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Normals (THEY HURT)

Blitz3D Forums/Blitz3D Programming/Normals (THEY HURT)

Makepool(Posted 2003) [#1]
Why does the collision normals command report an impossible figure in this code? With the cube that the sphere collides with at its default rotation the collisions normals correctly reports x1, y0, z0. When the cube is rotated to a 45 degree angle, to my reckoning it should report x0.5, y-0.5, z0. Instead I get a physically impossible figure of x0.7, y-0.7, z0.

Any ideas?

Here’s the code


Graphics3D 800,600

SetBuffer BackBuffer()

Const WALLS=1
Const BALLS=2


camera=CreateCamera()
CameraRange camera,0.1,1000 
CameraZoom camera,1.4


light=CreateLight(1)
PositionEntity light,0,0,-500
AmbientLight 100,100,100


ball1=CreateSphere(8)
PositionEntity ball1,0,0,15
EntityType ball1,BALLS


wall=CreateCube()
PositionEntity wall,-3,0.5,15
RotateEntity wall,0,0,45;EDIT ME OUT
EntityType wall,WALLS



Collisions BALLS,WALLS,2,2


While Not KeyDown( 1 )
	UpdateWorld
	RenderWorld

	MoveEntity ball1,-0.01,0,0
	
	If CountCollisions ( Ball1 ) >0 Then 
		Text 0,0,"x "+CollisionNX#( wall,1 )
		Text 0,10,"y "+CollisionNY#( wall,1 )
		Text 0,20,"z "+CollisionNZ#( wall,1 )
	EndIf
	Flip
Wend



Jim Teeuwen(Posted 2003) [#2]
I get a 'Collision index out of Range' error as soon as the sphere hits the cube


Floyd(Posted 2003) [#3]
The vectors ( 0.5, -0.5, 0.0 ) and ( 0.7, -0.7, 0.0 ) point in the same direction.

Normals are always scaled to have length 1.0.

So the second vector is correct as Sqr(0.5) = 0.707...


jhocking(Posted 2003) [#4]
I was about to ask what is wrong with .7,-.7,0
The magnitude of the vector is irrelevant, all that matters is the direction.


sswift(Posted 2003) [#5]
Tink of a a normal as a point that lies on a sphere with a radius of 1.0.

0.7 0.7 0 may be misleading and appear to be greater than 1, but it's NOT. You do not dtermine distance by adding the components, you have to do this equation:

d = sqr(x^2 + y^2 + z^2)

And as you will see if you plug in the values, if you plug in 0.7, for X and Y, you get 1.

Try plotting the points on a graph. If you plotted 1,1 0,1 -1,0 0,-1 and the four variations of 0.5,0.5, then you'd get something that looks ike a diamond, not a circle.


Makepool(Posted 2003) [#6]
Yeah sorry I wasn't thinking.


Bot Builder(Posted 2003) [#7]
You need to do a

Text 0,0,"x "+CollisionNX#( ball1,1 )

not a

Text 0,0,"x "+CollisionNX#( wall,1 )

The collisions only register for the ball1. to the wall, it never had a collision.