The problem is in those nested for() loops. You are calling 400 times the constructor and only keeping the last 16 that have the same values. Foe each one of the 16 times of the first loop, you call the second for loop() 5 times and for each of this two (16*5=80) you are calling another 5 times resulting in 400 calls with wrong values. Only the ones from last iteration.

If you want run this and look at the console to see what you were doing.

Hi v.k,

Thanks for your reply. I don't get how the constructor is being called multiple times.

But the output I am trying to produce is

1. void setup() {
2.   size(600, 300);
3.   smooth();
4. }
5. void draw() {
6.   stroke(1);
7.   background(#DAEBF2);
8.     for (int i = 0; i < width; i+=20) {//j is for the x coordinate
9.       for (int j = 0; j < height; j+=20) {//k is for the y coordinate 
10.     line(i, j, i+10, j+10);//this is just as an example
11.       }
12.     }
13.   }

where each line is an object and element in an array.

The first of your code is closer but the second seems to just give one line.

Thanks for your help,

Shane

Hi v.k,

This is exactly what i was trying to do. I would not have thought to use a 2D array. Thanks also for the clear explanation on the for() loop iterations.

Thank you very much for your help, I really appreciate it.

Shane

Glad to help. :-)

Thanks for this but I'm going to stay with the 2D array for now.

I have been able to create a vector field that points toward the mouse position. But the problem now is that the vectors to the right of the mouse point away instead of toward.

1. int wid = 600;
2. int hei = 300;
3. float theta = 0;
4. int numVectorsX = wid/20;
5. int numVectorsY = hei/19;
6. Field[][] vectors = new Field[numVectorsX][numVectorsY];
7. void setup() {
8.   size(600, 300);
9.   smooth();
10.   noStroke();
11.   for (int i = 0; i < numVectorsX; i++) {
12.     for (int j = 0; j < numVectorsY; j+=2) {
13.       int l = 10;//will be determined by some multiple of the inverse of the distance to mouse position
14.       // x, y, l, theta
15.       vectors[i][j] = new Field(i*10, j*10, l, theta);
16.     }
17.   }
18. }
19. void draw() {
20.   frameRate(24);
21.   stroke(1);
22.   background(#DAEBF2);
23.   for (int i = 0; i < numVectorsX; i++) {
24.     for (int j = 0; j < numVectorsY - 2; j+=2) {
25.       // x, y, l, theta
26.       vectors[i][j].plot();
27.     }
28.   }
29. }
30. class Field {
31.   float x, y, l, theta;
32.   //Constructor
33.   Field(float xpos, float ypos, float lpos, float thetapos) {
34.     x = xpos;
35.     y = ypos;
36.     l = lpos;
37.     theta = thetapos;
38.   }
39.   void plot() {
40.     float theta = atan((mouseY-y)/(mouseX-x));
41.     pushMatrix();
42.     translate(x, y);
43.     rotate(theta);
44.     line(0, 0, l, 0);
45.     translate(l, 0);
46.     beginShape();
47.     vertex(0, -3);
48.     vertex(0, 3);
49.     vertex(3, 0);
50.     endShape(CLOSE);
51.     popMatrix();
52.   }
53. }

I tried using an if() statement in the plot() method

1.  void plot() {
2.     if(mouseX - x < 0){
3.       x *= -1;
4.     }
5.     float theta = atan((mouseY-y)/(mouseX-x));
6.     pushMatrix();
7.     translate(x, y);
8.     rotate(theta);
9.     line(0, 0, l, 0);
10.     translate(l, 0);
11.     beginShape();
12.     vertex(0, -3);
13.     vertex(0, 3);
14.     vertex(3, 0);
15.     endShape(CLOSE);
16.     popMatrix();
17.   }
18. }

But this messes everything up. Any hints would be greatly appreciated.

Thanks,

Shane

I got it!

