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Merge pull request #1473 from renaudbedard/aabb-ray-intersect-fix
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Fix to the ray-AABB intersection to resolve cases where hitting an edge ...
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@tomspilman
tomspilman committed Mar 1, 2013
2 parents 07a3a34 + 4507d09 commit ebe16b6
Showing 1 changed file with 80 additions and 70 deletions.
150 changes: 80 additions & 70 deletions MonoGame.Framework/Ray.cs
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Expand Up @@ -83,78 +83,88 @@ public override int GetHashCode()
return Position.GetHashCode() ^ Direction.GetHashCode();
}


// adapted from http://www.scratchapixel.com/lessons/3d-basic-lessons/lesson-7-intersecting-simple-shapes/ray-box-intersection/
public float? Intersects(BoundingBox box)
{
//first test if start in box
if (Position.X >= box.Min.X
&& Position.X <= box.Max.X
&& Position.Y >= box.Min.Y
&& Position.Y <= box.Max.Y
&& Position.Z >= box.Min.Z
&& Position.Z <= box.Max.Z)
return 0.0f;// here we concidere cube is full and origine is in cube so intersect at origine

//Second we check each face
Vector3 maxT = new Vector3(-1.0f);
//Vector3 minT = new Vector3(-1.0f);
//calcul intersection with each faces
if (Position.X < box.Min.X && Direction.X != 0.0f)
maxT.X = (box.Min.X - Position.X) / Direction.X;
else if (Position.X > box.Max.X && Direction.X != 0.0f)
maxT.X = (box.Max.X - Position.X) / Direction.X;
if (Position.Y < box.Min.Y && Direction.Y != 0.0f)
maxT.Y = (box.Min.Y - Position.Y) / Direction.Y;
else if (Position.Y > box.Max.Y && Direction.Y != 0.0f)
maxT.Y = (box.Max.Y - Position.Y) / Direction.Y;
if (Position.Z < box.Min.Z && Direction.Z != 0.0f)
maxT.Z = (box.Min.Z - Position.Z) / Direction.Z;
else if (Position.Z > box.Max.Z && Direction.Z != 0.0f)
maxT.Z = (box.Max.Z - Position.Z) / Direction.Z;

//get the maximum maxT
if (maxT.X > maxT.Y && maxT.X > maxT.Z)
{
if (maxT.X < 0.0f)
return null;// ray go on opposite of face
//coordonate of hit point of face of cube
float coord = Position.Z + maxT.X * Direction.Z;
// if hit point coord ( intersect face with ray) is out of other plane coord it miss
if (coord < box.Min.Z || coord > box.Max.Z)
return null;
coord = Position.Y + maxT.X * Direction.Y;
if (coord < box.Min.Y || coord > box.Max.Y)
return null;
return maxT.X;
}
if (maxT.Y > maxT.X && maxT.Y > maxT.Z)
{
if (maxT.Y < 0.0f)
return null;// ray go on opposite of face
//coordonate of hit point of face of cube
float coord = Position.Z + maxT.Y * Direction.Z;
// if hit point coord ( intersect face with ray) is out of other plane coord it miss
if (coord < box.Min.Z || coord > box.Max.Z)
return null;
coord = Position.X + maxT.Y * Direction.X;
if (coord < box.Min.X || coord > box.Max.X)
return null;
return maxT.Y;
}
else //Z
{
if (maxT.Z < 0.0f)
return null;// ray go on opposite of face
//coordonate of hit point of face of cube
float coord = Position.X + maxT.Z * Direction.X;
// if hit point coord ( intersect face with ray) is out of other plane coord it miss
if (coord < box.Min.X || coord > box.Max.X)
return null;
coord = Position.Y + maxT.Z * Direction.Y;
if (coord < box.Min.Y || coord > box.Max.Y)
return null;
return maxT.Z;
}
const float Epsilon = 1e-6f;

float? tMin = null, tMax = null;

if (Math.Abs(Direction.X) < Epsilon)
{
if (Position.X < box.Min.X || Position.X > box.Max.X)
return null;
}
else
{
tMin = (box.Min.X - Position.X) / Direction.X;
tMax = (box.Max.X - Position.X) / Direction.X;

if (tMin > tMax)
{
var temp = tMin;
tMin = tMax;
tMax = temp;
}
}

if (Math.Abs(Direction.Y) < Epsilon)
{
if (Position.Y < box.Min.Y || Position.Y > box.Max.Y)
return null;
}
else
{
var tMinY = (box.Min.Y - Position.Y) / Direction.Y;
var tMaxY = (box.Max.Y - Position.Y) / Direction.Y;

if (tMinY > tMaxY)
{
var temp = tMinY;
tMinY = tMaxY;
tMaxY = temp;
}

if ((tMin.HasValue && tMin > tMaxY) || (tMax.HasValue && tMinY > tMax))
return null;

if (!tMin.HasValue || tMinY > tMin) tMin = tMinY;
if (!tMax.HasValue || tMaxY < tMax) tMax = tMaxY;
}

if (Math.Abs(Direction.Z) < Epsilon)
{
if (Position.Z < box.Min.Z || Position.Z > box.Max.Z)
return null;
}
else
{
var tMinZ = (box.Min.Z - Position.Z) / Direction.Z;
var tMaxZ = (box.Max.Z - Position.Z) / Direction.Z;

if (tMinZ > tMaxZ)
{
var temp = tMinZ;
tMinZ = tMaxZ;
tMaxZ = temp;
}

if ((tMin.HasValue && tMin > tMaxZ) || (tMax.HasValue && tMinZ > tMax))
return null;

if (!tMin.HasValue || tMinZ > tMin) tMin = tMinZ;
if (!tMax.HasValue || tMaxZ < tMax) tMax = tMaxZ;
}

// having a positive tMin and a negative tMax means the ray is inside the box
// we expect the intesection distance to be 0 in that case
if ((tMin.HasValue && tMin < 0) && tMax > 0) return 0;

// a negative tMin means that the intersection point is behind the ray's origin
// we discard these as not hitting the AABB
if (tMin < 0) return null;

return tMin;
}


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