public static bool TestTriangleBoxAndGetCenterOfMassUV(Math.Vector2 a, Math.Vector2 b, Math.Vector2 c, Math.Vector2 boxMin, Math.Vector2 boxMax, out Math.Vector2 centerUV)
{
if (TestTriangleBox(a, b, c, boxMin, boxMax) == false)
{
centerUV = Math.Vector2.Zero;
return(false);
}
// we know the box and the triangle intersect, but do we need to find the cetroid?
centerUV.X = (boxMin.X + boxMax.X) * 0.5f;
centerUV.Y = (boxMin.Y + boxMax.Y) * 0.5f;
if (IsPointInTriangle(centerUV, a, b, c, out centerUV))
{
return(true);
}
if (float.IsNaN(centerUV.X) || float.IsNaN(centerUV.Y))
{
// ugh... whatever... just keep going
return(true);
}
// apparently the texel intersects 1 or more triangle edges, which means we need
// to clip the triangle and square.
List <Math.Vector2> subject = new List <Math.Vector2>();
subject.Add(boxMin);
subject.Add(new Math.Vector2(boxMin.X, boxMax.Y));
subject.Add(boxMax);
subject.Add(new Math.Vector2(boxMax.X, boxMin.Y));
List <Math.Vector2> outputList = subject;
// UV coords may be mirrored, which means winding order is backwards, will screw up everything below.
// So check to see if they are, and if they are, rearrange them so they aren't.
Math.Vector2 center = (a + b + c) / 3.0f;
Math.Plane2D ab = Math.Plane2D.CreateFromEdge(a, b);
Math.Plane2D bc = Math.Plane2D.CreateFromEdge(b, c);
Math.Plane2D ca = Math.Plane2D.CreateFromEdge(c, a);
bool reversed = false;
if (Math.Plane2D.IsPointInFrontOfPlane(ab, center) == false ||
Math.Plane2D.IsPointInFrontOfPlane(bc, center) == false ||
Math.Plane2D.IsPointInFrontOfPlane(ca, center) == false)
{
// doh, winding order seems to be reversed. Swap c and a.
Math.Vector2 d = a;
a = c;
c = d;
ab = Math.Plane2D.CreateFromEdge(a, b);
bc = Math.Plane2D.CreateFromEdge(b, c);
ca = Math.Plane2D.CreateFromEdge(c, a);
reversed = true;
}
// side A
List <Math.Vector2> inputList = new List <Math.Vector2>(outputList);
outputList.Clear();
Math.Vector2 S = inputList[inputList.Count - 1];
foreach (Math.Vector2 E in inputList)
{
if (Math.Plane2D.IsPointInFrontOfPlane(ab, E))
{
if (Math.Plane2D.IsPointInFrontOfPlane(ab, S) == false)
{
Math.Vector2 i;
TestLineLineIntersection(S, E, a, b, out i);
outputList.Add(i);
}
outputList.Add(E);
}
else if (Math.Plane2D.IsPointInFrontOfPlane(ab, S))
{
Math.Vector2 i;
TestLineLineIntersection(S, E, a, b, out i);
outputList.Add(i);
}
S = E;
}
if (outputList.Count == 0)
{
return(true);
}
// side B
inputList = new List <Math.Vector2>(outputList);
outputList.Clear();
S = inputList[inputList.Count - 1];
foreach (Math.Vector2 E in inputList)
{
if (Math.Plane2D.IsPointInFrontOfPlane(bc, E))
{
if (Math.Plane2D.IsPointInFrontOfPlane(bc, S) == false)
{
Math.Vector2 i;
TestLineLineIntersection(S, E, b, c, out i);
outputList.Add(i);
}
outputList.Add(E);
}
else if (Math.Plane2D.IsPointInFrontOfPlane(bc, S))
{
Math.Vector2 i;
TestLineLineIntersection(S, E, b, c, out i);
outputList.Add(i);
}
S = E;
}
if (outputList.Count == 0)
{
return(true);
}
// side C
inputList = new List <Math.Vector2>(outputList);
outputList.Clear();
S = inputList[inputList.Count - 1];
foreach (Math.Vector2 E in inputList)
{
if (Math.Plane2D.IsPointInFrontOfPlane(ca, E))
{
if (Math.Plane2D.IsPointInFrontOfPlane(ca, S) == false)
{
Math.Vector2 i;
TestLineLineIntersection(S, E, c, a, out i);
outputList.Add(i);
}
outputList.Add(E);
}
else if (Math.Plane2D.IsPointInFrontOfPlane(ca, S))
{
Math.Vector2 i;
TestLineLineIntersection(S, E, c, a, out i);
outputList.Add(i);
}
S = E;
}
if (outputList.Count == 0)
{
return(true);
}
// at this point we've got a clipped list of points, so now we need to find the "center of mass"
centerUV = Math.Vector2.Zero;
float area = 0;
outputList.Add(outputList[0]);
for (int i = 0; i < outputList.Count - 1; i++)
{
float second = outputList[i].X * outputList[i + 1].Y - outputList[i + 1].X * outputList[i].Y;
centerUV += (outputList[i] + outputList[i + 1]) * second;
area += second;
}
centerUV /= 6 * area * 0.5f;
// if we reversed the windings, undo it, so that the output UV coords are correct
if (reversed)
{
Math.Vector2 d = a;
a = c;
c = d;
}
if (float.IsNaN(centerUV.X) || float.IsNaN(centerUV.Y))
{
centerUV = boxMax;
}
IsPointInTriangle(centerUV, a, b, c, out centerUV);
return(true);
}
public static bool IsPointInFrontOfPlane(Plane2D plane, Vector2 point)
{
return(plane.Normal.Dot(point) + plane.Distance >= 0);
}