 10 1998 - 17:50:53 PDT