缩放后确定鼠标在 HTML5 画布上的位置

Determining mouse position on an HTML5 canvas after zooming

本文关键字：位置 HTML5 鼠标缩放更新时间：2023-09-26

我正在开发一些HTML5软件，其中涉及画布的使用。在一个画布上，我需要能够缩放并允许用户在鼠标单击时在画布上涂鸦。到目前为止，我已经在我找到的一些示例的帮助下使缩放工作。问题是缩放后，我的绘图工具上的鼠标位置不正常。在进行任何缩放之前，我可以画得很好。以下是缩放的代码：

//Zoom
        mainCanvas.onmousewheel = function(event) {
            var mousex = event.clientX - mainCanvas.offsetLeft;
            var mousey = event.clientY - mainCanvas.offsetTop;
            var wheel = event.wheelDelta / 120;
            //n or -n
            var zoom = 0;
            if(wheel < 0) {
                zoom = 1 / 2;
                if(currentzoom == 1)
                    return;
            } else {
                mousex = event.clientX - mainCanvas.offsetLeft;
                mousey = event.clientY - mainCanvas.offsetTop;
                zoom = 2;
                if(currentzoom == 32)
                    return;
            }
            currentzoom *= zoom;
            mainContext.translate(originx, originy);
            mainContext.scale(zoom, zoom);
            mainContext.translate(-(mousex / scale + originx - mousex / (scale * zoom ) ), -(mousey / scale + originy - mousey / (scale * zoom ) ));
            originx = (mousex / scale + originx - mousex / (scale * zoom ) );
            originy = (mousey / scale + originy - mousey / (scale * zoom ) );
            scale *= zoom;
            draw(mainContext, gridArray);
        }

就像我说的，变焦不是实际问题，只是问题的根源。以下是确定绘图工具鼠标位置的代码：

//this function determines the mouse position relative to the canvas element
        function ev_canvas(ev) {
            if(ev.layerX || ev.layerX == 0) {//Firefox, IE
                ev._x = ev.layerX;
                ev._y = ev.layerY;
            } else if(ev.offsetX || ev.offsetX == 0) {//Opera
                ev._x = ev.offsetX;
                ev._y = ev.offsetY;
            }
            var func = tool[ev.type];
            if(func) {
                func(ev);
            }
        }

我确定问题出在后一个代码块上，但我不确定要解决它。任何帮助将不胜感激。

我怀疑这是一段依赖于一些全局变量的代码片段，例如currentzoom

因此，如果我正确理解这个问题，问题在于您如何使用画布进行鼠标控制和缩放。我怀疑当您缩放时，DOM 将鼠标光标放置在最初渲染的图片上的位置。因此，如果放大 200% 并将鼠标放置在画布中心左侧 100 像素的位置，则画布的行为就像鼠标位于中心左侧 200 像素一样。

currentzoom = 1;
originX = 0;
originY = 0;
function ev_canvas(ev) {
        if(ev.layerX || ev.layerX == 0) {//Firefox, IE
            ev._x = ev.layerX * currentzoom / 1 - originX;
            ev._y = ev.layerY * currentzoom / 1 - originY;
        } else if(ev.offsetX || ev.offsetX == 0) {//Opera
            ev._x = ev.offsetX * currentzoom / 1 - originX;
            ev._y = ev.offsetY * currentzoom / 1 - originY;
        }
        var func = tool[ev.type];
        if(func) {
            func(ev);
        }
    }

保留

/ 1，以防将来的用户想要将非"1"值设置为 currentzoom 。

对于Joomla网站，您可以使用鼠标悬停缩放 - 这是一个Joomla扩展，使您能够从Joomla网页查看更大版本的缩略图。现在，您可以轻松浏览图像库：只需将鼠标光标移到缩略图上即可查看完整尺寸的图像，而无需加载新页面。在此处下载 http://joomlaboat.com/mouse-over-zoom

