我正在尝试实现一个应用程序，在该应用程序中，用户可以在给定区域内拖放多个对象。我正在使用 html5 canvas 标签来实现这一点。当内部只有一个对象可以拖放时 Canvas 然后代码工作正常，但是当我尝试在 Canvas 内独立拖动多个对象时我没有得到所需的输出..
这里是拖放一个对象的工作示例，具有绘图功能
function draw() {
clear();
ctx.fillStyle = "#FAF7F8";
rect(0,0,WIDTH,HEIGHT);
ctx.fillStyle = "#444444";
rect(x - 15, y - 15, 30, 30);
我认为在 draw() 函数中添加更多对象就可以了，所以我在 draw() 函数中为新对象添加了代码，如此链接所示
function draw() {
clear();
ctx.fillStyle = "#FAF7F8";
rect(0,0,WIDTH,HEIGHT);
ctx.fillStyle = "#444444";
rect(x - 15, y - 15, 30, 30);
ctx.fillStyle = "#ff550d";
rect(x - 25, y - 25, 30, 30);
ctx.fillStyle = "#800080";
rect(x - 35, y - 35, 30, 30);
ctx.fillStyle = "#0c64e8";
rect(x - 45, y - 45, 30, 30);
}
我似乎无法理解我需要在 MyMove()、MyUp() 和 MyDown() 函数中进行哪些更改才能使对象相互独立移动。 请帮忙
最佳答案
当移动 1 个(或更多)形状时，过程是:
创建定义每个形状的对象:
// an array of objects that define different rectangles
var rects=[];
rects.push({x:75-15,y:50-15,width:30,height:30,fill:"#444444",isDragging:false});
rects.push({x:75-25,y:50-25,width:30,height:30,fill:"#ff550d",isDragging:false});
rects.push({x:75-35,y:50-35,width:30,height:30,fill:"#800080",isDragging:false});
rects.push({x:75-45,y:50-45,width:30,height:30,fill:"#0c64e8",isDragging:false});
鼠标按下:
- 获取当前鼠标位置
- 在鼠标下方的任何形状上设置
isDragging标志 - 保存当前鼠标位置
在鼠标移动中:
- 获取当前鼠标位置
- 计算鼠标移动了多远(distance = newMousePosition-oldMousePosition)
- 将距离添加到正在拖动的任何形状的位置
- 保存当前鼠标位置
- 用新位置的形状重新绘制场景
在鼠标弹起中:
- 清除所有
isDragging标志
这是带注释的代码和演示:http://jsfiddle.net/m1erickson/qm9Eb/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
window.onload=function(){
// 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 rectangles
var rects=[];
rects.push({x:75-15,y:50-15,width:30,height:30,fill:"#444444",isDragging:false});
rects.push({x:75-25,y:50-25,width:30,height:30,fill:"#ff550d",isDragging:false});
rects.push({x:75-35,y:50-35,width:30,height:30,fill:"#800080",isDragging:false});
rects.push({x:75-45,y:50-45,width:30,height:30,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(x,y,w,h) {
ctx.beginPath();
ctx.rect(x,y,w,h);
ctx.closePath();
ctx.fill();
}
// clear the canvas
function clear() {
ctx.clearRect(0, 0, WIDTH, HEIGHT);
}
// redraw the scene
function draw() {
clear();
ctx.fillStyle = "#FAF7F8";
rect(0,0,WIDTH,HEIGHT);
// redraw each rect in the rects[] array
for(var i=0;i<rects.length;i++){
var r=rects[i];
ctx.fillStyle=r.fill;
rect(r.x,r.y,r.width,r.height);
}
}
// 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 rect to see if mouse is inside
dragok=false;
for(var i=0;i<rects.length;i++){
var r=rects[i];
if(mx>r.x && mx<r.x+r.width && my>r.y && my<r.y+r.height){
// if yes, set that rects isDragging=true
dragok=true;
r.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<rects.length;i++){
rects[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<rects.length;i++){
var r=rects[i];
if(r.isDragging){
r.x+=dx;
r.y+=dy;
}
}
// redraw the scene with the new rect positions
draw();
// reset the starting mouse position for the next mousemove
startX=mx;
startY=my;
}
}
}; // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>
关于javascript - 在 HTML5 Canvas 中拖放多个对象，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24926028/