Re: PVD

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Wed, 12 Jul 1995 02:44:44 -0600

> I am trying to write a simple plan-view display in Perfomer which means
> I need to keep the eye point pitched straight down, scroll around
> the database, and draw some routes. The first problem I have is
> getting an orthogonal frustum. I use pfMakeOrthoFrust and supply
> it with the channel size and also set ChanAutoAspect to
> PFFRUST_CALC_NONE. When I do this, it looks as though the screen
> is not being cleared because the stats start painting the screen.
> Are there any other calls that have to be made to get an orthogonal
> frustum beside pfMakeOrthoFrust and pfChanAutoAspect?
>

This sounds like it a tag clear problem. Where are your clip planes,
and are you clipping out geometry? Try changing the clear screen method,
to avoid using a tag clear.

> Second problem is that I need to be able to draw line segments
> on the map. How do I get world coodinates from a mouse position
> without having to pick objects.

Ortographic plan views is the easiest case for trying this
Apply an appropriate scale and translation to the mouse coordinates.

Should be something like:

xporldcoord = xleftscreenworldcoord + MOUSEX/windowpixelwidth *
         (xrightscreenworldcoord - xleftscreenworldcoord);

and similar for ypos.

-- 
Angus Dorbie,
The Reality Centre,
Silicon Graphics Ltd, UK
dorbie++at++reading.sgi.com

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