Canvas Test Spiral

Testing some stuff

by joquery

HTML

<canvas id="myCanvas" width="300" height="200"></canvas>

<div>
    <button id="start">Start</button>
    <button id="stop">Stop</button>
    <button id="next">Next</button>
    <button id="reset">Reset</button>
</div>

CSS

#myCanvas {
    background: #fafaee;
}

JavaScript

var context;
var canvas;
var drawInterval = 1000.0 / 30.0;
var duration = 2;
var stepping = 1 / (duration * drawInterval);
var intervalId;

var progress = 0.0;

var lastSnake = 0;

var draw = function() {
    
    if (progress + stepping > 1) {
        progress = 1;
    } else {
        progress += stepping;
    }  
    
    var w = canvas.width;
    var h = canvas.height;
    
    context.save();
    context.beginPath();
    
    //////////////////
    
    var canvasMidW = w/2;
    var canvasMidH = h/2;
    
    var snakeCount = 10;
    var snakeHeight = h / snakeCount;
    
    
    
    if (lastSnake % 2 === 0) {
        console.log("left to right");
        
        var newWidth = (snakeCount * w * progress) - (lastSnake * w);
        
        context.moveTo(0, lastSnake * snakeHeight);
        context.lineTo(newWidth, lastSnake * snakeHeight);
        context.lineTo(newWidth, lastSnake * snakeHeight + snakeHeight);
        context.lineTo(0, lastSnake * snakeHeight + snakeHeight);
        
        context.closePath();
        
    } else {
        console.log("right to left");
        
        var newWidth = -(snakeCount * w * progress) + ((lastSnake + 1) * w);
        
        context.moveTo(w, lastSnake * snakeHeight);
        context.lineTo(newWidth, lastSnake * snakeHeight);
        context.lineTo(newWidth, lastSnake * snakeHeight + snakeHeight);
        context.lineTo(w, lastSnake * snakeHeight + snakeHeight);
        
        context.closePath();
    }
    
    if (progress > ( (lastSnake +1) / snakeCount)) {
        lastSnake += 1;
        console.log("increment lastSnake: " + lastSnake);
    }
    
    //////////////////

    context.clip();
    
    context.rect(0,0,canvas.width,canvas.height);
       context.fillStyle="red";
    context.fillRect(0,0,canvas.width,canvas.height);
    
    if (progress === 1) {
        clearInterval(intervalId);
    }
    context.restore();
};



var startAnimation = function() {

    intervalId = setInterval(draw,...