使用html5画布创建形状后使用鼠标拖动形状
[英]Dragging Shapes using mouse after creating them with html5 canvas
问题描述
我在html画布上绘制了一些圆圈，我的代码如下所示：
HTML：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>WebTunings</title>
<link href="index.css" rel="stylesheet">
<script src="index.js"></script>
</head>
<body>
<canvas id="canvas" width="600" height="600"></canvas>
<div id="controls">
<p><label>Fill: <input id="fillBox" type="checkbox" checked="checked"></label></p>
<div class="lightBorder">
<p><input type="radio" name="shape" value="circle" checked="checked">Circle</p>
</div>
<p><input id="clearCanvas" type="button" value="reset"></p>
</div>
</body>
</html>
使用Javascript：
var canvas,
context,
dragging = false,
dragStartLocation,
snapshot;
function getCanvasCoordinates(event) {
var x = event.clientX - canvas.getBoundingClientRect().left,
y = event.clientY - canvas.getBoundingClientRect().top;
return {x: x, y: y};
}
function takeSnapshot() {
snapshot = context.getImageData(0, 0, canvas.width, canvas.height);
}
function restoreSnapshot() {
context.putImageData(snapshot, 0, 0);
}
function drawCircle(position) {
var radius = Math.sqrt(Math.pow((dragStartLocation.x - position.x), 2) + Math.pow((dragStartLocation.y - position.y), 2));
context.beginPath();
context.arc(dragStartLocation.x, dragStartLocation.y, radius, 0, 2 * Math.PI, false);
context.fillStyle = getRndColor();
}
function draw(position) {
var fillBox = document.getElementById("fillBox"),
shape = document.querySelector('input[type="radio"][name="shape"]:checked').value;
if (shape === "circle") {
drawCircle(position);
}
if (fillBox.checked) {
context.fill();
} else {
context.stroke();
}
}
function dragStart(event) {
dragging = true;
dragStartLocation = getCanvasCoordinates(event);
takeSnapshot();
}
function drag(event) {
var position;
if (dragging === true) {
restoreSnapshot();
position = getCanvasCoordinates(event);
draw(position, "polygon");
}
}
function dragStop(event) {
dragging = false;
restoreSnapshot();
var position = getCanvasCoordinates(event);
draw(position, "polygon");
}
function getRndColor() {
var r = 255*Math.random()|0,
g = 255*Math.random()|0,
b = 255*Math.random()|0;
return 'rgb(' + r + ',' + g + ',' + b + ')';
}
function eraseCanvas(){
context.clearRect(0, 0, canvas.width, canvas.height);
}
function init() {
canvas = document.getElementById("canvas");
context = canvas.getContext('2d');
context.strokeStyle = 'green';
context.lineWidth = 4;
context.lineCap = 'round';
clearCanvas = document.getElementById("clearCanvas");
canvas.addEventListener('mousedown', dragStart, false);
canvas.addEventListener('mousemove', drag, false);
canvas.addEventListener('mouseup', dragStop, false);
clearCanvas.addEventListener("click", eraseCanvas, false);
}
window.addEventListener('load', init, false);
现在我想做的是每当我绘制多个圆圈时，我想选择一个随机圆圈并将其拖动到画布上的另一个地方，适用于每个圆圈。 我想只使用html5和javascript没有其他第三方库。 有没有办法做到这一点？ 任何帮助都会很棒......
