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Thread: how to change coordinates

  1. #1
    Junior Member
    Join Date
    Nov 2009
    Posts
    1

    how to change coordinates

    Hi,

    I am developping a 2D API based on OpenVG and I am using AmanithVG implementation for now.
    However I would like to use a coordinate system where 0,0 corresponds to top left (like GDI or
    quartz) instead of bottom left, so how can I did this ?

    I suppose I need something like :

    vgSeti(VG_MATRIX_MODE, VG_MATRIX_PATH_USER_TO_SURFACE);
    vgLoadMatrix( ?, ?, ?, ?, ?, ?, ?, ?, ?);
    vgSeti(VG_MATRIX_MODE, VG_MATRIX_IMAGE_USER_TO_SURFACE);
    vgLoadMatrix( ?, ?, ?, ?, ?, ?, ?, ?, ?);
    ...

    Let's say my window is width x height what should I pass to vgLoadMatrix ?

    Thanks

  2. #2

    Re: how to change coordinates

    It's been a while, but you can probably scale based on the size of your window, rotate by 270 or -90 then translate by -height.

  3. #3
    Senior Member
    Join Date
    Feb 2006
    Posts
    115

    Re: how to change coordinates

    No, just vgScale(1,-1), and vgTranslate(0, height);
    not sure which order though off the top of my head.

  4. #4

    Re: how to change coordinates

    Good point Ivo! Couldn't remember the easiest way to inverse the y. The negative scale is ringing some bells.

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