December 03, 2020, 08:10:03 PM

### Author Topic: [bb] 2D Point in Triangle by sswift [ 1+ years ago ]  (Read 683 times)

#### BlitzBot

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•  • Posts: 1 ##### [bb] 2D Point in Triangle by sswift [ 1+ years ago ]
« on: June 29, 2017, 12:28:38 AM »
Title : 2D Point in Triangle
Author : sswift
Posted : 1+ years ago

Description : I haven't actually tested this function, as I didn't end up needing it, but I based it off a ray intersect function I wrote in 3D which I know worked, so it should work.

Code :
Code: BlitzBasic
1. ; -------------------------------------------------------------------------------------------------------------------
2. ; This function tells you if a point is inside a triangle, in 2D.
3. ; It also calculates the UV coordinates of said point as part of the intersection test, but does not return them.
4. ;
5. ; Pxy is a point.
6. ;
7. ; V0xy, V1xy, and V2xy, are the locations of the three vertices of the triangle.
8. ;
9. ; For these vertices, V0 is location of UV(0,0), V1 is the location of UV(1, 0), and V2 is the location of UV(0,1)
10. ;
11. ; These are important to know if you want to return the exact location in texture space of the collision, but
12. ; you don't have to worry about them if you only want to find out if a collision occured.
13. ; -------------------------------------------------------------------------------------------------------------------
14. Function PointInTri(Px#, Py#, V0x#, V0y#, V1x#, V1y#, V2x#, V2y#)
15.
16.         ; vector(e1,v1,v0)
17.         E1x# = V1x# - V0x#
18.         E1y# = V1y# - V0y#
19.
20.         ; vector(e2,v2,v0)
21.         E2x# = V2x# - V0x#
22.         E2y# = V2y# - V0y#
23.
24.         ; crossproduct(h,d,e2)
25.         Hx# = -E2y#
26.         Hy# =  E2x#
27.
28.         ; a = dotproduct(e1,h)
29.         A# = (E1x# * Hx#) + (E1y# * Hy#)
30.
31.         F# = 1.0 / A#
32.
33.         ; vector(s,p,v0)
34.         Sx# = Px# - V0x#
35.         Sy# = Py# - V0y#
36.
37.         ;u = f * (dotProduct(s,h))
38.         U# = F# * ((Sx# * Hx#) + (Sy# * Hy#))
39.
40.         ; If the value of the U coordinate is outside the range of values inside the triangle,
41.         ; then the ray has intersected the plane outside the triangle.
42.         If (U# < 0) Or (U# > 1)
43.                 Return False
44.         EndIf
45.
46.         ; crossProduct(q,s,e1)
47.         Qz# = (Sx# * E1y#) - (E1x# * Sy#)
48.
49.         ; v = f * dotProduct(d,q)
50.         V# = F# * Qz#
51.
52.         ; If the value of the V coordinate is outside the range of values inside the triangle,
53.         ; then the ray has intersected the plane outside the triangle.
54.         If (V# < 0) Or (V# > 1) Then Return False
55.
56.         ; U + V together cannot exceed 1.0 or the point is not in the triangle.
57.         ; If you imagine the triangle as half a square this makes sense.  U=1 V=1 would be in the
58.         ; lower left hand corner which would be in the second triangle making up the square.
59.         If (U# + V#) > 1 Then Return False
60.
61.         ; The point was in the triangle. Yay!
62.         Return True
63.
64.         ; Note that you could also return the U and V coordinates calculated in this function
65.         ; if you need those values!
66.
67. End Function