javascript 在HTML5画布中拖放多个对象

8dtrkrch 于 2023-02-21 发布在 Java

关注(0)|答案(2)|浏览(134)

我正在尝试实现一个应用程序，其中用户可以拖放多个对象在一个给定的区域..我使用html5 canvas标签来实现这一点..当只有一个对象拖放到画布内，那么代码工作正常，但当我尝试拖动多个对象独立的画布内，那么我没有得到所需的输出..
下面是使用draw函数仅拖放一个对象的工作示例
http://jsfiddle.net/KZ99q/

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会起作用，所以我在draw（）函数中添加了新对象的代码，如以下链接所示
http://jsfiddle.net/KZ99q/1/

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);
}

我似乎不能理解我需要在MyMove（），MyUp（）和MyDown（）函数中进行哪些更改才能使对象彼此独立地移动。

JavaScript

来源：https://stackoverflow.com/questions/24926028/drag-and-drop-multiple-objects-in-html5-canvas

2条答案

按热度按时间

nmpmafwu1#

移动1个（或多个）形状时，步骤如下：
创建定义每个图形的对象：

// 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});

按下鼠标时：

获取当前鼠标位置
在鼠标下的任何形状上设置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（距离=新鼠标位置-旧鼠标位置）
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
用新位置的形状重画场景

在鼠标抬起中：

清除所有isDragging标志

下面是带注解的代码和演示：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>

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wqsoz72f2#

svg {
  background-color: #FFF;
  cursor: default;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  -o-user-select: none;
  user-select: none;
}

svg:not(.active):not(.ctrl) {
  cursor: crosshair;
}

path.link {
  fill: none;
  stroke: #000;
  stroke-width: 4px;
  cursor: default;
}

svg:not(.active):not(.ctrl) path.link {
  cursor: pointer;
}

path.link.selected {
  stroke-dasharray: 10,2;
}

path.link.dragline {
  pointer-events: none;
}

path.link.hidden {
  stroke-width: 0;
}

circle.node {
  stroke-width: 1.5px;
  cursor: pointer;
}

circle.node.reflexive {
  stroke: #000 !important;
  stroke-width: 2.5px;
}

text {
  font: 12px sans-serif;
  pointer-events: none;
}

text.id {
  text-anchor: middle;
  font-weight: bold;
}

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javascript 在HTML5画布中拖放多个对象

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