HTML Canvas Image Drag and drop

Description

HTML Canvas Image Drag and drop

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<!DOCTYPE HTML>
<html>
    <head>
    <script>
 function writeMessage(context, message){
                context.font = "18pt Calibri";
                context.fillStyle = "black";
                context.fillText(message, 10, 25);
            }/*from w  w w . j a  v  a2s.  c  o m*/
            
            function drawImage(image1){
                var events = new Events("myCanvas");
                var canvas = events.getCanvas();
                var context = events.getContext();
                
                var rectX = canvas.width / 2 - image1.width / 2;
                var rectY = canvas.height / 2 - image1.height / 2;
                var draggingRect = false;
                var draggingRectOffsetX = 0;
                var draggingRectOffsetY = 0;
                
                events.setDrawStage(function(){
                    var mousePos = this.getMousePos();
                    
                    if (draggingRect) {
                        rectX = mousePos.x - draggingRectOffsetX;
                        rectY = mousePos.y - draggingRectOffsetY;
                    }
                    
                    // clear the canvas
                    this.clear();
                    writeMessage(context, "Drag and drop the car...");
                    
                    this.beginRegion();
                    context.drawImage(image1, rectX, rectY, image1.width, image1.height);
                    // draw rectangular region for image
                    context.beginPath();
                    context.rect(rectX, rectY, image1.width, image1.height);
                    context.closePath();
                    
                    this.addRegionEventListener("mousedown", function(){
                        draggingRect = true;
                        var 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.closeRegion();
                });
            }
            
            window.onload = function(){
                // load image
                image1 = new Image();
                image1.onload = function(){
                    drawImage(this);
                };
                image1.src = "image1.png";
            };
class Events {
    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() {
        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.animating && 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() {
        const that = this;
        
        if (this.drawStage !== undefined) {
            this.drawStage();
        }
        
        // desktop events
        this.canvas.addEventListener("mousedown", evt => {
            that.mouseDown = true;
            that.reset(evt);
        }, false);
        
        this.canvas.addEventListener("mousemove", evt => {
            that.reset(evt);
        }, false);
        
        this.canvas.addEventListener("mouseup", evt => {
            that.mouseUp = true;
            that.reset(evt);
        }, false);
        
        this.canvas.addEventListener("mouseover", evt => {
            that.reset(evt);
        }, false);
        
        this.canvas.addEventListener("mouseout", evt => {
            that.mousePos = null;
        }, false);
        
        // mobile events
        this.canvas.addEventListener("touchstart", evt => {
            evt.preventDefault();
            that.touchStart = true;
            that.reset(evt);
        }, false);
        
        this.canvas.addEventListener("touchmove", evt => {
            evt.preventDefault();
            that.reset(evt);
        }, false);
        
        this.canvas.addEventListener("touchend", evt => {
            evt.preventDefault();
            that.touchEnd = true;
            that.reset(evt);
        }, false);
    }

    getMousePos(evt) {
        return this.mousePos;
    }

    getTouchPos(evt) {
        return this.touchPos;
    }

    setMousePosition(evt) {
        const mouseX = evt.clientX - this.getCanvasPos().left + window.pageXOffset;
        const 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
            const touch = evt.touches[0]; // Get the information for finger #1
            const touchX = touch.pageX - this.getCanvasPos().left + window.pageXOffset;
            const touchY = touch.pageY - this.getCanvasPos().top + window.pageYOffset;
            
            this.touchPos = {
                x: touchX,
                y: touchY
            };
        }
    }

    beginRegion() {
        this.currentRegion = {};
        this.regionIndex++;
    }

    addRegionEventListener(type, func) {
        let event = (type.indexOf('touch') == -1) ? `on${type}` : type;
        this.currentRegion[event] = func;
    }

    closeRegion() {
        const 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();
            }
        }
    }
}

        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="600" height="250" style="border:1px solid black;">
        </canvas>
    </body>
</html>



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