Canvas 调整大小后删除它自己 HTML5/JavaScript

Question

我制作了canvas，你可以在上面画画。而且它还响应屏幕尺寸。但是如果我调整浏览器的大小，即使是一个像素...... Canvas 清除它自己。有什么办法可以防止这种情况发生吗？请注意，在我的代码中，您会看到当 he/she 在 canvas（绘图）上时阻止用户滚动的代码。您还将看到用于移动设备的代码（以便移动用户可以使用 canvas）。但是出于某种原因，“滚动阻止”在 IOS 设备上不起作用。

#pen {
    background-color: rgba(0, 0, 0, .2);
}

#paper {
    display: grid;
    column-count: 1;
}

#canvasORG {
    width: 97.5vw;
    height: 90vh;
    cursor: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='40' height='48' viewport='0 0 100 100' style='fill:black;font-size:24px;'><text y='50%'>✍️</text></svg>") 5 27, auto;
}

#colors {
    padding-top: 5px;
    display: flex;
    flex-wrap: wrap;
    flex-direction: row;
}

#black {
    width: 30px;
    height: 30px;
    background: black;
}

#black:hover {
    background: rgba(0, 0, 0, .1);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<!DOCTYPE html>
<html lang="en">

<head>
    <link rel="shortcut icon" type="image/icon" href="images/IYN_logo.png" />
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="styles.css">
    <script src="script.js"></script>
</head>

<body>

        <div id="paper">
            <div id="canvasORG">
                <canvas id="canvas" style="background-color: white; border:2px solid;"></canvas>
            </div>
            <div id="colors">
                &emsp;
                <div id="black" onclick="color(this)"></div>&nbsp;
                &emsp;
                <button id="pen" style="height: 50px; font-size: 25px; padding-bottom: 5px;">✍</button>
            </div>
        </div>

        <script>
            const points = [];
            const canvas = document.getElementById("canvas");
            const mouse = { x: 0, y: 0, button: false }
            const ctx = canvas.getContext("2d");
            canvas.addEventListener("mousemove", mouseEvents);
            canvas.addEventListener("mousedown", mouseEvents);
            canvas.addEventListener("mouseup", mouseEvents);
            var x = "black",
                y = 5 * 4;
            const canvasORG = document.getElementById("canvasORG");

            (function () {
                window.addEventListener("resize", resizeCanvas, false);
                canvas.width = canvasORG.clientWidth;
                canvas.height = canvasORG.clientHeight;

                function resizeCanvas() {
                    canvas.width = canvasORG.clientWidth;
                    canvas.height = canvasORG.clientHeight;
                    //DRAW ALL
                    //ctx.fillStyle = 'white';
                    //ctx.fillRect(0, 0, canvas.width, canvas.height)
                }
                resizeCanvas();
            })();

            function mouseEvents(e) {
                mouse.x = e.pageX - 1;
                mouse.y = e.pageY - 1;
                const lb = mouse.button;
                mouse.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : mouse.button;
                if (mouse.button) {
                    if (!lb) { points.length = 0 }
                    points.push({ x: mouse.x, y: mouse.y });
                    drawPoints();
                }
            }

            function drawPoints() {
                $(this).scrollTop(0);
                ctx.strokeStyle = x;
                ctx.lineWidth = y;
                ctx.lineCap = "round";
                ctx.lineJoin = "round";
                ctx.beginPath();
                if (mode == "pen") {
                    ctx.globalCompositeOperation = "source-over";
                    for (const p of points) { ctx.lineTo(p.x, p.y); }
                    ctx.stroke();
                } else {
                    ctx.globalCompositeOperation = "destination-out";
                    ctx.arc(mouse.x, mouse.y, 8, 0, Math.PI * 2, false);
                    ctx.stroke();
                    ctx.fill();
                }
            }

            function color(obj) {
                switch (obj.id) {
                    case "black":
                        x = "black";
                        break;
                }
            }

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

            // Get the position of a touch relative to the canvas
            function getTouchPos(canvasDom, touchEvent) {
                var rect = canvasDom.getBoundingClientRect();
                return {
                    x: touchEvent.touches[0].clientX - rect.left,
                    y: touchEvent.touches[0].clientY - rect.top
                };
            }

            document.getElementById("canvas").onwheel = function (event) {
                event.preventDefault();
            };

            document.getElementById("canvas").onmousewheel = function (event) {
                event.preventDefault();
            };

            canvas.addEventListener("touchstart", function (event) { event.preventDefault() })
            canvas.addEventListener("touchmove", function (event) { event.preventDefault() })
            canvas.addEventListener("touchend", function (event) { event.preventDefault() })
            canvas.addEventListener("touchcancel", function (event) { event.preventDefault() })

            var mode = "pen";
            $("#pen").click(function () {
                mode = "pen";
            });
            $("#eraser").click(function () {
                mode = "eraser"
            });
        </script>
</body>