1 个解决方案
解决方案1
8 已采纳 2015-02-02 20:10:28
画布不会“记住”它绘制圆圈或矩形的位置，因此您必须进行记忆。 这通常通过在javascript对象中定义每个圆或矩形并将所有这些形状保存在shapes []数组中来完成。
// an array of objects that define different shapes
var shapes=[];
// define 2 rectangles
shapes.push({x:10,y:100,width:30,height:30,fill:"#444444",isDragging:false});
shapes.push({x:80,y:100,width:30,height:30,fill:"#ff550d",isDragging:false});
// define 2 circles
shapes.push({x:150,y:100,r:10,fill:"#800080",isDragging:false});
shapes.push({x:200,y:100,r:10,fill:"#0c64e8",isDragging:false});
然后你可以在javascript中监听鼠标事件。 当浏览器发出鼠标事件时，您可以调用函数作为响应。 这是告诉您想要收听鼠标事件的浏览器：
// listen for mouse events
canvas.onmousedown = myDown;
canvas.onmouseup = myUp;
canvas.onmousemove = myMove;
您可以使用鼠标事件功能（myDown，myUp，myMove）进行拖动。
在mousedown事件（由myDown函数处理）时，您测试每个形状以查看鼠标是否在阵列中的一个形状内。 如果鼠标位于1+形状内，则在这些1+形状上设置
isDragging标志，并设置dragok标志以指示您需要跟踪鼠标以进行拖动。在鼠标移动事件（由myMove函数处理）后，您可以移动任何被拖动的形状，即自上一次鼠标移动后鼠标拖动的距离。
在mouseup事件（由myUp函数处理）时，您可以通过清除dragok标志来停止拖动操作。
这是带注释的示例代码和演示：
// get canvas related references var canvas=document.getElementById("canvas"); var ctx=canvas.getContext("2d"); var BB=canvas.getBoundingClientRect(); var offsetX=BB.left; var offsetY=BB.top; var WIDTH = canvas.width; var HEIGHT = canvas.height; // drag related variables var dragok = false; var startX; var startY; // an array of objects that define different shapes var shapes=[]; // define 2 rectangles shapes.push({x:10,y:100,width:30,height:30,fill:"#444444",isDragging:false}); shapes.push({x:80,y:100,width:30,height:30,fill:"#ff550d",isDragging:false}); // define 2 circles shapes.push({x:150,y:100,r:10,fill:"#800080",isDragging:false}); shapes.push({x:200,y:100,r:10,fill:"#0c64e8",isDragging:false}); // listen for mouse events canvas.onmousedown = myDown; canvas.onmouseup = myUp; canvas.onmousemove = myMove; // call to draw the scene draw(); // draw a single rect function rect(r) { ctx.fillStyle=r.fill; ctx.fillRect(rx,ry,r.width,r.height); } // draw a single rect function circle(c) { ctx.fillStyle=c.fill; ctx.beginPath(); ctx.arc(cx,cy,cr,0,Math.PI*2); ctx.closePath(); ctx.fill(); } // clear the canvas function clear() { ctx.clearRect(0, 0, WIDTH, HEIGHT); } // redraw the scene function draw() { clear(); // redraw each shape in the shapes[] array for(var i=0;i<shapes.length;i++){ // decide if the shape is a rect or circle // (it's a rect if it has a width property) if(shapes[i].width){ rect(shapes[i]); }else{ circle(shapes[i]); }; } } // handle mousedown events function myDown(e){ // tell the browser we're handling this mouse event e.preventDefault(); e.stopPropagation(); // get the current mouse position var mx=parseInt(e.clientX-offsetX); var my=parseInt(e.clientY-offsetY); // test each shape to see if mouse is inside dragok=false; for(var i=0;i<shapes.length;i++){ var s=shapes[i]; // decide if the shape is a rect or circle if(s.width){ // test if the mouse is inside this rect if(mx>sx && mx<s.x+s.width && my>sy && my<s.y+s.height){ // if yes, set that rects isDragging=true dragok=true; s.isDragging=true; } }else{ var dx=sx-mx; var dy=sy-my; // test if the mouse is inside this circle if(dx*dx+dy*dy<sr*sr){ dragok=true; s.isDragging=true; } } } // save the current mouse position startX=mx; startY=my; } // handle mouseup events function myUp(e){ // tell the browser we're handling this mouse event e.preventDefault(); e.stopPropagation(); // clear all the dragging flags dragok = false; for(var i=0;i<shapes.length;i++){ shapes[i].isDragging=false; } } // handle mouse moves function myMove(e){ // if we're dragging anything... if (dragok){ // tell the browser we're handling this mouse event e.preventDefault(); e.stopPropagation(); // get the current mouse position var mx=parseInt(e.clientX-offsetX); var my=parseInt(e.clientY-offsetY); // calculate the distance the mouse has moved // since the last mousemove var dx=mx-startX; var dy=my-startY; // move each rect that isDragging // by the distance the mouse has moved // since the last mousemove for(var i=0;i<shapes.length;i++){ var s=shapes[i]; if(s.isDragging){ s.x+=dx; s.y+=dy; } } // redraw the scene with the new rect positions draw(); // reset the starting mouse position for the next mousemove startX=mx; startY=my; } }
body{ background-color: ivory; } #canvas{border:1px solid red;}
<h4>Drag one or more of the shapes</h4> <canvas id="canvas" width=300 height=300></canvas>
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