你可以在HTML Canvas中有多个剪辑区域吗？

Question

我有一些代码将一堆图像加载到隐藏的img元素中,然后是一个Javascript循环,将每个图像放到画布上.但是,我想剪切每个图像,使其在放置在画布上时为圆形.

我的循环看起来像这样:

    $$('#avatars img').each(function(avatar) {
        var canvas = $('canvas');
        var context = canvas.getContext('2d');

        var x = Math.floor(Math.random() * canvas.width);
        var y = Math.floor(Math.random() * canvas.height);

        context.beginPath();
        context.arc(x+24, y+24, 20, 0, Math.PI * 2, 1);
        context.clip();

        context.strokeStyle = "black";

        context.drawImage(document.getElementById(avatar.id), x, y);

        context.stroke();
    });

问题是,只绘制(或可见)第一个图像.

如果我删除剪切逻辑:

    $$('#avatars img').each(function(avatar) {
        var canvas = $('canvas');
        var context = canvas.getContext('2d');

        var x = Math.floor(Math.random() * canvas.width);
        var y = Math.floor(Math.random() * canvas.height);

        context.drawImage(document.getElementById(avatar.id), x, y);
    });

然后绘制我的所有图像.

有没有办法让每张图片分别剪裁？

我尝试将剪切区域重置为图像之间的整个画布,但这不起作用.

Answer 1

您应该尝试保存当前上下文状态,然后将其还原:

        canvas = document.getElementById("area");
        context = canvas.getContext('2d');

        $("#avatars img").each(function(avatar) {

            var x = Math.floor(Math.random() * canvas.width);
            var y = Math.floor(Math.random() * canvas.height);

            context.save();//push current state into canvas
            context.beginPath();
            context.arc(x + 24, y + 24, 20, 0, Math.PI * 2, 1);
            context.clip();

            context.strokeStyle = "black";

            //draw image this way
            var img = new Image();
            img.src = avatar.src;
            img.onload = function() {
                context.drawImage(img, x, y);
            };

            context.stroke();
            context.restore();//restore context to the state

        });

我想当你调用drawImage方法时,你还需要通过添加一个已存在于avatar.src参数中的源代码行将image参数设置为Image类.

您应该查看Canvas State的参考文档