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技術者またはクライアントが署名用に使用するキャンバスを追加したページがあります。私はそれを働かせ、キャンバスの中に描くことができました。しかし、ページを少し下にスクロールすると、描画が開始される位置がマウスのポイントよりも高くなります。ページをもう一度上にスクロールすると、描画が開始される位置はマウスの点に直接戻ります。キャンバス内のマウスの位置が正しくないページがスクロールしたときに正しく表示されない
ページがスクロールされているかどうかにかかわらず、XとYの正しい位置を取得する方法を教えてください。
これは私がやったことです：
HTML：
<body onload="init();">
<div id="dialogSignature" runat="server" style="padding-top:10px; display:none; ">
<canvas id="myCanvas" width="400" height="200" style="border:2px solid;"></canvas>
<img id="canvasimg" style="position:absolute;top:10%;left:52%;" style="display:none;">
</body>
<table>
<tr>
<td>
<input type="button" value="Clear" id="clr" size="23" onclick="erase()" class="myButton" >
</td>
<td>
<button class="myButton" onclick="javascript:UploadPic();return false;">Sumbit</button>
</td>
</tr>
</table>
<asp:Label ID="lblText" runat="server" Text="Label" Visible="false"></asp:Label>
<asp:Label ID="lblScopeIdentity" runat="server" Text="sss" Visible="false"></asp:Label>
</div>
Javascriptを：以下
<script type="text/javascript">
var canvas, ctx, flag = false,
prevX = 0,
currX = 0,
prevY = 0,
currY = 0,
dot_flag = false;
var x = "black",
y = 2;
function init() {
canvas = document.getElementById('myCanvas');
ctx = canvas.getContext("2d");
w = canvas.width;
h = canvas.height;
canvas.addEventListener("mousemove", function (e) {
findxy('move', e)
}, false);
canvas.addEventListener("mousedown", function (e) {
findxy('down', e)
}, false);
canvas.addEventListener("mouseup", function (e) {
findxy('up', e)
}, false);
canvas.addEventListener("mouseout", function (e) {
findxy('out', e)
}, false);
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);
// 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 getTouchPos(canvasDom, touchEvent) {
var rect = canvasDom.getBoundingClientRect();
return {
x: touchEvent.touches[0].clientX - rect.left,
y: touchEvent.touches[0].clientY - rect.top
};
}
function color(obj) {
switch (obj.id) {
case "green":
x = "green";
break;
case "blue":
x = "blue";
break;
case "red":
x = "red";
break;
case "yellow":
x = "yellow";
break;
case "orange":
x = "orange";
break;
case "black":
x = "black";
break;
case "white":
x = "white";
break;
}
if (x == "white") y = 14;
else y = 2;
}
function draw() {
ctx.beginPath();
ctx.moveTo(prevX, prevY);
ctx.lineTo(currX, currY);
ctx.strokeStyle = x;
ctx.lineWidth = y;
ctx.stroke();
ctx.closePath();
}
function erase() {
var m = confirm("Want to clear");
if (m) {
ctx.clearRect(0, 0, w, h);
document.getElementById("canvasimg").style.display = "none";
}
}
function save() {
document.getElementById("canvasimg").style.border = "2px solid";
var dataURL = canvas.toDataURL();
document.getElementById("canvasimg").src = dataURL;
document.getElementById("canvasimg").style.display = "inline";
}
function findxy(res, e) {
if (res == 'down') {
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.offsetLeft;
currY = e.clientY - canvas.offsetTop;
flag = true;
dot_flag = true;
if (dot_flag) {
ctx.beginPath();
ctx.fillStyle = x;
ctx.fillRect(currX, currY, 2, 2);
ctx.closePath();
dot_flag = false;
}
}
if (res == 'up' || res == "out") {
flag = false;
}
if (res == 'move') {
if (flag) {
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.offsetLeft;
currY = e.clientY - canvas.offsetTop;
draw();
}
}
}
var scopeIdentityUse = "<%=scopeIdentityJS1%>";
var Pic = document.getElementById("myCanvas").toDataURL("image/png");
Pic = Pic.replace(/^data:image\/(png|jpg);base64,/, "")
$.ajax({
type: 'POST',
url: 'Save_Picture.aspx/UploadPic',
data: '{ "imageData" : "' + Pic + '", "param" : "' + scopeIdentityUse + '" }',
contentType: 'application/json; charset=utf-8',
dataType: 'json',
success: function (msg) {
document.location.href = 'CreatePDFReport.aspx'
//alert("Done, Picture Uploaded.");
}
});
</script>