HTML5 Game - Dragging and dropping images

Introduction

The following code shows how to drag-and-drop an image.
Demo

<!DOCTYPE HTML>
<html>
    <head>
        <script>
class EventManager{/*from  w ww. ja v  a 2  s. co m*/
   constructor(canvasId){
    this.canvas = document.getElementById(canvasId);
    this.context = this.canvas.getContext("2d");
    this.drawStage = undefined;
    this.listening = false;
    
    // desktop flags
    this.mousePos = null;
    this.mouseDown = false;
    this.mouseUp = false;
    this.mouseOver = false;
    this.mouseMove = false;
    
    // mobile flags
    this.touchPos = null;
    this.touchStart = false;
    this.touchMove = false;
    this.touchEnd = false;
    
    // Region Events
    this.currentRegion = null;
    this.regionIndex = 0;
    this.lastRegionIndex = -1;
    this.mouseOverRegionIndex = -1;
  }
  getContext(){
    return this.context;
  }

  getCanvas(){
    return this.canvas;
  }
  clear(){
    this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
  }
  getCanvasPos = function(){
    let obj = this.getCanvas();
    let top = 0;
    let left = 0;
    while (obj.tagName != "BODY") {
        top += obj.offsetTop;
        left += obj.offsetLeft;
        obj = obj.offsetParent;
    }
    return {
        top: top,
        left: left
    };
  }
  setDrawStage(func){
    this.drawStage = func;
    this.listen();
  }
  reset(evt){
    if (!evt) {
        evt = window.event;
    }
    
    this.setMousePosition(evt);
    this.setTouchPosition(evt);
    this.regionIndex = 0;
    
    if (this.drawStage !== undefined) {
        this.drawStage();
    }
    
    // desktop flags
    this.mouseOver = false;
    this.mouseMove = false;
    this.mouseDown = false;
    this.mouseUp = false;
    
    // mobile touch flags
    this.touchStart = false;
    this.touchMove = false;
    this.touchEnd = false;
  }  
  listen(){
    let that = this;
    
    if (this.drawStage !== undefined) {
        this.drawStage();
    }
    
    // desktop events
    this.canvas.addEventListener("mousedown", function(evt){
        that.mouseDown = true;
        that.reset(evt);
    }, false);
    
    this.canvas.addEventListener("mousemove", function(evt){
        that.reset(evt);
    }, false);
    
    this.canvas.addEventListener("mouseup", function(evt){
        that.mouseUp = true;
        that.reset(evt);
    }, false);
    
    this.canvas.addEventListener("mouseover", function(evt){
        that.reset(evt);
    }, false);
    
    this.canvas.addEventListener("mouseout", function(evt){
        that.mousePos = null;
    }, false);
    
    // mobile events
    this.canvas.addEventListener("touchstart", function(evt){
        evt.preventDefault();
        that.touchStart = true;
        that.reset(evt);
    }, false);
    
    this.canvas.addEventListener("touchmove", function(evt){
        evt.preventDefault();
        that.reset(evt);
    }, false);
    
    this.canvas.addEventListener("touchend", function(evt){
        evt.preventDefault();
        that.touchEnd = true;
        that.reset(evt);
    }, false);
  }
  getMousePos(evt){
    return this.mousePos;
  }
  getTouchPos(evt){
    return this.touchPos;
  }
  setMousePosition(evt){
    let mouseX = evt.clientX - this.getCanvasPos().left + window.pageXOffset;
    let mouseY = evt.clientY - this.getCanvasPos().top + window.pageYOffset;
    this.mousePos = {
        x: mouseX,
        y: mouseY
    };
  }
  setTouchPosition(evt){
    if (evt.touches !== undefined && evt.touches.length == 1) { // Only deal with one finger
        let touch = evt.touches[0]; // Get the information for finger #1
        let touchX = touch.pageX - this.getCanvasPos().left + window.pageXOffset;
        let touchY = touch.pageY - this.getCanvasPos().top + window.pageYOffset;
        
        this.touchPos = {
            x: touchX,
            y: touchY
        };
    }
  }
  beginRegion = function(){
    this.currentRegion = {};
    this.regionIndex++;
  }
  addRegionEventListener = function(type, func){
     let event = (type.indexOf('touch') == -1) ? 'on' + type : type;
     this.currentRegion[event] = func;
  }
  closeRegion(){
    let pos = this.touchPos || this.mousePos;
    
    if (pos !== null && this.context.isPointInPath(pos.x, pos.y)) {
        if (this.lastRegionIndex != this.regionIndex) {
            this.lastRegionIndex = this.regionIndex;
        }
        
