[Pdmtl] [PD] [PD-announce] four more fractal videos, and reposting the two previous ones

Mathieu Bouchard matju at artengine.ca
Ven 4 Fév 11:09:17 EST 2011

On Fri, 4 Feb 2011, jack at rybn.org wrote:
>> On Fri, 4 Feb 2011, patko wrote:
>> Même les polygones concaves sont pas supportés directement par OpenGL !
> It is easy to draw a concave polygon with [polygon] in GEM !

Then why is your patch doing it by gluing many small triangles instead of 
one big 192-sided polygonal contour ? I didn't mean simply something that 
looks like a concave polygon, I mean a method of building a shape that 
involves drawing a single list of vertices.

That's because if one tries to make something 192-sided with a single 
[polygon], you write [polygon 192] and you have 193 inlets that have to be 
connected !

Ok, *some* concave polygons are supported by GEM/GL. For example, in 
trianglefan mode, you set a centre, and you put triangle vertices all 
around. This means that the concavities can't go in any direction one 
could want, because in some directions, triangles will overlap areas that 
are meant to not be part of the polygon.

Concave polygons that can't be drawn so easily, are the one that contains 
no single point from which straight lines to all vertices stay completely 
inside of the polygon. In that case, they have to be broken down in more 
complicated ways.

Those are difficulties that can be completely avoided by using a plain 
Bresenham rasteriser such as XFillPolygon (from X11) or GridFlow's 
[#draw_polygon] (two distinct implementations of basically the same idea).

> It is easy to build a Koch fractal with GEM. Open the patch join to this
> message.

Yeah, indeed one can use [gemlist].

Now who wants to make something that looks 3-D with that ? (with 

(BTW, can you make it so you don't have to copy-paste each time you want a 
new level to the fractal ? because in my patch, I just have to change a 

| Mathieu Bouchard ---- tél: +1.514.383.3801 ---- Villeray, Montréal, QC

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