https://processing.org/download

Starter Code

float timestep = 0.1;

float spaceship_mass = 2;
float gravitational_constant = 10;

float current_position = 256;
float current_velocity = 0;

float error = 0.0;

void setup() {
  size(512, 512);
}

void draw() {
  // // jim's setup
  // origin at center of screen
  // x-axis points right
  // y-axis points up
  scale(1, -1);
  translate(width / 2, -height / 2);
  float transformedMouseX = mouseX - width / 2;
  float transformedMouseY = -mouseY + height / 2;

  // // controller
  float target_position = transformedMouseY;
  // TODO: float proportional_gain = ???;
  // TODO: float derivative_gain = ???;
  // TODO: set thruster_force
  float thruster_force = 0.0;
  {
    // TODO: error = ???;
  }

  // // actuator limits
  // thruster_force = clamp(thruster_force, 0.0, 100.0);
  if (thruster_force < 0.0) {
    thruster_force = 0.0;
  }
  if (thruster_force > 100.0) {
    thruster_force = 100.0;
  }

  // // physics
  // semi-implicit euler
  float current_acceleration = -gravitational_constant + thruster_force / spaceship_mass; // a = F / m
  current_velocity += timestep * current_acceleration;
  current_position += timestep * current_velocity;

  // // draw
  background(255);
  fill(255);
  line(-width / 2, 0.0, width / 2, 0.0);
  line(-width / 8, target_position, width / 8, target_position);
  circle(0, current_position, 16.0);
  line(0.0, current_position, 0.0, current_position - thruster_force);
}