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Topic: Physics engine bug... Can't find it. (Read 536 times) |
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Fish-face
   
 
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Physics engine bug... Can't find it.
« on: Jul 30th, 2004, 11:20pm » |
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Hi, I recently started programming with processing and firstly, I'd like to say what brilliant language it is - easy, powerful and brilliant for the type of things I like creating.
Anyway, I have a bug in a physics engine I'm working on. There are two implementations - one involving springs, the other not. With springs, when friction is set to nothing, the system accelerates. In the other, the system decelerates.
I can't work out why this is... Could you have a go?
The URL for without springs is http://www.fishface.a.la/processing/processing.php?q=3
For with, http://www.fishface.a.la/processing/processing.php?q=4
Thanks for any help you can give.
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The C@ S@ on the M@
=Fish-Face=
~#Chris#~
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narain
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Re: Physics engine bug... Can't find it.
« Reply #1 on: Jul 31st, 2004, 5:38am » |
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The link isn't opening for me...
Could you post your code here?
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Fish-face
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Re: Physics engine bug... Can't find it.
« Reply #2 on: Jul 31st, 2004, 10:31am » |
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Awoops - self hosted. You probably tried when the server was off! Here's the code for no springs:
Code:float friction;
float gravity;
float wind, windy;
int keyPress=0;
boolean usewind=true;
int oldMouseY, oldMouseX;
int massnum=5, maxmass=100;
boolean starting = true;
Mass[] Masses = new Mass[maxmass];
void setup() {
size(250,200);
noStroke();
ellipseMode(CENTER_DIAMETER);
colorMode(HSB);
friction=0.99;
gravity=0.2;
wind=0.5;
windy=0.1;
for(int i=0; i<maxmass; i++) {
Masses[i]=new Mass((int)random(200),(int)random(200),random(5)+4);
}
}
void loop() {
if(keyPressed) {
if(keyPress==0) keyPress=1;
else keyPress=-1;
} else {
keyPress=0;
}
if(keyPress==1) {
if(key == UP && massnum < maxmass-1) {
massnum++;
//Masses[massnum-1]=new Mass((int)random(200),(int)random(200),random(5)+4);
} if(key == DOWN && massnum > 0) {
massnum--;
//Masses[massnum]=new Mass((int)random(200),(int)random(200),random(5)+4);
}
if(key == 'w') {
usewind=!usewind;
}
if(key == 'r' && friction > 0) {
friction-=0.01;
} if(key == 'f' && friction < 2) {
friction+=0.01;
}
if(key == 't' && gravity < 10) {
gravity+=0.1;
} if(key == 'g' && gravity > -10) {
gravity-=0.1;
}
}
background(0);
if(gravity>0) fill(0,0,255);
else fill(0,0,128);
rect(205,100-gravity*9,15,gravity*9);
if(friction>1) fill(0,0,128);
else fill(0,0,255);
rect(230,190-(2-friction)*90,15,(2-friction)*90);
if(usewind) {fill(50,255,255); ellipse(205,195,8,8);}
stroke(0,0,255);
line(200,0,200,200);
noStroke();
wind=wind+random(0.4)-0.2;
windy=windy+random(0.1)-0.05;
if(wind>1) wind=1;
if(wind<-1) wind=-1;
if(windy>0.4) windy=0.4;
if(windy<-0.4) windy=-0.4;
for(int i=0; i<massnum; i++) {
Masses[i].Force(0,gravity);
if(usewind) Masses[i].Force(wind,windy);
Masses[i].Update();
}
}
void keyPressed() {
}
void keyReleased() {
}
void mousePressed() {
if(mouseX>205 && mouseX<220) {
gravity=-(float)(mouseY-100)/9;
}
if(mouseX>230 && mouseX<250) {
friction=(float)((mouseY-2))/90;
}
}
class Mass {
float posx, posy; //Current position
float newx, newy; //New position
float velx, vely; //Velocity, to work out new position
float accel; //Acceleration, to work out velocity
float mass; //Mass, to work out acceleration
int id; //What index in the array?
boolean mouseIn;
Mass(float x, float y, float m) {
newx=x; newy=y;
mass=m;
}
void Force(float force_x, float force_y) {
accel=force_x/mass;
velx=velx+accel;
accel=force_y/mass;
vely=vely+accel;
}
void Update() {
velx=friction * velx;
vely=friction * vely;
if(!mousePressed) {
mouseIn=false;
} else if(mouseIn()) {
mouseIn=true;
}
if(mouseIn) {
Force(mouseX-newx, mouseY-newy);
}
if(newx+velx>195) {velx=-velx; newx=195;}
else if(newx+velx<5) {velx=-velx; newx=5;}
else {newx=newx+velx;}
if(newy+vely>195) {vely=-vely;newy=195;}
else if(newy+vely<5) {vely=-vely;newy=5;}
else {newy=newy+vely;}
for(int i=0;i<massnum;i++) {
float disX=newx-Masses[i].newx;
float disY=newy-Masses[i].newy;
if(sqrt(sq(disX) + sq(disY)) < 10 ) {
Masses[i].Force(velx-disX/2,vely-disY/2);
this.Force(-velx+disX/2,-vely+disY/2);
}
}
fill((150+velx*vely*20)%255,(200+vely*20)%255,200);
ellipse(newx,newy,10,10);
}
boolean mouseIn() {
float disX = newx - mouseX;
float disY = newy - mouseY;
if(sqrt(sq(disX) + sq(disY)) < 5 ) {
return true;
} else {
return false;
}
}
} |
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--
The C@ S@ on the M@
=Fish-Face=
~#Chris#~
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Fish-face
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Re: Physics engine bug... Can't find it.