1. int wid = 600;
2. int hei = 300;
3. float theta = 0;
4. int numVectorsX = wid/10;
5. int numVectorsY = hei/8;
6. Field[][] vectors = new Field[numVectorsX][numVectorsY];
7. void setup() {
8.   size(600, 300);
9.   smooth();
10.   noStroke();
11.   for (int i = 0; i < numVectorsX; i++) {
12.     for (int j = 0; j < numVectorsY; j++) {
13.       int l = 12;//will be determined by some multiple of the inverse of the distance to mouse position
14.       // x, y, l, theta
15.       vectors[i][j] = new Field(i*30, j*30, l, theta);
16.     }
17.   }
18. }
19. void draw() {
20.   frameRate(24);
21.   stroke(1);
22.   background(#DAEBF2);
23.   for (int i = 0; i < numVectorsX; i++) {
24.     for (int j = 0; j < numVectorsY - 2; j++) {
25.       // x, y, l, theta
26.       vectors[i][j].plot();
27.     }
28.   }
29. }
30. class Field {
31.   float x, y, l, theta;
32.   //Constructor
33.   Field(float xpos, float ypos, float lpos, float thetapos) {
34.     x = xpos;
35.     y = ypos;
36.     l = lpos;
37.     theta = thetapos;
38.   }
39.   void plot() {
40.     float theta = atan((mouseY-y)/(mouseX-x));
41.     if (mouseX < x) {
42.       theta += PI;
43.     }
44.     //theta *= -1; //points the field away from the mouse position
45.     pushMatrix();
46.     translate(x, y);
47.     rotate(theta);
48.     line(0, 0, l, 0);
49.     translate(l, 0);
50.     fill(0, 0, 0);
51.     beginShape();
52.     vertex(0, -3);
53.     vertex(0, 3);
54.     vertex(3, 0);
55.     endShape(CLOSE);
56.     popMatrix();
57.     noFill();
58.   }
59. }

Very cool! 

Yes i love it. I am simulating an electric magnetic field with the mouse position as a negative charge. But I will be able to do more like change the polarity of the charge and magnitude. Still a long way to go but getting there!

Thanks for your help,

Shane

You are currently drawing/calculating  2200 vectors on each frame while only 231 of them are visible.
It would improve performance by a lot if you only create as many vectors as you really need. Something like this:

1. int distance = 30;
   int numVectorsX = wid/distance + 1;
   int numVectorsY = hei/distance + 1;

And you would have to change line 24 to this:

1.     for (int j = 0; j < numVectorsY; j++) {
   

Good catch benja. This is a good example how "hard numbers" are to be avoided...

You may also change line 15 to:

Hi v.k,

With the distance at 10 is has a cool effect.

I have made the vector length correspond to the distance form the mouse so that it is more like a vector field.

I have previously written a sketch for a circle that I can:

make larger by dragging the right mouse button the circle

move by dragging the left mouse button

and change the polarity by clicking it with the right button.

I am now trying to add this to the above sketch.

I want to vector field always to point to the center of the circle. But the problem is that the vector field points to (mouseX, mouseY) which is in a different class to (x,y) the center of the circle. So how can I bring a field from one class into another class?

1. Control mouse; //Declare the object called mouse
2. int numVectorsX = 21;//20*30 is width 600 and add 1 to the 20
3. int numVectorsY = 11;
4. Field[][] vectors = new Field[numVectorsX][numVectorsY];
5. float theta = 0;
6. int l;
7. int r, g, b;
8. int distance = 30;
9. void setup() {
10.   size(600, 300);
11.   smooth();
12.   noStroke();
13.   //x, y, r, g, b, transparency, count, diameter... the fields
14.   mouse = new Control(300, 150, 0, 0, 255, 50, 1, 150); //Construct the object mouse
15.   float maxdist = sqrt(pow(height, 2)+pow(width, 2)) - 50;
16.   for (int i = 0; i < numVectorsX; i++) {
17.     for (int j = 0; j < numVectorsY; j++) {
18.       // xField, yField, l, theta, maxdist
19.       vectors[i][j] = new Field(i*distance, j*distance, l, theta, maxdist);
20.     }
21.   }
22. }
23. void draw() {
24.   frameRate(24);
25.   background(#DAEBF2);
26.   mouse.move();
27.   mouse.display();
28.   for (int i = 0; i < numVectorsX; i++) {
29.     for (int j = 0; j < numVectorsY; j++) {
30.       // xField, yField, l, theta
31.       vectors[i][j].plot();
32.     }
33.   }
34. }
35. void mouseReleased() {
36.   if (mouseButton == CENTER) {
37.     mouse.released();
38.   }
39. }
40. class Control {
41.   float x, y, r, g, b, transparency, diameter;
42.   int count;
43.   //Constructor
44.   Control(float xpos, float ypos, float rpos, float gpos, float bpos, float trans, int countpos, float diameterpos) {
45.     x = xpos;
46.     y = ypos;
47.     r = rpos;
48.     g = gpos;
49.     b = bpos;
50.     transparency = trans;
51.     count = countpos;
52.     diameter = diameterpos;
53.   }
54.   void move() {
55.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))&&(mousePressed == true)) {//tests to see if mouse is on charge
56.       if (mouseButton == LEFT) {
57.         x = mouseX;
58.         y = mouseY;
59.       }
60.       else if (mouseButton == RIGHT) {//dragging mouse toward centre decreases size of charge
61.         if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))>(0)) {
62.           diameter = diameter + 5; //increases size of diameter
63.           transparency -= 0.5;
64.         } //dragging mouse away from center increases size of charge
65.         else if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))<(0)) {
66.           if (diameter > 20) {//prevents diameter getting too small and circle disappearing
67.             diameter = diameter - 5; // decreases size of diameter
68.             transparency += 0.5;
69.           }
70.         }
71.       }
72.     }
73.   }
74.   void display() {
75.     fill(r, g, b, transparency);//fills the circle with colours red, green, blue
76.     ellipse(x, y, diameter, diameter);
77.   }
78.   void released() {
79.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))) {//tests to see if mouse is on charge
80.       count = (count + 1) % 2;
81.       if (count == 1) {//sets colour to blue once
82.         r = 0;
83.         b = 255;
84.       }
85.       else if (count == 0) {//set colour red to blue
86.         r = 255;
87.         b = 0;
88.       }
89.     }
90.   }
91. }
92. class Field {
93.   float xField, yField, l, theta, maxdist;
94.   //Constructor
95.   Field(float xFieldpos, float yFieldpos, float lpos, float thetapos, float maxdistpos) {
96.     xField = xFieldpos;
97.     yField = yFieldpos;
98.     l = lpos;
99.     theta = thetapos;
100.     maxdist = maxdistpos;
101.   }
102.   void plot() {
103.     stroke(1);
104.     fill(0, 0, 0);
105.     float theta = atan((mouseY-yField)/(mouseX-xField));
106.     if (mouseX < xField) {
107.       theta += PI;
108.     }
109.     //theta += PI; //points the field away from the mouse position for a positive charge
110.     float d = (sqrt(pow(mouseY-yField, 2) + pow(mouseX-xField, 2)));//should be 1/r^2 but not practical here
111.     float l = map(d, 0, maxdist, 15, 0);//the second last value is the maximum length of a vector
112.     pushMatrix();
113.     translate(xField, yField);
114.     rotate(theta);
115.     line(0, 0, l, 0);
116.     //translate(l, 0);
117.     beginShape();
118.     vertex(l, -3);
119.     vertex(l, 3);
120.     vertex(l + 3, 0);
121.     endShape(CLOSE);
122.     popMatrix();
123.     noFill();
124.     noStroke();
125.   }
126. }

