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how to zoom the image inside the canvas

Hi,

There is a canvas and inside canvas there is an image on the canvas.I want my canvas image to zoom.once this canvas imaged save in the mobile gallery it zoom whatever user want.I want it to zoom in my application.How can i do this.

please help me

 

Thanks and regards

Mohit Kumar

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4 回复
Marco Buettner

... why you didnt pay anything to write your applications? :)

http://stackoverflow.com/a/5526721

mohit kumar

Hi Marco Buettner,

I have done with whant i want,but here small problem.Here image zoom fine but my canvas is not moving according to the touch move,my image inside the canvas is moving and it zoom also.

when i written the code for touch move of canvas then zoom is not work.when zoom is work then touch move of canvas is not work.Please help me

my code is

 

<html>
<head>

<meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
    <meta name="description" content="Tizen basic template generated by Tizen Web IDE"/>
    <script src="js/main.js"></script>
    
</head>

<body>
    <!-- <div style="width:50%; height:60%; background-color:red;">
        <canvas id="mycanvas" style="width: 100%; height: 100%"></canvas>
    </div> -->
    
    
    <canvas id="mycanvas" style="width: 300px; height: 300px"></canvas>
    <script src="js/img-touch-canvas.js"></script>
    <script>
        var gesturableImg = new ImgTouchCanvas({
            canvas: document.getElementById('mycanvas'),
            path: "css/images/mohit.jpeg"
        });
    </script>
</body>
</html>

Here my js file below

img-touch-canvas.js

(function() {
    var root = this; //global object

    var ImgTouchCanvas = function(options) {
        if( !options || !options.canvas || !options.path) {
            throw 'ImgZoom constructor: missing arguments canvas or path';
        }

        this.canvas         = options.canvas;
        this.canvas.width   = this.canvas.clientWidth;
        this.canvas.height  = this.canvas.clientHeight;
        this.context        = this.canvas.getContext('2d');

        this.desktop = options.desktop || false; //non touch events
        
        this.position = {
            x: 0,
            y: 0
        };
        this.scale = {
            x: 0.5,
            y: 0.5
        };
        this.imgTexture = new Image();
        this.imgTexture.src = options.path;

        this.lastZoomScale = null;
        this.lastX = null;
        this.lastY = null;

        this.mdown = false; //desktop drag

        this.init = false;
        this.checkRequestAnimationFrame();
        requestAnimationFrame(this.animate.bind(this));

        this.setEventListeners();
    };


    ImgTouchCanvas.prototype = {
        animate: function() {
            //set scale such as image cover all the canvas
            if(!this.init) {
                if(this.imgTexture.width) {
                    var scaleRatio = null;
                    if(this.canvas.clientWidth > this.canvas.clientHeight) {
                        scaleRatio = this.canvas.clientWidth / this.imgTexture.width;
                    }
                    else {
                        scaleRatio = this.canvas.clientHeight / this.imgTexture.height;
                    }

                    this.scale.x = scaleRatio;
                    this.scale.y = scaleRatio;
                    this.init = true;
                }
            }

            this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);

            this.context.drawImage(
                this.imgTexture,
                this.position.x, this.position.y,
                this.scale.x * this.imgTexture.width,
                this.scale.y * this.imgTexture.height);

            requestAnimationFrame(this.animate.bind(this));
        },


        gesturePinchZoom: function(event) {
            var zoom = false;

            if( event.targetTouches.length >= 2 ) {
                var p1 = event.targetTouches[0];
                var p2 = event.targetTouches[1];
                var zoomScale = Math.sqrt(Math.pow(p2.pageX - p1.pageX, 2) + Math.pow(p2.pageY - p1.pageY, 2)); //euclidian distance

                if( this.lastZoomScale ) {
                    zoom = zoomScale - this.lastZoomScale;
                }

                this.lastZoomScale = zoomScale;
            }    

            return zoom;
        },

        doZoom: function(zoom) {
            if(!zoom) return;

