Ellipse colision

Programming Questions

iunnamed

in Programming Questions • 9 months ago

So I have this game: It's ellipses moving randomly and you have to hit them. The only thing I need is to make them collide against each other. Can anyone help me?

(to start you have to move the mouse to the ellipse in the middle)

thanks in advance

int numBolas = 10;
int pont, contador;
int bolas_pretas;
int contador_tempo=1;
int starttime;
boolean acertou,ja_entrou,menu=true;
Bola myBola = new Bola(20, 20, 1, 0.5);
Bola[] bolas = new Bola[numBolas];
void setup()
{
size(500, 500);
for (int i=0; i<numBolas;i++) {
bolas[i] = new Bola(random(width), random(height), random(1, 6), random(1, 6));
}
}
void draw() {
background(255);
if(menu==true){
fill(255);
rect(0,0,width,height);
fill(0);
text("Posiciona o rato na circufrência para começar", 30, 25);
ellipseMode(CENTER);
ellipse(width/2,height/2,30,30);
//desenho da mira:
stroke(2);
noFill();
ellipse(mouseX, mouseY, 30, 30);
line(mouseX+7.5, mouseY, mouseX+22.5, mouseY);
line(mouseX-7.5, mouseY, mouseX-22.5, mouseY);
line(mouseX, mouseY+7.5, mouseX, mouseY+22.5);
line(mouseX, mouseY-7.5, mouseX, mouseY-22.5);
}
if((mouseX ==width/2) && (mouseY==height/2))menu=false;
if(menu==false){
text(pont, 30, 25);
for (int i=0; i<numBolas; i++) {
bolas[i].update();
bolas[i].mousePressed();
bolas[i].tempo();
bolas[i].desenha();
}
//desenho da mira:
stroke(2);
noFill();
ellipse(mouseX, mouseY, 30, 30);
line(mouseX+7.5, mouseY, mouseX+22.5, mouseY);
line(mouseX-7.5, mouseY, mouseX-22.5, mouseY);
line(mouseX, mouseY+7.5, mouseX, mouseY+22.5);
line(mouseX, mouseY-7.5, mouseX, mouseY-22.5);
}
if (millis()>=starttime+1000) {
starttime=millis();
contador_tempo++;
ja_entrou=false;
}
if (contador_tempo%10==0) {
if(ja_entrou==false){
pont--;
ja_entrou=true;
}
}
}
void mousePressed() {
contador_tempo=1;
}
void mouseReleased() {
pont+=5*bolas_pretas;
if (bolas_pretas>=4) {
pont+=5;
}
if (acertou==false) {
pont-=5;
}
acertou=false;
}
class Bola {
float ypos, xpos, speedx, speedy, dista, cor1, cor2, cor3;
int score=0;
boolean count;
boolean esta_preta;
Bola (float x, float y, float s, float s2) {
xpos = x;
ypos = y;
speedy=s2;
speedx = s;
cor1=random(50,255);
cor2=random(50,255);
cor3=random(255);
count=true;
}
void desenha() {
fill(cor1, cor2, cor3);
ellipse(xpos, ypos, 40, 40);
}
void update() {
xpos += speedx;
ypos += speedy;
if (xpos>=480) speedx=-random(0.5, 4);
if (ypos>=480) speedy=-random(0.5, 4);
if (xpos<=20) speedx=random(0.5, 4);
if (ypos<=20) speedy=random(0.5, 4);
}
void mousePressed() {
menu=false;
if (mousePressed && (mouseButton == LEFT)) {
dista=dist(xpos, ypos, mouseX, mouseY);
// 15 é o raio das bolas
if (dista<=15) {
if(esta_preta==false){
bolas_pretas++;
}
acertou=true;
count=false;
cor1=0;
cor2=0;
cor3=0;
esta_preta=true;
}
}
}
void tempo() {
score=score+1;
if (score>=300) {
cor1=random(50,255);
cor2=random(50,255);
cor3=random(50,255);
count=true;
bolas_pretas--;
esta_preta=false;
}
if (count) {
score=0;
}
}
}

Replies(5)

calsign

Circle collision is, by far, the easiest form of collision (expect, perhaps, point collision). In your scenario, you say "ellipse", yet all of the objects that I see are circles... so I am assuming that you want circle collision.

