CSS /*Centering the gauge*/ #canvas {     display: block;     width: 300px;     margin: 100px auto; }   JavaScript
18/01/2017 06:56:24 PM

Phần mềm-Ứng dụng

Tạo biểu đồ Gauge bằng HTML5 Canvas và Javascript
HTML
<canvas id="canvas" width="300" height="300">
 
CSS
/*Centering the gauge*/
#canvas {
    display: block;
    width: 300px;
    margin: 100px auto;
}
 
JavaScript
<script language="JavaScript">
window.onload = function(){
    //canvas initialization
    var canvas = document.getElementById("canvas");
    var ctx = canvas.getContext("2d");
    //dimensions
    var W = canvas.width;
    var H = canvas.height;
    //Variables
    var degrees = 0;
    var new_degrees = 0;
    var difference = 0;
    var color = "lightgreen"; //green looks better to me
    var bgcolor = "#222";
    var text;
    var animation_loop, redraw_loop;
     
    function init()
    {
        //Clear the canvas everytime a chart is drawn
        ctx.clearRect(0, 0, W, H);
         
        //Background 360 degree arc
        ctx.beginPath();
        ctx.strokeStyle = bgcolor;
        ctx.lineWidth = 30;
        ctx.arc(W/2, H/2, 100, 0, Math.PI*2, false); //you can see the arc now
        ctx.stroke();
         
        //gauge will be a simple arc
        //Angle in radians = angle in degrees * PI / 180
        var radians = degrees * Math.PI / 180;
        ctx.beginPath();
        ctx.strokeStyle = color;
        ctx.lineWidth = 30;
        //The arc starts from the rightmost end. If we deduct 90 degrees from the angles
        //the arc will start from the topmost end
        ctx.arc(W/2, H/2, 100, 0 - 90*Math.PI/180, radians - 90*Math.PI/180, false); 
        //you can see the arc now
        ctx.stroke();
         
        //Lets add the text
        ctx.fillStyle = color;
        ctx.font = "50px bebas";
        text = Math.floor(degrees/360*100) + "%";
        //Lets center the text
        //deducting half of text width from position x
        text_width = ctx.measureText(text).width;
        //adding manual value to position y since the height of the text cannot
        //be measured easily. There are hacks but we will keep it manual for now.
        ctx.fillText(text, W/2 - text_width/2, H/2 + 15);
    }
     
    function draw()
    {
        //Cancel any movement animation if a new chart is requested
        if(typeof animation_loop != undefined) clearInterval(animation_loop);
         
        //random degree from 0 to 360
        new_degrees = Math.round(Math.random()*360);
        difference = new_degrees - degrees;
        //This will animate the gauge to new positions
        //The animation will take 1 second
        //time for each frame is 1sec / difference in degrees
        animation_loop = setInterval(animate_to, 1000/difference);
    }
     
    //function to make the chart move to new degrees
    function animate_to()
    {
        //clear animation loop if degrees reaches to new_degrees
        if(degrees == new_degrees) 
            clearInterval(animation_loop);
         
        if(degrees < new_degrees)
            degrees++;
        else
            degrees--;
             
        init();
    }
     
    //Lets add some animation for fun
    draw();
    redraw_loop = setInterval(draw, 2000); //Draw a new chart every 2 seconds   
}
</script>

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