Thanks,

Shane

Hi Benja,

Sorry I didn't see your post at first. I know what you mean that there is too much calculation and I think I've sorted it out above.

Thanks,

Shane

Hey,

You have to tell your Field-class where to point.
Create class-variables (for example "targetX" and "targetY") and replace all the "mouseX" and "mouseY" inside of Field with those.
Then create some function to change these variables from outside.

1.   void update(float x, float y){
       targetX = x;
       targetY = y;
     }
   

Hi Benja,

Thanks for clearly showing me how to take a field from one class and use it in another class. This is such a useful thing to be able to do. I did this as you suggested above and applied it so that when I change the polarity of the charge, by clicking the center mouse button, the field points either away or toward the charge.

I also changed the name of the class, previously called 'mouse' to 'charge' as you suggested. And I took out the line about the frame rate, that wasn't needed.

1. Control charge; //Declare the object called charge of the class called 'Control'
2. int numVectorsX = 21;//20*30 that's number of vectors across by spacing between each is width 600 and add 1 to the 20 is 21
3. int numVectorsY = 11;//10*30 that's number of vectors down by spacing between each is height 300 and add 1 to the 10 is 11
4. Field[][] vectors = new Field[numVectorsX][numVectorsY];//Declare the 2D array called 'vectors', the elements of which are objects of the class called 'Field'
5. float targetX = 300, targetY = 150, pol, fieldStrength, minDiameter, maxDiameter;//the field initially points to a singularity at the coordinate (300,150). targetX and targetY is where the field points to. 'pol' is the polarity of the charge
6. float theta = 0;//angle between charge and each vector
7. int magnitude;//length or magnitude of a vector
8. int r, g, b;//red green blue variables for charge colour
9. int distance = 30;//spacing between vectors, same for x and y directions
10. float Fieldstrength;
11. void setup() {
12.   size(600, 300);
13.   smooth();
14.   noStroke();
15.   //x, y, r, g, b, transparency, count, diameter, minChargediameter, maxChargediameter... the fields
16.   charge = new Control(300, 150, 0, 0, 255, 30, 1, 50, 20, 400); //Construct the object charge
17.   float maxdist = sqrt(pow(height, 2)+pow(width, 2)) - 50;//Uses pythagoras to calculate diagonal distance of the window. This is the max distance between the charge and any vector
18.   for (int i = 0; i < numVectorsX; i++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
19.     for (int j = 0; j < numVectorsY; j++) {
20.       // xField, yField, magnitude, theta, maxdist
21.       vectors[i][j] = new Field(i*distance, j*distance, magnitude, theta, maxdist);
22.     }
23.   }
24. }
25. void draw() {
26.   background(#DAEBF2);
27.   charge.move();
28.   charge.display();
29.   for (int i = 0; i < numVectorsX; i++) {
30.     for (int j = 0; j < numVectorsY; j++) {
31.       // xField, yField, l, theta
32.       vectors[i][j].plot();
33.       if (mousePressed) {
34.         vectors[i][j].update(charge.x, charge.y, charge.diameter, charge.minChargediameter, charge.maxChargediameter);//puts the fields x and y from the object 'charge' and put them into the object 'vectors', there they are set equal to targetX and targetY which is where the field points to
35.       }
36.       if (mouseButton == CENTER) {
37.         vectors[i][j].polarity(charge.r);//puts the field r from the object 'charge' and puts it into the object 'vectors', there it is set equal to 'pol'.
38.       }
39.     }
40.   }
41. }
42. void mouseReleased() {
43.   if (mouseButton == CENTER) {
44.     charge.released();
45.   }
46. }
47. class Control {
48.   float x, y, r, g, b, transparency, diameter, minChargediameter, maxChargediameter;
49.   int count;
50.   //Constructor
51.   Control(float xpos, float ypos, float rpos, float gpos, float bpos, float trans, int countpos, float diameterpos, float minChargediameterpos, float maxChargediameterpos) {
52.     x = xpos;
53.     y = ypos;
54.     r = rpos;
55.     g = gpos;
56.     b = bpos;
57.     transparency = trans;
58.     count = countpos;
59.     diameter = diameterpos;
