Question

我正在尝试使用下面的代码片段填充图像中的颜色，以便在画布的图像上填充颜色。它在帆布上成功填充颜色。现在，我正在尝试使用此代码片段擦除用户触摸的填充颜色，以便在画布的图像上擦除颜色。它的擦除颜色和在该触摸位置设置透明区域。现在我想在用户触摸时用颜色重新填充该区域，但由于透明像素，它不允许我在其上着色。那么有没有办法用颜色重新填充像素或者是否有其他方法可以从画布的图像中删除颜色？任何回复将不胜感激。

用于在画布图像上填充颜色的代码片段

var ctx = canvas.getContext('2d'),
    img = new Image;
img.onload = draw;
img.crossOrigin = 'anonymous';
img.src = "https://dl.dropboxusercontent.com/s/1alt1303g9zpemd/UFBxY.png";

    function draw(color) {
      ctx.drawImage(img, 0, 0);
    }
    canvas.onclick = function(e){
       var rect = canvas.getBoundingClientRect();
       var x = e.clientX-rect.left,
           y = e.clientY-rect.top;

        ctx.globalCompositeOperation = 'source-atop';
        ctx.fillStyle = 'blue';
        ctx.beginPath();
        ctx.arc(x-5,y-5,10,0,2*Math.PI);
        ctx.fill();

      }

用于擦除画布图像上的颜色的代码片段

(function() {
    // Creates a new canvas element and appends it as a child
    // to the parent element, and returns the reference to
    // the newly created canvas element


    function createCanvas(parent, width, height) {
        var canvas = {};
        canvas.node = document.createElement('canvas');
        canvas.context = canvas.node.getContext('2d');
        canvas.node.width = width || 100;
        canvas.node.height = height || 100;
        parent.appendChild(canvas.node);
        return canvas;
    }

    function init(container, width, height, fillColor) {
        var canvas = createCanvas(container, width, height);
        var ctx = canvas.context;
        // define a custom fillCircle method
        ctx.fillCircle = function(x, y, radius, fillColor) {
            this.fillStyle = fillColor;
            this.beginPath();
            this.moveTo(x, y);
            this.arc(x, y, radius, 0, Math.PI * 2, false);
            this.fill();
        };
        ctx.clearTo = function(fillColor) {
            ctx.fillStyle = fillColor;
            ctx.fillRect(0, 0, width, height);
        };
        ctx.clearTo(fillColor || "#ddd");

        // bind mouse events
        canvas.node.onmousemove = function(e) {
            if (!canvas.isDrawing) {
               return;
            }
            var x = e.pageX - this.offsetLeft;
            var y = e.pageY - this.offsetTop;
            var radius = 10; // or whatever
            var fillColor = '#ff0000';
            ctx.globalCompositeOperation = 'destination-out';
            ctx.fillCircle(x, y, radius, fillColor);
        };
        canvas.node.onmousedown = function(e) {
            canvas.isDrawing = true;
        };
        canvas.node.onmouseup = function(e) {
            canvas.isDrawing = false;
        };
    }

    var container = document.getElementById('canvas');
    init(container, 531, 438, '#ddd');

})();

Answer 1

警告未经测试的代码！

// create a clipping region using your erasing rect's x,y,width,height
context.save();
context.beginPath();
context.rect(erasingRectX,erasingRectY,erasingRectWidth,erasingRectHeight);
context.clip();

// redraw the original image.
// the image will be redrawn only into the erasing rects boundary
context.drawImage(yourImage,0,0);

// compositing: new pixels draw only where overlapping existing pixels
context.globalCompositeOperation='source-in';

// fill with your new color
// only the existing (clipped redrawn image) pixels will be colored
context.fillStyle='red';
context.fillRect(0,0,canvas.width,canvas.height);

// undo the clipping region
context.restore();

重新填充画布的擦除区域区域

1 个答案: