kinect physics tutorial for processing

Kinect Physics Tutorial for Processing

In this hands-on tutorial I will walk you through the steps needed to turn YOU into an interactive virtual polygon. Howawesome is that? To realise our creative end goal we will be using Processing and several of it’s contributed libraries. Obviously Iwill not be covering all the aspects or possibilities of these libraries. Rather this tutorial focuses on the specific steps needed toreach our proposed creative goal: letting you interact with the geometry on your screen in realtime. I will share three fullycommented code examples of increasing complexity that’ll give you a flying start. Of course from there, many moreopportunities for further exploration will arise.

Get kinectedYou will need a Kinect for this tutorial. While it is definitely possible to distill blobs from the image of a regular webcam, theKinect makes separating a person from the background really easy. There are a lot of fun things you can do with a Kinect, frompoint clouds to 3D skeletons to hand-tracking… but those have to wait for another time! ;-) In this tutorial we will be using theKinect as a very effective silhouette generator.

Installing Processing & librariesThere are over 100 libraries that extend the capabilities of Processing in areas like sound, video, computer vision, dataimport/export, math, geometry, physics and many more things. Processing 2.0 will feature a brand new system that facilitates aone-click method to install and update libraries. However for now, installation of libraries is still done manually. In most casesthis is fairly straightforward though. For detailed instruction on how to install contributed libraries, check this page. Below isthe list of all the libraries we will be using in this tutorial. Click on the names to go to the respective download locations. Eachcode example also indicates which libraries are required to run it. The easiest way to check if a library has been succesfullyinstalled, is to go to Sketch > Import Library and see if the library shows up on the list of contributed libraries. Make sure torestart the PDE after installing a library, because this list is only refreshed at startup. If somehow problems persist, please usethe Processing forum for support. Beyond this point I will be assuming necessary libraries have been installed.

- Processing 2.0b3 or 1.5.1 (examples tested & working with both)- SimpleOpenNI: A simple OpenNI wrapper for processing- v3ga blob detection library- Toxiclibs 020 (examples tested & working with 021 as well)

http://wiki.processing.org/w/How_to_Install_a_Contributed_Library

http://forum.processing.org/

http://processing.org/download/

http://code.google.com/p/simple-openni/

http://www.v3ga.net/processing/BlobDetection/index-page-download.html

http://hg.postspectacular.com/toxiclibs/downloads/

- PBox2D: A simple JBox2D wrapper library

Example 1: Kinect Silhouette (libs: SimpleOpenNI)Let’s start with a very basic example that only requires the SimpleOpenNI library, which might be the most problematic toinstall given the external depencies. I can recommend following the provided installation instruction closely. This is a very shortand very basic code example to make sure the Kinect and the SimpleOpenNI library are both installed and working correctly. Ifeverything works as intended, when running the first code example you should see a colored silhouette of yourself as you standin front of the Kinect camera (as shown above).

// Kinect Basic Example by Amnon Owed (15/09/12)

// import library

import SimpleOpenNI.*;

// declare SimpleOpenNI object

SimpleOpenNI context;

// PImage to hold incoming imagery

PImage cam;

void setup() {

// same as Kinect dimensions

size(640, 480);

// initialize SimpleOpenNI object

context = new SimpleOpenNI(this);

if (!context.enableScene()) {

// if context.enableScene() returns false

// then the Kinect is not working correctly

// make sure the green light is blinking

println("Kinect not connected!");

exit();

} else {

// mirror the image to be more intuitive

context.setMirror(true);

}

https://github.com/shiffman/PBox2D

http://www.creativeapplications.net/wp-content/uploads/2012/09/AmnonOwed-KinectPhysics-01.png


http://code.google.com/p/simple-openni/wiki/Installation

}

void draw() {

// update the SimpleOpenNI object

context.update();

// put the image into a PImage

cam = context.sceneImage().get();

// display the image

image(cam, 0, 0);

