CODEWITHSUNDEEP
javascriptjqueryhtmlfabricjs
High schooler
High schooler

Reputation: 1680

Adding grid over Fabric.js canvas

I just started using Fabric.js (I have to say, I'm impressed).

I want to add a grid over the fabric objects. In the following code, I am putting my grid canvas right over on the Fabric canvas. The problem here is that, I now cannot move my fabric objects!

<!DOCTYPE html>
<html>
<head>
  <meta http-equiv="content-type" content="text/html; charset=UTF-8">

  <script type='text/javascript' src='http://code.jquery.com/jquery-1.7.1.js'></script>
  <script type='text/javascript' src='http://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.2.0/fabric.all.min.js'></script>

</head>
<body>

<div style="height:480px;width:640px;border:1px solid #ccc;position:relative;font:16px/26px Georgia, Garamond, Serif;overflow:auto;">

 <canvas id="rubber" width="800" height="800" 
   style="position: absolute; left: 0; top: 0; z-index: 0;"></canvas>
 <canvas id="myCanvas" width="800" height="800" 
   style="position: absolute; left: 0; top: 0; z-index: 1;"></canvas>
</div>

<script>
//<![CDATA[ 
$(window).load(function(){
$(document).ready(function () {

    function renderGrid(x_size,y_size, color)
    {
        var canvas = $("#myCanvas").get(0);
        var context = canvas.getContext("2d");

        context.save();
        context.lineWidth = 0.5;
        context.strokeStyle = color;

        // horizontal grid lines
        for(var i = 0; i <= canvas.height; i = i + x_size)
        {
            context.beginPath();
            context.moveTo(0, i);
            context.lineTo(canvas.width, i);
            context.closePath();
            context.stroke();
        }

        // vertical grid lines
        for(var j = 0; j <= canvas.width; j = j + y_size)
        {
            context.beginPath();
            context.moveTo(j, 0);
            context.lineTo(j, canvas.height);
            context.closePath();
            context.stroke();
        }

        context.restore();
    }

    renderGrid(10,15, "gray");
});

});//]]>  

  var canvas = new fabric.Canvas('rubber');
  canvas.add(new fabric.Circle({ radius: 30, fill: '#f55', top: 100, left: 100 }));

  canvas.selectionColor = 'rgba(0,255,0,0.3)';
  canvas.selectionBorderColor = 'red';
  canvas.selectionLineWidth = 5;
</script>


</body>
</html>

I am hoping that there is a way to do this in Fabric itself.

Any help would be awesome, thanks!

Upvotes: 17

Views: 18254

Answers (8)

rafi
rafi

Reputation: 1543

Try this:

function draw_grid(grid_size) {

  grid_size || (grid_size = 25);
  currentCanvasWidth = canvas.getWidth();
  currentcanvasHeight = canvas.getHeight();


  // Drawing vertical lines
  var x;
  for (x = 0; x <= currentCanvasWidth; x += grid_size) {
      this.grid_context.moveTo(x + 0.5, 0);
      this.grid_context.lineTo(x + 0.5, currentCanvasHeight);
  }

  // Drawing horizontal lines
  var y;
  for (y = 0; y <= currentCanvasHeight; y += grid_size) {
      this.grid_context.moveTo(0, y + 0.5);
      this.grid_context.lineTo(currentCanvasWidth, y + 0.5);
  }

  grid_size = grid_size;
  this.grid_context.strokeStyle = "black";
  this.grid_context.stroke();
}

Upvotes: 4

matiss.andersons
matiss.andersons

Reputation: 135

I really liked @Draeli's answer, but it seemed it wasn't working with the latest fabric version. Fixed the old one and added one slight adjustment that was necessary for myself - centring the grid.

Anyhow, maybe someone else finds it useful:

const gridSize = 100;
const width = this.canvas.getWidth();
const height = this.canvas.getHeight();
const left = (width % gridSize) / 2;
const top = (height % gridSize) / 2;
const lines = [];
const lineOption = {stroke: 'rgba(0,0,0,1)', strokeWidth: 1, selectable: false};
for (let i = Math.ceil(width / gridSize); i--;) {
  lines.push(new fabric.Line([gridSize * i, -top, gridSize * i, height], lineOption));
}
for (let i = Math.ceil(height / gridSize); i--;) {
  lines.push(new fabric.Line([-left, gridSize * i, width, gridSize * i], lineOption));
}
const oGridGroup = new fabric.Group(lines, {left: 0, top: 0});

this.canvas.add(oGridGroup);

this.canvas - this supposedly is the fabric instance.

Upvotes: 1

Sanket Parikh
Sanket Parikh

Reputation: 469

Updated:

Answer is based on the code posted by rafi:

  1. I have updated the missing grid_context.

  2. Kindly replace "<your canvas Id>" with your canvas Id in string. For e.g. "myCanvas".

  3. Usually, any operation you do on the canvas will clear out grid on the canvas, register the after:render event on fabric.js canvas to redraw it. So you can always see it.

     var canvas = new fabric.Canvas(<your canvas Id>);
 canvas.on('after:render',function(ctx){
       draw_grid(25);
 });

 function draw_grid(grid_size) {
    grid_size || (grid_size = 25);
    var currentCanvas = document.getElementById(<your canvas Id>); 
    var grid_context = currentCanvas.getContext("2d"); 

    var currentCanvasWidth = canvas.getWidth();
    var currentCanvasHeight = canvas.getHeight();

