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Archive Notice: This thread is old and no longer active. It is here for reference purposes. This thread was created on an older version of the flipcode forums, before the site closed in 2005. Please keep that in mind as you view this thread, as many of the topics and opinions may be outdated.
 
Ronny Westereng

March 03, 1999, 07:34 PM

Hello, my question is this:

After a polygon has been clipped, if one have let's say, a worst case scenario of 8 edges in the clipped poly. Would it be better to use some triangulation algorithm to split the poly up and then use a triangel edge scanner, or would it be better to just scan each edge one by one
and then fill??? I am thinking in respect to easely implement texture mapping, wich I beleive is easiest done on triangles.

Another thing, I have had a look at Delunay triangulation, but the texts I have been reading just don't explain the theory clear enough for me, could eventually someone point me to an easy to grasp info file on this??

Ronny

 
Phantom

March 04, 1999, 04:09 AM

Ronny Westereng wrote:
>> Hello, my question is this:
>> After a polygon has been clipped, if one have let's say, a worst
>> case scenario of 8 edges in the clipped poly. Would it be better
>> to use some triangulation algorithm to split the poly up and then
>> use a triangel edge scanner, or would it be better to just scan
>> each edge one by one and then fill??? I am thinking in respect to
>> easely implement texture mapping, wich I beleive is easiest done
>> on triangles.

Check out my polygon filling document on the portal column page.
Filling convex polygons with more than three edges is not harder to
do than triangles. For triangles, there are some special cases, but
it wouldn't be efficient to first triangulate on the fly, and then
draw slightly faster using a triangle filler. Filling triangles is
certainly not easier, by the way, just slightly faster.
Hardware accelerators on the other hand REQUIRE triangles. If you
pass Glide a rectangle, for example, it will do delaunay triangulation
itself, and that takes time of course. So in that case, you might
want to do it yourself.

>> Another thing, I have had a look at Delunay triangulation, but
>> the texts I have been reading just don't explain the theory clear
>> enough for me, could eventually someone point me to an easy to grasp
>> info file on this??

I'm not an expert on this topic, so I'll leave this to someone else...
If no-one comes up with an answer, let me know.

 
Conor Stokes

March 27, 1999, 03:30 AM



Phantom wrote:
>>Ronny Westereng wrote:
>>>> Hello, my question is this:
>>>> After a polygon has been clipped, if one have let's say, a worst
>>>> case scenario of 8 edges in the clipped poly. Would it be better
>>>> to use some triangulation algorithm to split the poly up and then
>>>> use a triangel edge scanner, or would it be better to just scan
>>>> each edge one by one and then fill??? I am thinking in respect to
>>>> easely implement texture mapping, wich I beleive is easiest done
>>>> on triangles.
>>
>>Check out my polygon filling document on the portal column page.
>>Filling convex polygons with more than three edges is not harder to
>>do than triangles. For triangles, there are some special cases, but
>>it wouldn't be efficient to first triangulate on the fly, and then
>>draw slightly faster using a triangle filler. Filling triangles is
>>certainly not easier, by the way, just slightly faster.
>>Hardware accelerators on the other hand REQUIRE triangles. If you
>>pass Glide a rectangle, for example, it will do delaunay triangulation
>>itself, and that takes time of course. So in that case, you might
>>want to do it yourself.
>>
>>>> Another thing, I have had a look at Delunay triangulation, but
>>>> the texts I have been reading just don't explain the theory clear
>>>> enough for me, could eventually someone point me to an easy to grasp
>>>> info file on this??
>>
>>I'm not an expert on this topic, so I'll leave this to someone else...
>>If no-one comes up with an answer, let me know.
>>
Well, I have a triangle algo that is very quick, and I often use tessalation, and
I also often use shadow geometry. So, I will tell you the method I find easiest, which is this.
In a convex shape you take point one, point two and point three and make your first triangle.
Call these a, b and c. Then increment b and c so you have point 3 as b and c as point 4, and
draw another. This seems to give good results for me, very quickly.

Conor Stokes

 
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