Rotating a line without moving it in QML

[wysota]

"x" and "y" are defined relatively to the parent. Thus you cannot reference other item's "x" and "y" values as they are in a different coordinate system. This is similar to:

Item {
  id: i1
  x: 10
  Item {
    id: i2
    x: 10
  }
}

Item {
  id: i1
  x: 10
  Item {
    id: i2
    x: 10
  }
}

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Item "i2" has an absolute x value set to 20 as it is translated by 10 relative to its parent. If instead you do:

Item {
  id: i1
  x: 10
  Item {
    id: i2
    x: parent.x+10
  }
}

Item {
  id: i1
  x: 10
  Item {
    id: i2
    x: parent.x+10
  }
}

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Then i2.x == 20 and thus the absolute value is 30 and not 20.

In your code the transformation origin should be set to:

origin.x: line.width/2;
origin.y: line.height/2;

origin.x: line.width/2;
origin.y: line.height/2;

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which is equivalent to setting transformOrigin to Item.Center (which is the default).