From: jcaesar@mediaone.net
To: <ml@qoole.com>
Reply-To: ml@qoole.com
Date: Fri, 23 Jan 1998 13:50:53 -0800
Subject: Re: hint brushes???

You really need to understand how vis works it's magic, and how each brush
is converted to polygons.

Take this corner..

x
x
x
cyyyyyy9

x is one pipe, c is the room in the middle, y the other pipe, and 9 is your
player.  When bsp creates the polygons, it looks, for the sake of
simplicity, you'd have x and y each made of very long polygons.  Sometimes
that's true.  Sometimes it isn't.  Hint brushes work, when, in the example
here, the polygons ARE very long.

If the polygon goes the entire length of the pipe y, vis will check to see
if it can see into the x pipe.  If vis can see into any part of x, all of x
gets drawn.  Now in the game, from position 9 above, you cannot see into x.
But vis doesn't care how far along you are.  As soon as you step on that
polygon, vis assumes you can see into x, cause it checks from the other end
of the polygon as well.  (I know this is convoluted but bear with me).

In this example (with hint brush H)

x
x
x
cy1y1y1*Hy2y2y29

Now we have a hint brush.  This forces qbsp to make the original y pipe into
two pieces, y1 and y2.  From position 9, vis goes to the end of y2, and
can't see into x.  The result is that x is not drawn while you are on
polygon y2.  When you cross to position * on y1, vis (from the end of y1)
can see into x, and now x is drawn (NB: When I say x is drawn, It may be
invisible to you, but it is being rendered by the Q2 engine, behind the
walls of y).

Finally, this means when you are in y2, on the right side of the hint brush,
you don't have to render x.. saving polygons.  You could cut x in half as
well with a hint brush, and so on.

Again.. you really need to know what gl_showtris can show you (and you gotta
have full GL for that) and that's whether or not that polygon (in my example
pipe y) is one long one, or a bunch of small ones.  Placing Hint brushes
haphazardly won't be a benefit, but rather a really nice way to needlessly
increase compile times.  Used properly.. they are very cool.

Joel Caesar

PS If anyone puts this explanation on a www site, please gimme credit.. even
though it is long winded ;)

-----Original Message-----
From: wierd innocents <innocent29@hotmail.com>
To: ml@qoole.com <ml@qoole.com>
Date: Thursday, January 22, 1998 4:39 PM
Subject: hint brushes???


>ok, i read the plan update by one of the id guys and it told about the
>hint brushes.  i can see a good use for them and want to use them.  but
>what i dont understand is exactly how they work.
>
>do they cut off polyfaces of the bsp if the ones on the other side of
>the hint brush isnt visible from that angle of view?  say a tunnel that
>is behind a corner that isnt visible so hint cuts it off until visible?
>or if you hint off a selection it isnt drawn if you turn away from it?
>
>i do know about areaportals but hint is along the basic idea but totally
>different in visual and applications.  could someone try to explain
>this?
>
>thanks
>
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