}

Example 2: Kinect Flow (libs: SimpleOpenNI, v3ga)This second example takes things a little further. To turn a colored silhouette into a polygon, we need to first find it’s outercontour points and second find the correct order in which they form a polygon. To find the contour points of shapes, we can useblob detection. I’ve looked at several blob detection libraries and found v3ga to work quite well. First, it’s fast, which is



important because you want things to run in real-time. Second, it returns an array of ordered points. While not polygon-worthyyet, it’s an important step towards a correctly formed polygon. I’ve compressed all the relevant code into the createPolygon()method of the PolygonBlob class. I’ve found the code to work quite well in turning a blob into points into a correct polygon. Butof course, there may be room for improvement. Note that both the second and third example have been written for one personin front of a Kinect, but quick tests show that the code holds up reasonably well (although not perfect) for multiple persons.

There are many things you could do (besides 2d physics, we’ll get to that in a minute) once you have turned yourself into aquality polygon. I added a few experiments of mine at the end of the video. Some of the things you see there are triangulatingthe shape, voronoi-ifying the screen and using myself as a mask between two full HD videos (the originals can be found on myvimeo account). These preliminary experiments are just the tiny tip of the iceberg. There are so many things you could do.Which makes it all the more important that you think about what you want to create and which visual style you are after. In thiscode example the polygon shape is used to control the boundaries of a noise-based flow of particles. The code is simplified asmuch as possible and fully commented, so feel free to run and read the code to see what it does exactly. You will need the mainsketch and the two classes.

Main Sketch

// Kinect Flow Example by Amnon Owed (15/09/12)

// import libraries

import processing.opengl.*; // opengl

import SimpleOpenNI.*; // kinect

import blobDetection.*; // blobs

// this is a regular java import so we can use and extend the polygon class (see PolygonBlob)

import java.awt.Polygon;



// declare BlobDetection object

BlobDetection theBlobDetection;

// declare custom PolygonBlob object (see class for more info)

PolygonBlob poly = new PolygonBlob();

// PImage to hold incoming imagery and smaller one for blob detection

PImage cam, blobs;

// the kinect's dimensions to be used later on for calculations

int kinectWidth = 640;

int kinectHeight = 480;

// to center and rescale from 640x480 to higher custom resolutions

float reScale;

// background color

color bgColor;

// three color palettes (artifact from me storing many interesting color palettes as strings

in an external data file ;-)

http://vimeo.com/amnon/videos

String[] palettes = {

"-1117720,-13683658,-8410437,-9998215,-1849945,-5517090,-4250587,-14178341,-5804972,-3498634",

"-67879,-9633503,-8858441,-144382,-4996094,-16604779,-588031",

"-16711663,-13888933,-9029017,-5213092,-1787063,-11375744,-2167516,-15713402,-5389468,-2064585"

};

// an array called flow of 2250 Particle objects (see Particle class)

Particle[] flow = new Particle[2250];

// global variables to influence the movement of all particles

float globalX, globalY;

void setup() {

// it's possible to customize this, for example 1920x1080

size(1280, 720, OPENGL);








exit();

} else {



// calculate the reScale value

// currently it's rescaled to fill the complete width (cuts of top-bottom)

// it's also possible to fill the complete height (leaves empty sides)

reScale = (float) width / kinectWidth;

// create a smaller blob image for speed and efficiency

blobs = createImage(kinectWidth/3, kinectHeight/3, RGB);

// initialize blob detection object to the blob image dimensions

theBlobDetection = new BlobDetection(blobs.width, blobs.height);

theBlobDetection.setThreshold(0.2);

setupFlowfield();

}

}

void draw() {

// fading background

noStroke();

fill(bgColor, 65);

rect(0, 0, width, height);


context.update();



// copy the image into the smaller blob image

blobs.copy(cam, 0, 0, cam.width, cam.height, 0, 0, blobs.width, blobs.height);

// blur the blob image

blobs.filter(BLUR);

// detect the blobs

theBlobDetection.computeBlobs(blobs.pixels);