60.     minChargediameter = minChargediameterpos;
61.     maxChargediameter = maxChargediameterpos;
62.   }
63.   void move() {
64.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))&&(mousePressed == true)) {//tests to see if mouse is on charge
65.       if (mouseButton == LEFT) {
66.         x = mouseX;
67.         y = mouseY;
68.       }
69.       else if (mouseButton == RIGHT) {//dragging mouse toward centre decreases size of charge
70.         if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))>(0)) {
71.           if (diameter < maxChargediameter) {//prevents diameter getting too big, max diameter is 400
72.             diameter = diameter + 5; //increases size of diameter
73.             transparency += 0.5;
74.           }
75.         } //dragging mouse away from center increases size of charge
76.         else if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))<(0)) {
77.           if (diameter > minChargediameter) {//prevents diameter getting too small and circle disappearing, min diameter is 20
78.             diameter = diameter - 5; // decreases size of diameter
79.             transparency -= 0.5;
80.           }
81.         }
82.       }
83.     }
84.   }
85.   void display() {
86.     fill(r, g, b, transparency);//fills the charge with colours red, green, blue
87.     ellipse(x, y, diameter, diameter);//draws the charge
88.   }
89.   void released() {
90.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))) {//tests to see if mouse is on charge
91.       count = (count + 1) % 2;
92.       if (count == 1) {//sets colour to blue once
93.         r = 0;
94.         b = 255;
95.       }
96.       else if (count == 0) {//set colour red to blue
97.         r = 255;
98.         b = 0;
99.       }
100.     }
101.   }
102. }
103. class Field {
104.   float xField, yField, magnitude, theta, maxdist;
105.   //Constructor
106.   Field(float xFieldpos, float yFieldpos, float magnitudepos, float thetapos, float maxdistpos) {
107.     xField = xFieldpos;
108.     yField = yFieldpos;
109.     magnitude = magnitudepos;
110.     theta = thetapos;
111.     maxdist = maxdistpos;
112.   }
113.   void plot() {
114.     stroke(1);
115.     fill(0, 0, 0);
116.     float theta = atan((targetY-yField)/(targetX-xField));
117.     if (targetX < xField) {//without this the vectors on the right of screen will point away from charge and vectors on right of screen toward it. All should point away or toward it
118.       theta += PI;
119.     }
120.     if (pol == 0) {//if 'pol' is 0 then r = 0 in charge.released and so charge is blue and positive
121.       theta += PI; //points the field away from the charge position for a positive charge
122.     }   
123.     float d = (sqrt(pow(targetY-yField, 2) + pow(targetX-xField, 2)));//should be 1/r^2 but not practical here
124.     float maxFieldstrength, minFieldstrength = 0;
125.     float newVectorlengthmin = 15, newVectorlengthmax = 35;
126.     float minDiameter = 20, maxDiameter = 400;
127.     //float minChargediameter = 20, maxChargediameter = 400;
128.     maxFieldstrength = map(fieldStrength, minDiameter, maxDiameter, newVectorlengthmin, newVectorlengthmax);//maps the fieldStrength, which is the diameter of the charge, from the max and mix charge diameter to the max and min charger length
129.     float magnitude = map(d, 0, maxdist, maxFieldstrength, minFieldstrength);//the second last value is the maximum length of a vector. 2nd last value should a min and last a max value, inverting them puts longest vectors near charge
130.     pushMatrix();
131.     translate(xField, yField);
132.     rotate(theta);
133.     line(0, 0, magnitude, 0);
134.     beginShape();//this shape are the arrow heads of the vectors
135.     vertex(magnitude, -3);
136.     vertex(magnitude, 3);
137.     vertex(magnitude + 3, 0);
138.     endShape(CLOSE);
139.     popMatrix();
140.     noFill();
141.     noStroke();
142.   }
143.   void update(float x, float y, float diameter, float minChargediameter, float maxChargediameter) {
144.     targetX = x;
145.     targetY = y;
146.     fieldStrength = diameter;
147.     minDiameter = minChargediameter;
148.     maxDiameter = maxChargediameter;
149.   }
150.   void polarity(float r) {
151.     pol = r;
152.   }
153. }

