Thread: How to get the coordinates inside

  1. #1
    Registered User
    Join Date
    Dec 2008

    How to get the coordinates inside

    What's the algorithm on how to get the coordinates inside of:
    a) Square
    b) Triangle
    c) Circle
    d) Oval

    Example points.



  2. #2
    Registered User carrotcake1029's Avatar
    Join Date
    Apr 2008
    Unless I am missing something here, your question doesn't make sense. There is an infinite amount of points that can be found within a given space.

    Can you describe your problem in context?

  3. #3
    Registered User
    Join Date
    Aug 2006
    I had a similar problem when I programmed my collision detection algorithm. For example if I tried to detect collision with two rectangles I tried if the corners of one rect were inside the other rectangle. If you have a similar problem then it's probably a better idea to ask about it in a maths forum as it's more maths related than programming.

  4. #4
    Registered User
    Join Date
    Dec 2008

    I'm creating a program that can move any objects in the screen by just holding it with a mouse. I hope you get what I mean. I tried the formula on this site ( but sometimes even though the point is inside it says it is not.


    Yeah. I think I should post there. Thanks.

  5. #5
    Super Moderator VirtualAce's Avatar
    Join Date
    Aug 2001
    You want the formula for all points inside those objects then.

    A circle is the easiest since it is all points that lie equidistant from a center point.
    If the distance to center is larger than the radius then the point is outside the circle.

    A point in square (also works for rectangles) is:
    if (x > right) return;
    if (y > bottom) return;
    if (x < left) return;
    if (y < top) return;
    //If you get here point is inside the square/rectangle
    Points inside of a triangle and oval are not as trivial as the above examples. You should be able to find some info on google. However you can do this check.

    Choose a point outside of the primitive. Draw a line to the point in question. When you cross an edge of the primitive increase your count.

    All odd counts = point is inside the primitive.
    All even counts = point is outside of the primitive.

    However there is actually a point in triangle equation but I do not remember what it is.

    As for an oval they follow this equation (in 2D):

    d = (xcoef)(x * x) + (ycoef)(y * y)

    At xcoef = 1 and ycoef = 1 you get a perfect circle.

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