// [c_pendu] Ewing's pendulum simulation with spring and graph
// Leapfrog integration + frame export
// Clear only the pendulum area and keep the graph trajectory
// Each frame can be saved and converted into a video
// [c_pendu]**************************************************[Ver 0.00]
//  Caluclation of period for the EWING's pendulam     longer period
//  [leapfrog method]
//                          prog.by Y.Okamoto 1991.03/05-03/07
// **********************************************************************

float PI_ = 3.14159;
float RAD = PI_/180.0;

// Screen coordinates
float X00 = 200, Y00 = 350;   // hinge point
float DT = 0.02;
...
float L0 = 0.07;                // init spring length
float GAMMA = 0*RAD;
float THETA = 3*RAD;
float PHAI = 0*RAD;

float I_;
float BETA;
float B;

// Variables for calculation
float X, Y, L, CSA, SNA, P, AC;
float V = 0, T = 0;
float XX, YY, WXX, WYY, XXP, YYP;
float XX2, YY2, WX2, WY2;

// Frame saving settings
int frameCountMax = 600;  // Maximum number of frames to save (e.g., 500 → about 10 seconds)
boolean saveFrames = true; // Enable frame saving when true

void setup() {
  size(800, 600);
  
  // Initial coordinates
  X = L0*cos(PHAI);
  Y = L0*sin(PHAI);
}

void draw() {

  // Equations of motion
  ...
  
  // --- Clear the pendulum drawing area with black ---
  noStroke();
  fill(0);
  rect(0, 0, width, height - 160); // Clear only the upper part (keep the lower graph)

  // --- Leapfrog integration ---
  ...
  
  // Recalculation
  ...
  
  // Coordinate transformation
  ...
  
  // --- Pendulum drawing ---
  stroke(255);
  line(XX, YY, XXP, YYP);     // Spring
  line(WXX, WYY, X00, Y00);   // Boom
  ellipse(WXX, WYY, RW, RW);  // Bob

  // --- Time display ---
  ...
  
  // --- Draw lower graph (keep trajectory) ---
  float gy0 = height - 100; // Bottom of graph
  float gxScale = 20;       // Horizontal axis scale
  float gyScale = 800;      // Vertical axis scale

  stroke(0, 255, 0);
  point(gx0 + T*gxScale, gy0 - (WY - 0)*gyScale); // Plot of bob height

  // --- Frame saving ---
  if (saveFrames && frameCount <= frameCountMax) {
    if (frameCount % 1 == 0) {  // Save every 4 frames
      saveFrame("frames/frame-####.png");
    }
    if (frameCount == frameCountMax) {
      println("Frame saving completed (" + frameCountMax + "枚)");
      noLoop(); // Automatic stop
    }
  }
}