CODEWITHSUNDEEP
html5-canvaskonvajs
Daniel.S
Daniel.S

Reputation: 23

How to draw an inverted element on a layer in KonvaJS

is there any way to add a shape in KonvaJS which draws outside of it's boundries? Basically a "hole" in the layer, so that I can highlight a spot in the canvas by making everything around a circle darker (black with low opacity).

Any help is much appreciated!

Cheers

Edit: Here is an image of what I mean (I'm not allowed to embed it yet): https://i.sstatic.net/2yve2.jpg

I was hoping there might be something like this:

Konva.Circle({
  x: 100,
  y: 100,
  radius: 50,
  opacity: 0.3,
  fill: 'black',
  inverted: true
})

and this would then in turn "not draw" a circle, but everything around it would then take the given attributes. In this case it would all be darkend a bit besides the circle.

Upvotes: 2

Views: 1312

Answers (1)

lavrton
lavrton

Reputation: 20308

You can do this with a custom shape:

const shape = new Konva.Shape({
  width: stage.width(),
  height: stage.height(),
  // what is color of background ?
  fill: 'rgba(0,0,0,0.2)',
  sceneFunc: (ctx, shape) => {
    // draw background
    ctx.beginPath();
    ctx.moveTo(0, 0);
    ctx.lineTo(shape.width(), 0);
    ctx.lineTo(shape.width(), shape.height());
    ctx.lineTo(0, shape.height());
    ctx.lineTo(0, 0);

    // now cut circle from the background
    // we can do this by useing arc
    const x = 200;
    const y = 200;
    const radius = 10;
    // but it must be counter-clockwise
    // so the last argument true is very important here
    ctx.arc(200, 200, 100, 0, Math.PI * 2, true);
    ctx.fillStrokeShape(shape);
  },

  // remove shape from hit graph, so it is not visible for events
  listening: false
});

Demo: https://jsbin.com/tevejujafi/3/edit?html,js,output

Upvotes: 3

Related Questions