Now I've added to this so that the field strength changes (length of the vectors) if the charge is increased in size by dragging the left button.

Curiously if the charge goes outside the window and is released, it can't be got back!

Thanks,

Shane

Hi,

I am trying to write the object 'charges' in the class 'Electrons' as a element in a 1D array. For now this array has just one element. I am having a problem with line 42. where I try to pass fields from the object 'charges' in the class 'Electrons' to the objects 'vectors' in the class 'Field'.

1. int numCharges = 1;
2. Electrons[] charge = new Electrons[numCharges];//Declare the 1D array called 'charge', the elements of which are objects of the class called 'Electrons'
3. int numVectorsX = 21;//20*30 that's number of vectors across by spacing between each is width and add 1 to the number of vectors in the x-direction
4. int numVectorsY = 21;//10*30 that's number of vectors down by spacing between each is height and add 1 to the number of vectors in the y-direction
5. int distance = 30;//spacing between vectors, same for x and y directions
6. Field[][] vectors = new Field[numVectorsX][numVectorsY];//Declare the 2D array called 'vectors', the elements of which are objects of the class called 'Field'
7. float targetX = 300, targetY = 150, pol, fieldStrength, minDiameter, maxDiameter;//the field initially points to a singularity at the coordinate (300,150). targetX and targetY is where the field points to. 'pol' is the polarity of the charge
8. float theta = 0;//angle between charge and each vector
9. int magnitude;//length or magnitude of a vector
10. int r, g, b;//red green blue variables for charge colour
11. float Fieldstrength;
12. void setup() {
13.   int height, width;
14.   height = (numVectorsX - 1) * distance;
15.   width = (numVectorsY -1) * distance;
16.   size(height, width);
17.   smooth();
18.   noStroke();
19.   for (int i = 0; i < numCharges; i++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
20.     //x, y, r, g, b, transparency, count, initial diameter, minChargediameter, maxChargediameter... the fields
21.     charge[i] = new Electrons(300, 150, 0, 0, 255, 30, 1, 100, 20, 400); //Construct the object charge
22.   }
23.   float maxdist = sqrt(pow(height, 2) + pow(width, 2)) - 50;//Uses pythagoras to calculate diagonal distance of the window. This is the max distance between the charge and any vector
24.   for (int i = 0; i < numVectorsX; i++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
25.     for (int j = 0; j < numVectorsY; j++) {
26.       // xField, yField, magnitude, theta, maxdist
27.       vectors[i][j] = new Field(i*distance, j*distance, magnitude, theta, maxdist);
28.     }
29.   }
30. }
31. void draw() {
32.   background(#DAEBF2);
33.   for (int i = 0; i < numCharges; i++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
34.     charge[i].move();
35.     charge[i].display();
36.   }
37.   for (int i = 0; i < numVectorsX; i++) {
38.     for (int j = 0; j < numVectorsY; j++) {
39.       // xField, yField, l, theta
40.       vectors[i][j].plot();
41.       if (mousePressed) {
42.         vectors[i][j].update(charge[i].x, charge[i].y, charge[i].diameter, charge[i].minChargediameter, charge[i].maxChargediameter);//puts the fields x, y etc. from the object 'charge' into the object 'vectors', there they are set equal to targetX, targetY, etc. which is where the field points to
43.       }
44.       if (mouseButton == CENTER) {
45.         vectors[i][j].polarity(charge[i].r);//puts the field r from the object 'charge' and puts it into the object 'vectors', there it is set equal to 'pol'.
46.       }
47.     }
48.   }
49. }
50. void mouseReleased() {
51.   if (mouseButton == CENTER) {
52.     for (int i = 0; i < numCharges; i++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
53.       charge[i].released();
54.     }
55.   }
56. }
57. class Electrons {
58.   float x, y, r, g, b, transparency, diameter, minChargediameter, maxChargediameter;
59.   int count;
60.   //Constructor
61.   Electrons(float xpos, float ypos, float rpos, float gpos, float bpos, float trans, int countpos, float diameterpos, float minChargediameterpos, float maxChargediameterpos) {
62.     x = xpos;
63.     y = ypos;
64.     r = rpos;
65.     g = gpos;
66.     b = bpos;
67.     transparency = trans;
68.     count = countpos;
69.     diameter = diameterpos;
