如何在画布中复制动画

Question

I have this animation of a semicircle being drawn, and I basically want to copy it, and move the copy down 60px then add a delay of a second to the new one, So that it draws a "B"

html

<canvas id="thecanvas"></canvas>

script

var can = document.getElementById('thecanvas');
ctx = can.getContext('2d');
can.width = window.innerWidth;
can.height = window.innerHeight;

window.drawCircle = function (x, y) {
    segments = 90, /* how many segments will be drawn in the space */
    currentSegment = 0,
    toRadians = function (deg) {
        return (Math.PI / 180) * deg;
    },
    getTick = function (num) {
        var tick = toRadians(180) / segments; /*360=full, 180=semi, 90=quarter... */
        return tick * num;
    },
    segment = function (end) {
        end = end || getTick(currentSegment);
        ctx.clearRect(0, 0, can.width, can.height);
        ctx.beginPath();
        ctx.arc(x, y, 60, (1.5 * Math.PI), end + (1.5 * Math.PI), false);
        ctx.stroke();
        ctx.closePath();
    };

    ctx.lineWidth = 5;
    ctx.strokeStyle = 'rgba(0,0,0,0.5)';

    setTimeout(function render() {
        segment(getTick(currentSegment));
        currentSegment += 1;
        if (currentSegment < segments) {
            setTimeout(render, 5);
        } else {
            currentTick = 0;
        }
    }, 250);
};
drawCircle(100, 100); 

Here is a fiddle http://jsfiddle.net/zhirkovski/bJqdN/

Answer 1

first you can put the setTimeout function outside of your drawCircle method.

Then you have at least 2 options :

1. to create an "endDraw" Event which will be dispatched at the end of 1 draw. When this event is handle, just call again the drawCircle method. To achieve this, of course you need a main method to call the first drawCircle.

2. To make a better solution, you can describe a workflow of calls. ie describe a list of method to call and for each of them the start frame:

    var workflow = [{method:"drawCircle", frame:0, x:100, y:100}, //the first half circle at the frame 0, x=100, y=100 {method:"drawCircle", frame:1000, x:100, y:190}]; //the second half circle starting at frame 1000, x=100, y=190 

   The your main timer will just be configured to use this array to know what call to do