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javascriptreactjskonvajs

set origin coordinates for react-konva stage


I am using react-konva for drawing purposes. I have configured the stage and I am drawing certain shapes in that stage container. The problem I am facing is that the origin coordinates(0,0) are at the top left of the stage container. I want the center of the stage to be the origin(0,0). Here is the present code:

<Stage
  height={800}
  width={1200}
  style={{ backgroundColor: '#fff', border: 'solid'}}>
  {
    this.state.circlePoints.length !== 0 &&
    <LineComponent
      startX={1200/2}
      startY={800/2}
      endX={this.state.circlePoints[0].pointX*1.3}
      endY={this.state.circlePoints[0].pointY*1.3}
      startColor={firstCircle[0].outerColor}
      endColor={pmData[0].outerColor}
    />
  }
  <CircleComponent
    x={1200/2}
    y={800/2}
    outerRadius={firstCircle[0].weight*1200}
    outerColor={firstCircle[0].outerColor}
    innerRadius={firstCircle[0].weight*1200*0.3}
    innerColor={firstCircle[0].innerColor}
    shadowColor={firstCircle[0].innerColor}
    getCirclePoints={this.getCirclePoints}
  />
  {
    this.state.circlePoints.length !== 0 &&
    <CircleComponent
      x={this.state.circlePoints[0].pointX*1.3}
      y={this.state.circlePoints[0].pointY*1.3}
      outerRadius={pmData[0].weight*1200}
      outerColor={pmData[0].outerColor}
      innerRadius={pmData[0].weight*1200*0.3}
      innerColor={pmData[0].innerColor}
      shadowColor={pmData[0].innerColor}
    />
  }
</Stage>

Solution

  • Use the layer offset command to re-position the layer on the stage. In the example below you can see that I add the x and y axis then offset the layer 200px in to the page. Finally I draw a circle on the layer at (0,0) to confirm that the layer co-ordinates remain based on this location so that you do not have to do any translation on your drawing co-ordinates.

    var stage = new Konva.Stage({
          container: 'container',
          width: 600,
          height: 400
        });
    
    var layer = new Konva.Layer();
    stage.add(layer)
    
    var axisX = new Konva.Line({
          points: [-200, 0, 200, 0],
          stroke: 'red',
          strokeWidth: 2,
          lineCap: 'round',
          lineJoin: 'round'
        });
      
    var axisY = new Konva.Line({
          points: [0, 200, 0, -200],
          stroke: 'red',
          strokeWidth: 2,
          lineCap: 'round',
          lineJoin: 'round'
        });  
      
    layer.add(axisX)  
    layer.add(axisY)  
    
    // offset the layer on the stage
    layer.offsetX(-200)
    layer.offsetY(-200)
    
    // draw a circle at 0,0
    
        var circle = new Konva.Circle({
          x: 0,
          y: 0,
          radius: 70,
          stroke: 'black',
          strokeWidth: 4
        });
    
        // add the shape to the layer
        layer.add(circle);
    
    layer.draw();
    stage.draw();
    <!DOCTYPE html>
    <html>
    <head>
        <meta charset="utf-8" />
        <title></title>
    </head>
    <body>
      <div id="container"></div>
                
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
        <script src="https://cdn.rawgit.com/konvajs/konva/1.7.6/konva.min.js"></script>
        <script type="text/javascript" src="test.js"></script>
    
    
    
    </body>
    </html>