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/*************************************************************************
* *
* Open Dynamics Engine, Copyright (C) 2001,2002 Russell L. Smith. *
* All rights reserved. Email: russ@q12.org Web: www.q12.org *
* *
* This library is free software; you can redistribute it and/or *
* modify it under the terms of EITHER: *
* (1) The GNU Lesser General Public License as published by the Free *
* Software Foundation; either version 2.1 of the License, or (at *
* your option) any later version. The text of the GNU Lesser *
* General Public License is included with this library in the *
* file LICENSE.TXT. *
* (2) The BSD-style license that is included with this library in *
* the file LICENSE-BSD.TXT. *
* *
* This library is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files *
* LICENSE.TXT and LICENSE-BSD.TXT for more details. *
* *
*************************************************************************/
/*
test the Coulomb friction approximation.
a 10x10 array of boxes is made, each of which rests on the ground.
a horizantal force is applied to each box to try and get it to slide.
box[i][j] has a mass (i+1)*MASS and a force (j+1)*FORCE. by the Coloumb
friction model, the box should only slide if the force is greater than MU
times the contact normal force, i.e.
f > MU * body_mass * GRAVITY
(j+1)*FORCE > MU * (i+1)*MASS * GRAVITY
(j+1) > (i+1) * (MU*MASS*GRAVITY/FORCE)
(j+1) > (i+1) * k
this should be independent of the number of contact points, as N contact
points will each have 1/N'th the normal force but the pushing force will
have to overcome N contacts. the constants are chosen so that k=1.
thus you should see a triangle made of half the bodies in the array start to
slide.
*/
#include <ode/ode.h>
#include <drawstuff/drawstuff.h>
#include "texturepath.h"
#ifdef _MSC_VER
#pragma warning(disable:4244 4305) // for VC++, no precision loss complaints
#endif
// select correct drawing functions
#ifdef dDOUBLE
#define dsDrawBox dsDrawBoxD
#define dsDrawSphere dsDrawSphereD
#define dsDrawCylinder dsDrawCylinderD
#define dsDrawCapsule dsDrawCapsuleD
#endif
// some constants
#define LENGTH 0.2 // box length & width
#define HEIGHT 0.05 // box height
#define MASS 0.2 // mass of box[i][j] = (i+1) * MASS
#define FORCE 0.05 // force applied to box[i][j] = (j+1) * FORCE
#define MU 0.5 // the global mu to use
#define GRAVITY 0.5 // the global gravity to use
#define N1 10 // number of different forces to try
#define N2 10 // number of different masses to try
// dynamics and collision objects
static dWorldID world;
static dSpaceID space;
static dBodyID body[N1][N2];
static dJointGroupID contactgroup;
static dGeomID ground;
static dGeomID box[N1][N2];
// this is called by dSpaceCollide when two objects in space are
// potentially colliding.
static void nearCallback (void *, dGeomID o1, dGeomID o2)
{
int i;
// only collide things with the ground
int g1 = (o1 == ground);
int g2 = (o2 == ground);
if (!(g1 ^ g2)) return;
dBodyID b1 = dGeomGetBody(o1);
dBodyID b2 = dGeomGetBody(o2);
dContact contact[3]; // up to 3 contacts per box
for (i=0; i<3; i++) {
contact[i].surface.mode = dContactSoftCFM | dContactApprox1;
contact[i].surface.mu = MU;
contact[i].surface.soft_cfm = 0.01;
}
if (int numc = dCollide (o1,o2,3,&contact[0].geom,sizeof(dContact))) {
for (i=0; i<numc; i++) {
dJointID c = dJointCreateContact (world,contactgroup,contact+i);
dJointAttach (c,b1,b2);
}
}
}
// start simulation - set viewpoint
static void start()
{
dAllocateODEDataForThread(dAllocateMaskAll);
static float xyz[3] = {1.7772,-0.7924,2.7600};
static float hpr[3] = {90.0000,-54.0000,0.0000};
dsSetViewpoint (xyz,hpr);
}
// simulation loop
static void simLoop (int pause)
{
int i;
if (!pause) {
// apply forces to all bodies
for (i=0; i<N1; i++) {
for (int j=0; j<N2; j++) {
dBodyAddForce (body[i][j],FORCE*(i+1),0,0);
}
}
dSpaceCollide (space,0,&nearCallback);
dWorldStep (world,0.05);
// remove all contact joints
dJointGroupEmpty (contactgroup);
}
dsSetColor (1,0,1);
dReal sides[3] = {LENGTH,LENGTH,HEIGHT};
for (i=0; i<N1; i++) {
for (int j=0; j<N2; j++) {
dsDrawBox (dGeomGetPosition(box[i][j]),dGeomGetRotation(box[i][j]),
sides);
}
}
}
int main (int argc, char **argv)
{
int i,j;
dMass m;
// setup pointers to drawstuff callback functions
dsFunctions fn;
fn.version = DS_VERSION;
fn.start = &start;
fn.step = &simLoop;
fn.command = 0;
fn.stop = 0;
fn.path_to_textures = DRAWSTUFF_TEXTURE_PATH;
// create world
dInitODE2(0);
world = dWorldCreate();
space = dHashSpaceCreate (0);
contactgroup = dJointGroupCreate (0);
dWorldSetGravity (world,0,0,-GRAVITY);
ground = dCreatePlane (space,0,0,1,0);
// bodies
for (i=0; i<N1; i++) {
for (j=0; j<N2; j++) {
body[i][j] = dBodyCreate (world);
dMassSetBox (&m,1,LENGTH,LENGTH,HEIGHT);
dMassAdjust (&m,MASS*(j+1));
dBodySetMass (body[i][j],&m);
dBodySetPosition (body[i][j],i*2*LENGTH,j*2*LENGTH,HEIGHT*0.5);
box[i][j] = dCreateBox (space,LENGTH,LENGTH,HEIGHT);
dGeomSetBody (box[i][j],body[i][j]);
}
}
// run simulation
dsSimulationLoop (argc,argv,352,288,&fn);
dJointGroupDestroy (contactgroup);
dSpaceDestroy (space);
dWorldDestroy (world);
dCloseODE();
return 0;
}
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