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OpenGL Ray Tracing - Plane

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luongoFan    122
Hi, Im new to openGL, and had a question I hope someone can help me with. I have a maze, each wall which is made out of a Polygon. I want to implement some type of collision detection, either a bounding box, or ray tracing. I have read neHes site, as well as two others on ray tracing but I am still unsure on how you obtain the Plane information. You want to test if the ray intersects the plane, and then if that point is on the polygon, but how do you make a plane perpendicular to the polygon (wall)? Hope that was clear Thanks Edit: May have posted this in the wrong forum, if a mod would kindly move it to the correct one, it would be appreciated.

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Schmedly    366
I'm assuming that since you're using the term polygon, you have the vertices for your triangles or quads. Using those you need the get the normal of the plane (polygon) and it's distance from the origin. Compare that against your point.

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luongoFan    122
When I create each polygon, using glVertex3f(), and I also supply the normal for each polygon using glNormal().

When you say get the point from the origin. Is that the origin of the centre of the player?

My camera is on the person so to say, fisrt person.


Edit: If I cannot use the normal specified using glNormal() how would I go about calculating it?

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aleks_1661    188
What you need to use is the plane equation.

| |
| +-----------+ |
| c | | |
| +-----------+ |
| |
+-------------------+ < this is your world, lines are walls
c is your character (xyz) X is the origin

for a plane with surface normal N and distance from the origin D;
the distance between the plane and the point [xyz] is given by

(N.x * x) + (N.y * y) + (N.z * x) + D

if distace == 0 point is on plane > 0 is above the plane and <0 is below the plane.

To calculate the normal of the plane you need 3 points that lie apon it.

calculation is roughly...

v1 = point2 - point1;
v2 = point3 - point1;
N = crossproduct( v1, v2 );
normalise( N );
D = dotproduct( N, point1 );

check out this site, jsut found it quickly in google, may be of use

To use this in collision detection you just compare the distance from the plane to the character. the simplest method is to imagine a sphere around the character. if the distance to the plane is less than the radius of the sphere then there is a colision. the next step up is AABB's (axis aligned bounding boxes). likely to fit the object better.

hope this helped.

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