// clear the polygon (original functionality)

poly.reset();

// create the polygon from the blobs (custom functionality, see class)

poly.createPolygon();

drawFlowfield();

}

void setupFlowfield() {

// set stroke weight (for particle display) to 2.5

strokeWeight(2.5);

// initialize all particles in the flow

for(int i=0; i flow[i] = new Particle(i/10000.0);

}

// set all colors randomly now

setRandomColors(1);

}

void drawFlowfield() {

// center and reScale from Kinect to custom dimensions

translate(0, (height-kinectHeight*reScale)/2);

scale(reScale);

// set global variables that influence the particle flow's movement

globalX = noise(frameCount * 0.01) * width/2 + width/4;

globalY = noise(frameCount * 0.005 + 5) * height;

// update and display all particles in the flow

for (Particle p : flow) {

p.updateAndDisplay();

}

// set the colors randomly every 240th frame

setRandomColors(240);

}

// sets the colors every nth frame

void setRandomColors(int nthFrame) {

if (frameCount % nthFrame == 0) {

// turn a palette into a series of strings

String[] paletteStrings = split(palettes[int(random(palettes.length))], ",");

// turn strings into colors

color[] colorPalette = new color[paletteStrings.length];

for (int i=0; i colorPalette[i] = int(paletteStrings[i]);

}

// set background color to first color from palette

bgColor = colorPalette[0];

// set all particle colors randomly to color from palette (excluding first aka background

color)

for (int i=0; i flow[i].col = colorPalette[int(random(1, colorPalette.length))];

}

}

}

Particle class

// a basic noise-based moving particle

class Particle {

// unique id, (previous) position, speed

float id, x, y, xp, yp, s, d;

color col; // color

Particle(float id) {

this.id = id;

s = random(2, 6); // speed

}

void updateAndDisplay() {

// let it flow, end with a new x and y position

id += 0.01;

d = (noise(id, x/globalY, y/globalY)-0.5)*globalX;

x += cos(radians(d))*s;

y += sin(radians(d))*s;

// constrain to boundaries

if (x<-10) x=xp=kinectWidth+10;

if (x>kinectWidth+10) x=xp=-10;

if (y<-10) y=yp=kinectHeight+10;

if (y>kinectHeight+10) y=yp=-10;

// if there is a polygon (more than 0 points)

if (poly.npoints > 0) {

// if this particle is outside the polygon

if (!poly.contains(x, y)) {

// while it is outside the polygon

while(!poly.contains(x, y)) {

// randomize x and y

x = random(kinectWidth);

y = random(kinectHeight);

}

// set previous x and y, to this x and y

xp=x;

yp=y;

}

}

// individual particle color

stroke(col);

// line from previous to current position

line(xp, yp, x, y);

// set previous to current position

xp=x;

yp=y;

}

}

PolygonBlob class

// an extended polygon class with my own customized createPolygon() method (feel free to

improve!)

class PolygonBlob extends Polygon {

// took me some time to make this method fully self-sufficient

// now it works quite well in creating a correct polygon from a person's blob

// of course many thanks to v3ga, because the library already does a lot of the work

void createPolygon() {

// an arrayList... of arrayLists... of PVectors

// the arrayLists of PVectors are basically the person's contours (almost but not completely

in a polygon-correct order)

ArrayList> contours = new ArrayList>();

// helpful variables to keep track of the selected contour and point (start/end point)

int selectedContour = 0;

int selectedPoint = 0;

// create contours from blobs

// go over all the detected blobs

for (int n=0 ; n Blob b = theBlobDetection.getBlob(n);

// for each substantial blob...

if (b != null && b.getEdgeNb() > 100) {

// create a new contour arrayList of PVectors

ArrayList contour = new ArrayList();

// go over all the edges in the blob

for (int m=0; m // get the edgeVertices of the edge

EdgeVertex eA = b.getEdgeVertexA(m);

EdgeVertex eB = b.getEdgeVertexB(m);