« Reply #3 on: Jul 31st, 2004, 10:33am » |
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And for springs:
Code:float friction;
float gravity;
float wind, windy;
int keyPress=0;
boolean usewind=false;
int oldMouseY, oldMouseX;
int massnum=10, maxmass=100;
boolean starting = true;
Mass[] Masses = new Mass[maxmass];
float[][][] springs = new float[maxmass][maxmass][3];
void setup() {
size(250,200);
noStroke();
ellipseMode(CENTER_DIAMETER);
colorMode(HSB);
friction=0.99;
gravity=0.2;
wind=0.5;
windy=0.1;
for(int i=0; i<maxmass; i++) {
Masses[i]=new Mass((int)random(200),(int)random(200),random(5)+4);
}
/*Masses[0]=new Mass(100,100,8);
Masses[1]=new Mass(80,100,8);
Masses[2]=new Mass(120,100,8);
Masses[3]=new Mass(100,120,8);
Masses[4]=new Mass(100,80,8);*/
for(int i=0;i<maxmass;i++) {
for(int o=0;o<maxmass;o++) {
if(i != o) Spring(i,o,0.5,50,0.5);
}
}
}
void loop() {
if(keyPressed) {
if(keyPress==0) keyPress=1;
else keyPress=-1;
} else {
keyPress=0;
}
if(keyPress==1) {
if(key == UP && massnum < maxmass-1) {
massnum++;
//Masses[massnum-1]=new Mass((int)random(200),(int)random(200),random(5)+4);
} if(key == DOWN && massnum > 0) {
massnum--;
//Masses[massnum]=new Mass((int)random(200),(int)random(200),random(5)+4);
}
if(key == 'w') {
usewind=!usewind;
}
if(key == 'r' && friction > 0) {
friction-=0.01;
} if(key == 'f' && friction < 2) {
friction+=0.01;
}
if(key == 't' && gravity < 10) {
gravity+=0.1;
} if(key == 'g' && gravity > -10) {
gravity-=0.1;
}
}
background(0);
if(gravity>0) fill(0,0,255);
else fill(0,0,128);
rect(205,100-gravity*9,15,gravity*9);
if(friction>1) fill(0,0,128);
else fill(0,0,255);
rect(230,190-(2-friction)*90,15,(2-friction)*90);
if(usewind) {fill(50,255,255); ellipse(205,195,8,8);}
stroke(0,0,255);
line(200,0,200,200);
noStroke();
wind=wind+random(0.4)-0.2;
windy=windy+random(0.1)-0.05;
if(wind>1) wind=1;
if(wind<-1) wind=-1;
if(windy>0.4) windy=0.4;
if(windy<-0.4) windy=-0.4;
for(int i=0; i<massnum; i++) {
Masses[i].Force(0,gravity);
if(usewind) Masses[i].Force(wind,windy);
for(int s=0; s<massnum; s++) {
if(springs[i][s][0]>0) {
float distX=(float)Masses[i].newx-Masses[s].newx;
float distY=(float)Masses[i].newy-Masses[s].newy;
float dist=sqrt(sq(distX)+sq(distY));
if(int(dist)!=springs[i][s][1]) {
float targX=(float)distX/(dist/springs[i][s][1]);
float targY=(float)distY/(dist/springs[i][s][1]);
float forceX=(float)-springs[i][s][0]*(distX-targX)*springs[i][s][2];
float forceY=(float)-springs[i][s][0]*(distY-targY)*springs[i][s][2];
Masses[i].Force(forceX,forceY);
}
stroke(0,0,255); line(Masses[i].newx,Masses[i].newy,Masses[s].newx,Masses[s].newy);
noStroke();
}
}
Masses[i].Update();
}
}
void Spring(int m1, int m2, float k, int distance, float damp) {
springs[m1][m2][0]=k;
springs[m1][m2][1]=distance;
springs[m1][m2][2]=damp;
springs[m2][m1][0]=k;
springs[m2][m1][1]=distance;
springs[m2][m1][2]=damp;
}
void mousePressed() {
if(mouseX>205 && mouseX<220) {
gravity=-(float)(mouseY-100)/9;
}
if(mouseX>230 && mouseX<250) {
friction=(float)((mouseY-2))/90;
}
}
class Mass {
float posx, posy; //Current position
float newx, newy; //New position
float velx, vely; //Velocity, to work out new position
float accel; //Acceleration, to work out velocity
float mass; //Mass, to work out acceleration
int id; //What index in the array?
