Get center of sphere? - GameCreators Forum

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Carharttguy

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Joined: 8th Jul 2016

Location: Belgium

Posted: 22nd Mar 2017 14:39

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Hello

I want to get the center of a sphere object because I want to calculate if 2 meshes collide.
See this code:

+ Code Snippet

Function CheckSphereCollision(Sphere1, Sphere2)
	
	ax As Float
	ay As Float
	az As Float
	bx As Float
	by As Float
	bz As Float
	ar As Float
	br As Float
	distance As Float
	result As Integer

	ar = GetObjectSizeMaxY(Sphere1) - GetObjectSizeMinY(Sphere1)
	br = GetObjectSizeMaxY(Sphere2) - GetObjectSizeMinY(Sphere2)
	ax = GetObjectX(Sphere1) + ar/2
	ay = GetObjectY(Sphere1) + ar/2
	az = GetObjectZ(Sphere1) + ar/2
	bx = GetObjectX(Sphere2) + br/2
	by = GetObjectY(Sphere2) + br/2
	bz = GetObjectZ(Sphere2) + br/2
	
	distance = Sqrt((ax-bx)^2 + (ay-by)^2 + (az-bz)^2)
	
	Print(distance)
	Print(ar + br)
	
	If distance < (ar+br)^2
		Result = 1
	EndIf
	
EndFunction Result

Code is somewhat messy, it's the fault of my debugging :')
The formula for calculating the distance of 2 3D points should be correct, so I'm assuming I did something wrong with getting the center location of the sphere, altough, I cannot think what's wrong with it.
Any idea?

Thanks!

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Markus

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Location: Germany

Posted: 22nd Mar 2017 14:48 Edited at: 22nd Mar 2017 14:51

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the center its the sphere position or not?

if u using float here u should use .0 because 2 will be integer
/ 2.0

AGK (Steam) V2017.02.28 : Windows 10 Pro 64 Bit : AMD (17.2.1) Radeon R7 265 : Mac mini OS Sierra (10.12.2)

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Carharttguy

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Location: Belgium

Posted: 22nd Mar 2017 14:59

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Aha

The center of the sphere could be its position indeed.
But even then, the calculation is wrong in someway.

+ Code Snippet

Function CheckSphereCollision(Sphere1, Sphere2)
	
	ax As Float
	ay As Float
	az As Float
	bx As Float
	by As Float
	bz As Float
	ar As Float
	br As Float
	distance As Float
	result As Integer

	ar = GetObjectSizeMaxY(Sphere1) - GetObjectSizeMinY(Sphere1)
	br = GetObjectSizeMaxY(Sphere2) - GetObjectSizeMinY(Sphere2)
	ax = GetObjectX(Sphere1)
	ay = GetObjectY(Sphere1)
	az = GetObjectZ(Sphere1)
	bx = GetObjectX(Sphere2)
	by = GetObjectY(Sphere2)
	bz = GetObjectZ(Sphere2)
	
	distance = Sqrt((ax-bx)^2.0 + (ay-by)^2.0 + (az-bz)^2.0)
	
	Print(distance)
	Print(ar + br)
	
	If distance < (ar+br)^2.0
		Result = 1
	EndIf
	
EndFunction Result

The distance is +- 11, radius is 16. The radius is certainly correct.
So the distance must still be wrong, but in the image you can see clearly that the sphere is further away.

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Carharttguy

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Location: Belgium

Posted: 22nd Mar 2017 15:28

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I just found the problem! I took the diameter of both spheres, I needed the radius!

Stupid!

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Scraggle

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Location: Yorkshire

Posted: 23rd Mar 2017 07:50 Edited at: 23rd Mar 2017 07:50

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You should change your distance calculator, the way you are doing it is slower than it could be.
This

+ Code Snippet

(ax-bx)^2.0

Is exactly the same as this

+ Code Snippet

(ax-bx)*2

But it is considerably faster to use multiplication, here's the proof:

+ Code Snippet

t# = timer()
for k = 0 to 100000000
	v = v * 2
next k
t1# = timer()-t#
t# = timer()
for k = 0 to 100000000
	v = v ^ 2
next k
t2# = timer()-t#
	 
do
	print("Multiply: " + str(t1#))
	print("Squared : " + str(t2#))
	sync()
loop

Another method you can use to speed up the distance check (A LOT) is to square the result so that you can avoid square rooting the check.
Your distance check would be this

+ Code Snippet

distance = (ax-bx)*2 + (ay-by)*2 + (az-bz)*2

And then when checking if the distance is within a certain range you square the range, like this

+ Code Snippet

 if distance(...) < range*range then ...

AGK V2 user - Tier 1 (mostly)

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Carharttguy

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Location: Belgium

Posted: 23rd Mar 2017 08:17

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Hi Scraggle

I might be wrong, but I don't think *2 is the same as ^2

3*2 = 6
3^2 = 9

Or do I misunderstand you?

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Markus

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Posted: 23rd Mar 2017 09:43

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(ax-bx)^2.0 is (ax-bx)*(ax-bx)

AGK (Steam) V2017.02.28 : Windows 10 Pro 64 Bit : AMD (17.2.1) Radeon R7 265 : Mac mini OS Sierra (10.12.2)

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Scraggle

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Posted: 23rd Mar 2017 11:58

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Sorry, my bad!
Markus' multiplication example is the way to go.

AGK V2 user - Tier 1 (mostly)

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