// if both ain't null...

if (eA != null && eB != null) {

// get next and previous edgeVertexA

EdgeVertex fn = b.getEdgeVertexA((m+1) % b.getEdgeNb());

EdgeVertex fp = b.getEdgeVertexA((max(0, m-1)));

// calculate distance between vertexA and next and previous edgeVertexA respectively

// positions are multiplied by kinect dimensions because the blob library returns normalized

values

float dn = dist(eA.x*kinectWidth, eA.y*kinectHeight, fn.x*kinectWidth, fn.y*kinectHeight);

float dp = dist(eA.x*kinectWidth, eA.y*kinectHeight, fp.x*kinectWidth, fp.y*kinectHeight);

// if either distance is bigger than 15

if (dn > 15 || dp > 15) {

// if the current contour size is bigger than zero

if (contour.size() > 0) {

// add final point

contour.add(new PVector(eB.x*kinectWidth, eB.y*kinectHeight));

// add current contour to the arrayList

contours.add(contour);

// start a new contour arrayList

contour = new ArrayList();

// if the current contour size is 0 (aka it's a new list)

} else {

// add the point to the list

contour.add(new PVector(eA.x*kinectWidth, eA.y*kinectHeight));

}

// if both distance are smaller than 15 (aka the points are close)

} else {

// add the point to the list


}

}

}

}

}

// at this point in the code we have a list of contours (aka an arrayList of arrayLists of

PVectors)

// now we need to sort those contours into a correct polygon. To do this we need two things:

// 1. The correct order of contours

// 2. The correct direction of each contour

// as long as there are contours left...

while (contours.size() > 0) {

// find next contour

float distance = 999999999;

// if there are already points in the polygon

if (npoints > 0) {

// use the polygon's last point as a starting point

PVector lastPoint = new PVector(xpoints[npoints-1], ypoints[npoints-1]);

// go over all contours

for (int i=0; i ArrayList c = contours.get(i);

// get the contour's first point

PVector fp = c.get(0);

// get the contour's last point

PVector lp = c.get(c.size()-1);

// if the distance between the current contour's first point and the polygon's last point is

smaller than distance

if (fp.dist(lastPoint) < distance) {

// set distance to this distance

distance = fp.dist(lastPoint);

// set this as the selected contour

selectedContour = i;

// set selectedPoint to 0 (which signals first point)

selectedPoint = 0;

}

// if the distance between the current contour's last point and the polygon's last point is

smaller than distance

if (lp.dist(lastPoint) < distance) {

// set distance to this distance

distance = lp.dist(lastPoint);



// set selectedPoint to 1 (which signals last point)

selectedPoint = 1;

}

}

// if the polygon is still empty

} else {

// use a starting point in the lower-right

PVector closestPoint = new PVector(width, height);

// go over all contours


// get the contour's first point


// get the contour's last point


// if the first point is in the lowest 5 pixels of the (kinect) screen and more to the left

than the current closestPoint

if (fp.y > kinectHeight-5 && fp.x < closestPoint.x) {

// set closestPoint to first point

closestPoint = fp;



// set selectedPoint to 0 (which signals first point)

selectedPoint = 0;

}

// if the last point is in the lowest 5 pixels of the (kinect) screen and more to the left

than the current closestPoint

if (lp.y > kinectHeight-5 && lp.x < closestPoint.y) {

// set closestPoint to last point

closestPoint = lp;



// set selectedPoint to 1 (which signals last point)

selectedPoint = 1;

}

}

}

// add contour to polygon

ArrayList contour = contours.get(selectedContour);

// if selectedPoint is bigger than zero (aka last point) then reverse the arrayList of points

if (selectedPoint > 0) { Collections.reverse(contour); }

// add all the points in the contour to the polygon

for (PVector p : contour) {

addPoint(int(p.x), int(p.y));

}

// remove this contour from the list of contours

contours.remove(selectedContour);

