Re: Math.cos() problems

Knute Johnson wrote:
Brandon McCombs wrote:
Hello,

I'm trying to do something simple but Java turns it into a federal case. All I want to do is draw a couple circles on a Graphics2D canvas with one movable and attracted to the 2nd one which is stationary. Basically I'm just trying to get basic functionality working that simulates gravitational attraction between the spheres.

I had everything working concerning the movement calculations (force, acceleration, velocity) up to the point of performing the calculation that would generate each new pixel positions for the circle that I am allowing to move. I ran into problems because I had to determine the angle between the moving circle and the stationary one and use the angle in the equations x = rCos(angle) and y = rSin(angle) so I could determine how much the movable circle should move.

The problem is that I have no clue how Java is calculating the cosine and xine of the angle I calculate (even calculating the angle is a chore which may be confusing the problem even further). With respect to what screen location are the trig functions being evaluated? (0,0) on the drawing canvas? Does it matter? I thought it did especially since my angle is based on the location of one of my circles and it isn't at 0,0 on the canvas. Where am I going wrong? This is frustrating. If you need more info let me know.

thanks

Could it be that you are getting messed up because they y axis is upside down? Add pi to your angle before calculating.


Well that was one problem I noticed last night after I posted. I'm doing other stuff that I shouldn't be but I haven't had time to fix it yet. When I simplify the code I may end up with it working properly. I'm aware of -pi/2 and pi/2 as the range for cosine although whether I was correctly taking that into account last night is another issue. I'm also aware that the java methods use radians for input/output which I've been correctly taking into account. It's been a while since I did a lot of trig stuff though. I'll try again when I have time. thanks guys
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