[Radiance-general] Re: scripting genprism | no explicit holes problem

[Greg Ward]

Maybe I'm being naive, but I've had good luck creating connecting seams 
between arbitrary vertices in holey polygons.  Make sure the outer 
vertices are in counter-clockwise order around the normal, and the 
interior (hole) vertices are clockwise.  Then, the algorithm goes 
something like this:

	First N vertices are N vertices of outer contour
		Next M1 vertices are M1 vertices of hole 1
		Close hole loop with vertex that is copy of the first hole vertex
		Close seam by adding copy of last outer contour vertex
		Repeat 3 steps above for each hole contour

In Radiance, polygon seams can cross all over each other and it doesn't 
create any artifacts.  This is how fonts are rendered, for example.  
This is also why I never bothered implementing holes in polygons; I 
never found where seams caused a problem, and I couldn't think of any 
way besides seams for implementing holes.

-Greg

> From: "Jelle Feringa // EZCT / Paris" <jelle.feringa at ezct.net>
> Date: January 6, 2005 6:07:03 AM PST
>
> Dear All,
>
> I'm working on a python script which I use to generate polygon 
> description
> to describe walls, in order to automate an architectural design 
> process.
> (building on the  http://www.dezentral.de/soft/Polygon/index.html 
> module)
>
> Using an excellent library, all my functions are in place... the data 
> is
> ready to be shipped to genprism... if it wasn't for No Explicit Holes
> Problem
>
> Here you see (simplified) version of a polygon I'd like genprism to 
> produce
> a wall from...
>
> [(4.059, 4.0599), (3.939, 4.059), (3.93, 3.93), (4.059, 3.99), (8.0, 
> 0.0),
> (0.0, 0.0), (0.0, 8.0), (8.0, 8.0)]
>
> Nothing special, except I need to find a way to produce the Invisible 
> Seams,
> since holes aren't supported explicitly.
>
> I'm almost sure some of you have been running into this problem as 
> well, and
> so far I haven't been able to find a suitable solution for my problem 
> so far
> (I'm learning programming... so please go easy on me ;-)
>
> If you're as fortunate as me and also have a copy of the excellent 
> Rendering
> with Radiance, this problem is described at page 52 / 145.
>
> #described, there's no suggestion of dealing with the problem...
>
> Your help is appreciated!
>
> Cheers,
> Jelle