Starling-Simulation

Flocking simulation of starling murmuration using web graphics library (webGL) and openGL shader language in javascript.

Checkout the demo here

Flocking behavior

Flocking is a the motion of birds together and flocking behavior is a type of behavior exhibited when a group of birds, called a flock, are in flight.

Starling mumuration

Starlings are small to medium-sized passerine birds in the family Sturnidae. It is known as murmuration, when a huge flocks of starling in migration form shape-shifting flight patterns. A good example is shown below -

About the program

We have used GLSL(OpenGL Shading Language) for bird's position, bird's velocity, bird's geometry and the vertices of bird's geomtery. A shading language is a graphics programming language adapted to programming shader effects. There is a hardware-based parallelization when computing in GPU, which makes the GPU particularly fit to process & render graphics.

An Example For Fragment-Shader To Develop an Understanding in Shaders

<script id="BoidPositionFragmentShader" type="x-shader/x-fragment"></script>

• type="x-shader/x-fragment" has no actual use and isn't an official terminology. It is an informal way as shown in many tutorials to use this to inform the code reader that it is a fragment shader program. Browser ignores such tag, which are undefined. We will avoid it to reduce confusion, and instead use comments to increase readability.

uniform float clock;
uniform float del_change;
void main()	{
	vec2 textcoordi = gl_FragCoord.xy / resolution.xy;
	vec4 temp_position = texture2D( PositionTexture, textcoordi );
	vec3 position = temp_position.xyz;
	vec3 velocity = texture2D( VeloctiyTexture, textcoordi ).xyz;

	float wcoordinate = temp_position.w;

	wcoordinate = mod( ( wcoordinate + del_change*2.0 +
		length(velocity.xz) * del_change * 3. +
		max(velocity.y, 0.0) * del_change * 6. ), 50.0 );

	gl_FragColor = vec4( position + velocity * del_change * 15. , wcoordinate );}

• gl_FragCoord, resolution and texture2D are predefined global variables for fragment coordinates, resolution of window (opened) and the texture lookup function (to get color information about texture), for more.
• uniform is a qualifier of shader, which can be used in both vertex and fragment shaders. Its read-only for shaders. There are other two qualifiers, namely attribute and varying, for more.
• vec2, vec3, vec4 are types in shader for respectively two, three and four coordinate vectors.

Structures in Simulation

Boid Geometry Implementation

• The boid implemented here is a combination of 3 triangles, one acting as a body (whose one angle is very small, i.e., making it look like actual body, additional features at end), and the other 2 acting as wings, which we will be using while flapping.

• vertex_append function takes a list of argument and then appends it in the BufferAttribute of Float32Array.

function vertex_append() {
	for (var i = 0; i < arguments.length; i++) {
		vertices.array[v++] = arguments[i];
	}
}

• Here is how we define the boid's body. The calls of vertex_append function are in order as body, left wing and right wing.

for (var i = 0; i < birds; i++ ) {
	vertex_append(
		0, -0, -6,
		0, 1, -15,
		0, 0, 8); //body call
	vertex_append(
		0, 0, -4,
		-6, 0, 0,
		0, 0, 4); //left wing call
	vertex_append(
		0, 0, 4,
		6, 0, 0,
		0, 0, -4); //right wing call
}

• Here is a part of THREE.BirdGeometry for initiating the function call, and showing its usage for some more variables and attributes.

THREE.BirdGeometry = function () {

THREE.BufferGeometry.call(this);

var vertices = new THREE.BufferAttribute( new Float32Array( points * 3 ), 3 );

this.addAttribute( 'position', vertices );

• THREE.BufferAttribute stores data for an attribute associated with a BufferGeometry, for more.

• Function to initiate birds is named as initBirds(), it renders vertex and fragment, and shader material and then creates an object of THREE.Mesh as -

var birdMesh = new THREE.Mesh( geometry, material );

Creating a Rotating 3D Frame with Orbital Controls

• This is a brief version of the code, with comments to increase understandibility, used to create 3D frame with orbital controls.

• guiControls() is an important function for 3D frame setting, it includes the initial setting of rotation, light, intensity, angle and a lot of shadow variables.

