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Bug Reports / Triangle Collision Detection Bug?

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destroy89

17

Years of Service

User Offline

Joined: 27th Jan 2007

Location:

Posted: 15th Jun 2007 22:37

Ok. Long code segment. I'm trying to use collision detection on 2d dimensional 3d rendered triangles in the same plane (no Z is used). Try my code. Can you explain why it doesn't collide properly? It switches from default to poly based detection halfway through.

Is this a bug in dark basic? Should I try it with objects that have a dimension in the Z axis?

See code...

sync on

MAKE OBJECT TRIANGLE 7, -3,0,0, 4,3,0, 5,-1,0
MAKE OBJECT TRIANGLE 9, -3,0,0, 4,7,0, 6,-1,0

sync
sync

wait 100
`wait key

position object 7, 0,-8,20

position object 9, 0,-18,20

sync
sync

wait 100

show object bounds 7

show object bounds 9

position object 9, 0 , -12 , 1
wait 500

`----------------------------------------------------------
position object 7, -6, 6, 1
Collided3 = 0

repeat
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )

sync
 sync

wait 1
until Collided3 <> 0

wait 1000

`----------------------------------------------------------
position object 7, -5, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

sync
 sync

wait 1
until Collided3 <> 0

wait 1000

`----------------------------------------------------------
position object 7, -4, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

sync
 sync

wait 1
until Collided3 <> 0

wait 1000

SET OBJECT COLLISION TO POLYGONS 7
SET OBJECT COLLISION TO POLYGONS 9

`----------------------------------------------------------
position object 7, -6, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

sync
 sync

wait 3
until Collided3 <> 0

wait 1000

`----------------------------------------------------------
position object 7, -5, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

sync
 sync

wait 3
until Collided3 <> 0

wait 1000

`----------------------------------------------------------
position object 7, -4, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

sync
 sync

wait 3
until Collided3 <> 0

wait key

sync on

MAKE OBJECT TRIANGLE 7, -3,0,0, 4,3,0, 5,-1,0
MAKE OBJECT TRIANGLE 9, -3,0,0, 4,7,0, 6,-1,0



sync
sync

wait 100
`wait key






position object 7, 0,-8,20

position object 9, 0,-18,20



sync
sync

wait 100

show object bounds 7

show object bounds 9




position object 9, 0 , -12 , 1
wait 500




`----------------------------------------------------------
position object 7, -6, 6, 1
Collided3 = 0

repeat
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )


 sync
 sync

 wait 1
until Collided3 <> 0

wait 1000





`----------------------------------------------------------
position object 7, -5, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

 sync
 sync

 wait 1
until Collided3 <> 0

wait 1000





`----------------------------------------------------------
position object 7, -4, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

 sync
 sync

 wait 1
until Collided3 <> 0

wait 1000





SET OBJECT COLLISION TO POLYGONS 7
SET OBJECT COLLISION TO POLYGONS 9


`----------------------------------------------------------
position object 7, -6, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

 sync
 sync

 wait 3
until Collided3 <> 0

wait 1000





`----------------------------------------------------------
position object 7, -5, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

 sync
 sync

 wait 3
until Collided3 <> 0

wait 1000





`----------------------------------------------------------
position object 7, -4, 6, 1
Collided3 = 0

repeat
 `if Collided3 = 0
 position object 7, object position x(7) , object position y(7) - .1 , object position z(7) ,
 Collided3 = Object HIT( 7 , 0 )
 `endif

 sync
 sync

 wait 3
until Collided3 <> 0


wait key

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destroy89

17

Years of Service

User Offline

Joined: 27th Jan 2007

Location:

Posted: 21st Jun 2007 17:54

Has anyone managed to perform collision detection properly on angled objects like triangles?

I want to be able to detect collisions like the image below, but when I use "set object collision to polygons <object #>" on both objects, the collision is detected far too late. If I use boxes based detection then it will detect too early. If I have one object set to boxes and the other to polygons, then it detects collisions properly for the one, but not for the other. Do I have to purchase plugins to have proper collision detection of polygon based objects?

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DSG

21

Years of Service

User Offline

Joined: 26th Aug 2002

Location: Hampshire, England

Posted: 21st Jun 2007 19:44

3D triangle-triangle intersection tests generally begin with a ray-plane intersection test using triangle edges.

The ray-plane intersection test relies on classifying each end-point of an edge (belonging to one triangle) to the plane that the other triangle lies in. The logic being that, if one edge vertex is behind or coincides with the triangle plane and the other vertex is in front or coincides with the triangle plane then a collision may have occurred.

Unfortunately, since your triangles all coincide on the same plane, the intersection algorithm is more likely to return incorrect results due to floating point precision errors when calculating the distance between each edge vertex and the plane (the distance values are important for determining intersections).

This is the likely cause of your collision detection issues. Additionally, the algorithm that DBP employs may not even consider coinciding triangles as colliding.

This isn't really a fault of DBP. Your best bet is to use some intersection tests designed specifically for 2D lines/triangles (either write your own or try searching this forum for existing implementations).

Danny Gregory BSc

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destroy89

17

Years of Service

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Joined: 27th Jan 2007

Location:

Posted: 21st Jun 2007 20:47 Edited at: 21st Jun 2007 20:49

Excellent. Very geometric answer. Does it help if I am rendering the 2d shapes with 3d objects so they have depth to collide with as well? [edit] I am currently testing with vertex modified cubes. DBP still has issues detecting collision this way.

I am probably going to use Nuclear Glory plugin to do it. Forgot I had it.

It is nice to know whether or not DBP can do it or why it can't though.

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