Gravity? Collision Platformer.

BlitzMax Forums/BlitzMax Beginners Area/Gravity? Collision Platformer.

Apollonius

(Posted 2007) [#1]

Well I'm not quite sure how to make gravity happen? I've been thinking of doing if not collision then ypox:+2 or something like that.

But my problem is when I look at the collision script i dont quite understand how to use it, could anyone should me a small example of:
Function CollideRect:Object[](x,y,w,h,collidemask%,writemask%,id:Object=Null)

Let's say i have a DrawRect for player and one for the ground... my second problem after that will be jumping.. more advance stuff in due time.

Thansk in advance

Grey Alien

(Posted 2007) [#2]

For gravity, you shouldn't just alter the y by a fixed value. What you need is a yspeed which starts at 0, then when there is no collision you increase yspeed by a small amount. Every frame you change the yposition of the character by yspeed. This what when you jump, you just set yspeed to a negative value and then gravity will make it go to zero (the top of the jump arc) and then beyond as the character falls down. You may wish to consider having a "terminal velocity" which is a maximum yspeed so you can never fall too fast (e.g. through platforms etc).

Hopefully someone can help you with the CollideRect code as it's a bit tricky.

ImaginaryHuman

(Posted 2007) [#3]

Yes what you really need is X,Y as the position of your object, then XAdd,YAdd as the speed at which it is moving, then you add 2 to the YAdd. Then when you do X:+XAdd and Y:+Yadd it will gradually increase the Y speed as the object falls. Handling collision and bouncing is a little more tricky. When the object hits the surface, depending on the dampening qualitities of the surface the YAdd should be inverted to become negative so the object bounces up the screen. Of course you keep adding 2 to the gravity so it slows down and gradually falls again. But if you want the object to come to a rest eventually you have to lose some of the `energy` when it bounces e.g. YAdd:-10 or something. I also recommend using floats otherwise you'll see quite jagged movement.

Amon	(Posted 2007) [#4]

Here you go. This is Jump code at its simplest

' Jump Code for Kaisuo
' By AMon

SuperStrict

Graphics 800 , 600

Global Dude:TImage = LoadImage("dude.png")

Global Jump:Int = 0 ' Tracks whether we can jump
Global Gravity:Float = 0.3 'Gravity applied to jumpheight
Global JumpHeight:Float = 7 ' How High we can jump

Global dudeX:Float = 380 
Global dudeY:Float = 520

While Not KeyHit(KEY_ESCAPE)
	
	Cls
	
		DrawImage Dude, DudeX , dudey , 0
		DrawLine 0 , 570 , 800 , 570  
		
		If KeyHit(KEY_SPACE)
			Jump = 1
		End If
		
		DoJump()
		
		If dudeY >= 570 - 50 
			dudeY = 570-50
			Jump = 0
			JumpHeight = 7
		End If		
	Flip
	
Wend

Function DoJump()

	If Jump = 1 
		dudeY:-JumpHeight
		JumpHeight:-Gravity
		
		If JumpHeight <=-5 Then jumpHeight = -5
	End If
	
End Function

Replace the image with anything. :)

assari

(Posted 2007) [#5]

A simple example of CollideRect

Strict
Local x:Int
Local y:Int
Graphics 640,480

ResetCollisions()
'SetColor 0,0,0 <--------------uncomment this out and see what happens
DrawRect    300,300,100,100
CollideRect 300,300,100,100,0,1 '<---comment this out to see what happens

Repeat 
  x = MouseX()
  y = MouseY()
  'check collision b/w a 10x10 rect against rect above
  If CollideRect(x ,y , 10 , 10 , 1 , 0)  
	SetColor 255,0,0
	DrawRect x , y , 5 , 5 '--note that collision is not against this
	SetColor 255,255,255
  EndIf
  Flip

Until KeyHit(KEY_ESCAPE) Or AppTerminate()

Also check out this tutorial
http://www.2dgamecreators.com/tutorials/gameprogramming/collision/T1%20Collision2.html

Apollonius

(Posted 2007) [#6]

Thanks everyone, sorry for the late replies(real life..)

I've been trying to figure out the collision between my two rectangle. I don't quite understand it yet with what you guys provided me. As for increasing gravity, well gonna add it after I can actually touch the ground and move right and left lol(same goes for jumping).

So let's start with my collision...
I'm not quite sure why my piece of code won't let me modify gravity..?

SuperStrict

Graphics 800,600,0

'********************************************************************************************
Global GameRoom:Int		=0
Global GameExit:Int		=False

ResetCollisions()

Local P1:TPlayer=New TPlayer; P1.Create(10.0 ,10.0 )
While Not GameExit=True
	If(KeyHit(KEY_ESCAPE))Or(AppTerminate())Then GameExit=True
	
	P1.Updates()
	MakeSolid(0,560,800,25)
	Flip 1
	Cls
Wend
End

Type TPlayer
	Field health:Int, mana:Int
	Field xpos:Float, ypos:Float
	Field maskw:Int=70, maskh:Int=120
	Field gravity:Float=1.0
	Field jump:Int=False
	Method Create( xstart:Float, ystart:Float )
		xpos=xstart
		ypos=ystart
	End Method
	Method Updates()
		If KeyDown(KEY_UP) 		Then ypos :- 5.0
		If KeyDown(KEY_DOWN) 	Then ypos :+ 5.0
		If KeyDown(KEY_LEFT) 	Then xpos :- 5.0
		If KeyDown(KEY_RIGHT) 	Then xpos :+ 5.0
		If KeyHit(KEY_SPACE)	Then jump = True
		
		ypos :+ gravity
		
		Self.Drawing()
		
	End Method
	Method Drawing()
		DrawRect xpos,ypos,maskw,maskh
		CollideRect xpos,ypos,maskw,maskh,0,1
	End Method
End Type

Function MakeSolid( x:Int, y:Int, w:Int, h:Int )
	DrawRect(x,y,w,h)
	If(CollideRect(x,y,w,h,1,0))Then
		P1.gravity=0
	EndIf
End Function

Not Quite sure how to design my level should I make a function which draws all the masked SOLID background that would collide with my player's rectangle mask?

*shake his head and goes take an advil* xD

tonyg

(Posted 2007) [#7]

So you've bought Bmax now then?

Apollonius

(Posted 2007) [#8]

hmm, what if i have roar ;D