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Collision problem

Blitz3D Forums/Blitz3D Beginners Area/Collision problem

Ash_UK(Posted 2006) [#1]
Hi guys :o) I am having a bit of a crisis with my code. When the ball hits the right side of the board, it doesn't reverse its direction for some reason. I have the code to print out the ball_x_speed variable, but it just displays an alternating number instead between 0 and 1.

here is my code:

Graphics3D 800,600
SetBuffer BackBuffer()

Const BALL_COL = 1
Const BOARD_COL = 2


Global CAMERA = CreateCamera()
PositionEntity CAMERA,0,54,-60
RotateEntity CAMERA,45,0,0

Global OMNI = CreateLight()
AmbientLight 170,170,170

Global BOARD = LoadMesh("models/game_board.3ds")
EntityType board,BOARD_COL

Global ball_x# = 0
Global ball_x_speed = 1
Global ball_z# = 0
Global ball = CreateSphere()
EntityType ball,BALL_COL
EntityRadius ball,4
ScaleEntity ball,2,2,2



Collisions BALL_COL,BOARD_COL,2,2

While Not KeyHit(1)
Cls
	
	PositionEntity ball,ball_x,2,ball_z

	ball_x = ball_x+ball_x_speed
	
	MoveEntity ball,ball_x_speed,0,0
	If EntityCollided(ball,BOARD_COL) Then ball_x_speed = 1-ball_x_speed
		
	
	UpdateWorld
	RenderWorld
	
	Text 0,0,ball_x_speed
	
	Flip
	
Wend
End


Thanks guys!


GfK(Posted 2006) [#2]
Should it not be ball_x_speed = 0 - ball_x_speed?


nrasool(Posted 2006) [#3]
Try the following

If EntityCollided(ball,BOARD_COL) Then ball_x_speed = ball_x_speed - 1



Ash_UK(Posted 2006) [#4]
Gfk :o) That doesn't seem to change the problem i'm afraid

nrasool :o) Erm, that does reverse the direction, but when the ball hits the left hand side it stays there and the ball_x_speed is decreasing.

Thanks for your help though guys :o)


GfK(Posted 2006) [#5]
Without seeing your board model this is a bit of educated guesswork.

You're using sliding collisions - have you tried using stop collisions instead? Its possible that after the initial collision the ball is always in contact with the board and that could be screwing things up.

Other than that, post the model in a ZIP file and I'll have a play.


Dreamora(Posted 2006) [#6]
It would be ball_x_speed = 0 - ball_x_speed or just *-1 which is the same in this case.


But the important thing is that you use positionentity and moveentity on the same entity. Thats the reason it can't get away anymore because if it collided it "turns around" but in the next loop you put it to the old position once again so it turns straight away again and will turn back to the board once again.


Ash_UK(Posted 2006) [#7]
Hmm :o) Here you go, this is a zip of the code with models. This may give you a better idea:

Breakout start


Thanks guys!


GfK(Posted 2006) [#8]
Fixed

1. My original bug fix was correct, except for:
2. You were doing collision-dependent stuff BEFORE UpdateWorld
3. Took out the redundant TurnEntity command - it wasn't doing anything!

[edit] Oh, I changed it to Stopcollisions, too. If you don't do this, the ball will slide along walls when it hits them at angles.

Graphics3D 1024,768
SetBuffer BackBuffer()

Const BALL_COL = 1
Const BOARD_COL = 2


Global CAMERA = CreateCamera()
PositionEntity CAMERA,0,54,-60
RotateEntity CAMERA,45,0,0

Global OMNI = CreateLight()
AmbientLight 190,190,190

Global BOARD = LoadMesh("models/game_board.3ds")
EntityType board,BOARD_COL

Global ball_x# = 0
Global ball_x_speed = 1
Global ball_z_speed = 1
Global ball_z# = 0
Global ball = CreateSphere()
EntityType ball,BALL_COL
EntityRadius ball,4
ScaleEntity ball,2,2,2

MoveEntity ball,0,2,0

Collisions BALL_COL,BOARD_COL,2,1

While Not KeyHit(1)
Cls

	ball_x = ball_x+ball_x_speed
	
;	TurnEntity board,0,0,0
	
	MoveEntity ball,ball_x_speed,0,0
	

	
	UpdateWorld
	If EntityCollided(ball,BOARD_COL) Then ball_x_speed = 0-ball_x_speed
	RenderWorld
	
	Text 0,0,ball_x_speed
	
	Flip
	
Wend
End



Ash_UK(Posted 2006) [#9]
Excellent :D Thankyou very much Gfk, I really appriciate your help. Thanks again! :o)


big10p(Posted 2006) [#10]
Just a small point: instead of
ball_x_speed = 0-ball_x_speed

you can simply do
ball_x_speed = -ball_x_speed

This will have no effect other than to make your code a little bit more understandable. Possibly. :P


Ross C(Posted 2006) [#11]
I don't understand... :oP


big10p(Posted 2006) [#12]
/me slaps Ross around a bit with a large trout :P


GfK(Posted 2006) [#13]
Just a small point: instead of

ball_x_speed = 0-ball_x_speed


you can simply do

ball_x_speed = -ball_x_speed


This will have no effect other than to make your code a little bit more understandable. Possibly. :P
Suppose thats a matter of preference. I find it clearer to read *with* the zero.


big10p(Posted 2006) [#14]
Yeah, it's definately just a matter of preference. I'm not even sure why I mentioned the aternative way, really. :)

P.S.

/me slaps Ross around a bit more with a large trout :P


Ross C(Posted 2006) [#15]
:(


big10p(Posted 2006) [#16]
You had enough of my trout, yet? I have plenty more. You have been warned! :P