Processing Stuff

button.pde

import java.util.ArrayList;

class Button {
  float[] coords;
  float[] dimensions;
  String text;
  Runnable function;
  
  float[] centre_coords;
  
  Button(float[] co, float[] dim, String txt, Runnable fn) {
    coords = co;
    dimensions = dim;
    text = txt;
    function = fn;
  }
  
  void drawText() {
    CentreText disp_text = new CentreText(text, 1,
                                          new float[] {centre_coords[0], centre_coords[1]},
                                          new float[] {dimensions[0], dimensions[1]});
    disp_text.displayText();
  }
  
  void drawButton() {
    centre_coords = new float[] {coords[0] + (dimensions[0] / 2),
                                 coords[1] + (dimensions[1] / 2)};
    rect(coords[0], coords[1], dimensions[0], dimensions[1]);
    
    drawText();
  }
  
  void clicked() {
    function.run();
  }
}

class ButtonWindow {
  ArrayList<float[]> window = new ArrayList<float[]>();
  ArrayList<Runnable> window_commands = new ArrayList<Runnable>();
  
  void addButton(Button btn) {
    window.add(new float[] {btn.coords[0], btn.coords[1],
                           btn.coords[0] + btn.dimensions[0],
                           btn.coords[1] + btn.dimensions[1]});
    window_commands.add(btn.function);
  }
  
  Runnable checkClick() {
    for (int a = 0; a < window.size(); a++) {
      if (window.get(a)[0] < mouseX && mouseX < window.get(a)[2] &&
          window.get(a)[1] < mouseY && mouseY < window.get(a)[3]) {
        return window_commands.get(a);
      }
    }
    return new Runnable() {
      public void run() {
      }
    };
  }
}

centretext.pde

class CentreText {
  String text;
  float font_size;
  float[] coords;
  float[] dimensions;
  
  float text_width;
  
  CentreText(String txt, int size, float[] co, float[] dim) {
    coords = co;
    text = txt;
    font_size = size;
    dimensions = dim;

    textSize(font_size);
    text_width = textWidth(text);
  }
  
  void changeFontSize() {
    textSize(1);
    font_size = (dimensions[0] - (dimensions[0] / 100)) / textWidth(text);
    if (font_size > dimensions[1]) {
      font_size = dimensions[1] - (dimensions[1] / 100);
    }
    textSize(font_size);
    text_width = textWidth(text);
  }
  
  void displayText() {
    changeFontSize();
    fill(#000000);
    text(text, coords[0] - (text_width / 2), coords[1] + (font_size / 3));
  }
}

progressbar.pde

class ProgressBar {
  float[] dimensions;
  float[] coords;
  int colour;
  ProgressBar(float[] dim, float[] co, int col) {
    dimensions = dim;
    coords = co;
    colour = col;
  }
  
  void fill_bar() {
    fill(#ffffff);
    rect(coords[0], coords[1], dimensions[0], dimensions[1]);
  }
  
  void update(float percent) {
    float progress_width;
    float x_axis;
    String percent_str = Double.toString(Math.ceil(percent * 100)) + "%";
    
    if (percent < 0.5) {
      progress_width = dimensions[0] * (1 - percent);
      x_axis = coords[0] + (dimensions[0] * (1 + percent) / 2);
    } else {
      progress_width = dimensions[0] * percent;
      x_axis = coords[0] + (progress_width / 2);
    }
    
    fill_bar();
    fill(colour);
    rect(coords[0], coords[1], dimensions[0] * percent, dimensions[1]);
    CentreText disp_percent = new CentreText(percent_str, 1,
                                             new float[] {x_axis,
                                                          coords[1] + (dimensions[1] / 2)},
                                             new float[] {progress_width, dimensions[1]});
    disp_percent.displayText();
  }
}

sketch.pde

ButtonWindow window = new ButtonWindow();
Button start = new Button(new float[] {10, 10},
                          new float[] {100, 50}, "Start",
                          new Runnable() {
                            public void run() {
                              progress_inc = 1;
                            }
                          });
                         
Button end = new Button(new float[] {120, 10},
                        new float[] {100, 50}, "End",
                        new Runnable() {
                          public void run() {
                            progress_inc = 0;
                          }
                        });
                         
ProgressBar other = new ProgressBar(new float[] {200, 20},
                                    new float[] {590, 10},
                                    #ff00ff);

float progress = 0;
float progress_inc = 0;
boolean click = true;

long start_time = System.currentTimeMillis();
int start_count = 0;

void process_prog() {
  progress = (progress + progress_inc) % 100;
  other.update(progress / 100);
}

void setup() {
  size(800, 800);
  start.drawButton();
  window.addButton(start);
  end.drawButton();
  window.addButton(end);
  other.update(0);
}

void draw() {
  if (mousePressed && click) {
    window.checkClick().run();
    click = false;
  } else if (!mousePressed) {
    click = true;
  }
  if ((System.currentTimeMillis() - start_time) / 100 > start_count) {
    start_count += 1;
    process_prog();
  }
}