# pixel level collision detection using VB/DX7

Started by Jan 18 2000 08:06 AM

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1 reply to this topic

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#1
Members - Reputation: **152**

Posted 18 January 2000 - 08:06 AM

I am writing a simple tile game and I already have it doing
collision detection using bounding boxes but now I want to go further and put in some pixel perfect collision detection. Anyone know where I can get some good VB/DX7 source code for this?? I haven''t been able to find any on the net so far. Help please. Thanks.
Marcus

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#2
Anonymous Poster_Anonymous Poster_*
Guests - Reputation:

Posted 23 January 2000 - 01:24 PM

I am having the same trouble and this still is not accurate enough. It is pretty damn close. If anyone finds out an answer to better collision detection then please post it

The way the code works

It uses 3 slope intercept equations to check if the point is inside of a 2D triangle. To check a 3D triangle it checks 3 triangles from one 3D triangle. Look at In3DPoly()

If you cannot read this code then sorry

''-------------------Codes starts here---------------------

Option Explicit

Private Type PointAPI

X As Single

Y As Single

End Type

Function InTriangle(Ray As PointAPI, V1 As PointAPI, V2 As PointAPI, V3 As PointAPI, Optional Accuracy As Single = 1) As Boolean

''this function uses Accuracy really badly and inaccurately so you can try to change it later

On Error Resume Next

Const TapVertex As Single = 1

Dim M As Single

Dim B As Single

Dim Temp As Single

Dim Intersected(2) As Boolean

''Tap verticies if necessary (this method can result to inaccuracy)

If (V1.X) = (V2.X) Then V1.X = V1.X + (TapVertex)

If (V1.X) = (V3.X) Then V3.X = V3.X + (TapVertex)

If (V2.X) = (V3.X) Then V2.X = V2.X + (TapVertex)

''1

M = (V1.Y - V3.Y) / (V1.X - V3.X)

B = V1.Y - (M * V1.X)

Temp = (M * Ray.X + B)

If V2.Y >= (M * V2.X + B) Then

If Not Ray.Y >= Temp - Accuracy Then Exit Function

Else

If Not Ray.Y <= Temp + Accuracy Then Exit Function

End If

''2

M = (V2.Y - V3.Y) / (V2.X - V3.X)

B = V2.Y - (M * V2.X)

Temp = (M * Ray.X + B)

If V1.Y >= (M * V1.X + B) Then

If Not Ray.Y >= Temp - Accuracy Then Exit Function

Else

If Not Ray.Y <= Temp + Accuracy Then Exit Function

End If

''3

M = (V1.Y - V2.Y) / (V1.X - V2.X)

B = V1.Y - (M * V1.X)

Temp = (M * Ray.X + B)

If V3.Y >= (M * V3.X + B) Then

If Not Ray.Y >= Temp - Accuracy Then Exit Function

Else

If Not Ray.Y <= Temp + Accuracy Then Exit Function

End If

If Err = 0 Then InTriangle = True

End Function

Function Get_Y_Int(Ray As D3DVECTOR, RayDirUp As Boolean, V1 As D3DVERTEX, V2 As D3DVERTEX, V3 As D3DVERTEX, ReturnValue As Long) As Boolean

On Error Resume Next

''First check if point is within the x and z of the triangle

If InTriangle(MakePoint(Ray.X, Ray.Z), MakePoint(V1.X, V1.Z), MakePoint(V2.X, V2.Z), MakePoint(V3.X, V3.Z)) = False Then Exit Function

Get_Y_Int = True

End Function

Function In3DPoly(Ray As D3DVECTOR, V1 As D3DVERTEX, V2 As D3DVERTEX, V3 As D3DVERTEX) As Boolean

If noclip = True Then Exit Function

If InTriangle(MakePoint(Ray.X, Ray.Y), MakePoint(V1.X, V1.Y), MakePoint(V2.X, V2.Y), MakePoint(V3.X, V3.Y)) = False Then ''Go down z

Exit Function

End If

If InTriangle(MakePoint(Ray.X, Ray.Z), MakePoint(V1.X, V1.Z), MakePoint(V2.X, V2.Z), MakePoint(V3.X, V3.Z)) = False Then ''Go down y

Exit Function

End If

If InTriangle(MakePoint(Ray.Z, Ray.Y), MakePoint(V1.Z, V1.Y), MakePoint(V2.Z, V2.Y), MakePoint(V3.Z, V3.Y)) = False Then ''Go down x

