insider

[romanize]

i know, there is a api function
PtInRegion Lib "gdi32" (ByVal hRgn As Long, ByVal X As Long, ByVal Y As Long) As Long
which detects if a point IS in a polygon .. but how can i find it out w/o (want to reinvent the wheel..)?

[THEROB]

There is a maths theorem that proves that from a point a line can be drawn in any direction - if this line croses the polygon an odd number of times then the point is inside the polygon - otherwise the point is outside

see this site:
http://astronomy.swin.edu.au/pbourke...ry/insidepoly/

[Guv]

A human being can easily apply that theorem, but really does not need it.

It does not seem easy to program that theorem, but it is doable.

To implement that theorem in a program, it looks like you must program the solution to a set of simultaneous equations in two unknowns for each side of the polygon. Furthermore, you would have to check each solution to make sure that the intersection point was not on an extension of a polygon side.

You could save some time byt chosing a line parallel to one or two sides of the polygon.

Is the theorem applicable to polygons with some comvex vertices?

Can you think of an easier way to use that theorem?

[romanize]

i actually already used that .. (have to bring the link again .. c 'cheap 3d' thread) its a small applet i am sometimes working on .. and the whole stuff with detecting if a point is outside an intersection of lines is quite a waste of mhzs, u can even c it blinking. of cos' its not exactly assemly, and still i don't know any better solutions for that. (understand nothing about OpenGL .. how can i start using that? books, links or anything?)
ciao

[parksie]

http://www.opengl.org
http://nehe.gamedev.net
http://www.parksie.net/simplegl/SimpleGL.html (VB only)

[romanize]

thanks ..