无法使图像在画布上可拖动 [英] Can't make image draggable on canvas

问题描述

  var img1 = new Image（）; 
 var img2 = new Image（）？ 
 var img3 = new Image（）; 
 var img4 = new Image（）; 
 var imageCount = 0，NUM_IMAGE = 4; 
 var ctx; 
 var WIDTH; 
 var HEIGHT; 
 
 // drag 
 var draggable = false; 
 var startX; 
 var startY; 
 //图像数组
 var images = []; 
 images.push（{image：img1，x：0，y：20，width：550，height：466}）; 
 images.push（{image：img2，x：476，y：170，width：230，height：240}）; 
 images.push（{image：img3，x：500，y：20，width：635，height：313}）; 
 images.push（{image：img4，x：910，y：328，width：219，height：134}）; 
 
 
 function init（）{
 ctx = $（'＃myCanvas'）[0] .getContext（2d）; 
 WIDTH = $（＃myCanvas）。width（）; 
 HEIGHT = $（＃myCanvas）。height（）; 
 ctx.fillStyle =＃A0DCE5; 
 ctx.fillRect（0,0，WIDTH，HEIGHT）; 
 loadResources（）; 
 $（'＃myCanvas'）。mousedown（onMouseDown）; 
 $（'＃myCanvas'）。mouseup（onMouseUp）; 
 $（'＃myCanvas'）。mousemove（onMouseMove）; 
 
 
} 
 
 function startInteraction（）{
 imageCount ++; 
 if（imageCount == NUM​​_IMAGES）
 render（）; 
} 
 
 function loadResources（）{
 img1.onload = startInteraction; 
 img1.src =america.png; 
 img2.onload = startInteraction; 
 img2.src =africa.png; 
 img3.onload = startInteraction; 
 img3.src =europe and asia.png; 
 img4.onload = startInteraction; 
 img4.src =australia.png; 
} 
 function image（image，x，y，width，height）{
 ctx.drawImage（image，x，y，width，height）
} 
 
 function render（）{
 for（var i = 0; i< images.length; i ++）{
 var r = images [i] 
 image（r.image，r.x，r.y，r.width，r.height）; 
} 
 
} 
 
函数onMouseDown（e）{
 
 //告诉浏览器我们正在处理这个鼠标事件
 e.preventDefault（）; 
 e.stopPropagation（）; 
 
 //获取当前位置
 var mx = parseInt（e.clientX  -  $（'＃myCanvas'）。offset（）。left）; 
 var my = parseInt（e.clientY  -  $（'＃myCanvas'）。offset（）。top）; 
 
 //测试看看鼠标是否在图像
 d = false; 
 for（var i = 0; i< images.length; i ++）{
 var r = images [i]; 
 if（mx> rx&& mx< r.x + r.width&&& my> ry&&&&&&&& r.y + r.height）{
 //如果true设置为dragging = true 
 draggable = true; 
} 
} 
 //保存鼠标位置
 startX = mx; 
 startY = my; 
} 
 
 function onMouseUp（e）{
 //告诉我们正在处理这个鼠标事件的浏览器
 e.preventDefault（）; 
 e.stopPropagation（）; 
 
 draggable = false; 
 for（var i = 0; i< images.length; i ++）{
 images [i] .isDragging = false; 
} 
} 
 
 function onMouseMove（e）{
 //如果我们可以拖动一个图像
 if（draggable）{
 
 //告诉浏览器我们正在处理这个鼠标事件
 e.preventDefault 
 e.stopPropagation 
 
 //获取当前mouseposition 
 var mx = parseInt e.clientX $（'＃myCanvas'）。offset（）。left）; 
 var my = parseInt（e.clientY  -  $（'＃myCanvas'）。offset（）。top）; 
 
 //计算鼠标移动的距离; 
 
 var dx = mx  -  startX; 
 var dy = my  -  startY; 
 
 //通过鼠标移动的距离移动每个图像
 for（var i = 0; i  var r = images [i] ; 
 if（r.isDragging）{
 r.x + = dx; 
 r.y + = dy; 
} 
} 
 //渲染图像
 render（）; 
 