// the while loop above makes all of this code loop until the number of contours is zero

// at that time all the points in all the contours have been added to the polygon... in the

correct order (hopefully)

}

}

}

Example 3: Kinect Physics (libs: SimpleOpenNI, v3ga, Toxiclibs, PBox2D)All right, now for the pièce de résistance of this tutorial. Realtime interaction with onscreen geometry. To do this we will beusing Daniel Shiffman’s PBox2D library, which is a Processing wrapper library for the Jbox2D library, which is a port of the C++Box2D library. Gotta love open source! ;-) This code example builds on the work done in the previous example. ThecreatePolygon() method is nearly identical. The PolygonBlob class is now extending Toxiclibs’ Polygon2D class. The maindifference is that code has been added to create and destroy box2d bodies (which will allow 2D physics).

What this code does in words: create a silhouette from a person, turn this silhouette into points, turn these points into apolygon, turn this polygon into a deflective shape in the box2d physics world. Because all the other geometry is transferred intothe same physics world, interaction between person and onscreen geometry becomes possible. Of course there are somechallenges, in addition to the mentioned steps. For example, while the original virtual geometry is pretty solid, the person’scontours are ever changing, especially when the person is moving around a lot. This will result in errors in the collisiondetection (aka geometry will end up inside a person). That is also one of the reasons to use Toxiclibs, because it has methodsthat help us check if a point is inside a polygon and if so, to find the closest point on the outer contours and move the geometryto that point. It’s a bit of a quick workaround, but it works quite well. When moving slowly or not at all, this workaround isn’tused anyway, since the regular collision detection will be effective under those conditions. However if a person is moving aroundquickly and you don’t want geometry inside the person nor delete it, then this shortcut is useful. Although at times it may causesome non-physically correct overlapping of shapes near the contours. All in all, you can see in the video that using thiscombination of techniques allows you to interact with the falling shapes on your screen. Again, to run the code you will need themain sketch and the two classes.

Main Sketch




https://github.com/shiffman/PBox2D

http://www.jbox2d.org/

http://box2d.org/

// Kinect Physics Example by Amnon Owed (15/09/12)

// import libraries

import processing.opengl.*; // opengl

import SimpleOpenNI.*; // kinect

import blobDetection.*; // blobs

import toxi.geom.*; // toxiclibs shapes and vectors

import toxi.processing.*; // toxiclibs display

import pbox2d.*; // shiffman's jbox2d helper library

import org.jbox2d.collision.shapes.*; // jbox2d

import org.jbox2d.common.*; // jbox2d

import org.jbox2d.dynamics.*; // jbox2d



// declare BlobDetection object

BlobDetection theBlobDetection;

// ToxiclibsSupport for displaying polygons

ToxiclibsSupport gfx;

// declare custom PolygonBlob object (see class for more info)

PolygonBlob poly;

// PImage to hold incoming imagery and smaller one for blob detection

PImage cam, blobs;

// the kinect's dimensions to be used later on for calculations

int kinectWidth = 640;

int kinectHeight = 480;

// to center and rescale from 640x480 to higher custom resolutions

float reScale;

// background and blob color

color bgColor, blobColor;

// three color palettes (artifact from me storing many interesting color palettes as strings

in an external data file ;-)

String[] palettes = {

"-1117720,-13683658,-8410437,-9998215,-1849945,-5517090,-4250587,-14178341,-5804972,-3498634",

"-67879,-9633503,-8858441,-144382,-4996094,-16604779,-588031",

"-1978728,-724510,-15131349,-13932461,-4741770,-9232823,-3195858,-8989771,-2850983,-10314372"

};

color[] colorPalette;

// the main PBox2D object in which all the physics-based stuff is happening

PBox2D box2d;

// list to hold all the custom shapes (circles, polygons)

ArrayList polygons = new ArrayList();

void setup() {

// it's possible to customize this, for example 1920x1080

size(1280, 720, OPENGL);








exit();

