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Add patterns with images and colors to polygons using FabricJS

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Add patterns with images and colors to polygons using FabricJS

We can create a polygon object by creating an instance of fabric.Polygon. A polygonal object can be described by any closed shape consisting of a set of connected straight line segments. Since it is one of the basic elements of FabricJS, we can also easily customize it by applying properties like angle, opacity, etc. In order to add patterns and colors to polygons, we can use the Pattern class in FabricJS.

Grammar

new fabric.Pattern( options: Object, callback: function )

parameter

  • options (optional) − This parameter is an Object which provides additional customizations to our object. Using this parameter offsetX, cross-origin and a lot of other properties can be changed related to the Pattern.

  • callback − This parameter is a function called after the callback is initialized. This parameter is optional.

Example 1: Create an instance of fabric.Pattern() and add it to our polygon object

Let's look at a code example to see how to create an instance of fabric.Pattern and add it to the canvas. Here, we create a polygon object whose shape is a rectangle (an irregular polygon). We initialize the createPattern function which will add the pattern to our rectangle. Finally, we call the createPattern function and pass it the required URL. 

<!DOCTYPE html>
<html>
<head>
   <!-- Adding the Fabric JS Library-->
   <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head> 
<body>
   <h2>
      Creating an instance of fabric.Pattern() and adding it to our Polygon object
   </h2>
   <p>You can see that a pattern has been created</p>
   <canvas id="canvas"></canvas>
   <script>
      
      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);
      
      // Initiating the createPattern function which loads image

      // and adds the image as pattern to the rect object
      function createPattern(url) {
         fabric.util.loadImage(url, function (img) {
            rect.set(
               "fill",
               new fabric.Pattern({
                  source: img,
               })
            );
            canvas.renderAll();
         });
      }
      
      // Initiating a Polygon object
      var rect = new fabric.Polygon(
         [
            { x: 0, y: 0 },
            { x: 500, y: 0 },
            { x: 500, y: 200 },
            { x: 0, y: 200 },
         ],
         {
            left: 50, 
            top: 20,
            stroke: "black",
         }
      );
      
      // Adding it to the canvas
      canvas.add(rect);

      // Calling the createPattern function
      createPattern("https://www.tutorialspoint.com/images/logo.png");
   </script>
</body>
</html>

Example 2: Adding a pattern of images and colors to our polygons

Let's look at a code example to see how to create a dynamic pattern with an image and color for our polygon object. In this case, we used the fromURL method to load the image and initialized a fabric.StaticCanvas() object, which is one of the main rendering surfaces of FabricJS and is useful for creating Dynamic patterns are crucial.

We used the setBackgroundColor method to set the background color for the polygon. Finally, we add the polygon object to the canvas. 

<!DOCTYPE html>
<html>
<head>
   <!-- Adding the Fabric JS Library-->
   <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head>
<body>
   <h2>Adding a pattern with Image and Colour to our Polygon</h2>
   <p>You can see that a pattern with image and colour has been created and further use the number field to change the pattern density</p>
   <label>Add a width value(50-500): </label>
   <input type="number" id="changeWidth" value="50"/>
   <canvas id="canvas"></canvas>
   <script>
      
      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);
      
      // Initiating the colour that we want to fill the pattern with
      var imgColor = "rgba(216,228,188,0.5)";
 
      // Using fromURL method to load image and add to canvas
 
      // further setting the dimensions and background colour
      fabric.Image.fromURL(
         "https://www.tutorialspoint.com/images/logo.png",
         function (img) {
            img.scaleToWidth(100);
            img.scaleToHeight(90);
            var patternSourceCanvas = new fabric.StaticCanvas();
            patternSourceCanvas.add(img);
            patternSourceCanvas.renderAll();
            patternSourceCanvas.setBackgroundColor(
               imgColor,
               patternSourceCanvas.renderAll.bind(patternSourceCanvas)
            );
            
            // Initiating a Pattern object
            var pattern = new fabric.Pattern({
               source: patternSourceCanvas.getElement(),
               repeat: "repeat",
            });
            
            // Adding a polygon object to the canvas
            canvas.add(
               
               // Initiate a polygon object
               new fabric.Polygon(
                  [
                     { x: -100, y: -175 },
                     { x: 100, y: -175 },
                     { x: 200, y: 0 },
                     { x: 100, y: 175 },
                     { x: -100, y: 175 },
                     { x: -200, y: 0 },
                  ],
                  {
                     top: 30,
                     left: 10,
                     strokeWidth: 3,
                     stroke: "#96c8a2",
                     fill: pattern,
                     objectCaching: false,
                     scaleX: 0.5,
                     scaleY: 0.5,
                  }
               )
            );
            
            // Using getElementById and targeting the input tag with the id as "changeWidth"
            document.getElementById("changeWidth").oninput = function () {
               img.scaleToWidth(parseInt(this.value, 10));
               patternSourceCanvas.setDimensions({
                  width: img.getScaledWidth(),
                  height: img.getScaledHeight(),
               });
               canvas.requestRenderAll();
            };
         }
      );
   </script>
 </body>
</html>

in conclusion

In this tutorial, we use two simple examples to demonstrate how to use FabricJS to add images and patterns of color to polygons.

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