在鼠标移动中获取fabric.js中图像像素的rgb值

Question

how to get rgb values of image in fabric.js on mouse move. I used getFill() method of image object, but it is returning (0,0,0). Please help me

Answer 1

FabricJS does not have a native method for getting the pixel colors.

The workaround is to use native html5 canvas to fetch the pixel data:

• Create your Fabric image objects. Be sure to specify crossOrigin as 'anonymous' otherwise the canvas will be tainted with a security violation and then the pixel data will be unavailable.

• Listen on Fabric's 'mouse:move' event. When it fires, get the current mouse position and use native canvas's context.getImageData to fetch that pixel's color array.

Good luck with your project!

Here's annotatede code and a Demo:

 // create a Fabric.Canvas var canvas = new fabric.Canvas("canvas"); // get a reference to <p id=results></p> // (used to report pixel color under mouse) var results = document.getElementById('results'); // get references to the html canvas element & its context var canvasElement = document.getElementById('canvas'); var ctx = canvasElement.getContext("2d"); // create a test Fabric.Image addFabricImage('https://dl.dropboxusercontent.com/u/139992952/multple/colorBar.png'); // listen for mouse:move events canvas.on('mouse:move', function(e) { // get the current mouse position var mouse = canvas.getPointer(ee); var x = parseInt(mouse.x); var y = parseInt(mouse.y); // get the color array for the pixel under the mouse var px = ctx.getImageData(x, y, 1, 1).data; // report that pixel data results.innerHTML = 'At [' + x + ' / ' + y + ']: Red/Green/Blue/Alpha = [' + px[0] + ' / ' + px[1] + ' / ' + px[2] + ' / ' + px[3] + ']'; }); // create a Fabric.Image at x,y using a specified imgSrc function addFabricImage(imgSrc, x, y) { // create a new javascript Image object using imgSrc var img = new Image(); // be sure to set crossOrigin or else // cross-domain imgSrc's will taint the canvas // and then we can't get the pixel data // IMPORTANT!: the source domain must be properly configured // to allow crossOrigin='anonymous' img.crossOrigin = 'anonymous'; // when the Image object is fully loaded, // use it to create a new fabric.Image object img.onload = function() { var fabImg = new fabric.Image(this, { left: 30, top: 30 }); canvas.add(fabImg); } // use imgSrc as the image source img.src = imgSrc; } 

 body { background-color: ivory; } canvas { border: 1px solid red; } 

 <script src="http://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.4.0/fabric.min.js"></script> <p id="results">Move mouse over canvas</p> <canvas id=canvas width=300 height=300></canvas>