"Strings"

Programming Questions

dlillard5

in Programming Questions • 1 year ago

Not the datatype. I've been trying to recreate a sketch called strings that you can see here. He explains the idea pretty well, and so I tried to recreate it. As far as I can tell, my sketch is finding the nearest not connected point accurately, but I think the problem is with my loop for checking for intersections.

I tried to comment to explain, and a lot of the code is the segment intersection function, but sorry for posting so much code.

ArrayList dots=new ArrayList();
ArrayList connections=new ArrayList();
void setup() {
size(500, 500);
background(0);
smooth();
for (int i=0;i<100;i++) {
dots.add(new d(random(0, width), random(0, height), i));
}
connections.add(new connection(-100, -100, -100, -100));//not a connection that will be checked
}
void draw() {
for (int i=dots.size()-1;i>0;i--) {
d d1 = (d) dots.get(i);
d1.update();
}
}
class d {//class for dot
float x, y;
boolean connected=false;
int id;
d(float cx, float cy, int cid) {
x=cx;
y=cy;
id=cid;
}
void update() {
float closest=100000;
int closeid=0;
boolean intersection=true;
float x3=-101;
float y3=-101;
for (int i=dots.size()-1;i>0;i--) {//loop to find the closest dot
d d1 = (d) dots.get(i);
if (d1.id==id) {
}
else {
if (d1.connected==false && connected==false) {
if (dist(x, y, d1.x, d1.y)<closest) {//if it is closer than the closest one so far
closest=dist(x, y, d1.x, d1.y);
closeid=d1.id;
x3=d1.x;
y3=d1.y;
}
}
}
}
for (int j=connections.size()-1;j>0;j--) {//loop through the connections and check to see if the connection with the closest dot intersects with any of them
connection c1=(connection) connections.get(j);
//get connection x's and y's
float x1=c1.x1;
float x2=c1.x2;
float y1=c1.y1;
float y2=c1.y2;
if(x3!=-101 && y3!=-101){
}else{
if (segIntersection(x1, y1, x2, y2, x, y, x3, y3)!=null) {//check if they are intersecting
intersection=true;
}
}
}
for (int i=dots.size()-1;i>0;i--) {//loop to pick out that dot and draw a line
d d1 = (d) dots.get(i);
if (d1.id==id) {//skip yourself
continue;
}
if (d1.id==closeid && intersection==false) {//if you aren't intersecting and if the dot that has been looped to is the dot you're looking for
stroke(0, 168, 255);
line(x, y, d1.x, d1.y);
connected=true;
d1.connected=true;
connections.add(new connection(x, y, d1.x, d1.y));//record the connection
}
}
stroke(255, 70);
point(x, y);
}
}
class connection {//class to record all the connections that have been made
float x1, y1, x2, y2;
connection(float cx1, float cy1, float cx2, float cy2) {
x1=cx1;
y1=cy1;
x2=cx2;
y2=cx2;
}
}
/**
@author Ryan Alexander
*/
PVector segIntersection(float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4)
{
float bx = x2 - x1;
float by = y2 - y1;
float dx = x4 - x3;
float dy = y4 - y3;
float b_dot_d_perp = bx * dy - by * dx;
if (b_dot_d_perp == 0) {
return null;
}
float cx = x3 - x1;
float cy = y3 - y1;
float t = (cx * dy - cy * dx) / b_dot_d_perp;
if (t < 0 || t > 1) {
return null;
}
float u = (cx * by - cy * bx) / b_dot_d_perp;
if (u < 0 || u > 1) {
return null;
}
return new PVector(x1+t*bx, y1+t*by);
}

Replies(2)

hellochar

Re: "Strings"

1 year ago

If you just want to get it done, I'd say to not re-invent the wheel and instead use toxiclibs. It has a http://toxiclibs.org/docs/core/toxi/geom/Line2D.html#intersectLine(toxi.geom.Line2D) Line2D class and an "intersectLine" method for testing.

Unfortunately, I have no idea what your code is doing. Care to run me through it?

dlillard5

Re: "Strings"

1 year ago

Okay let me run you through it. The idea is to place a large number of dots randomly on the screen (2D). Then, pick a dot at random and draw a line from that dot to the next nearest dot. The problem is, the line that's drawn can't intersect with any lines that currently exist.

