如何将画布代码转换为渲染矩形到svg

将其转换为SVG非常简单。

唯一的小问题是，我们必须添加一些处理，以满足当矩形的宽度或高度是负的。Canvas2D不介意，但SVG介意。

另外，在绘制拖拽句柄时，没有一种简单的方法来模拟异或操作。所以我把它们改成纯蓝色。

var canvas = document.getElementById('canvas'),
    rect = {
        x: 150,
        y: 100,
        w: 123,
        h: 58
    },
    handlesSize = 8,
    currentHandle = false,
    drag = false
    svgns = 'http://www.w3.org/2000/svg';
function init() {
    canvas.addEventListener('mousedown', mouseDown, false);
    canvas.addEventListener('mouseup', mouseUp, false);
    canvas.addEventListener('mousemove', mouseMove, false);
}
function point(x, y) {
    return {
        x: x,
        y: y
    };
}
function dist(p1, p2) {
    return Math.sqrt((p2.x - p1.x) * (p2.x - p1.x) + (p2.y - p1.y) * (p2.y - p1.y));
}
function getHandle(mouse) {
    if (dist(mouse, point(rect.x, rect.y)) <= handlesSize) return 'topleft';
    if (dist(mouse, point(rect.x + rect.w, rect.y)) <= handlesSize) return 'topright';
    if (dist(mouse, point(rect.x, rect.y + rect.h)) <= handlesSize) return 'bottomleft';
    if (dist(mouse, point(rect.x + rect.w, rect.y + rect.h)) <= handlesSize) return 'bottomright';
    if (dist(mouse, point(rect.x + rect.w / 2, rect.y)) <= handlesSize) return 'top';
    if (dist(mouse, point(rect.x, rect.y + rect.h / 2)) <= handlesSize) return 'left';
    if (dist(mouse, point(rect.x + rect.w / 2, rect.y + rect.h)) <= handlesSize) return 'bottom';
    if (dist(mouse, point(rect.x + rect.w, rect.y + rect.h / 2)) <= handlesSize) return 'right';
    return false;
}
function mouseDown(e) {
    if (currentHandle) drag = true;
    draw();
}
function mouseUp() {
    drag = false;
    currentHandle = false;
    draw();
}
function mouseMove(e) {
    var previousHandle = currentHandle;
    var svgPos = this.getBoundingClientRect();
    if (!drag) currentHandle = getHandle(point(e.pageX - svgPos.left, e.pageY - svgPos.top));
    if (currentHandle && drag) {
        var mousePos = point(e.pageX - svgPos.left, e.pageY - svgPos.top);
        switch (currentHandle) {
            case 'topleft':
                rect.w += rect.x - mousePos.x;
                rect.h += rect.y - mousePos.y;
                rect.x = mousePos.x;
                rect.y = mousePos.y;
                break;
            case 'topright':
                rect.w = mousePos.x - rect.x;
                rect.h += rect.y - mousePos.y;
                rect.y = mousePos.y;
                break;
            case 'bottomleft':
                rect.w += rect.x - mousePos.x;
                rect.x = mousePos.x;
                rect.h = mousePos.y - rect.y;
                break;
            case 'bottomright':
                rect.w = mousePos.x - rect.x;
                rect.h = mousePos.y - rect.y;
                break;
            case 'top':
                rect.h += rect.y - mousePos.y;
                rect.y = mousePos.y;
                break;
            case 'left':
                rect.w += rect.x - mousePos.x;
                rect.x = mousePos.x;
                break;
            case 'bottom':
                rect.h = mousePos.y - rect.y;
                break;
            case 'right':
                rect.w = mousePos.x - rect.x;
                break;
        }
    }
    if (drag || currentHandle != previousHandle) draw();
}
function draw() {
    //ctx.clearRect(0, 0, canvas.width, canvas.height);
    while (canvas.firstChild) {
        canvas.removeChild(canvas.firstChild);
    }
    //ctx.fillStyle = 'black';
    //ctx.fillRect(rect.x, rect.y, rect.w, rect.h);
    var svgrect = document.createElementNS(svgns, 'rect');
    svgrect.setAttribute('x', Math.min(rect.x, rect.x+rect.w));
    svgrect.setAttribute('y', Math.min(rect.y, rect.y+rect.h));
    svgrect.setAttribute('width', Math.abs(rect.w));
    svgrect.setAttribute('height', Math.abs(rect.h));
    canvas.appendChild(svgrect);
    if (currentHandle) {
        var posHandle = point(0, 0);
        switch (currentHandle) {
            case 'topleft':
                posHandle.x = rect.x;
                posHandle.y = rect.y;
                break;
            case 'topright':
                posHandle.x = rect.x + rect.w;
                posHandle.y = rect.y;
                break;
            case 'bottomleft':
                posHandle.x = rect.x;
                posHandle.y = rect.y + rect.h;
                break;
            case 'bottomright':
                posHandle.x = rect.x + rect.w;
                posHandle.y = rect.y + rect.h;
                break;
            case 'top':
                posHandle.x = rect.x + rect.w / 2;
                posHandle.y = rect.y;
                break;
            case 'left':
                posHandle.x = rect.x;
                posHandle.y = rect.y + rect.h / 2;
                break;
            case 'bottom':
                posHandle.x = rect.x + rect.w / 2;
                posHandle.y = rect.y + rect.h;
                break;
            case 'right':
                posHandle.x = rect.x + rect.w;
                posHandle.y = rect.y + rect.h / 2;
                break;
        }
        //ctx.globalCompositeOperation = 'xor';
        //ctx.beginPath();
        //ctx.arc(posHandle.x, posHandle.y, handlesSize, 0, 2 * Math.PI);
        //ctx.fill();
        //ctx.globalCompositeOperation = 'source-over';
        var circ = document.createElementNS(svgns, 'circle');
        circ.setAttribute('cx', posHandle.x);
        circ.setAttribute('cy', posHandle.y);
        circ.setAttribute('r', handlesSize);
        circ.setAttribute('fill', 'blue');
        canvas.appendChild(circ);
    }
}
init();
draw();

<svg id="canvas" width="500" height="500"></svg>