2d object collision - GameCreators Forum

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mmmpie

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Posted: 24th Apr 2006 05:02

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How do i do 2D object collision so when a circle you control hits a square it will not go throuh it. I think it has to do with sotoring an restoring old position but im not shure.

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General Sephiro

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Posted: 24th Apr 2006 20:11 Edited at: 24th Apr 2006 20:12

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basic layout

You have the position of the character(a.k.a. circle)

Then a square that you do not want the circle to go through

The Theory Behind it
`----------------------------------------
Get position of the box and width by bredth
For example the box is 10 x 10

If Circle position goes into the box's square within the 10 x 10 field then position the circle back to where it was before it was moved.

Some Example code

+ Code Snippet

`Stores old position
OldPosX# = X#
OldPosY# = Y#

`Controls etc.. here
If Upkey()=1 then Y# = Y# + 1
If Downkey()=1 then Y# = Y# - 1
If Leftkey()=1 then X# = X# + 1
If Rightkey()=1 then X# = X# - 1

`Collistion code
If X# > SqaurePosX - 5 and X# < SquarePosX + 5
    If Y# > SqaurePosY - 5 and Y# < SquarePosY + 5
       X# = OldPosX#
       Y# = OldPosY#
    endif
Endif

http://www.hybridwolves.co.uk

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zenassem

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Posted: 24th Apr 2006 20:28 Edited at: 24th Apr 2006 20:38

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use sprites.

Pay close attention to the difference between sprite hitand sprite collisioncommands.

Which one you use will depend on how accurate the collision needs to be and how much transparent space is around your circle sprite.

I can't remeber which is which off-hand, but one command will detect the collision of the bounding rectangles of the sprites, the other will take into consideration the transparent portion of a sprite allowing the sprite to overlap until a nontransparent portion collides.

I hope that makes sense to you.

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Pincho Paxton

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Posted: 25th Apr 2006 00:14

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There are a few ways as you can see. There are about 5 different ways to do that.

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mmmpie

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Posted: 25th Apr 2006 04:27

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thanks for the code but could you put the box and circle in to your example script. i cant seem to fit it in right

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General Sephiro

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Posted: 27th Apr 2006 03:00 Edited at: 27th Apr 2006 03:05

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Edit->> Haha i realise now i used 3d objects.., oh wel same theory behind it. X and Y positions in all....

This is a full working example... i did within 1 minute

+ Code Snippet

`Make level...
make object sphere 1,50
Make object Cube 2,50
`Position cube randomly
CubePosX = 0-200 + Rnd(400)
CubePosY = 0-200 + Rnd(400)

`Position cube
Position object 2,CubePosX,0,CubePosY

`Set up camera
Position camera 0,500,0
Point camera 0,0,0

`Make background black
Backdrop on
Color Backdrop RGB(0,0,0)


`Main Loop
Do
	`Old Positions
	OldX = X
	OldY = Y
	`Movement
	If Upkey()=1 then Inc Y,5
	If Downkey()=1 then Dec Y,5
	If LeftKey()=1 then Dec X,5
	If Rightkey()=1 then Inc X,5
	
	`Collistion
	If X > CubePosX - 50 and X < CubePosX + 50
		If Y > CubePosY - 50 and Y < CubePosY + 50
			Set cursor 25,25
			Print "HITTTT!!!"
			X = OldX
			Y = OldY
		endif
	endif

	`Position Sphere
	Position object 1,X,0,Y

        `Refresh Screen
	Sync
Loop

You will notice i used 50, instead of 25 for the collistion. As you have to take into account the sphere's size

http://www.hybridwolves.co.uk

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X_MEN

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Posted: 27th Apr 2006 23:27

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hope this help

+ Code Snippet

`--------------------------------------------

`---------use the arrow key to move


`--------------------------------------------
sync on
ink rgb(255,0,0),0
box 0,0,32,32
get image 1,0,0,32,32
cls
ink rgb(0,255,0),0
circle 10,10,8
get image 2,0,0,20,20

sprite 2,120,120,2
do
oldx=posx:oldy=posy

if leftkey()=1 then posx=posx-2
if rightkey()=1 then posx=posx+2
if upkey()=1 then posy=posy-2
if downkey()=1 then posy=posy+2


sprite 1,posx,posy,1
col=sprite collision(2,1)
if col>0 then posx=oldx:posy=oldy :set cursor 120,10: print "hit circle "

sync
loop

You can do it if you try

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