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Thread: Finding the end of a moving sprite

  1. #1
    Join Date
    Dec 2007

    Finding the end of a moving sprite

    I'm currently building a cannon launching game, where the player adjusts a cannon's angle in order to help fire it. What I need to be able to do is find where the end of this cannon is, such that I can start firing a cannon shell from that point.

    I ran some initial testing, and trying to use x and y coordinates doesn't work. They'll only track the original positions, not the new ones. Trying to use rotations to find the point didn't help either.

    The cannon is angled using rotation, within a range of 0 to 15 degrees. In addition, the cannon movieclip is composed of three areas. These areas are named "cannon_load", "cannon_launch", and "cannon_barrel". The third area is the one where I need to find the far end of.

    Any ideas?

  2. #2
    Senior Member
    Join Date
    Oct 2007
    Leeds, UK
    If you know:

    * the x,y coordinates of the other end of the cannon (the end that the shells DON'T come out of) (call that point (baseX,baseY) )

    * the length of the cannon (call it L)

    * the angle between the cannon and the horizontal (call it A)

    then trigonometry tells you that the far end of the cannon is the point

    (baseX + L*Math.cos(A*Math.PI/180), baseY + L*Math.sin(A*Math.PI/180) )

  3. #3
    Join Date
    Dec 2007
    Wow, I never thought I'd see an applicable use for such advanced math.

    Anyway, I ran that formula, using the cannon's registration point as the base, since this was the only point of the cannon that would never change. It worked perfectly. Thanks very much.

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