            //new scale
            var currentScale = this.scale.x;
            var newScale = this.scale.x + zoom/100;
            

            //some helpers
            var deltaScale = newScale - currentScale;
            var currentWidth    = (this.imgTexture.width * this.scale.x);
            var currentHeight   = (this.imgTexture.height * this.scale.y);
            var deltaWidth  = this.imgTexture.width*deltaScale;
            var deltaHeight = this.imgTexture.height*deltaScale;


            //by default scale doesnt change position and only add/remove pixel to right and bottom
            //so we must move the image to the left to keep the image centered
            //ex: coefX and coefY = 0.5 when image is centered <=> move image to the left 0.5x pixels added to the right
            var canvasmiddleX = this.canvas.clientWidth / 2;
            var canvasmiddleY = this.canvas.clientHeight / 2;
            var xonmap = (-this.position.x) + canvasmiddleX;
            var yonmap = (-this.position.y) + canvasmiddleY;
            var coefX = -xonmap / (currentWidth);
            var coefY = -yonmap / (currentHeight);
            var newPosX = this.position.x + deltaWidth*coefX;
            var newPosY = this.position.y + deltaHeight*coefY;

            //edges cases
            var newWidth = currentWidth + deltaWidth;
            var newHeight = currentHeight + deltaHeight;
            
            if( newWidth < this.canvas.clientWidth ) return;
            if( newPosX > 0 ) { newPosX = 0; }
            if( newPosX + newWidth < this.canvas.clientWidth ) { newPosX = this.canvas.clientWidth - newWidth;}
            
            if( newHeight < this.canvas.clientHeight ) return;
            if( newPosY > 0 ) { newPosY = 0; }
            if( newPosY + newHeight < this.canvas.clientHeight ) { newPosY = this.canvas.clientHeight - newHeight; }


            //finally affectations
            this.scale.x    = newScale;
            this.scale.y    = newScale;
            this.position.x = newPosX;
            this.position.y = newPosY;
        },

        doMove: function(relativeX, relativeY) {
            if(this.lastX && this.lastY) {
              var deltaX = relativeX - this.lastX;
              var deltaY = relativeY - this.lastY;
              var currentWidth = (this.imgTexture.width * this.scale.x);
              var currentHeight = (this.imgTexture.height * this.scale.y);

              this.position.x += deltaX;
              this.position.y += deltaY;


              //edge cases
              if( this.position.x > 0 ) {
                this.position.x = 0;
              }
              else if( this.position.x + currentWidth < this.canvas.clientWidth ) {
                this.position.x = this.canvas.clientWidth - currentWidth;
              }
              if( this.position.y > 0 ) {
                this.position.y = 0;
              }
              else if( this.position.y + currentHeight < this.canvas.clientHeight ) {
                this.position.y = this.canvas.clientHeight - currentHeight;
              }
            }

            this.lastX = relativeX;
            this.lastY = relativeY;
        },

        setEventListeners: function() {
            // touch
            this.canvas.addEventListener('touchstart', function(e) {
                this.lastX          = null;
                this.lastY          = null;
                this.lastZoomScale  = null;
            }.bind(this));

            this.canvas.addEventListener('touchmove', function(e) {
                e.preventDefault();
                
                if(e.targetTouches.length == 2) { //pinch
                    this.doZoom(this.gesturePinchZoom(e));
                }
                else if(e.targetTouches.length == 1) {
                    var relativeX = e.targetTouches[0].pageX - this.canvas.getBoundingClientRect().left;
                    var relativeY = e.targetTouches[0].pageY - this.canvas.getBoundingClientRect().top;                
                    this.doMove(relativeX, relativeY);
                }
            }.bind(this));

