Circular movement

BlitzMax Forums/BlitzMax Beginners Area/Circular movement

Gavin Beard

(Posted 2007) [#1]

Hi all,

I know this should be basic but i just cant seem to get it right, i want an object moving around another one at a fixed distance from the center point at a constant velocity, it is in 2d, i've got it moving in arcs, ovals etc, but never in a circle :-)

i was simply using:

  x=x+cos((pi/180)+angle)*radius
  y=y+sin((pi/180)+angle)*radius

many thanks

rockford

(Posted 2007) [#2]

A very simple piece of code here -

Graphics 640,480,32,60,0


HideMouse

While Not KeyHit(key_escape)


DrawText("+",MouseX(),MouseY())

DrawText("o",MouseX()+Cos(n)*50,MouseY()+Sin(n)*50)

n:+1


Flip

Cls

Wend

End

If you want the orbit bigger/smaller, then change the 50 ((n)*50) value. If you want the "o" to go in the opposite direction, then use n:-1. If you want orbit to be faster, then increase the (n:+/-) value.

Hope that helps :)

Gavin Beard

(Posted 2007) [#3]

thanks alot, shall check this out when at PC in afew hours, thanks for fast reply

ImaginaryHuman

(Posted 2007) [#4]

x=x+cos((pi/180)+angle)*radius
y=y+sin((pi/180)+angle)*radius

Here you shouldn't be ADDING the calculation to X and Y, you are not calculating a position relative to the last position, you are calculating a whole new position relative to a center point.

x=CenterX+(Radius*(Cos(Angle)))
Y=CenterY+(Radius*(Sin(Angle)))

Jesse

(Posted 2007) [#5]

Gavin, How is it that you don't get a circular motion from your equation. I tryed it out and it works fine. here:

SetHandle(10,10)
Graphics 800,600
Local angle# = 0.0
Local radius# = 100.0
Repeat
	'Cls()
	x# = MouseX()
	y# = MouseY()
	angle = (angle+0.5) Mod 360.0
	x1=x+Cos((Pi/180.0)+angle)*radius
  	y1=y+Sin((Pi/180.0)+angle)*radius
	DrawOval x1,y1,5,5
	Flip(0)
Until KeyDown(key_escape)

although there is no need for the (pi/180.0) blitzmax sin and cos functions are set for degrees not radians.
the only reason I think you would get an oval is if you have a wide screen. setting it at 640,480 would give a distorted image. if that is the case you would have to compensate by using a different radius for each x and y.

Gavin Beard

(Posted 2007) [#6]

Hi,

Thanks to all, i was running in window mode, 640,480 but i get an oval movement rather than circular, tis very wierd indeed, unfortunatly i am still at work at the moment so cant test till i get home.

I am most certain it is something i have done, as always :)

ImaginaryHuman

(Posted 2007) [#7]

What is the aspect ratio of your screen resolution?

Gavin Beard

(Posted 2007) [#8]

its a 4:3 ratio, sorted it anyway, turns out i had forgot to set 1 variable :-)

thanks for eveyone's help, much appreciated