Canvas-2D-Context-API-Primer/slider.html at master · rroa/Canvas-2D-Context-API-Primer · GitHub

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<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width,user-scalable=no">
        <meta name="description" content="Canvas 2D Context API Primer">
        <meta name="keywords" content="HTML,JavaScript">
        <meta name="author" content="Raul Roa">
        <title>Touch Events</title>
        <style type="text/css">
            canvas {
                position: absolute;
                top: 10px;
                left: 10px;
                background-color: white;
                border-radius: 25px;
                border: 1px solid #404040;
            }

            .slider {
                position: absolute;
                top: 115px;
                left: 85px;
                width: 152px;
                height: 52px;
            }

            .bar {
                position: relative;
                top: 30px;
                width: 152px;
                height: 2px;
                background-color: #404040;
            }

            .knob {
                position: relative;
                left: 0;
                border: 1px solid #404040;
                background-color: #c0c0c0;
                width: 50px;
                height: 50px;
                border-radius: 25px;
            }
        </style>
        <script>
            window.onload = function () {
                // Get the canvas element
                //
                var canvas = document.getElementById('canvas');

                // Get a reference to the drawing context
                //
                var ctx = canvas.getContext('2d');

                // Get a reference to the slider div
                //
                var slider = document.getElementById("slider");

                // Get a reference to the slider knob
                //
                var knob = document.getElementById("knob");

                // Get a reference to the image
                //
                var image = document.getElementById("image");

                var mouseIsDown = 0;
                var knobMid = knob.offsetWidth / 2;
                var margin = canvas.offsetLeft - 1;

                // Binding events
                //
                slider.addEventListener("touchstart", function(event) {
                    touchXY(event);
                }, false);

                slider.addEventListener("touchmove", function(event) {
                    touchXY(event);
                }, false);

                slider.addEventListener("mousedown", function(event) {
                    mouseDown(event);
                }, false);

                slider.addEventListener("mousemove", function(event) {
                    mouseXY(event);
                }, false);

                slider.addEventListener("mouseup", function(event) {
                    mouseUp(event);
                }, false);

                // Draw text
                //
                textInit();
                showVal();


                function mouseDown(event){
                    mouseIsDown = 1;
                    mouseXY(event);
                }

                function mouseUp(event){
                    mouseIsDown = 0;
                }

                function mouseXY(event){
                    if(mouseIsDown){
                        var mouseX = event.pageX - slider.offsetLeft;

                        if (mouseX >= 0 && mouseX <= slider.offsetWidth ) {
                            setKnob(mouseX);
                        }
                    }
                }

                function touchXY(event){
                    event.preventDefault();

                    var touchX = event.touches[0].pageX - slider.offsetLeft;
                    if(touchX >= 0 && touchX <= slider.offsetWidth){
                        setKnob(touchX);
                    }
                }

                function textInit() {
                    ctx.fillStyle = "red";
                    ctx.font = "24pt Helvetica";
                    ctx.textAlign = "center";
                    ctx.textBaseline = "bottom";
                }

                function showVal() {
                    // value goes from 0 to slider-width minus knob width
                    //
                    var sliderVal = knob.offsetLeft;

                    // Save state
                    //
                    ctx.save();

                    // Clear canvas
                    //
                    ctx.clearRect(0, 0, canvas.width, canvas.height);

                    var scale = 0.25 + sliderVal / 400;

                    // Scale the image
                    //
                    ctx.scale(scale, scale);
                    ctx.drawImage(image, 0, 0);

                    // Restore state
                    //
                    ctx.restore();

                    // Draw text
                    //
                    ctx.fillText(sliderVal, canvas.width / 2, canvas.height - 5);

                    setTimeout(showVal, 16);
                }

                function setKnob(x) {
                    var knobX = x - knobMid;

                    knobX = Math.max(knobX, 0);
                    knobX = Math.min(knobX, slider.offsetWidth - knob.offsetWidth);

                    if(knob){
                        knob.style.left = knobX + 'px';
                    }
                }
            };
        </script>
    </head>

    <body>
        <canvas id="canvas" width="300" height="200" tabindex='0' class="default">
            This browser or document mode doesn't support canvas
        </canvas>

        <div class="slider" id="slider">
            <div class="bar"></div>
            <div id="knob" class="knob"></div>
        </div>

        <img id="image" style="display:none" src="butterfly.png" />
    </body>
</html>