            if(this.desktop) {
                // keyboard+mouse
                window.addEventListener('keyup', function(e) {
                    if(e.keyCode == 187 || e.keyCode == 61) { //+
                        this.doZoom(5);
                    }
                    else if(e.keyCode == 54) {//-
                        this.doZoom(-5);
                    }
                }.bind(this));

                window.addEventListener('mousedown', function(e) {
                    this.mdown = true;
                    this.lastX = null;
                    this.lastY = null;
                }.bind(this));

                window.addEventListener('mouseup', function(e) {
                    this.mdown = false;
                }.bind(this));

                window.addEventListener('mousemove', function(e) {
                    var relativeX = e.pageX - this.canvas.getBoundingClientRect().left;
                    var relativeY = e.pageY - this.canvas.getBoundingClientRect().top;

                    if(e.target == this.canvas && this.mdown) {
                        this.doMove(relativeX, relativeY);
                    }

                    if(relativeX <= 0 || relativeX >= this.canvas.clientWidth || relativeY <= 0 || relativeY >= this.canvas.clientHeight) {
                        this.mdown = false;
                    }
                }.bind(this));
            }
        },

        checkRequestAnimationFrame: function() {
            var lastTime = 0;
            var vendors = ['ms', 'moz', 'webkit', 'o'];
            for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
                window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
                window.cancelAnimationFrame =
                  window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
            }

            if (!window.requestAnimationFrame) {
                window.requestAnimationFrame = function(callback, element) {
                    var currTime = new Date().getTime();
                    var timeToCall = Math.max(0, 16 - (currTime - lastTime));
                    var id = window.setTimeout(function() { callback(currTime + timeToCall); },
                      timeToCall);
                    lastTime = currTime + timeToCall;
                    return id;
                };
            }

            if (!window.cancelAnimationFrame) {
                window.cancelAnimationFrame = function(id) {
                    clearTimeout(id);
                };
            }
        }
    };

    root.ImgTouchCanvas = ImgTouchCanvas;
}).call(this);

 

 

I am fresher please help me.I have no more experience.

 

Thanks and regards

Mohit Kumar

 

Palitsyna

Hello,

you can use scale() method. Here is the example:

http://www.w3schools.com/tags/canvas_scale.asp

Alex Dem

Hi,
There are many code examples (how to use canvas) in intenet
Simplest code snippet (as simple as it could be, just insert into html file),  even jquery mobile is not used:
 

<html>
<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
    <meta name="description" content="Tizen basic template generated by Tizen Web IDE"/>

        <style>
            body {
                margin: 0px;
                padding: 0px;
            }

            #wrapper {
                position: relative;
                border: 1px solid #9C9898;
                width: 200px;
                height: 200px;
            }

            #buttonWrapper {
                position: absolute;
                width: 30px;
                top: 2px;
                right: 2px;
            }

            input[type =
            "button"] {
                padding: 5px;
                width: 30px;
                margin: 0px 0px 2px 0px;
            }
        </style>
        <script>
            function draw(scale){
                var canvas = document.getElementById("myCanvas");
                var context = canvas.getContext("2d");
                // clear canvas
                context.clearRect(0, 0, canvas.width, canvas.height);
                context.scale(scale, scale);
                context.drawImage(image, 0 , 0 , canvas.width, canvas.height);
            }

            window.onload = function(){
                var canvas = document.getElementById("myCanvas");

                image = new Image();
                image.src = 'images/tizen_32.png';

                // add button event listeners
                document.getElementById("plus").addEventListener("click", function(){
                    draw(1.2);             
                 }, false);

                document.getElementById("minus").addEventListener("click", function(){
                    draw(0.8);
                }, false);

                image.onload = function () {
                    draw(1.0);
                }
            };
        </script>
    </head>
    <body>
        <div id="wrapper">
            <canvas id="myCanvas" width="200" height="200">
            </canvas>
            <div id="buttonWrapper">
                <input type="button" id="plus" value="+"><input type="button" id="minus" value="-">
            </div>
        </div>
    </body>
</html>