How to implement the dragBounfunc, boundBoxFunc of a Tranformer Rectangle and in React Konva?

Question

I'm trying to draw a rectangle on an image with React Konva, and get the coordinate of its 4 corners. I have calculated and return the coordinate of 4 corners quite accurately but the problem is I still couldn't implement the dragBoundFunc (to bound the rectangle in the canvas when dragging) and the boundBoxFunc (to bound the rectangle in the canvas when transform (rotate, scale)).

One solution I can think of is get the min and max X,Y coordinate of 4 corners, then if the min < 0 and the max > dimension of the canvas then return false. However I still have not managed to do it, you can checkout my sandbox here. Thanks for your help.

score 3 · Answer 1 · answered Jun 30 '20 at 20:42

For dragging functionality you can do this:

shape.on('dragmove', () => {
  const box = shape.getClientRect();
  const absPos = shape.getAbsolutePosition();
  const offsetX = box.x - absPos.x;
  const offsetY = box.y - absPos.y;
  
  const newAbsPos = {...absPos}
  if (box.x < 0) {
    newAbsPos.x = -offsetX;
  }
  if (box.y < 0) {
    newAbsPos.y = -offsetY;
  }
  if (box.x + box.width > stage.width()) {
    newAbsPos.x = stage.width() - box.width - offsetX;
  }
  if (box.y + box.height > stage.height()) {
    newAbsPos.y = stage.height() - box.height - offsetY;
  }
  shape.setAbsolutePosition(newAbsPos)
});

The idea above is just to limit absolute position of a node.

For transforming is a bit more complex and may require polishing for smooth work. But I tried this:

let oldAttrs;
shape.on('transform', () => {
  const box = shape.getClientRect();
  const isOut = box.x < 0 || box.y < 0 || box.x + box.width > stage.width() || box.y + box.height > stage.height();
  
  if (isOut) {
    shape.setAttrs(oldAttrs);
  } else {
    oldAttrs = {...shape.getAttrs()};
  }
});

So if the position of shape is out of visible viewport we just need to reset attributes back to previous values.

Demo: https://jsbin.com/gakelemuru/2/edit?js,output

How to implement the dragBounfunc, boundBoxFunc of a Tranformer Rectangle and in React Konva?

1 Answers1