; -------------------------------------------------------------------------------------------------------------------
; This function returns TRUE if a ray intersects a triangle.
;
; It also calculates the UV coordinates of said colision as part of the intersection test,
; but does not return them.
;
; V0xyz, V1xyz, and V2xyz are the locations of the three vertices of the triangle.
;
; V0 is location of UV(0,0). V1 is the location of UV(1, 0). V2 is the location of UV(0,1)
; These are important to know if you want to return the exact location in texture space of the collision, but
; you don't have to worry about them if you only want to find out if a collision occured.
;
; Pxyz is a point on the line.
;
; Dxyz is a vector providing the slope of the line.
; -------------------------------------------------------------------------------------------------------------------
Function Ray_Intersect_Triangle(Px#, Py#, Pz#, Dx#, Dy#, Dz#, V0x#, V0y#, V0z#, V1x#, V1y#, V1z#, V2x#, V2y#, V2z#)
; A couple definitions for vector operations:
;crossproduct(a,b,c) =
;ax = (by * cz) - (cy * bz)
;ay = (bz * cx) - (cz * bx)
;az = (bx * cy) - (cx * by)
;dotproduct(v,q) = (vx * qx) + (vy * qy) + (vz * qz)
; vector(e1,v1,v0)
E1x# = V1x# - V0x#
E1y# = V1y# - V0y#
E1z# = V1z# - V0z#
; vector(e2,v2,v0)
E2x# = V2x# - V0x#
E2y# = V2y# - V0y#
E2z# = V2z# - V0z#
; crossproduct(h,d,e2)
Hx# = (Dy# * E2z#) - (E2y# * Dz#)
Hy# = (Dz# * E2x#) - (E2z# * Dx#)
Hz# = (Dx# * E2y#) - (E2x# * Dy#)
; a = dotproduct(e1,h)
A# = (E1x# * Hx#) + (E1y# * Hy#) + (E1z# * Hz#)
; If the ray is parallel to the plane then it does not intersect it.
If (A# > -0.00001) And (A# < 0.00001)
Return False
EndIf
F# = 1.0 / A#
; vector(s,p,v0)
Sx# = Px# - V0x#
Sy# = Py# - V0y#
Sz# = Pz# - V0z#
;u = f * (dotProduct(s,h))
U# = F# * ((Sx# * Hx#) + (Sy# * Hy#) + (Sz# * Hz#))
; If the value of the U coordinate is outside the range of values inside the triangle,
; then the ray has intersected the plane outside the triangle.
If (U# < 0.0) Or (U# > 1.0)
Return False
EndIf
; crossProduct(q,s,e1)
Qx# = (Sy# * E1z#) - (E1y# * Sz#)
Qy# = (Sz# * E1x#) - (E1z# * Sx#)
Qz# = (Sx# * E1y#) - (E1x# * Sy#)
; v = f * dotProduct(d,q)
V# = F# * ((Dx# * Qx#) + (Dy# * Qy#) + (Dz# * Qz#))
; If the value of the V coordinate is outside the range of values inside the triangle,
; then the ray has intersected the plane outside the triangle.
;
; U + V cannot exceed 1.0 or the point is not in the triangle.
;
; If you imagine the triangle as half a square this makes sense. U=1 V=1 would be in the
; lower left hand corner which would be in the second triangle making up the square.
If (V# < 0.0) Or ((U# + V#) > 1.0)
Return(False)
EndIf
; The point was in the triangle. Yay!
Return True
; Note that you could also return the U and V coordinates calculated from this function
; if you need those values!
End Function