 //为下一次鼠标移动重置鼠标位置; 
 startX = mx; 
 startY = my; 
} 
} 
 
 
 
 $（document）.ready（init）; 
  

我有真正的困难试图获取图像移动和每个教程我看看我只是可以以了解它。

有没有明显的事我做错了？

解决方案

在画布上拖动1+图片时，过程为：

在mousedown：

• 获取当前的鼠标位置




• 保存当前鼠标位置

在mousemove中：

• 获取当前鼠标位置


• 计算鼠标移动的距离（distance = newMousePosition-oldMousePosition）


• 将

的距离添加到任何图像的位置
• 保存当前

鼠标位置和mouseout：

• 清除所有isDragging标志

这是注释代码和演示：

  // canvas related stuffvar canvas = document.getElementById（myCanvas）; var ctx = canvas.getContext（2d）; var WIDTH = canvas.width; var HEIGHT = canvas.height; ctx.fillStyle =＃A0DCE5; $ myCanvas = $（'＃myCanvas'）; // dragvar isDragging = false; var startX; var startY; //图像对象数组varar = []; var NUM_IMAGES = 0; // queue up 4 test imagesaddImage（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');//触发所有图像loadfor（var i = 0; i  

 {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>拖动图像。< / h4> ;< canvas id =myCanvaswidth = 400 height = 400>< / canvas>  

var img1 = new Image();
var img2 = new Image();
var img3 = new Image();
var img4 = new Image();
var imageCount = 0, NUM_IMAGES=4;
var ctx;
var WIDTH;
var HEIGHT;

 //drag
var draggable = false;
var startX;
var startY;
//array of images
var images=[];
images.push({image:img1, x:0, y:20, width:550, height:466});
images.push({image:img2, x:476, y:170, width:230, height:240});
images.push({image:img3, x:500, y:20, width:635, height:313});
images.push({image:img4, x:910, y:328, width:219, height:134});


function init(){
  ctx = $('#myCanvas')[0].getContext("2d");
  WIDTH = $("#myCanvas").width();
  HEIGHT = $("#myCanvas").height();
  ctx.fillStyle = "#A0DCE5";
  ctx.fillRect(0,0,WIDTH,HEIGHT);
  loadResources();
  $('#myCanvas').mousedown(onMouseDown);
  $('#myCanvas').mouseup(onMouseUp);
  $('#myCanvas').mousemove(onMouseMove);


}

function startInteraction() {
    imageCount++;
    if (imageCount ==NUM_IMAGES)
        render();
}

function loadResources() {
    img1.onload = startInteraction;
    img1.src = "america.png";
    img2.onload = startInteraction;
    img2.src = "africa.png";
    img3.onload = startInteraction;
    img3.src = "europe and asia.png";
    img4.onload = startInteraction;
    img4.src = "australia.png";
}
function image(image,x,y,width,height) {
    ctx.drawImage(image,x,y,width,height)
}

function render() {
    for(var i=0;i<images.length;i++){
            var r=images[i];
            image(r.image,r.x,r.y,r.width,r.height);
        }

}

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 image
    d = 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 is dragging=true
            draggable=true;
        }
    }
    //save mouse position
    startX=mx;
    startY=my;
}

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

    draggable = false;
    for(var i=0;i<images.length;i++){
        images[i].isDragging=false;
    }
}

function onMouseMove(e){
    //if we can drag an image
    if(draggable){

        //tell brower 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;
            }
        }
        //re render the images
        render();

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



$(document).ready(init);

I am having real difficulty trying to get images to move and every tutorial i look at I just can seem to understand it.

Is there something blindingly obvious I'm doing wrong?

解决方案

When dragging 1+ images on a canvas, the procedure is:

In mousedown:

• get the current mouse position
• set the isDragging flag on any image that is under the mouse
• save the current mouse position

In mousemove:

• get the current mouse position
• calculate how far the mouse has moved ( distance = newMousePosition-oldMousePosition )
• add the distance to the position of any image that isDragging
• save the current mouse position
• redraw the scene with images in their new positions

In mouseup and mouseout:

• clear all isDragging flags

Here's annotated code and a Demo:

// 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 the images.</h4>
<canvas id="myCanvas" width=400 height=400></canvas>

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