Gravity

BlitzPlus Forums/BlitzPlus Beginners Area/Gravity

Pille

(Posted 2007) [#1]

Hi,

I need a physics routine for throwing a stone in 2D. This means, a person throws a stone, and it flies as real as possible through the air and lands at another point. Can you help me?

thx,
teddy

CS_TBL

(Posted 2007) [#2]

Without really testing, my estimation is that your stone needs an angle and a decaying speed (in the end, pixelwise, this will be converted to a deltaX and deltaY using sine and cosine) while gravity pulls the stone done, this gravity is then just added or subtracted from the stone's Y coord.

so:

start:
* convert stone angle+speed to deltaX and deltaY (float values!)
* add or sub a gravity amount
* draw stone
* multiply the stone speed with 0.999 or something
loop

Don't have this angle+speed converting formula at hand, it's not difficult tho, but it's probably
deltax=sin(angle)*speed
deltay=cos(angle)*speed

ohwell it probably *is* the fomula anyway.. :P

Perhaps another method is tho change the angle instead of just the y-coord.

bryan970

(Posted 2007) [#3]

I haven't personally tried this (I'm can't load blitz plus at work I tried once and got busted DOH!!!) anyway I think something like this might work I'll try it at home tonight if I think about it and see what I did wrong

Type rock
field V1 ; horizontal velocity you are throwing at
field height; the initial height you are throwing at
field Angle ; angle you are throwing at in radians
field x,y
end type

intiitialize your rock with whatever you are starting with
global rock.rock = new rock
rock\v1 = whatever
rock\angle = whatever
rock\height = whatever
rock\x = whatever

;in your main loop somewhere

if rock\y < rock\height ; if your y is less than your height you are back where you started from vertically

drawimage(rockimage, rock\x, rock\y)
UpdateRock()
end if

Function UpdateRock()
rock\y = rock\x * (Tan(rock\angle)) - (((4.9) * (rock\x ^ 2)) / ((rock\V1 ^ 2) * ((Cos(angle)) ^ 2)))

rock\x = rock\x + 1 ;increment by a pixel or whatever you want

end function

bryan970

(Posted 2007) [#4]

actually looking at this I guess you would want to increment your x value by your initial velocity

rock\x = rock\x + rock\V1

CS_TBL

(Posted 2007) [#5]

oops, I made code :P

window=CreateWindow("oO",0,0,640,480)

canvas=CreateCanvas(0,0,640,480,window)

timer=CreateTimer(25)



Global stone_angle
Global stone_speed#
Global stone_x#
Global stone_y#
Global gravity_delta#
Global gravity#

reset

Repeat
	WaitEvent()
	If EventID()=$803 End
	
	If EventID()=$4001

		stone_x=stone_x+Sin(stone_angle)*stone_speed
		stone_y=stone_y+Cos(stone_angle)*stone_speed
		stone_y=stone_y+gravity

		gravity=gravity*gravity_delta
		stone_speed=stone_speed*.985
	
		SetBuffer CanvasBuffer(canvas)

			Cls

			Color 255,0,0
			Rect 320,240,4,4,1
			Color 255,255,0
			Rect stone_x,stone_y,4,4,1
			Color 0,255,0
			Rect 0,400,640,4,1
		
		FlipCanvas canvas
	EndIf

	If EventID()=$201 reset ; mouseclick @ canvas
	
Forever

Function reset()
	stone_angle=Rnd(180)+90
	stone_speed#=4
	stone_x#=320
	stone_y#=240
	gravity_delta#=1.06
	gravity#=1
End Function

click mouse on the canvas..