Exit Function

End If

In3DPoly = True

End Function

Private Function MakePoint(X As Single, Y As Single) As PointAPI

With MakePoint

.X = X

.Y = Y

End With

End Function

Questions or better solutions? Please mail me

ManilaThrilla@juno.com

The way the code works

It uses 3 slope intercept equations to check if the point is inside of a 2D triangle. To check a 3D triangle it checks 3 triangles from one 3D triangle. Look at In3DPoly()

If you cannot read this code then sorry

''-------------------Codes starts here---------------------

Option Explicit

Private Type PointAPI

X As Single

Y As Single

End Type

Function InTriangle(Ray As PointAPI, V1 As PointAPI, V2 As PointAPI, V3 As PointAPI, Optional Accuracy As Single = 1) As Boolean

''this function uses Accuracy really badly and inaccurately so you can try to change it later

On Error Resume Next

Const TapVertex As Single = 1

Dim M As Single

Dim B As Single

Dim Temp As Single

Dim Intersected(2) As Boolean

''Tap verticies if necessary (this method can result to inaccuracy)

If (V1.X) = (V2.X) Then V1.X = V1.X + (TapVertex)

If (V1.X) = (V3.X) Then V3.X = V3.X + (TapVertex)

If (V2.X) = (V3.X) Then V2.X = V2.X + (TapVertex)

''1

M = (V1.Y - V3.Y) / (V1.X - V3.X)

B = V1.Y - (M * V1.X)

Temp = (M * Ray.X + B)

If V2.Y >= (M * V2.X + B) Then

If Not Ray.Y >= Temp - Accuracy Then Exit Function

Else

If Not Ray.Y <= Temp + Accuracy Then Exit Function

End If

''2

M = (V2.Y - V3.Y) / (V2.X - V3.X)

B = V2.Y - (M * V2.X)

Temp = (M * Ray.X + B)

If V1.Y >= (M * V1.X + B) Then

If Not Ray.Y >= Temp - Accuracy Then Exit Function

Else

If Not Ray.Y <= Temp + Accuracy Then Exit Function

End If

''3

M = (V1.Y - V2.Y) / (V1.X - V2.X)

B = V1.Y - (M * V1.X)

Temp = (M * Ray.X + B)

If V3.Y >= (M * V3.X + B) Then

If Not Ray.Y >= Temp - Accuracy Then Exit Function

Else

If Not Ray.Y <= Temp + Accuracy Then Exit Function

End If

If Err = 0 Then InTriangle = True

End Function

Function Get_Y_Int(Ray As D3DVECTOR, RayDirUp As Boolean, V1 As D3DVERTEX, V2 As D3DVERTEX, V3 As D3DVERTEX, ReturnValue As Long) As Boolean

On Error Resume Next

''First check if point is within the x and z of the triangle

If InTriangle(MakePoint(Ray.X, Ray.Z), MakePoint(V1.X, V1.Z), MakePoint(V2.X, V2.Z), MakePoint(V3.X, V3.Z)) = False Then Exit Function

Get_Y_Int = True

End Function

Function In3DPoly(Ray As D3DVECTOR, V1 As D3DVERTEX, V2 As D3DVERTEX, V3 As D3DVERTEX) As Boolean

If noclip = True Then Exit Function

If InTriangle(MakePoint(Ray.X, Ray.Y), MakePoint(V1.X, V1.Y), MakePoint(V2.X, V2.Y), MakePoint(V3.X, V3.Y)) = False Then ''Go down z

Exit Function

End If

If InTriangle(MakePoint(Ray.X, Ray.Z), MakePoint(V1.X, V1.Z), MakePoint(V2.X, V2.Z), MakePoint(V3.X, V3.Z)) = False Then ''Go down y

Exit Function

End If

If InTriangle(MakePoint(Ray.Z, Ray.Y), MakePoint(V1.Z, V1.Y), MakePoint(V2.Z, V2.Y), MakePoint(V3.Z, V3.Y)) = False Then ''Go down x

Exit Function

End If

In3DPoly = True

End Function

Private Function MakePoint(X As Single, Y As Single) As PointAPI

With MakePoint

.X = X

.Y = Y

End With

End Function

Questions or better solutions? Please mail me

ManilaThrilla@juno.com