boolean mouseIn;
Mass(float x, float y, float m) {
newx=x; newy=y;
mass=m;
}
void Force(float force_x, float force_y) {
accel=force_x/mass;
velx=velx+accel;
accel=force_y/mass;
vely=vely+accel;
}
void Update() {
velx=friction * velx;
vely=friction * vely;
if(!mousePressed) {
mouseIn=false;
} else if(mouseIn()) {
mouseIn=true;
}
if(mouseIn) {
Force(mouseX-newx, mouseY-newy);
}
if(newx+velx>195) {velx=-velx; newx=195;}
else if(newx+velx<5) {velx=-velx; newx=5;}
else {newx=newx+velx;}
if(newy+vely>195) {vely=-vely;newy=195;}
else if(newy+vely<5) {vely=-vely;newy=5;}
else {newy=newy+vely;}
for(int i=0;i<massnum;i++) {
float disX=newx-Masses[i].newx;
float disY=newy-Masses[i].newy;
if(sqrt(sq(disX) + sq(disY)) < 10 ) {
Masses[i].Force(velx-disX/2,vely-disY/2);
this.Force(-velx+disX/2,-vely+disY/2);
}
}
fill((150+velx*vely*20)%255,(200+vely*20)%255,200);
ellipse(newx,newy,10,10);
}
boolean mouseIn() {
float disX = newx - mouseX;
float disY = newy - mouseY;
if(sqrt(sq(disX) + sq(disY)) < 5 ) {
return true;
} else {
return false;
}
}
} |
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--
The C@ S@ on the M@
=Fish-Face=
~#Chris#~
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fjen
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Re: Physics engine bug... Can't find it.
« Reply #4 on: Jul 31st, 2004, 1:34pm » |
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on Jul 31st, 2004, 10:33am, Fish-face wrote: Code:
.....
for(int i=0; i<massnum; i++) {
Masses[i].Force(0,gravity);
if(usewind) Masses[i].Force(wind,windy);
for(int s=0; s<massnum; s++) {
if(springs[i][s][0]>0) {
// Masses[i].newx, Masses[i].newy are float allready
float distX=(float)Masses[i].newx-Masses[s].newx;
float distY=(float)Masses[i].newy-Masses[s].newy;
float dist=sqrt(sq(distX)+sq(distY));
if(int(dist)!=springs[i][s][1]) {
// distX, distY, dist are float allready
float targX=(float)distX/(dist/springs[i][s][1]);
float targY=(float)distY/(dist/springs[i][s][1]);
// all are float ...
float forceX=(float)-springs[i][s][0]*(distX-targX)*springs[i][s][2];
float forceY=(float)-springs[i][s][0]*(distY-targY)*springs[i][s][2];
Masses[i].Force(forceX,forceY);
}
....
void Spring(int m1, int m2, float k, int distance, float damp) {
springs[m1][m2][0]=k;
springs[m1][m2][1]=distance;
springs[m1][m2][2]=damp;
springs[m2][m1][0]=k;
springs[m2][m1][1]=distance;
springs[m2][m1][2]=damp;
....
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removing the unneccesary typecasting "(float)" made it stop collapsing. there is no need to cast a float to a float ... not sure what's happening inside of java then.
replace the for-loop with:
Code:
for(int s=0; s<massnum; s++) {
if(springs[i][s][0]>0) {
float distX=Masses[i].newx-Masses[s].newx;
float distY=Masses[i].newy-Masses[s].newy;
float dist=sqrt(sq(distX)+sq(distY));
if(int(dist)!=springs[i][s][1]) {
float targX=distX/(dist/springs[i][s][1]);
float targY=distY/(dist/springs[i][s][1]);
float forceX=-springs[i][s][0]*(distX-targX)*springs[i][s][2];
float forceY=-springs[i][s][0]*(distY-targY)*springs[i][s][2];
Masses[i].Force(forceX,forceY);
}
stroke(0,0,255); line(Masses[i].newx,Masses[i].newy,Masses[s].newx,Masses[s].newy); noStroke();
}
}
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hope this helps a little ... best flo.
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Fish-face
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Re: Physics engine bug... Can't find it.
« Reply #5 on: Jul 31st, 2004, 2:11pm » |
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Didn't see any improvement...
I copied the Mass class into a new project, and it worked as expected with friction set to 1.
I tried commenting out all of the loop code bar Update(), too, and the problem persisted in the existing project. This would seem to indicate that the problem lies elsewhere... but I can't find it!
Possibly unrelated, but I noticed that as you decreased the friction, it became a number it shouldn't be. It goes to 0.9600004 or something similar. Then to 0.9700005...
Thanks for your help, so far!
EDIT: Correction, I realized that I'd not copied over the collision procedure. That last for loop in the Mass class was the culprit - the mass was colliding with itself.
However, with springs still has its error... It will accelerate even with friction < 1.
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| « Last Edit: Jul 31st, 2004, 2:36pm by Fish-face » |
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--
The C@ S@ on the M@
=Fish-Face=
~#Chris#~
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