70.     minChargediameter = minChargediameterpos;
71.     maxChargediameter = maxChargediameterpos;
72.   }
73.   void move() {
74.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))&&(mousePressed == true)) {//tests to see if mouse is on charge
75.       if (mouseButton == LEFT) {
76.         x = mouseX;
77.         y = mouseY;
78.       }
79.       else if (mouseButton == RIGHT) {//dragging mouse toward centre decreases size of charge
80.         if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))>(0)) {
81.           if (diameter < maxChargediameter) {//prevents diameter getting too big, max diameter is 400
82.             diameter = diameter + 5; //increases size of diameter
83.             transparency += 0.5;
84.           }
85.         } //dragging mouse away from center increases size of charge
86.         else if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))<(0)) {
87.           if (diameter > minChargediameter) {//prevents diameter getting too small and circle disappearing, min diameter is 20
88.             diameter = diameter - 5; // decreases size of diameter
89.             transparency -= 0.5;
90.           }
91.         }
92.       }
93.     }
94.   }
95.   void display() {
96.     fill(r, g, b, transparency);//fills the charge with colours red, green, blue
97.     ellipse(x, y, diameter, diameter);//draws the charge
98.   }
99.   void released() {
100.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))) {//tests to see if mouse is on charge
101.       count = (count + 1) % 2;
102.       if (count == 1) {//sets colour to blue once
103.         r = 0;
104.         b = 255;
105.       }
106.       else if (count == 0) {//set colour red to blue
107.         r = 255;
108.         b = 0;
109.       }
110.     }
111.   }
112. }
113. class Field {
114.   float xField, yField, magnitude, theta, maxdist;
115.   //Constructor
116.   Field(float xFieldpos, float yFieldpos, float magnitudepos, float thetapos, float maxdistpos) {
117.     xField = xFieldpos;
118.     yField = yFieldpos;
119.     magnitude = magnitudepos;
120.     theta = thetapos;
121.     maxdist = maxdistpos;
122.   }
123.   void plot() {
124.     float theta = atan((targetY-yField)/(targetX-xField));
125.     if (targetX < xField) {//without this the vectors on the right of screen will point away from charge and vectors on right of screen toward it. All should point away or toward it
126.       theta += PI;
127.     }
128.     if (pol == 0) {//if 'pol' is 0 then r = 0 in charge.released and so charge is blue and positive
129.       theta += PI; //points the field away from the charge position for a positive charge
130.     }   
131.     float d = (sqrt(pow(targetY-yField, 2) + pow(targetX-xField, 2)));//should be 1/r^2 but not practical here
132.     float maxFieldstrength, minFieldstrength = 0;
133.     float newVectorlengthmin = 10, newVectorlengthmax = 35;
134.     float minDiameter = 20, maxDiameter = 400;
135.     maxFieldstrength = map(fieldStrength, minDiameter, maxDiameter, newVectorlengthmin, newVectorlengthmax);//maps the fieldStrength, which is the diameter of the charge, from the max and mix charge diameter to the max and min charger length
136.     if (d > maxFieldstrength) {
137.       float magnitude = map(d, 0, maxdist, maxFieldstrength, minFieldstrength);//the second last value is the maximum length of a vector. 2nd last value should a min and last a max value, inverting them puts longest vectors near charge
138.       float fieldTransparency = map(d, 0, maxdist, 205, -20);
139.       stroke(1, fieldTransparency);
140.       fill(0, 0, 0, fieldTransparency);
141.       pushMatrix();
142.       translate(xField, yField);
143.       rotate(theta);
144.       line(0, 0, magnitude, 0);
145.       beginShape();//this shape are the arrow heads of the vectors
146.       vertex(magnitude, -3);
147.       vertex(magnitude, 3);
148.       vertex(magnitude + 3, 0);
149.       endShape(CLOSE);
150.       popMatrix();
151.       noFill();
152.       noStroke();
153.     }
154.   }
155.   void update(float x, float y, float diameter, float minChargediameter, float maxChargediameter) {
156.     targetX = x;
157.     targetY = y;
158.     fieldStrength = diameter;
159.     minDiameter = minChargediameter;
160.     maxDiameter = maxChargediameter;
161.   }
162.   void polarity(float r) {
163.     pol = r;
164.   }
165. }

