# WebGL - Cube Rotation

In this chapter, we will take an example to demonstrate how to draw a rotating 3D cube using WebGL.

## Example – Draw a Rotating 3D Cube

The following program shows how to draw a rotating 3D cube −

```<!doctype html>
<html>
<body>
<canvas width = "570" height = "570" id = "my_Canvas"></canvas>

<script>
/*============= Creating a canvas =================*/
var canvas = document.getElementById('my_Canvas');
gl = canvas.getContext('experimental-webgl');

/*============ Defining and storing the geometry =========*/

var vertices = [
-1,-1,-1, 1,-1,-1, 1, 1,-1, -1, 1,-1,
-1,-1, 1, 1,-1, 1, 1, 1, 1, -1, 1, 1,
-1,-1,-1, -1, 1,-1, -1, 1, 1, -1,-1, 1,
1,-1,-1, 1, 1,-1, 1, 1, 1, 1,-1, 1,
-1,-1,-1, -1,-1, 1, 1,-1, 1, 1,-1,-1,
-1, 1,-1, -1, 1, 1, 1, 1, 1, 1, 1,-1,
];

var colors = [
5,3,7, 5,3,7, 5,3,7, 5,3,7,
1,1,3, 1,1,3, 1,1,3, 1,1,3,
0,0,1, 0,0,1, 0,0,1, 0,0,1,
1,0,0, 1,0,0, 1,0,0, 1,0,0,
1,1,0, 1,1,0, 1,1,0, 1,1,0,
0,1,0, 0,1,0, 0,1,0, 0,1,0
];

var indices = [
0,1,2, 0,2,3, 4,5,6, 4,6,7,
8,9,10, 8,10,11, 12,13,14, 12,14,15,
16,17,18, 16,18,19, 20,21,22, 20,22,23
];

// Create and store data into vertex buffer
var vertex_buffer = gl.createBuffer ();
gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

// Create and store data into color buffer
var color_buffer = gl.createBuffer ();
gl.bindBuffer(gl.ARRAY_BUFFER, color_buffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);

// Create and store data into index buffer
var index_buffer = gl.createBuffer ();
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, index_buffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indices), gl.STATIC_DRAW);

var vertCode = 'attribute vec3 position;'+
'uniform mat4 Pmatrix;'+
'uniform mat4 Vmatrix;'+
'uniform mat4 Mmatrix;'+
'attribute vec3 color;'+//the color of the point
'varying vec3 vColor;'+

'void main(void) { '+//pre-built function
'gl_Position = Pmatrix*Vmatrix*Mmatrix*vec4(position, 1.);'+
'vColor = color;'+
'}';

var fragCode = 'precision mediump float;'+
'varying vec3 vColor;'+
'void main(void) {'+
'gl_FragColor = vec4(vColor, 1.);'+
'}';

/* ====== Associating attributes to vertex shader =====*/

gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);
gl.vertexAttribPointer(position, 3, gl.FLOAT, false,0,0) ;

// Position
gl.enableVertexAttribArray(position);
gl.bindBuffer(gl.ARRAY_BUFFER, color_buffer);
gl.vertexAttribPointer(color, 3, gl.FLOAT, false,0,0) ;

// Color
gl.enableVertexAttribArray(color);

/*==================== MATRIX =====================*/

function get_projection(angle, a, zMin, zMax) {
var ang = Math.tan((angle*.5)*Math.PI/180);//angle*.5
return [
0.5/ang, 0 , 0, 0,
0, 0.5*a/ang, 0, 0,
0, 0, -(zMax+zMin)/(zMax-zMin), -1,
0, 0, (-2*zMax*zMin)/(zMax-zMin), 0
];
}

var proj_matrix = get_projection(40, canvas.width/canvas.height, 1, 100);

var mov_matrix = [1,0,0,0, 0,1,0,0, 0,0,1,0, 0,0,0,1];
var view_matrix = [1,0,0,0, 0,1,0,0, 0,0,1,0, 0,0,0,1];

// translating z
view_matrix[14] = view_matrix[14]-6;//zoom

/*==================== Rotation ====================*/

function rotateZ(m, angle) {
var c = Math.cos(angle);
var s = Math.sin(angle);
var mv0 = m[0], mv4 = m[4], mv8 = m[8];

m[0] = c*m[0]-s*m[1];
m[4] = c*m[4]-s*m[5];
m[8] = c*m[8]-s*m[9];

m[1]=c*m[1]+s*mv0;
m[5]=c*m[5]+s*mv4;
m[9]=c*m[9]+s*mv8;
}

function rotateX(m, angle) {
var c = Math.cos(angle);
var s = Math.sin(angle);
var mv1 = m[1], mv5 = m[5], mv9 = m[9];

m[1] = m[1]*c-m[2]*s;
m[5] = m[5]*c-m[6]*s;
m[9] = m[9]*c-m[10]*s;

m[2] = m[2]*c+mv1*s;
m[6] = m[6]*c+mv5*s;
m[10] = m[10]*c+mv9*s;
}

function rotateY(m, angle) {
var c = Math.cos(angle);
var s = Math.sin(angle);
var mv0 = m[0], mv4 = m[4], mv8 = m[8];

m[0] = c*m[0]+s*m[2];
m[4] = c*m[4]+s*m[6];
m[8] = c*m[8]+s*m[10];

m[2] = c*m[2]-s*mv0;
m[6] = c*m[6]-s*mv4;
m[10] = c*m[10]-s*mv8;
}

/*================= Drawing ===========================*/
var time_old = 0;

var animate = function(time) {

var dt = time-time_old;
rotateZ(mov_matrix, dt*0.005);//time
rotateY(mov_matrix, dt*0.002);
rotateX(mov_matrix, dt*0.003);
time_old = time;

gl.enable(gl.DEPTH_TEST);
gl.depthFunc(gl.LEQUAL);
gl.clearColor(0.5, 0.5, 0.5, 0.9);
gl.clearDepth(1.0);

gl.viewport(0.0, 0.0, canvas.width, canvas.height);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
gl.uniformMatrix4fv(Pmatrix, false, proj_matrix);
gl.uniformMatrix4fv(Vmatrix, false, view_matrix);
gl.uniformMatrix4fv(Mmatrix, false, mov_matrix);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, index_buffer);
gl.drawElements(gl.TRIANGLES, indices.length, gl.UNSIGNED_SHORT, 0);

window.requestAnimationFrame(animate);
}
animate(0);
</script>
</body>
</html>
```

If you run this example, it will produce the following output −