Chapter 7: Solar system

by Stéphane Cabaret

JavaScript

var paper = Raphael(0, 0, 1000, 1000);

paper.customAttributes.progress = function (v) {
    var path = this.data("mypath");
    if (!path) {
        return {
            transform: "t0,0"
        };
    }
    var len = path.getTotalLength();
    var point = path.getPointAtLength(v * len);
    
    return {
        transform: "T" + point.x + "," + point.y
    };
};

//http://nineplanets.org/data.html
var orbits = {
    Mercury: { distance: 57910, period: 87.97, eccen: 0.21 },
    Venus: { distance: 108200, period: 224.70, eccen: 0.01},
    Earth: { distance: 149600, period: 365.26, eccen: 0.02},
    Mars: { distance: 227940, period: 686.98, eccen: 0.09 }
};

//http://nineplanets.org/data1.html
var radii = {
    Sun: 695000,
    Mercury: 2440,
    Venus: 6052,
    Earth: 6378,
    Mars: 3397,
};

//chosen haphazardly
var colors = {
    Sun: "yellow",
    Mercury: "gray",
    Venus: "brown",
    Earth: "blue",
    Mars: "red"
}

// chosen some scales by trial and error to get the solar sysem on the screen
var ORBIT_SCALE = 1.0 / 1000,
    PLANET_SCALE = 1.0 / 600,
    MS_PER_DAY = 100;

//center at the middle of the canvas
var CENTER = {x: paper.width / 2, y: paper.height / 2};

// the sun needs extra scaling
var Sun = paper.circle(CENTER.x, CENTER.y, radii.Sun * PLANET_SCALE / 50).attr("fill", colors.Sun);

var label_pos = 13;

function planet(name, data) {    
    // calculate the long and short arms of the elliptical orbit
    // Also get focus from eccentricity of orbit
    // http://nineplanets.org/help.html#semim
    var perigee = data.distance * (1 - data.eccen) * ORBIT_SCALE,
        apogee = data.distance * (1 + data.eccen) * ORBIT_SCALE,
        focus = data.eccen * apogee,
        x = CENTER.x + focus - apogee,
        y = CENTER.y;

    // labels
    var label = paper.text(10, label_pos, name + ": 0").attr("text-anchor", "start");
    label_pos += 20;    
    
    var path = "M" + x + "," + y;     
    path += "a" + apogee + "," + perigee + " 0 1,1 " +...