} else {



// calculate the reScale value

// currently it's rescaled to fill the complete width (cuts of top-bottom)

// it's also possible to fill the complete height (leaves empty sides)

reScale = (float) width / kinectWidth;

// create a smaller blob image for speed and efficiency

blobs = createImage(kinectWidth/3, kinectHeight/3, RGB);

// initialize blob detection object to the blob image dimensions

theBlobDetection = new BlobDetection(blobs.width, blobs.height);

theBlobDetection.setThreshold(0.2);

// initialize ToxiclibsSupport object

gfx = new ToxiclibsSupport(this);

// setup box2d, create world, set gravity

box2d = new PBox2D(this);

box2d.createWorld();

box2d.setGravity(0, -20);

// set random colors (background, blob)

setRandomColors(1);

}

}

void draw() {

background(bgColor);


context.update();



// copy the image into the smaller blob image

blobs.copy(cam, 0, 0, cam.width, cam.height, 0, 0, blobs.width, blobs.height);

// blur the blob image

blobs.filter(BLUR, 1);

// detect the blobs

theBlobDetection.computeBlobs(blobs.pixels);

// initialize a new polygon

poly = new PolygonBlob();

// create the polygon from the blobs (custom functionality, see class)

poly.createPolygon();

// create the box2d body from the polygon

poly.createBody();

// update and draw everything (see method)

updateAndDrawBox2D();

// destroy the person's body (important!)

poly.destroyBody();

// set the colors randomly every 240th frame

setRandomColors(240);

}

void updateAndDrawBox2D() {

// if frameRate is sufficient, add a polygon and a circle with a random radius

if (frameRate > 29) {

polygons.add(new CustomShape(kinectWidth/2, -50, -1));

polygons.add(new CustomShape(kinectWidth/2, -50, random(2.5, 20)));

}

// take one step in the box2d physics world

box2d.step();

// center and reScale from Kinect to custom dimensions

translate(0, (height-kinectHeight*reScale)/2);

scale(reScale);

// display the person's polygon

noStroke();

fill(blobColor);

gfx.polygon2D(poly);

// display all the shapes (circles, polygons)

// go backwards to allow removal of shapes

for (int i=polygons.size()-1; i>=0; i--) {

CustomShape cs = polygons.get(i);

// if the shape is off-screen remove it (see class for more info)

if (cs.done()) {

polygons.remove(i);

// otherwise update (keep shape outside person) and display (circle or polygon)

} else {

cs.update();

cs.display();

}

}

}

// sets the colors every nth frame

void setRandomColors(int nthFrame) {

if (frameCount % nthFrame == 0) {

// turn a palette into a series of strings

String[] paletteStrings = split(palettes[int(random(palettes.length))], ",");

// turn strings into colors

colorPalette = new color[paletteStrings.length];

for (int i=0; i colorPalette[i] = int(paletteStrings[i]);

}

// set background color to first color from palette

bgColor = colorPalette[0];

// set blob color to second color from palette

blobColor = colorPalette[1];

// set all shape colors randomly

for (CustomShape cs: polygons) { cs.col = getRandomColor(); }

}

}

// returns a random color from the palette (excluding first aka background color)

color getRandomColor() {

return colorPalette[int(random(1, colorPalette.length))];

}

CustomShape class

// usually one would probably make a generic Shape class and subclass different types (circle,

polygon), but that

// would mean at least 3 instead of 1 class, so for this tutorial it's a combi-class

CustomShape for all types of shapes

// to save some space and keep the code as concise as possible I took a few shortcuts to

prevent repeating the same code

class CustomShape {

// to hold the box2d body

Body body;

// to hold the Toxiclibs polygon shape

Polygon2D toxiPoly;

// custom color for each shape

color col;

// radius (also used to distinguish between circles and polygons in this combi-class

float r;

CustomShape(float x, float y, float r) {

this.r = r;

// create a body (polygon or circle based on the r)

makeBody(x, y);

// get a random color

col = getRandomColor();