如果图片不适合窗口，则会自动调整图片大小。您可以自定义扩展程序，还有很多其他选项。为了加载透明图像，没有背景，只需使用.png图像。

试试这个：

<!DOCTYPE HTML>
<html>
    <head>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.js"></script>
        <style>
            body {
                margin: 0px;
                padding: 0px;
            }
            #wrapper {
                position: relative;
                border: 1px solid #9C9898;
                width: 578px;
                height: 200px;
            }
            #buttonWrapper {
                position: absolute;
                width: 30px;
                top: 2px;
                right: 2px;
            }
            input[type =
            "button"] {
                padding: 5px;
                width: 30px;
                margin: 0px 0px 2px 0px;
            }
        </style>
        <script>
            function draw(scale, translatePos){
                var canvas = document.getElementById("myCanvas");
                var context = canvas.getContext("2d");
                // clear canvas
                context.clearRect(0, 0, canvas.width, canvas.height);
                context.save();
                context.translate(translatePos.x, translatePos.y);
                context.scale(scale, scale);
                context.beginPath(); // begin custom shape
                context.moveTo(-119, -20);
                context.bezierCurveTo(-159, 0, -159, 50, -59, 50);
                context.bezierCurveTo(-39, 80, 31, 80, 51, 50);
                context.bezierCurveTo(131, 50, 131, 20, 101, 0);
                context.bezierCurveTo(141, -60, 81, -70, 51, -50);
                context.bezierCurveTo(31, -95, -39, -80, -39, -50);
                context.bezierCurveTo(-89, -95, -139, -80, -119, -20);
                context.closePath(); // complete custom shape
                var grd = context.createLinearGradient(-59, -100, 81, 100);
                grd.addColorStop(0, "#8ED6FF"); // light blue
                grd.addColorStop(1, "#004CB3"); // dark blue
                context.fillStyle = grd;
                context.fill();
                context.lineWidth = 5;
                context.strokeStyle = "#0000ff";
                context.stroke();
                context.restore();
            }
            window.onload = function(){
                var canvas = document.getElementById("myCanvas");
                var translatePos = {
                    x: canvas.width / 2,
                    y: canvas.height / 2
                };
                var scale = 1.0;
                var scaleMultiplier = 0.8;
                var startDragOffset = {};
                var mouseDown = false;
                // add button event listeners
                document.getElementById("plus").addEventListener("click", function(){
                    scale /= scaleMultiplier;
                    draw(scale, translatePos);
                }, false);
                document.getElementById("minus").addEventListener("click", function(){
                    scale *= scaleMultiplier;
                    draw(scale, translatePos);
                }, false);
                // add event listeners to handle screen drag
                canvas.addEventListener("mousedown", function(evt){
                    mouseDown = true;
                    startDragOffset.x = evt.clientX - translatePos.x;
                    startDragOffset.y = evt.clientY - translatePos.y;
                });
                canvas.addEventListener("mouseup", function(evt){
                    mouseDown = false;
                });
                canvas.addEventListener("mouseover", function(evt){
                    mouseDown = false;
                });
                canvas.addEventListener("mouseout", function(evt){
                    mouseDown = false;
                });
                canvas.addEventListener("mousemove", function(evt){
                    if (mouseDown) {
                        translatePos.x = evt.clientX - startDragOffset.x;
                        translatePos.y = evt.clientY - startDragOffset.y;
                        draw(scale, translatePos);
                    }
                });
                draw(scale, translatePos);
            };

            jQuery(document).ready(function(){
               $("#wrapper").mouseover(function(e){
                  $('#status').html(e.pageX +', '+ e.pageY);
               }); 
            })  
        </script>
    </head>
    <body onmousedown="return false;">
        <div id="wrapper">
            <canvas id="myCanvas" width="578" height="200">
            </canvas>
            <div id="buttonWrapper">
                <input type="button" id="plus" value="+"><input type="button" id="minus" value="-">
            </div>
        </div>
        <h2 id="status">
        0, 0
        </h2>
    </body>
</html>

非常适合我的鼠标移动跟踪。恩乔伊!!

我得到了一个更好的脚本来获取画布上的鼠标位置：

function writeMessage(canvas, message) {
        var context = canvas.getContext('2d');
        context.clearRect(0, 0, canvas.width, canvas.height);
        context.font = '18pt Calibri';
        context.fillStyle = 'black';
        context.fillText(message, 10, 25);
      }
      function getMousePos(canvas, evt) {
        var rect = canvas.getBoundingClientRect(), root = document.documentElement;
        // return relative mouse position
        var mouseX = evt.clientX - rect.top - root.scrollTop;
        var mouseY = evt.clientY - rect.left - root.scrollLeft;
        return {
          x: mouseX,
          y: mouseY
        };
      }
      window.onload = function() {
        var canvas = document.getElementById('myCanvas');
        var context = canvas.getContext('2d');
        canvas.addEventListener('mousemove', function(evt) {
          var mousePos = getMousePos(canvas, evt);
          var message = "Mouse position: " + mousePos.x + "," + mousePos.y;
          writeMessage(canvas, message);
        }, false);
      };

尝试一下，如果有任何问题，请发表评论..