Comments on: Super fast triangle/rectangle intersection test

By: jun

jun — Mon, 09 Nov 2009 20:49:59 +0000

lab9, in your function for calculating the line equation y=mx+c, what if xb = xa ?

By: jun

jun — Mon, 09 Nov 2009 18:05:09 +0000

Kristof Neirynck, there is some error in your function. thanks!

# //if all points of the triangle are on one side of the rect
# if((l>x0 && l>x1 && l>x2)
# || (ry1 && t>y2)
# || (b # ){
# return false;
# }

By: eli

eli — Fri, 26 Jun 2009 21:56:52 +0000

I did some coding today and offloaded the intersection test into a Pixel Bender filter.. naturally, it is slow as hell (takes 100 times as long) if you run it synchronously cause you have to create a new job each time the function runs..

But, if we can construct a new test that has 100000 random triangles drawn.. and the intersect test sets the triangle to green or red depending on if it is inside the Culling rectangle.. then we could make a test to take advantage of Pixel Benders ability to run asynchronously.

Though, I think that the small amount of calculations is probably just a bad fit for using a pixel bender filter.. the overhead in creating the new job may just be too much..

By: Jidolstar

Jidolstar — Wed, 03 Jun 2009 07:23:07 +0000

Thank you. This article is very good.

By: Iain

Iain — Sun, 31 May 2009 21:56:19 +0000

Surely we want to go the other way – only cull triangles where every point is off-screen – otherwise you see them disappearing and it looks clunky?

By: Kristof Neirynck

Kristof Neirynck — Sun, 31 May 2009 14:30:48 +0000

Tried to implement the simplest optimizations.
Check if one of the vertexes of the triangle is inside the rectangle and check if all vertexes are on one side of the rectangle. This filters out approximately 88% of triangles.
Obviously I still need to use your lineRectangleIntersect after that.
Seems to run slightly faster.

http://wonderfl.kayac.com/code/6d3fe69ca3450a2ba452c0085aaedd6e8e339fa5

By: lab9

lab9 — Sun, 31 May 2009 12:47:00 +0000

and an another version:
http://wonderfl.kayac.com/code/1c3708bc3d5fa42c3d223cfd1091530a4aac8f14

all is done in the same function, so the code is pretty redondant, but runs really fast.

By: lab9

lab9 — Sat, 30 May 2009 23:21:17 +0000

You’re right, intersection is absolutely needed to make it work correctly.

I just tried an another version for intersection. It runs pretty well:

http://wonderfl.kayac.com/code/40ad55a14049d30d08a5282252f2047f27476948

By: Seb Lee-Delisle

Seb Lee-Delisle — Sat, 30 May 2009 22:14:22 +0000

That is some bloody good optimisation work there on the vector maths – very impressed. But yes, sadly there are several cases where no points are inside either of the two shapes, and the line intersections would still be required after all… but let’s keep working!

By: lab9

lab9 — Sat, 30 May 2009 21:45:44 +0000

here is the wonderfl version

http://wonderfl.kayac.com/code/9ac50d76e60fb98ba5617a71d07f7c09a17e78cc