Thanks,

Shane

Well withou digging in your code... You are using the same 'i' from the for loop() to call charge[i], well charge is 1 element, so you got array out of bounds. Just changing this to 0 (as there's only one element) solves to me, yo gonna have to make different when this array grows though 

Hi v.k,

Yes I see it now. I think I'll have to have different for() loops for the different arrays. Well I'll go and have a think about this.

Thanks again,

Shane

Hi,

I can now create any number of charges. The vector field from each charge is always visible. But how could I sum the fields and display only the sum of them?

1. int numCharges = 4;//the number of charges
2. Electrons[] charge = new Electrons[numCharges];//Declare the 1D array called 'charge', the elements of which are objects of the class called 'Electrons'
3. int numVectorsX = 21;//20*30 that's number of vectors across by spacing between each is width and add 1 to the number of vectors in the x-direction
4. int numVectorsY = 11;//10*30 that's number of vectors down by spacing between each is height and add 1 to the number of vectors in the y-direction
5. int distance = 30;//spacing between vectors, same for x and y directions
6. Field[][] vectors = new Field[numVectorsX][numVectorsY];//Declare the 2D array called 'vectors', the elements of which are objects of the class called 'Field'
7. float targetX = 300, targetY = 150, pol, fieldStrength, minDiameter, maxDiameter;//the field initially points to a singularity at the coordinate (300,150). targetX and targetY is where the field points to. 'pol' is the polarity of the charge
8. float theta = 0;//angle between charge and each vector
9. int magnitude;//length or magnitude of a vector
10. int r, g, b;//red green blue variables for charge colour
11. float Fieldstrength;
12. void setup() {
13.   size(600, 300);
14.   smooth();
15.   noStroke();
16.   for (int k = 0; k < numCharges; k++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
17.     //x, y, r, g, b, transparency, count, initial diameter, minChargediameter, maxChargediameter... the fields
18.     charge[k] = new Electrons(100 + (100*k), 100 + (50*k), 0, 0, 255, 30, 1, 100, 20, 400); //Construct the object charge
19.   }
20.   float maxdist = 400;
21.   for (int i = 0; i < numVectorsX; i++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
22.     for (int j = 0; j < numVectorsY; j++) {
23.       // xField, yField, magnitude, theta, maxdist
24.       vectors[i][j] = new Field(i*distance, j*distance, magnitude, theta, maxdist);
25.     }
26.   }
27. }
28. void draw() {
29.   background(#DAEBF2);
30.   for (int k = 0; k < numCharges; k++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
31.     charge[k].move();
32.     charge[k].display();
33.   }
34.   for (int k = 0; k < numCharges; k++) {
35.     for (int i = 0; i < numVectorsX; i++) {
36.       for (int j = 0; j < numVectorsY; j++) {
37.         // xField, yField, l, theta
38.         vectors[i][j].plot();
39.         vectors[i][j].update(charge[k].x, charge[k].y, charge[k].diameter, charge[k].minChargediameter, charge[k].maxChargediameter);//puts the fields x, y etc. from the object 'charge' into the object 'vectors', there they are set equal to targetX, targetY, etc. which is where the field points to
40.         vectors[i][j].polarity(charge[k].r);//puts the field r from the object 'charge' into the object 'vectors', there it is set equal to 'pol'.
41.       }
42.     }
43.   }
44. }
45. void mouseReleased() {
46.   if (mouseButton == CENTER) {
47.     for (int k = 0; k < numCharges; k++) {//these loops populate the 2D array, each element of this array is an object and each object is a vector
48.       charge[k].released();
49.     }
50.   }
51. }
52. class Electrons {
53.   float x, y, r, g, b, transparency, diameter, minChargediameter, maxChargediameter;
54.   int count;
55.   //Constructor
56.   Electrons(float xpos, float ypos, float rpos, float gpos, float bpos, float trans, int countpos, float diameterpos, float minChargediameterpos, float maxChargediameterpos) {
57.     x = xpos;
58.     y = ypos;
59.     r = rpos;
60.     g = gpos;
61.     b = bpos;
62.     transparency = trans;
63.     count = countpos;
64.     diameter = diameterpos;
65.     minChargediameter = minChargediameterpos;
66.     maxChargediameter = maxChargediameterpos;
67.   }
68.   void move() {
69.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))&&(mousePressed == true)) {//tests to see if mouse is on charge