}

void makeBody(float x, float y) {

// define a dynamic body positioned at xy in box2d world coordinates,

// create it and set the initial values for this box2d body's speed and angle

BodyDef bd = new BodyDef();

bd.type = BodyType.DYNAMIC;

bd.position.set(box2d.coordPixelsToWorld(new Vec2(x, y)));

body = box2d.createBody(bd);

body.setLinearVelocity(new Vec2(random(-8, 8), random(2, 8)));

body.setAngularVelocity(random(-5, 5));

// depending on the r this combi-code creates either a box2d polygon or a circle

if (r == -1) {

// box2d polygon shape

PolygonShape sd = new PolygonShape();

// toxiclibs polygon creator (triangle, square, etc)

toxiPoly = new Circle(random(5, 20)).toPolygon2D(int(random(3, 6)));

// place the toxiclibs polygon's vertices into a vec2d array

Vec2[] vertices = new Vec2[toxiPoly.getNumPoints()];

for (int i=0; i Vec2D v = toxiPoly.vertices.get(i);

vertices[i] = box2d.vectorPixelsToWorld(new Vec2(v.x, v.y));

}

// put the vertices into the box2d shape

sd.set(vertices, vertices.length);

// create the fixture from the shape (deflect things based on the actual polygon shape)

body.createFixture(sd, 1);

} else {

// box2d circle shape of radius r

CircleShape cs = new CircleShape();

cs.m_radius = box2d.scalarPixelsToWorld(r);

// tweak the circle's fixture def a little bit

FixtureDef fd = new FixtureDef();

fd.shape = cs;

fd.density = 1;

fd.friction = 0.01;

fd.restitution = 0.3;

// create the fixture from the shape's fixture def (deflect things based on the actual circle

shape)

body.createFixture(fd);

}

}

// method to loosely move shapes outside a person's polygon

// (alternatively you could allow or remove shapes inside a person's polygon)

void update() {

// get the screen position from this shape (circle of polygon)

Vec2 posScreen = box2d.getBodyPixelCoord(body);

// turn it into a toxiclibs Vec2D

Vec2D toxiScreen = new Vec2D(posScreen.x, posScreen.y);

// check if this shape's position is inside the person's polygon

boolean inBody = poly.containsPoint(toxiScreen);

// if a shape is inside the person

if (inBody) {

// find the closest point on the polygon to the current position

Vec2D closestPoint = toxiScreen;

float closestDistance = 9999999;

for (Vec2D v : poly.vertices) {

float distance = v.distanceTo(toxiScreen);

if (distance < closestDistance) {

closestDistance = distance;

closestPoint = v;

}

}

// create a box2d position from the closest point on the polygon

Vec2 contourPos = new Vec2(closestPoint.x, closestPoint.y);

Vec2 posWorld = box2d.coordPixelsToWorld(contourPos);

float angle = body.getAngle();

// set the box2d body's position of this CustomShape to the new position (use the current

angle)

body.setTransform(posWorld, angle);

}

}

// display the customShape

void display() {

// get the pixel coordinates of the body

Vec2 pos = box2d.getBodyPixelCoord(body);

pushMatrix();

// translate to the position

translate(pos.x, pos.y);

noStroke();

// use the shape's custom color

fill(col);

// depending on the r this combi-code displays either a polygon or a circle

if (r == -1) {

// rotate by the body's angle

float a = body.getAngle();

rotate(-a); // minus!

gfx.polygon2D(toxiPoly);

} else {

ellipse(0, 0, r*2, r*2);

}

popMatrix();

}

// if the shape moves off-screen, destroy the box2d body (important!)

