G3DLine -intersectsLine:

On Monday, October 21, 2002, at 02:08  PM, Brent Gulanowski wrote:

> This method does a blanket failure if the direction vectors are 
> parallel. I am not a geometry math whiz, but as far as I can tell, 
> this ignores the case where the lines are coincident.

I've been looking more closely at this class, and I have some 
suggestions.

By having a factor ivar (_t), we are in fact defining a line segment, 
not a line. In which case, I don't understand the decision to describe 
the object using the origin/vector approach. Really, a line and a line 
segment are two different things. I wonder if we should make this a 
true line and remove the factor. IMHO, a line segment is best described 
as origin/endpoint -- I'm not sure whether such a simple object needs a 
class definition or not.

If we make the line class more generalized, I also recommend 
standardizing it further by making the origin point the point on the 
line which is closest to the origin of the coordinate system. This 
could be done with a no side effects method (return a new, standardized 
line). Suggested implementation provided. I'd appreciate if you could 
check my code, btw. It depends on the fact that the direction vector is 
normalized when producing the distance along the line to the new origin 
(calculated with G3DScalarProduct3fv).

-(G3DLine *) standardize {

   // nearestP = knownP + [knownP . directionVec]*directionVec  ... use 
origin for knownP

   G3DTuple3f nearestP;
   float temp[3];

   G3DScaleVector3fv( temp, [direction elements], G3DScalarProduct3fv( 
[origin elements], [direction elements] ) );
   G3DVectorAdd3fv( temp, [origin elements], temp );
   nearestP = [[G3DTuple3f alloc] initWithElements:temp];

   // OK, this is where I freak out from not having autorelease. What is 
GNUstep doing in these cases?
   // This is being returned with a ref count of 1, and so violates the 
Cocoa standard

   return [[G3DLine alloc] initWithOrigin:nearestP direction:direction 
factor: _t];

}

Note: if you like my other idea (dump the factor ivar), the last line 
would look like:

return [[G3DLine alloc] initWithOrigin:nearestP direction:direction];

because we'd have to change the relevant init method.

--
Brent Gulanowski				[email protected]

http://inkubator.idevgames.com/
Working together to make great software.