Because the circle has an equal distance from its center to any given point on its border, you can simply check to see if the distance from the target point to the center of the circle is less than the circle's radius. This check translates rather nicely to code:

if(dist(testX, testY, circleCenterX, circleCenterY) < circleRadius) {
//The test point is inside the circle
}

Now, this is all if I'm understanding you correctly... and you want the ellipses to respond to touching the point in the middle of the screen. If you want the ellipses to bounce off of each other, then that is a great deal more complicated...

friendgin..

Re: Ellipse colision

9 months ago

As far as ellipses bouncing off each other...

The only thing you need to calculate is the final velocities.

The tangential velocity of each of the circles will be conserved while the normal velocity of each should be switched. Pvector will help with that. You then combine the two vectors (tangent and normal) of velocity for each ball (you may need to perform some basic transformations) and you wind up with your post bounce velocity.

Example:

for 2 balls A and B, and 2 states i (initial-before collision), and f (final-after collision). t means tangential and n means normal.

V_At_f=V_At_i

V_Bt_f=V_Bt_i

V_An_f=V_Bn_i

V_Bn_f=V_An_i

You find out what each of these components are using a dot product of the initial velocity vector and the normal/tangential directions determined using pvector.

iunnamed

Re: Ellipse colision

9 months ago

Thanks for the fast answer!

@ calsign

Yes, I mean circle.

dist() would be the logical solution but I dont know how to calculate the distance between two circles in the same array.

@ friendgin

So ... I've created two PVectors, location(xpos,ypos) and velocity(xspeed,yspeed) but I'm not really sure what to do with them

calsign

Re: Ellipse colision

9 months ago

Okay... in each ball's update() method, you need to run through every other ball and check to see if the distance between the two balls is smaller than their combined radii. If that is the case, then you have a collision. I think friendgin will be able to help you with the math...

friendgin..

Re: Ellipse colision

9 months ago

Vector maths ahead. Lets hope I don't make any mistakes. If anything is unclear please ask.

The first thing you need to do is find the normal vector that goes between the location of the 2 circles (A and B) that are within the collision radius. The sub() command in PVector should help with this.

normal = location_A - location_B

Now you need to normalise both the normal vector, as well as your velocity vectors. This means making them all of unit length. This is done by dividing the components of the vector by the length of the vector, or by using the normalize() command. I will use a _o to describe a normalised vector

now you want to dot() product- dot()-the velocity and the normal vectors using http://processing.org/reference/PVector_dot_.html. Your result will be the normal component of velocity in each case. The sign of the result will dictate which direction it is moving in. Lets call the results of this V_norm_A_o and V_norm_B_o.

To calculate the tangential velocities, subtract the normal velocities from the normalised velocity vectors using the sub() command again. ie. V_tan_A_o = V_A_o - V_norm_A_o.

Now you need to unnormalise the tangential and normal components, do this by multiplying each of them by the magnitude (length) of the original velocity vectors respectively. (note that I am using the terms "normal" (_norm) and "normalise" (_o) but they do not mean the same thing).

ie. V_tan_A = V_tan_A_o * mag(V_A)

V_norm_A = V_norm_A_o * mag(V_A)

Final step, combine the vectors back together using add().

V_new_A = V_tan_A + V_norm_B

V_new_B = V_tan_B + V_norm_A

Summary:

sub() on posA and posB - [1]

normalize() [1] along with the 2 velocity vectors (individually) - [2]

dot() the normalized velocity vectors with the normalised [1] gained in step [2] to give the normal components - [3]

sub() the step [3] normal components from the normalised velocity vectors from step [2] to give the tangential components - [4]

Multiply the tangential [4] and normal [3] components by their original non-normalised velocity vectors' magnitudes - [5]

add() the tangential of A and normal of B to get the final velocity for A and vice versa. [6]

===============================================================

IMPORTANT EDIT: You need to multiply the dot products by the normalised "normal" vector from step [3] to make them vectors not scalars. You then use these normalised velocity vectors for the remainder of the process.

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