Newton's cradle

Programming Questions

allonestr..

in Programming Questions • 2 years ago

alt = "HELP purleeze, oldie needs help"

I've slogging away at this in varying forms for quite some time, and have finally got close. The balls are swinging - mimicking SHM*. The collisions are working the best ever. But I've been staring at it so long that I can't figure out how to drag the balls to the side to start it all off.

*Note that I say mimicking SHM, though I got that to work and have left in the code for it. Because the movement is frame-based it played hell with the collisions.

Note also that there's a lot of testing stuff in the code that I'd normally strip out before posting. And there's lots more to do that I can't test until I get the dragging to work.

Thanks

string

main tab

int numBobs = 5;
int[] swingDegrees;
float[] swingAngles;
Pendulum[] bobs;
float stringLength = 100;
float bobSize = 30;
color[] colours;
int frameSpeed = 32; //don't change this! 25-32
float xoffset;
float closestAngle = 100;
int closestAngleCount = 100;
void setup()
{
size(300, 300);
background(255);
smooth();
frameRate(frameSpeed);
// noLoop();
swingAngles = new float[17]; //magic number and angles found by experiment and observation
int[] swingDegrees = {38, 37, 34, 31, 26, 20, 14, 7, 0, -7, -14, -20, -26, -31, -34, -37, -38};
for(int a = 0; a < swingDegrees.length; a++)
{
    swingAngles[a] = radians(swingDegrees[a]);
}
// println(swingAngles);

xoffset = (width - (numBobs - 1) * bobSize) / 2;

bobs = new Pendulum[numBobs];
colours = new color[numBobs];
// color[] colours = {color(201, 58, 18), color(190, 96, 24), color(191, 170, 87), color(149, 130, 68), color(141, 171, 173)};

for(int b = 0; b < numBobs; b++)
{
    colours[b] = color(b * 255 / numBobs); // greyscale for testing
    bobs[b] = new Pendulum(swingAngles, stringLength, bobSize, colours[b]);
//    bobs[b] = new Pendulum(swingAngles, stringLength, bobSize, colours[(int)random(0, colours.length)]);
    bobs[b].setVertical();
}

// setStartPositions();
autoStartLeft();
// autoStartRight();
}
//void setStartPositions()
//{
// for(int b = 0; b < numBobs; b++)
// {
//    bobs[b].swinging = false;
//    bobs[b].count = 8;
// }
//}
void autoStartLeft()
{
bobs[0].count = 0;
bobs[0].swinging = true;
}
void autoStartRight()
{
bobs[numBobs - 1].count = 15;
bobs[numBobs - 1].swinging = true;
}

void draw()
{
background(255, 200);

if(numBobs > 1)
{
    click(bobs);
}
for(int b = 0; b < numBobs; b++)
{
    pushMatrix();
    translate(xoffset + b * bobSize, 100);
    bobs[b].display();
    popMatrix();
}
//}
//
//void mouseDragged()
//{
if(mousePressed)
{
for(int b = 0; b < numBobs; b++)
{
    float bobX = xoffset + b * bobSize + bobs[b].getBobCentre().x;
    float bobY = 100 + bobs[b].getBobCentre().y;
    if(dist(mouseX, mouseY, bobX, bobY) < bobSize / 2)
    {
      println("GRAB " + b);
      float dragX = (xoffset + b * bobSize) - mouseX;
      float dragAngle = asin(dragX / stringLength);
      println(dragX +" "+ degrees(dragAngle));

      if(pmouseX > mouseX) // drag clockwise
      {
        closestAngle = 100;
        closestAngleCount = 100;
        println("CLOCK");
        for(int a = 8; a < 17; a++) //swingAngles array is 17 long
        {
          float compareAngle = abs(swingAngles[a] - dragAngle);
          if(compareAngle < closestAngle)
          {
            closestAngle = compareAngle;
            closestAngleCount = a;
          }
        }
        for(int c = 0; c <= b; c++) // drag all those to left too
        {
          bobs[c].setCount(closestAngleCount);
        }
      }
      else if(pmouseX < mouseX) //drag anticlockwise
      {
        closestAngle = 100;
        closestAngleCount = 100;
        println("ANTI");
        for(int a = 0; a <= 8; a++) //swingAngles array is 17 long
        {
          float compareAngle = abs(swingAngles[a] - dragAngle);
          println(compareAngle);
          if(compareAngle < closestAngle)
          {
            closestAngle = compareAngle;
            closestAngleCount = a;
            println("a= " + a);
          }
        }
        for(int c = b; c < numBobs; c++) // drag all those to right too
        {
          bobs[c].count = closestAngleCount;
        }
      }
    }
}
}
}
void keyPressed()
{
if(keyCode == 32) //spacebar
{
    for(int b = 0; b < numBobs; b++) bobs[b].setVertical();
}
if(key == 'l' || key == 'L')
{
    autoStartLeft();
}
if(key == 'r' || key == 'R')
{
    autoStartRight();
}
}

