Getting new coordinates

Discussion in 'Java' started by Chantal, Jan 24, 2006.

  1. Chantal

    Chantal Guest

    Hello,

    I'm translating and rotating a polygon with graphics2D (g2) and
    everything works fine :

    g2.translate(x, y);
    g2.rotate(r);
    g2.drawPolygon(pol);
    //reinit
    g2.translate(-x, -y);
    g2.rotate(-r);

    But I would like to know if it's possible to get the new coordinates of
    the polygon, I mean after the rotation and translation are done.

    To be complete, I'm doing a translation and a rotation on a image too.
    So i draw first my image and after I draw my polygon.
    So my image and polygon perfectly match but I need to get the new
    coordinates of my polygon.

    I tried to rotate and translate my polygon with maths without using
    dedicated graphics2D functions (the image is still translated and
    rotated with graphics2D) but the figures don't match anymore (several
    pixels of difference).

    So, if there was a possibility to get the new coordinates of my polygon
    with the first solution (everything done with graphics2D), it would be
    great !!

    Thanks in advance, :eek:)

    Chantal
     
    Chantal, Jan 24, 2006
    #1
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  2. Chantal wrote:
    > I'm translating and rotating a polygon with graphics2D (g2) and
    > everything works fine :
    >
    > g2.translate(x, y);
    > g2.rotate(r);
    > g2.drawPolygon(pol);
    > //reinit


    It is better to keep a copy of the original, instead of trying to
    reverse your operations, ...

    > g2.translate(-x, -y);
    > g2.rotate(-r);


    .... because this adds rounding errors.

    [...]
    > So, if there was a possibility to get the new coordinates of my polygon
    > with the first solution (everything done with graphics2D),


    There are no new polygon user space coordinates, since you have in no
    way translated the polygon. You have changed the origin and rotation of
    the device space coordinate system in which the polygon is drawn. Within
    that coordinate system the polygon user space coordinates are absolutely
    the same as before.

    So what is it what you really want?

    /Thomas
    --
    The comp.lang.java.gui FAQ:
    ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq
    http://www.uni-giessen.de/faq/archiv/computer-lang.java.gui.faq/
     
    Thomas Weidenfeller, Jan 24, 2006
    #2
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  3. Chantal

    Chantal Guest

    Hello Thomas,

    Thanks you for your answer.

    How to get original values ?

    What I wanted was to try to get the coordonnates of the rotated polygon
    but if it's only the device space system coordinates which is changed,
    I don't have certainly the possibility to get it. I'll try another way.

    Thanks again Thomas, :eek:)

    Chantal
     
    Chantal, Jan 24, 2006
    #3
  4. Chantal

    Chantal Guest

    Re,

    I get it I think : g2.getTransform().getTranslateX();

    etc...

    Thanks again
     
    Chantal, Jan 24, 2006
    #4
  5. Chantal

    Roedy Green Guest

    On 24 Jan 2006 04:59:15 -0800, "Chantal" <>
    wrote, quoted or indirectly quoted someone who said :

    >But I would like to know if it's possible to get the new coordinates of
    >the polygon, I mean after the rotation and translation are done.


    See http://mindprod.com/jgloss/affinetransform.html#MANUAL
    It shows you how to transform an individual point.

    Unfortunately that method requires you do the matrix multiply twice,
    once for the polygon for drawing and once for discovering where the
    transform put the points.
    --
    Canadian Mind Products, Roedy Green.
    http://mindprod.com Java custom programming, consulting and coaching.
     
    Roedy Green, Jan 24, 2006
    #5
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