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Cosine wave problem

BlitzMax Forums/BlitzMax Programming/Cosine wave problem

Torrente(Posted 2008) [#1]
In my program, I'm having an object move back and forth between two points, going faster in the middle. I achieve this using cosine, however it flickers badly at times, and I'm not sure why this happens.

		Local st:Float = ((Cos((MilliSecs()/time) Mod 360))+1)/2
		Local xdist:Int = x2 - x
		Local ydist:Int = y2 - y
		x = xdist*st
		y = ydist*st


st ends up being a float between 0 and 1, and then I base the coordinates on that.

I'm almost certain I've had this problem before, but I don't remember how I fixed it. The flickering is at its worst when I click the top of the window and release... not just because my use of Millisecs(), though -- it's as if it's drawing in two places at once.


ImaginaryHuman(Posted 2008) [#2]
Flip 1


Torrente(Posted 2008) [#3]
That doesn't seem to make a difference, but thanks!


Sledge(Posted 2008) [#4]
Had a quick bash at this:
Graphics 800,600

x1:Float = 100 'Point 1
y1:Float = 500

x2:Float = 500 'Point 2
y2:Float = 200

xc:Float = (x1+x2)*.5 'Center
yc:Float = (y1+y2)*.5

inc=0

While Not KeyHit(KEY_ESCAPE)
	px=xc+(Sin(inc))*(xc-x1)
	py=yc+(Sin(inc))*(yc-y1)
	
	Plot x1,y1
	Plot x2,y2
	Plot xc,yc
	Plot px,py

	Flip
	Cls
	inc=inc+1
Wend



Who was John Galt?(Posted 2008) [#5]
If your phase (the variable in the brackets of the cos bit) i.e: cos(phase) varies too quickly the value can literally 'rotate' from one side of the cos function to the other in a frame. This give the appearance of plotting in two places.


Torrente(Posted 2008) [#6]
Sledge: That seems to be precisely what I needed, thanks!

Nomen: That sounds like exactly what I was seeing. Why does this happen, though?