在 HTML5 Canvas 中拖放多个对象

时间：2023-02-24

本文介绍了在 HTML5 Canvas 中拖放多个对象的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着跟版网的小编来一起学习吧！

问题描述

我正在尝试实现一个应用程序，其中用户可以在给定区域内拖放多个对象..我正在使用 html5 canvas 标签来实现这个..当只有一个对象可以拖放时画布然后代码工作正常，但是当我尝试在画布内独立拖动多个对象时，我没有得到所需的输出..

I'm trying to implement an application in which the user can drag and drop multiple objects inside a given area..I'm using html5 canvas tag to implement this..When there is only one object to drag and drop inside the canvas then the code is working fine, but when i try to drag multiple objects independently inside the canvas then i'm not getting the desired output..

这里是使用绘图功能仅拖放一个对象的工作示例

Here is the working example of drag and drop of only one object with the draw function

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这样做，所以我在 draw() 函数中添加了新对象的代码，如此链接所示

I thought adding more objects in draw() function will do so i added code for new objects in the draw() function like shown in this link

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彼此独立移动..请帮忙

I can't seem to understand what changes do i need to make in the MyMove(), MyUp() and MyDown() functions to make the objects move independently of one another.. Please Help

推荐答案

当移动1个(或多个)形状时，过程是:

When moving 1 (or more) shapes, the procedure is:

创建定义每个形状的对象:

Create objects that define each shape:

// 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});

在鼠标按下时:

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(距离 = newMousePosition-oldMousePosition)
将距离添加到拖动的任何形状的位置
保存当前鼠标位置
用新位置的形状重绘场景

在鼠标上移:

清除所有 isDragging 标志

这里是注释代码和演示:http://jsfiddle.net/m1erickson/qm9Eb/

Here's annotated code and a Demo: 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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在 HTML5 Canvas 中拖放多个对象

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