Draw rectangle on mousedown event












0














I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs







share|improve this question
























  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15
















0














I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs







share|improve this question
























  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15














0












0








0







I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs







share|improve this question















I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs




javascript html5-canvas fabricjs






share|improve this question















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edited Nov 20 '18 at 9:28







xepe

















asked Nov 19 '18 at 20:58









xepexepe

5016




5016












  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15


















  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15
















What do you mean by 'it isn't working for me'?
– Konowy
Nov 19 '18 at 23:32




What do you mean by 'it isn't working for me'?
– Konowy
Nov 19 '18 at 23:32












Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
– xepe
Nov 20 '18 at 9:15




Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
– xepe
Nov 20 '18 at 9:15












1 Answer
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oldest

votes


















1














I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



  const point = new fabric.Point(offsetX, offsetY);

  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)

  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





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    I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



      const point = new fabric.Point(offsetX, offsetY);
    
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
    
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





    share|improve this answer


























      1














      I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



        const point = new fabric.Point(offsetX, offsetY);
      
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
      
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





      share|improve this answer
























        1












        1








        1






        I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



          const point = new fabric.Point(offsetX, offsetY);
        
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
        
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





        share|improve this answer












        I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



          const point = new fabric.Point(offsetX, offsetY);
        
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
        
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 20 '18 at 9:22









        xepexepe

        5016




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