Collision problem.

General Discussion
#1

Hi all!

Has anyone had a problem like a picture below?

790×590

I attached a collision sphere to an avatar names “Girl”.
And export a model names “Box”,create from a box in 3DsMax7, and export it as “pos” type.

When I run an application and control the girl walking through the box.
The collision sphere hasn’t touch the box yet,
but the program detect as they are collide already. (as a picture above)

Any idea? :cry:

#2

This is only a vague recollection… I seem to recall that there might be a small error in the handling of scale factors in the collision system.

Is it possible that there is a scale factor applied to the girl or the box? Perhaps the sphere is being rendered smaller than it actually is, or something like that.

#3

Yes,it is.
I set the girl’s scale to 0.0012.
it is very small ,isn’t it. :blush:

Thank you for your advise!
I will fix it.

#4

is there any work going on fixing scaling problems in the collisions system?

#5

I believe that the collision system works for uniform scales. The thing it doesn’t handle well is non-uniform scales. The problem is that under a non-uniform scale, a sphere is no longer a sphere, and requires a more complex, more expensive intersection test.

I have little interest in supporting this more complex, more expensive intersection test. Spheres are enough work. So that’s why non-uniform scales are not supported by the collision system, and we have no plans for supporting them.

Usually it is a problem when there is a non-uniform scale on the object the sphere is colliding into, and more often then not when there is a non-uniform scale on a wall, it was used to construct the wall and has no other purpose. In this case, it is easy to do:

wall.flattenLight()

which applies the scale onto the vertices and removes it. This is generally a good thing to do anyway, since it improves rendering performance. Otherwise Panda has to apply that scale to the wall every frame in real time.

David

#6

thank you for clearing uniform scaling. So we can setScale(3) or setScale(.0001) and it would still work? For some reason i think we had problems with that too during pyweek AFF: Iron Angels game(https://discourse.panda3d.org/viewtopic.php?t=3087&highlight=pyweek). But we had problems with every thing then…

#7

For scale larger than 1, the result is still better than if it’s smaller than 1.

from pandac.PandaModules import *
import direct.directbase.DirectStart
from direct.interval.IntervalGlobal import *

def pingpongIval(ival, wait=0):
    return Sequence(
                ival,
                Wait(wait),
                Func(ival.start, 0, ival.getDuration(),-1),
                Wait(ival.getDuration())
                )

base.setBackgroundColor(0,0,0)
base.cTrav = CollisionTraverser()
base.cTrav.showCollisions(render)
GRAVhandler = CollisionHandlerGravity()

for b in range(6):
    box=loader.loadModel('misc/rgbCube')
    box.reparentTo(render)
    box.setPos(0,-b*.8,-b*.5)
    box.setP(10)
    box.setCollideMask(BitMask32.bit(0))

smileyIvalDum = render.attachNewNode('')
smiley = smileyIvalDum.attachNewNode('')
#############################################################
scale=.07  # <------  CHANGE THE SCALE
#############################################################
smiley.setScale(scale)
arrow=loader.loadModel('misc/Dirlight')
arrow.reparentTo(smiley)
arrow.setP(-90)
arrow.setZ(2.5/scale)
arrow.setScale(Vec3(.5,.3,.0001)/scale)
smileyCN=smiley.attachCollisionRay('smiley',0,0,2./scale,0,0,-1,BitMask32.bit(0),BitMask32.allOff())
smileyCN.show()
pingpongIval( smileyIvalDum.posInterval(7,Point3(0,-4,20),Point3(0,0,20)) ).loop()

GRAVhandler.addCollider(smileyCN,smiley)
base.cTrav.addCollider(smileyCN,GRAVhandler)

camera.setPos(10,-10,5)
camera.lookAt(0,-2.5,-1)
mat4=Mat4(camera.getMat())
mat4.invertInPlace()
base.mouseInterfaceNode.setMat(mat4)

run()