html5 – 使用CSS3可以创建这种图像屏蔽效果吗？

<canvas id="canvas1" width="400" height="400"></canvas>

var can = document.getElementById('canvas1');
var ctx = can.getContext('2d');

can.addEventListener('mousemove',function(E) {
var mouse = getMouse(e,can);
redraw(mousE);
},falsE);


function redraw(mousE) {
console.log('a');
can.width = can.width;
ctx.drawImage(img,0);
ctx.beginPath();
ctx.rect(0,500,500);
ctx.arc(mouse.x,mouse.y,70,Math.PI*2,truE)
ctx.clip();
ctx.drawImage(img2,0);
}

var img = new Image();
img.onload = function() {
redraw({x: -450,y: -500})
}
    img.src = 'http://placekitten.com/400/400';

var img2 = new Image();
img2.onload = function() {
redraw({x: -450,y: -500})
}
    img2.src = 'http://placekitten.com/400/395';


function getMouse(e,canvas) {
var element = canvas,offsetX = 0,offsetY = 0,mx,my;

if (element.offsetParent !== undefined) {
    do {
        offsetX += element.offsetLeft;
        offsetY += element.offsetTop;
    } while ((element = element.offsetParent));
}

mx = e.pageX - offsetX;
my = e.pageY - offsetY;

return {
    x: mx,y: my
};
}

解决方法@H_944_14@

这是使用背景图像的替代方法.它更灵活,你得到一个圆形(或任意形状)视口：

http://jsfiddle.net/maackle/66uCs/

HTML

<div class="masker">
    <img class="base" src="http://lorempixel.com/400/400/cats/1" />
    <div class="overlay"></div>
</div>

CSS

.masker {
    position: relative;
}
.overlay {
    position: absolute;
    display: none;
    width: 100px;
    height: 100px;
    border-radius: 50%;
    BACkground: url(http://lorempixel.com/400/400/cats/2) no-repeat;
}

jQuery 1.10.1

$('.masker').on('mousemove',function (E) {
    var r,x,y,top,left,bottom,right,attr,$base,$overlay;
    r = 100;
    $base = $(this).find('.base');
    $overlay = $(this).find('.overlay');
    x = e.pageX - $base.offset().left;
    y = e.pageY - $base.offset().top;
    top = y - r / 2;
    left = x - r / 2;
    if (x < 0 || y < 0 || x > $base.width() || y > $base.height()) {
        $overlay.hide();
    } else {
        $overlay.show().css({
            'BACkground-position': '' + (-left) + 'px ' + (-top) + 'px','left': left,'top': top
        });
    }
});

//just for good measure
$('.masker').on('mouSEOut',function (E) {
    $(this).find('.overlay').hide();
});