ODE Tutorial 5: Hello a Simulation World !

This time,  I show a super simple sample program which uses ODE (Open Dynamics Engine) .  In many programming books, printing “Hellow World” is the first sample program.  For physics simulation programming books, I think a simulation of free fall is the most simple  example.

A screen shot of  free fall

[code]
// hello.cpp by Kosei Demura

#include //ODE the header file
#include //drawing header file

#ifdef dDOUBLE
#define dsDrawSphere dsDrawSphereD
#endif

static dWorldID world; // For kinetics calculation
dBodyID ball; // Ball
const dReal radius = 0.2, mass = 1.0; // Radius of ball [m], weight of ball [kg]

// Simulation loop is called and executed each simlation loop.
// dynamics is calculated by dWorldStep().
static void simLoop (int pause)
{
const dReal *pos, *R;

// If you want more accuracy, you should set step size more small
// in this case, step size is 0.01 [s]
dWorldStep (world,0.01);

dsSetColor (1.0,0.0,0.0); // Setting of red (R, G, B)
pos = dBodyGetPosition (ball); // Getting the position of the ball
R = dBodyGetRotation (ball); // Getting the orientation of the ball
dsDrawSphere (pos, R, radius); // Drawing the sphere as the ball
}

void START ()
{ //setting of camera
static float xyz [ 3 ] = {0.0, -3.0,1.0}; // Position of a view point [m]
static float hpr [ 3 ] = {90.0,0.0,0.0}; // Direction of a gaze [°]
dsSetViewpoint (xyz, hpr); // Setting of the view point and the gaze
}

// Please read from main functional here.
int main (int argc, char **argv)
{
dReal x0 = 0.0, y0 = 0.0, dReal z0 = 1.0; // Initial position of a ball
dMass m1;

dsFunctions fn; // Class for draw staff
fn.version = DS_VERSION; // Version of draw staff
fn.start = &start; // Preprocessing function of simulation
fn.step = &simLoop; // A function is called with each step of simulation
fn.command = NULL; // A function for a key board
// In the case of no function, appointing the NULL pointer
fn.stop = NULL; //
fn.path_to_textures = “../.. /drawstuff/textures”; // Path to the texture files

// Creation of the world for dynamics calculation
world = dWorldCreate ();
dWorldSetGravity (world,0,0, -0.001); // Acceleration of free fall [m/s^2]

// Creation of a ball
body = dBodyCreate (world); // Creation of a ball
dMassSetZero (&m1); // Initialization of a weight parameter m1
dMassSetSphereTotal (&m1, mass, radius); // Calculating m1 of the ball
dBodySetMass (ball, &m1); // Setting m1 to the ball
dBodySetPosition (ball, x0, y0, z0); // Setting the position of the ball

// Simulation loop
dsSimulationLoop (argc, argv,352,288, &fn); // Window Size 352 x 288

// Destruction of the world
dWorldDestroy (world);

return 0;
}
[/code]

This is the program of free fall of the red ball.  “world” is the software container where kinetics is calculated. Being for the first time to experient the world of physics, let’s call this sample program as “Hello World”.

The function which starts with the small letter ‘d’  is the API (Application Program Interface), and the function which starts with ‘ds’ is the API of  drawstuff. Drawstuff is the library for ODE, to test sample programs.

Now, let’s downloadthis file, and excute the program as follows !

Execution method
1. Sample1.tgz download under /home/ user name /src/ode/ode
2. From now on please execute the command below with the terminal. The $ is prompt.
$ cd /home/ user name /src/ode/ode
$ tar xvzf sample1.tgz
$ cd  sample1
$ make
3. Execution
$. /sample1

The red ball is falling slowly, but passing through the ground, and vanished.
To tell the truth it meaning that collision detection function is not installed in the program above.

The next time, collision detection function is added in this program.

(last modified 2008-1-13)