[英]Scrolling issue with Canvas style.left/top
我正在為畫布應用程序制作放大鏡,但我遇到了滾動問題。 本質上,目標是獲取一個畫布,並在添加圖像(在本例中為 cgm 圖像)並對其進行快照,將其放大並將其繪制到覆蓋它並跟隨鼠標的第二個較小的畫布上(最好拖動/鼠標向下和向上,但我使用 mousemove 進行測試)。 我相信問題出在我的主要應用程序的 zoom.style.top 和 zoom.style.left 注意我的上邊距為 70px 所以請記住這一點。
這是我寫的一個簡單的例子
<!-- language: lang-js -->
var canvas = document.getElementById("canvas1");
var ctx = canvas.getContext("2d");
var ox = canvas.width / 2;
var oy = canvas.height / 2;
ctx.font = "42px serif";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.fillStyle = "blue";
ctx.fillRect(ox / 2, oy / 2, ox, oy);
function magnify() {
var main = document.getElementById("canvas1");
var ctx = main.getContext('2d')
var base64 = main.toDataURL('image/png', 0);
drawing = new Image();
drawing.onload = () => {
var zoom = document.getElementById("tCanvas");
var zoomCtx = zoom.getContext('2d');
zoomCtx.drawImage(drawing, 0, 0);
}
main.addEventListener("mousemove", function(e) {
var zoom = document.getElementById("tCanvas");
var zoomCtx = zoom.getContext('2d');
zoomCtx.clearRect(0, 0, zoom.width, zoom.height);
zoomCtx.drawImage(main, e.x, e.y, 200, 200, 0, 0, 300, 300);
zoom.style.top = e.pageY - 70 + "px"
zoom.style.left = e.pageX - 10 + "px"
e.pageY = -150
e.pageX = -150
zoom.style.display = "block";
});
main.addEventListener("mouseleave", function() {
var zoom = document.getElementById("tCanvas");
zoom.style.display = "none";
});
drawing.src = base64;
};
<canvas id="tCanvas" class="cgm" height="100" width="100" style="background-color:white; position: absolute; display: none; z-
index:1;border:1px solid red;"> </canvas>
<canvas tabindex=1 class="cgm" id="canvas1" style="position:relative; background:white;
left:0;right:0;margin:auto;z-index:1;margin-top:70px; "></canvas>
<p></p>
<button id="zoom" onclick="magnify();">Zoom</button>
這是一個供參考的小提琴(我修復了顯示滾動問題的高度)。
我在你的 JSFiddle 上簡化了很多代碼。
看看這是否是您正在尋找的行為:
const canvas = document.getElementById("canvas1"); const ctx = canvas.getContext("2d"); const zoom = document.getElementById("tCanvas"); const zoomCtx = zoom.getContext('2d'); for (let i = 10; i < 20; i++) for (let j = -60; j < 800; j += 60) ctx.fillText(j + i, i * 20 - 180, i * 9 + j); function getMousePos(evt) { var rect = canvas.getBoundingClientRect() return { x: evt.clientX - rect.left, y: evt.clientY - rect.top } } canvas.addEventListener("mousemove", function(e) { zoomCtx.clearRect(0, 0, zoom.width, zoom.height); let pos = getMousePos(e) zoomCtx.drawImage(canvas, pos.x, pos.y, 200, 200, 0, 0, 300, 300); zoom.style.top = e.pageY - 10 + "px" zoom.style.left = e.pageX - 10 + "px" zoom.style.display = "block"; }); canvas.addEventListener("mouseleave", function() { zoom.style.display = "none"; });
#tCanvas { border: 1px solid red; display: none; position: absolute; background-color: #808080; pointer-events: none; } #canvas1 { background-color: #808080; }
<canvas id="tCanvas" width=100 height=100></canvas> <canvas id="canvas1" width=240 height=800></canvas>
我認為您的問題與pointer-events: none;
頂部畫布阻止事件到達底部畫布。
此外,您不必在每個函數上聲明您的document.getElementById("..
,這些應該是全局常量
對於長畫布的問題,我們需要在計算中使用canvas.getBoundingClientRect
來獲取鼠標在畫布中的真實位置
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