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TheBlob
12-06-2001, 11:13 AM
Hi!
Well, my problem is the following:
I have a point p(x|y) and three points a,b,c forming a triangle. How can I check, if the point p is in the triangle??
Maybe someone has a good, working function?
Please help!
TheBlob!

Leyder Dylan
12-06-2001, 02:17 PM
Here's a link.
http://www.gametutorials.com/Tutorials/Advanced/OpenGL_Pg2.htm

"Polygon Detection"

It's works !

Yeah !!!!!!!!!!!!!!!

Iceman
12-06-2001, 04:40 PM
I have exactly what u need ...




//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Determine if a two dimensional point lies within the confines of a given
// two dimensional triangle.
//
// From Dr. Dobbs Journal, October, 2000

bool IsPointInsideFace(
double pX,
double pY,
double v0x,
double v0y,
double v1x,
double v1y,
double v2x,
double v2y
)
{
double x0, x1, x2, y1, u, v, denom;
x1 = v1x - v0x;

if ( x1 == 0.0 )
{
// Triangle points 0 and 1 have the same X value

// Zero area test - can be removed if triangle is known to be valid
x2 = v2x - v0x;
if ( ( x2 == 0.0 ) | |

// Compute u and check bounds
( ( u = (pX - v0x) / x2 ) < 0.0 ) &amp;#0124; &amp;#0124;
( u > 1.0 ) &amp;#0124; &amp;#0124;

// Zero area test - remove if known to be valid
( ( y1 = v1y - v0y ) == 0.0 ) &amp;#0124; &amp;#0124;

// Compute v and check bounds
( ( v = ( (pY - v0y) - u *
( v2y - v0y ) ) / y1 ) < 0.0 ) )
{

// Missed for some reason
return false;
}

}
else
{
// Triangle points 0 and 1 have a different X value
// Compute denom and check for zero area triangle - check
// is not needed if triangle known to be valid.
x2 = v2x - v0x;
y1 = v1y - v0y;
denom = ( v2y - v0y ) * x1 - x2 * y1;
if ( ( denom == 0.0 ) &amp;#0124; &amp;#0124;

// Compute u and check bounds
( ( u = ( (pY - v0y) * x1 - (x0 = pX - v0x) * y1 ) / denom ) < 0.0 ) &amp;#0124; &amp;#0124;
( u > 1.0 ) &amp;#0124; &amp;#0124;

// Compute v & check bounds
( ( v = ( x0 - u * x2 ) / x1 ) < 0.0 ) )
{

// Missed for some reason
return false;
}
}

// Check gamma
if ( u + v > 1.0 )
{
// Outside third edge
return false;
}

return true;
}

Lsea
12-07-2001, 02:02 AM
I have a simple method :
TEST the point P is in triangle ABC or not
add the area of PAB,PBC,PCA ,if the total is equal to the area of ABC ,then we know the point P is in the triangle ,otherwise is out.
right?

Iceman
12-07-2001, 09:06 AM
Sure, but benchmark it against the above algorithm and I am willing to bet that it looses in terms of raw performance. If you get a chance to do so please post the results here ... thx