在 Canvas 上书写时避免滚动

Question

我在平板电脑 canvas 上书写时遇到问题。

这个canvas应该用来在平板电脑上签名。

它在我的 MacBook 和 iPad 上运行良好，但在 Android 平板电脑上运行不佳。

当我在这个平板电脑上写字时，网站会上下滚动，无法签名。

你有什么建议吗？

非常感谢！

const signature = (currentId) => {
    window.requestAnimFrame = (function (callback) {
        return (
            window.requestAnimationFrame ||
            window.webkitRequestAnimationFrame ||
            window.mozRequestAnimationFrame ||
            window.oRequestAnimationFrame ||
            window.msRequestAnimaitonFrame ||
            function (callback) {
                window.setTimeout(callback, 1000 / 60);
            }
        );
    })();

    var canvas = document.getElementById("sig-canvas");
    var ctx = canvas.getContext("2d");
    ctx.strokeStyle = "#222222";
    ctx.lineWidth = 4;

    var element = document.getElementById("canvasContainer");
    var positionInfo = element.getBoundingClientRect();
    ctx.canvas.width = positionInfo.width;
    ctx.canvas.height = positionInfo.height - 40;

    var drawing = false;
    var mousePos = {
        x: 0,
        y: 0,
    };
    var lastPos = mousePos;

    canvas.addEventListener(
        "mousedown",
        function (e) {
            drawing = true;
            lastPos = getMousePos(canvas, e);
        },
        false
    );

    canvas.addEventListener(
        "mouseup",
        function (e) {
            drawing = false;
        },
        false
    );

    canvas.addEventListener(
        "mousemove",
        function (e) {
            mousePos = getMousePos(canvas, e);
        },
        false
    );

    // Add touch event support for mobile
    canvas.addEventListener("touchstart", function (e) {}, false);

    canvas.addEventListener(
        "touchmove",
        function (e) {
            var touch = e.touches[0];
            var me = new MouseEvent("mousemove", {
                clientX: touch.clientX,
                clientY: touch.clientY,
            });
            canvas.dispatchEvent(me);
        },
        false
    );

    canvas.addEventListener(
        "touchstart",
        function (e) {
            mousePos = getTouchPos(canvas, e);
            var touch = e.touches[0];
            var me = new MouseEvent("mousedown", {
                clientX: touch.clientX,
                clientY: touch.clientY,
            });
            canvas.dispatchEvent(me);
        },
        false
    );

    canvas.addEventListener(
        "touchend",
        function (e) {
            var me = new MouseEvent("mouseup", {});
            canvas.dispatchEvent(me);
        },
        false
    );

    function getMousePos(canvasDom, mouseEvent) {
        var rect = canvasDom.getBoundingClientRect();
        return {
            x: mouseEvent.clientX - rect.left,
            y: mouseEvent.clientY - rect.top,
        };
    }

    function getTouchPos(canvasDom, touchEvent) {
        var rect = canvasDom.getBoundingClientRect();
        return {
            x: touchEvent.touches[0].clientX - rect.left,
            y: touchEvent.touches[0].clientY - rect.top,
        };
    }

    function renderCanvas() {
        if (drawing) {
            ctx.moveTo(lastPos.x, lastPos.y);
            ctx.lineTo(mousePos.x, mousePos.y);
            ctx.stroke();
            lastPos = mousePos;
        }
    }

    // Prevent scrolling when touching the canvas
    document.body.addEventListener(
        "touchstart",
        function (e) {
            if (e.target == canvas) {
                e.preventDefault();
            }
        },
        false
    );
    document.body.addEventListener(
        "touchend",
        function (e) {
            if (e.target == canvas) {
                e.preventDefault();
            }
        },
        false
    );
    document.body.addEventListener(
        "touchmove",
        function (e) {
            if (e.target == canvas) {
                e.preventDefault();
            }
        },
        false
    );

    (function drawLoop() {
        requestAnimFrame(drawLoop);
        renderCanvas();
    })();

    function clearCanvas() {
        canvas.width = canvas.width;
    }

    // Set up the UI
    var clearBtn = document.getElementById("sig-clearBtn");
    var submitBtn = document.getElementById("sig-submitBtn");
    clearBtn.addEventListener(
        "click",
        function (e) {
            clearCanvas();
        },
        false
    );
    submitBtn.addEventListener(
        "click",
        function (e) {
            var dataUrl = canvas.toDataURL();
            auszahlen(currentId, dataUrl);
        },
        false
    );
};

Answer 1

在 addEventListener 的回调中添加 e.preventDefault() 是解决方案。谢谢海沃氏！

在 Canvas 上书写时避免滚动

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