// and return true (which will lead to the removal of this CustomShape object)

boolean done() {

Vec2 posScreen = box2d.getBodyPixelCoord(body);

boolean offscreen = posScreen.y > height;

if (offscreen) {

box2d.destroyBody(body);

return true;

}

return false;

}

}

PolygonBlob class

// an extended polygon class quite similar to the earlier PolygonBlob class (but extending

Toxiclibs' Polygon2D class instead)

// The main difference is that this one is able to create (and destroy) a box2d body from it's

own shape

class PolygonBlob extends Polygon2D {

// to hold the box2d body

Body body;

// the createPolygon() method is nearly identical to the one presented earlier

// see the Kinect Flow Example for a more detailed description of this method (again, feel

free to improve it)

void createPolygon() {

ArrayList> contours = new ArrayList>();

int selectedContour = 0;

int selectedPoint = 0;

// create contours from blobs

for (int n=0 ; n Blob b = theBlobDetection.getBlob(n);

if (b != null && b.getEdgeNb() > 100) {

ArrayList contour = new ArrayList();

for (int m=0; m EdgeVertex eA = b.getEdgeVertexA(m);

EdgeVertex eB = b.getEdgeVertexB(m);

if (eA != null && eB != null) {

EdgeVertex fn = b.getEdgeVertexA((m+1) % b.getEdgeNb());

EdgeVertex fp = b.getEdgeVertexA((max(0, m-1)));

float dn = dist(eA.x*kinectWidth, eA.y*kinectHeight, fn.x*kinectWidth, fn.y*kinectHeight);

float dp = dist(eA.x*kinectWidth, eA.y*kinectHeight, fp.x*kinectWidth, fp.y*kinectHeight);

if (dn > 15 || dp > 15) {

if (contour.size() > 0) {

contour.add(new PVector(eB.x*kinectWidth, eB.y*kinectHeight));

contours.add(contour);

contour = new ArrayList();

} else {


}

} else {


}

}

}

}

}

while (contours.size() > 0) {

// find next contour

float distance = 999999999;

if (getNumPoints() > 0) {

Vec2D vecLastPoint = vertices.get(getNumPoints()-1);

PVector lastPoint = new PVector(vecLastPoint.x, vecLastPoint.y);




if (fp.dist(lastPoint) < distance) {

distance = fp.dist(lastPoint);


selectedPoint = 0;

}

if (lp.dist(lastPoint) < distance) {

distance = lp.dist(lastPoint);


selectedPoint = 1;

}

}

} else {

PVector closestPoint = new PVector(width, height);




if (fp.y > kinectHeight-5 && fp.x < closestPoint.x) {

closestPoint = fp;


selectedPoint = 0;

}

if (lp.y > kinectHeight-5 && lp.x < closestPoint.y) {

closestPoint = lp;


selectedPoint = 1;

}

}

}

// add contour to polygon

ArrayList contour = contours.get(selectedContour);

if (selectedPoint > 0) { Collections.reverse(contour); }

for (PVector p : contour) {

add(new Vec2D(p.x, p.y));

}

contours.remove(selectedContour);

}

}

// creates a shape-deflecting physics chain in the box2d world from this polygon

void createBody() {

// for stability the body is always created (and later destroyed)

BodyDef bd = new BodyDef();

body = box2d.createBody(bd);

// if there are more than 0 points (aka a person on screen)...

if (getNumPoints() > 0) {

// create a vec2d array of vertices in box2d world coordinates from this polygon

Vec2[] verts = new Vec2[getNumPoints()];

for (int i=0; i Vec2D v = vertices.get(i);

verts[i] = box2d.coordPixelsToWorld(v.x, v.y);

}

// create a chain from the array of vertices

ChainShape chain = new ChainShape();

chain.createChain(verts, verts.length);

// create fixture in body from the chain (this makes it actually deflect other shapes)

body.createFixture(chain, 1);

}

}

// destroy the box2d body (important!)

void destroyBody() {

box2d.destroyBody(body);

}

}

This is a hands-on tutorial so feel free to run the code, tweak it, read the comments to learn what it does exactly and perhapsmake some other cool stuff with it. Either physics-based or just using the polygon itself to create some interesting visualexperiments as I did at the end of my video. Good luck and happy coding! :D

kinect physics tutorial for processing

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