70.       if (mouseButton == LEFT) {
71.         x = mouseX;
72.         y = mouseY;
73.       }
74.       else if (mouseButton == RIGHT) {//dragging mouse toward centre decreases size of charge
75.         if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))>(0)) {
76.           if (diameter < maxChargediameter) {//prevents diameter getting too big, max diameter is 400
77.             diameter = diameter + 5; //increases size of diameter
78.             transparency += 0.5;
79.           }
80.         } //dragging mouse away from center increases size of charge
81.         else if (((dist(mouseX, mouseY, x, y))-(dist(pmouseX, pmouseY, x, y)))<(0)) {
82.           if (diameter > minChargediameter) {//prevents diameter getting too small and circle disappearing, min diameter is 20
83.             diameter = diameter - 5; // decreases size of diameter
84.             transparency -= 0.5;
85.           }
86.         }
87.       }
88.     }
89.   }
90.   void display() {
91.     fill(r, g, b, transparency);//fills the charge with colours red, green, blue
92.     ellipse(x, y, diameter, diameter);//draws the charge
93.   }
94.   void released() {
95.     if (((dist(mouseX, mouseY, x, y))<(diameter/2))) {//tests to see if mouse is on charge
96.       count = (count + 1) % 2;
97.       if (count == 1) {//sets colour to blue once
98.         r = 0;
99.         b = 255;
100.       }
101.       else if (count == 0) {//set colour red to blue
102.         r = 255;
103.         b = 0;
104.       }
105.     }
106.   }
107. }
108. class Field {
109.   float xField, yField, magnitude, theta, maxdist;
110.   //Constructor
111.   Field(float xFieldpos, float yFieldpos, float magnitudepos, float thetapos, float maxdistpos) {
112.     xField = xFieldpos;
113.     yField = yFieldpos;
114.     magnitude = magnitudepos;
115.     theta = thetapos;
116.     maxdist = maxdistpos;
117.   }
118.   void plot() {
119.     float theta = atan((targetY-yField)/(targetX-xField));
120.     if (targetX < xField) {//without this the vectors on the right of screen will point away from charge and vectors on right of screen toward it. All should point away or toward it
121.       theta += PI;
122.     }
123.     if (pol == 0) {//if 'pol' is 0 then r = 0 in charge.released and so charge is blue and positive
124.       theta += PI; //points the field away from the charge position for a positive charge
125.     }   
126.     float d = (sqrt(pow(targetY-yField, 2) + pow(targetX-xField, 2)));//should be 1/r^2 but not practical here
127.     float maxFieldstrength, minFieldstrength = 0;
128.     float newVectorlengthmin = 10, newVectorlengthmax = 35;
129.     float minDiameter = 20, maxDiameter = 400;
130.     maxFieldstrength = map(fieldStrength, minDiameter, maxDiameter, newVectorlengthmin, newVectorlengthmax);//maps the fieldStrength, which is the diameter of the charge, from the max and mix charge diameter to the max and min charger length
131.     if (d > maxFieldstrength) {
132.       float magnitude = map(d, 0, maxdist, maxFieldstrength, minFieldstrength);//the second last value is the maximum length of a vector. 2nd last value should a min and last a max value, inverting them puts longest vectors near charge
133.       float fieldTransparency = map(d, 0, maxdist, 205, -20);
134.       stroke(1, fieldTransparency);
135.       fill(0, 0, 0);
136.       pushMatrix();
137.       translate(xField, yField);
138.       rotate(theta);
139.       line(0, 0, magnitude, 0);
140.       beginShape();//this shape are the arrow heads of the vectors
141.       vertex(magnitude, -3);
142.       vertex(magnitude, 3);
143.       vertex(magnitude + 3, 0);
144.       endShape(CLOSE);
145.       popMatrix();
146.       noFill();
147.       noStroke();
148.     }
149.   }
150.   void update(float x, float y, float diameter, float minChargediameter, float maxChargediameter) {
151.     targetX = x;
152.     targetY = y;
153.     fieldStrength = diameter;
154.     minDiameter = minChargediameter;
155.     maxDiameter = maxChargediameter;
156.   }
157.   void polarity(float r) {
158.     pol = r;
159.   }
160. }

Thanks,

Shane

Hi Petras,

You could not have got me back thinking about this problem as a better time. I will have time over the next three weeks to work on it starting tomorrow.

So thank you for looking at it and I will reply with my effort soon.

Thanks,

Shane