I need the function "atan2"

[arono]

Hi,

I need this function to calculate collisions with circles.  I have the x,y point of the collision between a ball and the circumference of a circle.  I also know the center x,y of the circle and its radius.  In order to determine what angle the ball will take after it collides, I need to know the angle of that collision point to the center of the circle. 

In order to calculate this, i need function atan2.  Unfortunately it isn't in the Microsoft SDK that was installed with IWBasic.  Is there another library I can access?

Thanks.

[billhsln]

I found this equation that is supposed to replace ATAN2.

angle = (y/x) - ((1/3)*(y/x))*((1/3)*(y/x))*((1/3)*(y/x)) + ((1/5)*(y/x))*((1/5)*(y/x))*((1/5)*(y/x))*((1/5)*(y/x))*((1/5)*(y/x))

Maybe it will work for you?

Bill

[GWS]

Hi Arono,

I find it's often useful to write your own function.  Once declared in your program, it becomes part of the language .. 

Here's one for the atan2(y,x) function ..

Code Select Expand


' Test Routine for atan2(y,x) function ..

openconsole
cls

def pi,coeff_1,coeff_2,abs_y,angle,r,x,y:double

declare atan2(y:double,x:double)

autodefine "off"
setprecision 10

pi = 4 * atan(1)

coeff_1 = pi / 4
coeff_2 = 3 * coeff_1

' example for atan2(1,1) .. angles in radians
x = 1
y = 1

atan2(y,x)

print angle
' should give answer pi/4 = 0.7853981634


do:until inkey$<>""
closeconsole
end


sub atan2(y,x)

abs_y = abs(y)

if (x >= 0)
r = (x - abs_y) / (x + abs_y)
angle = coeff_1 - coeff_1 * r
else
r = (x + abs_y) / (abs_y - x)
angle = coeff_2 - coeff_1 * r
endif

if (y < 0) then angle = -angle

return



It seems to be working OK, but I haven't tested it fully ....

Best wishes,

Graham

[fasecero]

Another alternative, if you are willing to use the C runtime library

Code Select Expand

/*
Compile as a CONSOLE target
*/

DECLARE CDECL EXTERN _atan2(double y, double x), double ' The C runtime uses CDECL EXTERN and not CDECL IMPORT

PRINT _atan2(4, 8)
PRINT:PRINT "Press any key to close"
DO:UNTIL INKEY$<>""

[Brian]

Fasecero,
On another tack, how do you find out what functions are available in the C runtimes? The atan2 seemed very elegant
Brian

[fasecero]

Hi Brian, you can check in here for CRT math functions

https://msdn.microsoft.com/en-us/library/y0ybw9fy.aspx

[Brian]

Wow, there's a heck of a lot of stuff in there when you dig down. There must be something I can use! Thanks a lot,

Brian