Alright so the first section of the code:

ArrayList dots=new ArrayList();
ArrayList connections=new ArrayList();
void setup() {
size(500, 500);
background(0);
smooth();
for (int i=0;i<100;i++) {//add 100 dots
dots.add(new d(random(0, width), random(0, height), i));
}
connections.add(new connection(-100, -100, -100, -100));
}
void draw() {
for (int i=dots.size()-1;i>0;i--) {
d d1 = (d) dots.get(i);
d1.update();
}
}

Okay so that part was pretty standard, just creating ArrayLists for classes and updating all the objects in the list.

The next part of the code is the dot class:

class d {//class for dot
float x, y;
boolean connected=false;
int id;
d(float cx, float cy, int cid) {
x=cx;
y=cy;
id=cid;
}
void update() {
float closest=100000;//arbitrary large number
int closeid=0;//arbitrary #
boolean intersection=true;//boolean for whether or not the connection will make an intersection... will be set to false later
float x3=-101;//arbitrary again
float y3=-101;//arbitrary again
for (int i=dots.size()-1;i>0;i--) {//loop to find the closest dot out of all the dots
d d1 = (d) dots.get(i);
if (d1.id!=id) {// if the ID is not the same as the current object's
if (d1.connected==false && connected==false) {//if both dots aren't connected
if (dist(x, y, d1.x, d1.y)<closest) {//if it is closer than the closest one so far
closest=dist(x, y, d1.x, d1.y);//reset the new closest point
closeid=d1.id;
x3=d1.x;//record the location of the line that might be drawn to (if it doesn't intersect)
y3=d1.y;
}
}
}
}
for (int j=connections.size()-1;j>0;j--) {//loop through all of the current connections and check to see if the connection with the closest dot intersects with any of them
connection c1=(connection) connections.get(j);
//get connection x's and y's
float x1=c1.x1;
float x2=c1.x2;
float y1=c1.y1;
float y2=c1.y2;
if(x3!=-101 && y3!=-101){
}else{
if (segIntersection(x1, y1, x2, y2, x, y, x3, y3)!=null) {//check if they are intersecting
intersection=true;
}
}
}
for (int i=dots.size()-1;i>0;i--) {//loop to pick out that dot and draw a line
d d1 = (d) dots.get(i);
if (d1.id==id) {//skip yourself
continue;
}
if (d1.id==closeid && intersection==false) {//if you aren't intersecting and if the dot that has been looped to is the dot you're looking for
stroke(0, 168, 255);
line(x, y, d1.x, d1.y);
connected=true;
d1.connected=true;
connections.add(new connection(x, y, d1.x, d1.y));//record the connection
}
}
stroke(255, 70);
point(x, y);
}
}

So the 3 loops that are in the update part of the d class are for finding the nearest dot, checking if a line from the object's location to that nearest one and then picking out the ID of that dot and drawing a line.

class connection {//class to record all the connections that have been made
float x1, y1, x2, y2;
connection(float cx1, float cy1, float cx2, float cy2) {
x1=cx1;
y1=cy1;
x2=cx2;
y2=cx2;
}
}

The connection class is just a simple class to record the x's and y's of all the connections that have been made so far.

/**
@author Ryan Alexander
*/
PVector segIntersection(float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4)
{
float bx = x2 - x1;
float by = y2 - y1;
float dx = x4 - x3;
float dy = y4 - y3;
float b_dot_d_perp = bx * dy - by * dx;
if (b_dot_d_perp == 0) {
return null;
}
float cx = x3 - x1;
float cy = y3 - y1;
float t = (cx * dy - cy * dx) / b_dot_d_perp;
if (t < 0 || t > 1) {
return null;
}
float u = (cx * by - cy * bx) / b_dot_d_perp;
if (u < 0 || u > 1) {
return null;
}
return new PVector(x1+t*bx, y1+t*by);
}

Finally that part of the code was not written by me, and that is just math to determine if 2 lines are touching, if they are not touching than it returns null.

So I think that my code is successfully finding the nearest dot, but there's something wrong with my intersection part, and I don't have a clue what it could be, because I think it all makes sense logically.

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