# Sierpinski triangle

This example shows the power of JavaScript and requires a bit more advanced JavaScript programming.

### The underlying JavaScript code

        board = JXG.JSXGraph.initBoard('box', {originX: 10, originY: 390, unitX: 380, unitY: 380});

var level = 0;
function run() {
JXG.JSXGraph.freeBoard(board);
board = JXG.JSXGraph.initBoard('box', {originX: 10, originY: 390, unitX: 380, unitY: 380});
level++;
board.suspendUpdate();
paint();
board.unsuspendUpdate();
}

function paint() {
// Initial triangle
var xCoords = [0, 1, 0.5];
var yCoords = [0, 0, 1];
drawPolygon(xCoords, yCoords, level);
drawTriangle({x:0,y:0}, {x:1,y:0}, {x:0.5,y:1}, level);
}

function drawPolygon(xCoords, yCoords,level) {
p1 = board.createElement('point', [xCoords[0], yCoords[0]], {visible:false,name:''});
p2 = board.createElement('point', [xCoords[1], yCoords[1]], {visible:false,name:''});
p3 = board.createElement('point', [xCoords[2], yCoords[2]], {visible:false,name:''});
var colors=['#000000','#665566','#994499','#BB33BB','#EE99FF','#FFCCFF'];
l1 = board.createElement('line',[p1,p2],{straightFirst:false,straightLast:false,strokeColor:colors[level%6],name:''});
l2 = board.createElement('line',[p2,p3],{straightFirst:false,straightLast:false,strokeColor:colors[level%6],name:''});
l3 = board.createElement('line',[p3,p1],{straightFirst:false,straightLast:false,strokeColor:colors[level%6],name:''});
}

function drawTriangle(a, b, c, level) {
if (level==0) return;
level -= 1;

// In das übergebene Dreieck, wird ein auf dem Kopf stehendes Dreieck eingefügt
var xCoords = [c.x, (c.x+b.x)/2, (a.x+c.x)/2];
var yCoords = [b.y, (c.y+a.y)/2, (c.y+a.y)/2];

drawPolygon(xCoords, yCoords,level);

// 3 neue Dreiecke bestimmen
a1 = a;
b1 = {x:c.x, y:b.y};
c1 = {x:(a.x+c.x)/2, y:(c.y+a.y)/2};
drawTriangle(a1, b1, c1, level);

a2 = {x:c.x, y:b.y};
b2 = b;
c2 = {x:(c.x+b.x)/2, y:(c.y+a.y)/2};
drawTriangle(a2, b2, c2, level);

a3 = {x:(a.x+c.x)/2, y:(c.y+a.y)/2};
b3 = {x:(c.x+b.x)/2, y:(c.y+a.y)/2};
c3 = c;
drawTriangle(a3, b3, c3, level);
}
paint();