    // Drawing vertical lines
    var x;
    for (x = 0; x <= currentCanvasWidth; x += grid_size) {
       grid_context.moveTo(x + 0.5, 0);
       grid_context.lineTo(x + 0.5, currentCanvasHeight);
    }

    // Drawing horizontal lines
    var y;
    for (y = 0; y <= currentCanvasHeight; y += grid_size) {
      grid_context.moveTo(0, y + 0.5);
      grid_context.lineTo(currentCanvasWidth, y + 0.5);
    }
   grid_context.strokeStyle = "#0000002b";
   grid_context.stroke();
 }

Upvotes: 0

YaakovHatam
YaakovHatam

Reputation: 2344

Here is my solution, works with Fabric Js 4. at the end there is 2 events listeners that append the grid when object moving and remove the grid when object move end. (improvement of @draeli answer https://stackoverflow.com/a/35936606/1727357 )

(function () {
    const gcd = (a, b) => {
        if (!b) {
            return a;
        }
        return gcd(b, a % b);
    }
    const gridWidth = canvas.getWidth();
    const gridHeight = canvas.getHeight();

    const oGridGroup = [];
    console.log(gcd(gridWidth, gridHeight));

    const gridRows = gcd(gridWidth, gridHeight);
    const gridCols = gcd(gridWidth, gridHeight);

    const lineOption = { stroke: 'rgba(0,0,0,.1)', strokeWidth: 1, selectable: false, evented: false };

    for (let i = 0; i <= gridWidth; i += gridCols) {
        oGridGroup.push(new fabric.Line([i, 0, i, gridHeight], lineOption));
    }
    for (let i = 0; i <= gridHeight; i += gridRows) {
        oGridGroup.push(new fabric.Line([0, i, gridWidth, i], lineOption));
    }

    const theGorup = new fabric.Group(oGridGroup);
    theGorup.set({
        selectable: false,
        evented: false
    })

    canvas.on('mouse:down', function (event) {
        if (event.target) {
            canvas.add(theGorup);
        }
    });

    canvas.on('mouse:up', function (event) {
        canvas.remove(theGorup);

    });

}())

Upvotes: 0

Draeli
Draeli

Reputation: 162

A shorter version and more generic for copy/paste :

var oCanvas; // must be your canvas object
var gridWidth; // <= you must define this with final grid width
var gridHeight; // <= you must define this with final grid height

// to manipulate grid after creation
var oGridGroup = new fabric.Group([], {left: 0, top: 0});

var gridSize = 20; // define grid size

// define presentation option of grid
var lineOption = {stroke: 'rgba(0,0,0,.4)', strokeWidth: 1, selectable:false, strokeDashArray: [3, 3]};

// do in two steps to limit the calculations
// first loop for vertical line
for(var i = Math.ceil(gridWidth/gridSize); i--;){
    oGridGroup.add( new fabric.Line([gridSize*i, 0, gridSize*i, gridHeight], lineOption) );
}
// second loop for horizontal line
for(var i = Math.ceil(gridHeight/gridSize); i--;){
    oGridGroup.add( new fabric.Line([0, gridSize*i, gridWidth, gridSize*i], lineOption) );
}
// Group add to canvas
oCanvas.add(oGridGroup);

Upvotes: 6

John
John

Reputation: 2033

This two lines of code will work:

var gridsize = 5;
for(var x=1;x<(canvas.width/gridsize);x++)
                        {
                            canvas.add(new fabric.Line([100*x, 0, 100*x, 600],{ stroke: "#000000", strokeWidth: 1, selectable:false, strokeDashArray: [5, 5]}));
                            canvas.add(new fabric.Line([0, 100*x, 600, 100*x],{ stroke: "#000000", strokeWidth: 1, selectable:false, strokeDashArray: [5, 5]}));
                    }

Upvotes: 13

Tom
Tom

Reputation: 4652

My solution is - 

var width = canvas.width;
var height = canvas.height;

var j = 0;
var line = null;
var rect = [];
var size = 20;

console.log(width + ":" + height);

for (var i = 0; i < Math.ceil(width / 20); ++i) {
    rect[0] = i * size;
    rect[1] = 0;

    rect[2] = i * size;
    rect[3] = height;

    line = null;
    line = new fabric.Line(rect, {
        stroke: '#999',
        opacity: 0.5,
    });

    line.selectable = false;
    canvas.add(line);
    line.sendToBack();

}

for (i = 0; i < Math.ceil(height / 20); ++i) {
    rect[0] = 0;
    rect[1] = i * size;

    rect[2] = width;
    rect[3] = i * size;

    line = null;
    line = new fabric.Line(rect, {
        stroke: '#999',
        opacity: 0.5,
    });
    line.selectable = false;
    canvas.add(line);
    line.sendToBack();

}

canvas.renderAll();

You have to save all line objects for removing grid, or you can added all line objects to a group, and you can remove the group for removing grid, well I think this is not elegant one, but worked.

Upvotes: 4

n2code
n2code

Reputation: 31

If you don't insist on generating your grid dynamically you might want to consider the native overlay image function that fabric.js provides.

var canvas = new fabric.Canvas('rubber');
canvas.setOverlayImage('grid.png', canvas.renderAll.bind(canvas));

It won't hinder interactions with the objects on the canvas at all.

Upvotes: 3

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