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http://jsfiddle.net/m1erickson/2Us2S/

**我正在使用此代码，如何将拖放的图像设置为可拖动的。我尝试过使用 jquery，但我需要在画布中拖动相同的内容。开导我 。**

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var $canvas = $("#canvas");
var canvasOffset = $canvas.offset();
var offsetX = canvasOffset.left;
var offsetY = canvasOffset.top;

var image1 = new Image();
image1.src = "https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house32x32transparent.png";

var $house = $("#house");
var $canvas = $("#canvas");

$house.draggable({
    helper: 'clone',
});
// set the data payload
$house.data("image", image1); // key-value pair

$canvas.droppable({
    drop: dragDrop,
});


function dragDrop(e, ui) {
    var element = ui.draggable;
    var data = element.data("url");
    var x = parseInt(ui.offset.left - offsetX);
    var y = parseInt(ui.offset.top - offsetY);
    ctx.drawImage(element.data("image"), x - 1, y);
}
4

1 回答 1

2

一旦你在画布上绘制图像，房子就变成了画布上不记得的、不可移动的像素。你不能再使用 jQuery 来拖动房子了。

画布通过擦除画布并在更改的位置重新绘制内容来“移动”事物。

画布通过监听鼠标事件“拖动”：

  • In mousedown，检查鼠标是否在画布上绘制的任何房子上。您可以通过记住房屋的绘制位置来做到这一点，然后使用房屋的边界框使用鼠标位置进行测试。设置一个isDragging标志来指示房子被鼠标击中并且应该被拖动。

  • In mousemove, 重新绘制自上次鼠标移动后鼠标移动距离的房子。

  • In mouseup & mouseout, 拖拽操作结束所以清除isDragging标志。

要创建一个边界框来进行测试，您至少需要跟踪房屋图像的宽度和高度以及它在画布上的放置位置的 x,y。您通常将此信息保存在 javascript 对象中。

这是带注释的代码和演示：

// canvas related stuff
var canvas=document.getElementById("myCanvas");
var ctx=canvas.getContext("2d");
var WIDTH = canvas.width;
var HEIGHT = canvas.height;
ctx.fillStyle = "#A0DCE5";
$myCanvas=$('#myCanvas');

//drag
var isDragging = false;
var startX;
var startY;

//array of image objects
var images=[];
var NUM_IMAGES=0;

// queue up 4 test images
addImage(20,20,0.50,'https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house204-1.jpg');
addImage(240,20,0.50,'https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house204-2.jpg');
addImage(20,220,0.50,'https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house204-3.jpg');
addImage(240,220,0.50,'https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house204-4.jpg');

// trigger all images to load
for(var i=0;i<images.length;i++){
  images[i].image.src=images[i].url;
}


//////////////////////////////
// functions
//////////////////////////////

// queue up another image
function addImage(x,y,scaleFactor,imgURL){
  var img=new Image();
  img.crossOrigin='anonymous';
  img.onload=startInteraction;
  images.push({image:img,x:x,y:y,scale:scaleFactor,isDragging:false,url:imgURL});
  NUM_IMAGES++;
}

// called after each image fully loads
function startInteraction() {

  // return until all images are loaded
  if(--NUM_IMAGES>0){return;}

  // set all images width/height
  for(var i=0;i<images.length;i++){
    var img=images[i];
    img.width=img.image.width*img.scale;
    img.height=img.image.height*img.scale;
  }

  // render all images
  renderAll();

  // listen for mouse events
  $myCanvas.mousedown(onMouseDown);
  $myCanvas.mouseup(onMouseUp);
  $myCanvas.mouseout(onMouseUp);
  $myCanvas.mousemove(onMouseMove);

}

// flood fill canvas and 
// redraw all images in their assigned positions
function renderAll() {
  ctx.fillRect(0,0,WIDTH,HEIGHT);
  for(var i=0;i<images.length;i++){
    var r=images[i];
    ctx.drawImage(r.image,r.x,r.y,r.width,r.height);
  }
}

// handle mousedown events
function onMouseDown(e){

  // tell browser we're handling this mouse event
  e.preventDefault();
  e.stopPropagation();

  //get current position
  var mx=parseInt(e.clientX-$myCanvas.offset().left);
  var my=parseInt(e.clientY-$myCanvas.offset().top);

  //test to see if mouse is in 1+ images
  isDragging = false;
  for(var i=0;i<images.length;i++){
    var r=images[i];
    if(mx>r.x && mx<r.x+r.width && my>r.y && my<r.y+r.height){
      //if true set r.isDragging=true
      r.isDragging=true;
      isDragging=true;
    }
  }
  //save mouse position
  startX=mx;
  startY=my;
}

// handle mouseup and mouseout events
function onMouseUp(e){
  //tell browser we're handling this mouse event
  e.preventDefault();
  e.stopPropagation();

  // clear all the dragging flags
  isDragging = false;
  for(var i=0;i<images.length;i++){
    images[i].isDragging=false;
  }
}

// handle mousemove events
function onMouseMove(e){

  // do nothing if we're not dragging
  if(!isDragging){return;}

  //tell browser we're handling this mouse event
  e.preventDefault
  e.stopPropagation

  //get current mouseposition
  var mx = parseInt(e.clientX-$myCanvas.offset().left);
  var my = parseInt(e.clientY-$myCanvas.offset().top);

  //calculate how far the mouse has moved;
  var dx = mx - startX;
  var dy = my - startY;

  //move each image by how far the mouse moved
  for(var i=0;i<images.length;i++){
    var r=images[i];
    if(r.isDragging){
      r.x+=dx;
      r.y+=dy;
    }
  }

  //reset the mouse positions for next mouse move;
  startX = mx;
  startY = my;

  //re render the images
  renderAll();

}
body{ background-color: ivory; }
canvas{border:1px solid red;}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>Drag a house with the mouse.</h4>
<canvas id="myCanvas" width=400 height=400></canvas>

于 2015-01-11T22:46:13.440 回答