<!-- create a perspective camera -->
camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 1, 3000 );

<!-- create a scene on available canvas with some background(optional)-->
scene = new THREE.Scene();
scene.background = new THREE.Color( 0x87ceeb);

<!-- rendering the crafted scenes and displaying on canvas -->
renderer = new THREE.WebGLRenderer({});

<!-- setting up the object for orbit control -->
controls = new THREE.OrbitControls( camera, renderer.domElement );
controls.addEventListener( 'change', render );

<!-- initiating the camera position -->
camera.position.x = 500;
camera.lookAt(scene.position);

<!-- Initiating the GUI controls for rotation, light, intensity, angle, shadow and exponent -->
guiControls = new function(){
}

<!-- Creating object for spotlight and adding to scence-->
spotLight = new THREE.SpotLight(0xffffff);
scene.add(spotLight);

Algorithm of Separation, Cohesion, and Alignment.

Separation

• distSquared is the square of distance between the current position of canvas texture rendered ( at that time ) and each point on resolution window ( for boids ).
• We shall add a velocity vector away from the velocity.now, with change proportional to the rendering time ( del_change ) and the amount any boid is closer to some other boid on the old texture.
• zoneRadiusSquared is a design choice, we set its value to 35.0 ( a hit and trial technique ).

percent = distSquared / zoneRadiusSquared;
if ( percent < separationThresh ) { 
	f = (separationThresh / percent - 1.0) * del_change;
	velocity -= normalize(dir) * f;
}

Alignment

• We deal with alignment by creating a reference direction and then adjusting it using trignometric function with change proportional to the rendering time.

else if{
float adjustedPercent = ( percent - separationThresh ) / (alignmentThresh - separationThresh);
birdVelocity = texture2D( VeloctiyTexture, ref ).xyz;
f = ( 0.5 - cos( adjustedPercent * PI_2 ) * 0.5 + 0.5 ) * del_change;
velocity += normalize(birdVelocity) * f;
}

Cohesion

• Similar to aligment, we normalise the change and add in velocity vector.

else {
float adjustedPercent = ( percent - alignmentThresh ) / (1.0 - alignmentThresh);
f = ( 0.5 - ( cos( adjustedPercent * PI_2 ) * -0.5 + 0.5 ) ) * del_change;
velocity += normalize(dir) * f;
}

Importance of requestAnimationFrame()

• It allows you to execute code on the next available screen repaint, taking the guess work out of getting in sync with the user's browser and hardware readiness to make changes to the screen.

• Code running inside background tabs in your browser are either paused or slowed down significantly (to 2 frames per second or less) automatically to further save user system resources.

Folder-Terminology

• js-libs: Static javascript library files from three.js and some from webGL-js.
• js-func: Functions in javascript used in the program.
• buffer: Contains the buffer vertex shader program
• shader: Shader programs are the ones that are compiled in graphical processing unit.
• laTex: Mathematical modeling in LaTex.
• css: Used CSS stylesheets in the markup code.
• img: Images that shall be used in the front-end code.

Running Locally

• Just run the index.html file, having the embedded javascript files in it.

• Run on local server

  • install npm
  • install http-server (or similar package)
  • run the http-server from the folder where the script is located
  • Go the local server claimed by http-server

• For linux users the terminal commands are as follows-

   sudo apt-get install -y nodejs
   sudo apt-get install npm
   sudo npm install http-server -g
   http-server -c-1
  
  

Points of Improvement

• The 3D sky can be made much better with clouds (as a shader program). It is looking dull with a single color, I found this repo of clouds, give it a view.

• Bird's shapes are very basic, it can be made more realistic if Blender is used to export 3D bird-object to JSON, which then can be used as a material in Three.BirdGeometry.

• Actual predator can be introduced, for simulation of falcon attack in a starling murmuration. I tried making it with mouse pointer, but due to the 3D camera textures, it is unintuitive to guess the proper algorithm, although mine works when birds are close to moving mouse but I am uncertain about its usage.

Thanks to

• Thanks for the three.js Javascript 3D library and the examples.

• This project by OwenMcNaughton for camera, scene, and 3D-viewpoint support.

Informational Documents

• Mathematical model of flocking behavior
• Boids-algorithm - Pseudocode
• Research Paper - Craig Reynold's simulation

A Useful Container

• Overleaf LaTex editor - mathematical modeling, click here
• A video of falcon attack on flock of starling.

Contributing

Found a bug or have a suggestion? Feel free to create an issue or make a pull request!

Know the Developer

• Ask him out for a cup of coffee (preferably female gender), find his blog here.