        // handle onmousedown
        if (this.mouseDown && this.currentRegion.onmousedown !== undefined) {
            this.currentRegion.onmousedown();
            this.mouseDown = false;
        }
        
        // handle onmouseup
        else if (this.mouseUp && this.currentRegion.onmouseup !== undefined) {
            this.currentRegion.onmouseup();
            this.mouseUp = false;
        }
        
        // handle onmouseover
        else if (!this.mouseOver && this.regionIndex != this.mouseOverRegionIndex && this.currentRegion.onmouseover !== undefined) {
            this.currentRegion.onmouseover();
            this.mouseOver = true;
            this.mouseOverRegionIndex = this.regionIndex;
        }
        
        // handle onmousemove
        else if (!this.mouseMove && this.currentRegion.onmousemove !== undefined) {
            this.currentRegion.onmousemove();
            this.mouseMove = true;
        }
        
        // handle touchstart
        if (this.touchStart && this.currentRegion.touchstart !== undefined) {
            this.currentRegion.touchstart();
            this.touchStart = false;
        }
        
        // handle touchend
        if (this.touchEnd && this.currentRegion.touchend !== undefined) {
            this.currentRegion.touchend();
            this.touchEnd = false;
        }
        
        // handle touchmove
        if (!this.touchMove && this.currentRegion.touchmove !== undefined) {
            this.currentRegion.touchmove();
            this.touchMove = true;
        }
        
    }
    else if (this.regionIndex == this.lastRegionIndex) {
        this.lastRegionIndex = -1;
        this.mouseOverRegionIndex = -1;
        
        // handle mouseout condition
        if (this.currentRegion.onmouseout !== undefined) {
            this.currentRegion.onmouseout();
        }
    }
}
}

            function writeMessage(context, message){
                context.font = "18pt Calibri";
                context.fillStyle = "black";
                context.fillText(message, 10, 25);
            }
            
            function drawImage(jetImage){
                let events = new EventManager("myCanvas");
                let canvas = events.getCanvas();
                let context = events.getContext();
                
                let rectX = canvas.width / 2 - jetImage.width / 2;
                let rectY = canvas.height / 2 - jetImage.height / 2;
                let draggingRect = false;
                let draggingRectOffsetX = 0;
                let draggingRectOffsetY = 0;
                
                events.setDrawStage(function(){
                    let mousePos = this.getMousePos();
                    
                    if (draggingRect) {
                        rectX = mousePos.x - draggingRectOffsetX;
                        rectY = mousePos.y - draggingRectOffsetY;
                    }
                    
                    // clear the canvas
                    this.clear();
                    
                    this.beginRegion();
                    context.drawImage(jetImage, rectX, rectY, jetImage.width, jetImage.height);
                    // draw rectangular region for image
                    context.beginPath();
                    context.rect(rectX, rectY, jetImage.width, jetImage.height);
                    context.closePath();
                    
                    this.addRegionEventListener("mousedown", function(){
                        draggingRect = true;
                        let mousePos = events.getMousePos();
                        
                        draggingRectOffsetX = mousePos.x - rectX;
                        draggingRectOffsetY = mousePos.y - rectY;
                    });
                    this.addRegionEventListener("mouseup", function(){
                        draggingRect = false;
                    });
                    this.addRegionEventListener("mouseover", function(){
                        document.body.style.cursor = "pointer";
                    });
                    this.addRegionEventListener("mouseout", function(){
                        document.body.style.cursor = "default";
                    });
                    this.addRegionEventListener("mousemove", function(){
                        writeMessage(context, rectX+"/"+rectY);
                    });
                                        
                    this.closeRegion();
                });
            }
            
            window.onload = function(){
                jetImage = new Image();
                jetImage.onload = function(){
                    drawImage(this);
                };
                jetImage.src = "http://java2s.com/style/demo/jet2.png";
            };
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="600" height="250" style="border:1px solid black;">
        </canvas>
    </body>
</html>
Note

To drag-and-drop an image, we can draw an invisible rectangular path on top of the image to provide a path for the image.
We can attach the mousedown, mouseup, and mousemove events to handle the three phases of drag-and-drop.
When the user drags-and-drops an image, both of the image and its corresponding rectangular path are being dragging and dropping.
HTML5 Game - Dragging and dropping images

Introduction

Demo

Note

Related Topic