Pendulum class

//comments #1 - uncomment these to see correct swinging motion (SHM)
// comments #2 - uncomment for good enough swinging motion
// neither will work with the other tabs here (the code has since evolved)
// for sensible results set framerate to 25-32, and stringLength to 100
// I've moved on to a fixed swing as the collision wasn't working well
class Pendulum
{
float angle;
float stringLength;
float bobSize;
color colour;
// float velocity = 0; //#1
// float gravity = 100;//98 //#1
// float swingGravity = gravity / frameSpeed; //#1
float[] swingAngles;
float friction = 0.99;

int count = 8;
Boolean swinging = false;
String swingDirection = "ANTICLOCK";

Pendulum(float[] swingAngles, float stringLength, float bobSize, color colour)
{
    this.stringLength = stringLength;
    this.bobSize = bobSize;
    this.colour = colour;
    this.swingAngles = swingAngles;
    this.angle = angle;
    this.count = count;
}

void display()
{
    float bobxpos = getBobCentre().x;
    float bobypos = getBobCentre().y;
    stroke(0);
    strokeWeight(2);
    line(0, 0, bobxpos, bobypos);
    noStroke();
    fill(colour);
    ellipse(bobxpos, bobypos, bobSize, bobSize);

    if(swinging)
    {
      angle = swingAngles[count];
      if(count == 0)
      {
        swingDirection = "ANTICLOCK";
      }
      if(count == 16)
      {
        swingDirection = "CLOCK";
      }
      if(swingDirection == "ANTICLOCK")
      {
        count++;
      }
      if(swingDirection == "CLOCK")
      {
        count--;
      }
    }
}
void setCount(int newCount)
{
    count = newCount;
}
void setVertical()
{
    setCount(8);
    swinging = false;
}
void setSwingLeft()
{
    swinging = true;
    swingDirection = "CLOCK";
}
void setSwingRight()
{
    swinging = true;
    swingDirection = "ANTICLOCK";
}
PVector getBobCentre()
{
    float bobCentreX = cos(angle + HALF_PI) * stringLength;
    float bobCentreY = sin(angle + HALF_PI) * stringLength;
    return new PVector(bobCentreX, bobCentreY);
}
}

// void swing()
// {
//    velocity += (swingGravity / stringLength) * sin(angle); //#1
//    velocity *= friction; //#1
//    angle -= velocity; //#1
//    velocity += (sin(angle) / frameRate); //#2
//    angle -= velocity; //#2
// }

click function

void click(Pendulum[] bobs)
{
    for(int b = 0; b < numBobs - 1; b++)
    {
      if(bobs[b].count > bobs[b+1].count)
      {
        // if both swinging
        if((bobs[b].swinging == true) && (bobs[b+1].swinging == true))
        {
//          println("both");
          int tempCount = bobs[b].count;
          bobs[b].count = bobs[b+1].count;
          bobs[b+1].count = tempCount;
          bobs[b].setSwingLeft();
          bobs[b+1].setSwingRight();
        } else
        // if left one swinging, right one still and so vertical
        if((bobs[b].swinging == true) && (bobs[b+1].swinging == false))
        {
//          println("left swinging");
          bobs[b].setVertical();
          bobs[b+1].setSwingRight();
        } else
        // if left one still and so vertical, right one swinging
        if((bobs[b+1].swinging == true) && (bobs[b].swinging == false))
        {
//          println("right swinging");
          bobs[b+1].setVertical();
          bobs[b].setSwingLeft();
        }
      }
    }
}

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