Mmeshintersector And Barycentric Coords

[uiron]

for this little thing i'm doing here i need a closest point on mesh (using MMeshIntersector for that) and barycentric coordinates of the face/triangle that was hit. the problem is, meshintersector only gives face/triangle/normal/point.

i guess the only way is to calculate barycentrics by myself (from the hit point and the triangle).

as i was lazy, i went as far as re-shooting to that point with mfnmesh.closestIntersection(), which gives me barycentrics, but this function fails on mesh borders (obviously).

what do i do?:] tried to find any decent info about calculating barycentric coords, found only 2-d examples mostly (and those look scary anyway).

[joojaa]

Its just the closest point on each edge of triangles as far as i understand. No code in front fo me.

[uiron]

found quite a nice prototype done in vector math, giving it a try currently, seems to work

CODE
// Compute the normal of the triangle
Vector N = Normalize(Cross(B-A,C-A));

// Compute twice area of triangle ABC
float AreaABC = Dot(N,Cross(B-A,C-A));

// Compute a
float AreaPBC = Dot(N,Cross(B-P,C-P));
float a = AreaPBC / AreaABC;

// Compute b
float AreaPCA = Dot(N,Cross(C-P,A-P));
float b = AreaPCA / AreaABC;

// Compute c
float c = 1.0f - a - b;

[uiron]

yeah, this algorithm worked quite fine, here's snipped from the class that does that in Python (just in case someone would need that in the future)

CODE
    # returns double area for the triangle
    def triangleArea(self,pts,n):
        #N dot ((B-A)cross(C-A))
        return n*((pts[1]-pts[0])^(pts[2]-pts[0]))

    # calculates barycentric coords for a point on a given triangle
    # triangle MVector[3]: source triangle
    # pt MVector: source point
    # returns float[3]
    def calcBary(self,triangle,pt):
        normal =  (triangle[1]-triangle[0])^(triangle[2]-triangle[0])
        normal = normal.normal()

        fullArea = self.triangleArea(triangle,normal)

        area23 = self.triangleArea([pt,triangle[1],triangle[2]], normal)
        area13 = self.triangleArea([pt,triangle[2],triangle[0]], normal)
        bary1 = area23/fullArea
        bary2 = area13/fullArea
        bary3 = 1.0-bary1-bary2
        return [bary1,bary2,bary3]