</html>

Answer 1

我会更改调整大小处理程序以在更改后重新绘制图像：

const temp = ctx.getImageData(0, 0, canvas.width, canvas.height);
canvas.width = canvasORG.clientWidth;
canvas.height = canvasORG.clientHeight;
ctx.putImageData(temp, 0, 0);

问题在于，如果调整后的尺寸小于绘图，那么现在离开 canvas 的部分将被破坏。

#pen {
    background-color: rgba(0, 0, 0, .2);
}

#paper {
    display: grid;
    column-count: 1;
}

#canvasORG {
    width: 97.5vw;
    height: 90vh;
    cursor: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='40' height='48' viewport='0 0 100 100' style='fill:black;font-size:24px;'><text y='50%'>✍️</text></svg>") 5 27, auto;
}

#colors {
    padding-top: 5px;
    display: flex;
    flex-wrap: wrap;
    flex-direction: row;
}

#black {
    width: 30px;
    height: 30px;
    background: black;
}

#black:hover {
    background: rgba(0, 0, 0, .1);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<!DOCTYPE html>
<html lang="en">

<head>
    <link rel="shortcut icon" type="image/icon" href="images/IYN_logo.png" />
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="styles.css">
    <script src="script.js"></script>
</head>

<body>

        <div id="paper">
            <div id="canvasORG">
                <canvas id="canvas" style="background-color: white; border:2px solid;"></canvas>
            </div>
            <div id="colors">
                &emsp;
                <div id="black" onclick="color(this)"></div>&nbsp;
                &emsp;
                <button id="pen" style="height: 50px; font-size: 25px; padding-bottom: 5px;">✍</button>
            </div>
        </div>

        <script>
            const points = [];
            const canvas = document.getElementById("canvas");
            const mouse = { x: 0, y: 0, button: false }
            const ctx = canvas.getContext("2d");
            canvas.addEventListener("mousemove", mouseEvents);
            canvas.addEventListener("mousedown", mouseEvents);
            canvas.addEventListener("mouseup", mouseEvents);
            var x = "black",
                y = 5 * 4;
            const canvasORG = document.getElementById("canvasORG");

            (function () {
                window.addEventListener("resize", resizeCanvas, false);
                canvas.width = canvasORG.clientWidth;
                canvas.height = canvasORG.clientHeight;

                function resizeCanvas() {
                    const temp = ctx.getImageData(0, 0, canvas.width, canvas.height);
                    canvas.width = canvasORG.clientWidth;
                    canvas.height = canvasORG.clientHeight;
                    ctx.putImageData(temp, 0, 0);
                }
                resizeCanvas();
            })();

            function mouseEvents(e) {
                mouse.x = e.pageX - 1;
                mouse.y = e.pageY - 1;
                const lb = mouse.button;
                mouse.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : mouse.button;
                if (mouse.button) {
                    if (!lb) { points.length = 0 }
                    points.push({ x: mouse.x, y: mouse.y });
                    drawPoints();
                }
            }

            function drawPoints() {
                $(this).scrollTop(0);
                ctx.strokeStyle = x;
                ctx.lineWidth = y;
                ctx.lineCap = "round";
                ctx.lineJoin = "round";
                ctx.beginPath();
                if (mode == "pen") {
                    ctx.globalCompositeOperation = "source-over";
                    for (const p of points) { ctx.lineTo(p.x, p.y); }
                    ctx.stroke();
                } else {
                    ctx.globalCompositeOperation = "destination-out";
                    ctx.arc(mouse.x, mouse.y, 8, 0, Math.PI * 2, false);
                    ctx.stroke();
                    ctx.fill();
                }
            }

            function color(obj) {
                switch (obj.id) {
                    case "black":
                        x = "black";
                        break;
                }
            }

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

            // Get the position of a touch relative to the canvas
            function getTouchPos(canvasDom, touchEvent) {
                var rect = canvasDom.getBoundingClientRect();
                return {
                    x: touchEvent.touches[0].clientX - rect.left,
                    y: touchEvent.touches[0].clientY - rect.top
                };
            }

            document.getElementById("canvas").onwheel = function (event) {
                event.preventDefault();
            };

            document.getElementById("canvas").onmousewheel = function (event) {
                event.preventDefault();
            };

            canvas.addEventListener("touchstart", function (event) { event.preventDefault() })
            canvas.addEventListener("touchmove", function (event) { event.preventDefault() })
            canvas.addEventListener("touchend", function (event) { event.preventDefault() })
            canvas.addEventListener("touchcancel", function (event) { event.preventDefault() })

            var mode = "pen";
            $("#pen").click(function () {
                mode = "pen";
            });
            $("#eraser").click(function () {
                mode = "eraser"
            });
        </script>
</body>

</html>

Canvas 调整大小后删除它自己 HTML5/JavaScript

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