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Need a function which returns points X,Y in a Circle

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MervinKoops MervinKoops is offline

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Need a function which returns points X,Y in a Circle

Sep 21st, 2009

Hello,

I need to create a function which takes parameters for a circle and checks if a given point(x,y) lies within the circle (or on the edge).

Like this:

 Help with Code Tags 
 C# Syntax (Toggle Plain Text) 
public static bool PointExistsInCircle(Double CircleX,Double CircleY,Double CircleRadius,Double PointX,Double PointY) 
{
needs to return 'true' if the point is in the circle, if not return 'false'.
}
public static bool PointExistsInCircle(Double CircleX,Double CircleY,Double CircleRadius,Double PointX,Double PointY) 
{
needs to return 'true' if the point is in the circle, if not return 'false'.
}

Could someone help me with this?, unfortunately i'm not good at math..

Mervin.

Last edited by MervinKoops; Sep 21st, 2009 at 5:50 pm.

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Re: Need a function which returns points X,Y in a Circle

Sep 21st, 2009

I'm not good at math either...LOL. Check out this thread, and see if you can come up with the formula you need. Then, if you need help with coding it, come on back here--OK?

Calculate Radius from X Y coord

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Re: Need a function which returns points X,Y in a Circle

Sep 21st, 2009

Well, the equation of a circle with radius R on the origin is $x^2+y^2=R^2$
All you have to do is test if this inequality is true or false : $x^2+y^2 <= R^2$
If it is true the point (x,y) is in the circle, if it is equal it is on the circle, else it lies outside the circle.
It should be rather easy to write that in C#.

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Re: Need a function which returns points X,Y in a Circle

Sep 21st, 2009

Ah okay thanks for the help

.

and what would be a formula which also takes an X and Y for the circle origin?

Last edited by MervinKoops; Sep 21st, 2009 at 6:11 pm.

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Re: Need a function which returns points X,Y in a Circle

Sep 21st, 2009

Don't know exactly what you mean here but I guess it is something like this $(x-a)^2+(y-b)^2 = R^2$
Where a and b are the new coordinates of the center. If a and b are both zero then the circle has its center at the origin.

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Re: Need a function which returns points X,Y in a Circle

Sep 21st, 2009

I don't understand the Circle X,Y, and Radius. Don't you just need a single center point and the radius, then draw the circle from there?

Last edited by sknake; Sep 21st, 2009 at 6:55 pm.

Scott Knake
Custom Software Development
Apex Software, Inc.

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Re: Need a function which returns points X,Y in a Circle

Sep 22nd, 2009

Take a look at online book at google - Physics for game programmers By Grant Palmer

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SUMMARY:

Determine if the point is inside the circle by computing the distance from the point to the center of the circle. If the distance is less than 1, the point is inside.
Help with Code Tags

C# Syntax (Toggle Plain Text)
double distance = Math.Sqrt((x-0.5)*(x-0.5) + (y-0.5)*(y-0.5));
if(distance<=0.5){
   ...
}
double distance = Math.Sqrt((x-0.5)*(x-0.5) + (y-0.5)*(y-0.5)); if(distance<=0.5){ ... }