Spaceship with gravity

Notes

Use the left and right arrow keys to rotate the ship. Press the up arrow key to turn on the engine.

The world now has gravity and a ground you can land on. The ship's ACCELERATION must be stronger than GRAVITY, or it will never be able to move up.

Source

/* @pjs preload="ship.png, ground.png"; */

Spritesheet ship;
PImage ground;

float ROTATION_SPEED = 2.8;
float ACCELERATION = 0.25;
float MAX_SPEED = 2.5;
float DRAG = 1;
float GRAVITY = 0.05;

boolean leftKeyDown, rightKeyDown, upKeyDown;

float angle = -90;
PVector shipPosition;
PVector shipVelocity;
PVector shipAcceleration;
float angularVelocity;

int ship_frame;

void setup(){
  size(640, 480);
  
  imageMode(CENTER);
  
  // Load images
  ground = loadImage("ground.png");
  ship = new Spritesheet(loadImage("ship.png"), 2);
  shipPosition = new PVector(width/2, height/2, 0);
  shipVelocity = new PVector(0,0,0);
  shipAcceleration = new PVector(0,0,0);
}

void draw(){
  background(#333333);
  
  if(leftKeyDown){
    angularVelocity = -ROTATION_SPEED; 
  }else if(rightKeyDown){
    angularVelocity = ROTATION_SPEED;
  }else{
    angularVelocity = 0; 
  }
  
  if(upKeyDown){
    shipAcceleration.set(cos(radians(angle)) * ACCELERATION, sin(radians(angle)) * ACCELERATION, 0);
    ship_frame = 1; 
  }else{
    shipAcceleration.set(0, 0, 0);
    ship_frame = 0; 
  }
  
  // Create some ground, adjust because of imageMode(CENTER)
  for(int i = 0; i < width; i += ground.width){
     image(ground, i + 16, height - ground.height/2); 
  }  
  
  shipVelocity.add(shipAcceleration);
  shipVelocity.limit(MAX_SPEED);
  if(shipAcceleration.mag() == 0){
    shipVelocity.mult(DRAG);
  }
  shipPosition.add(shipVelocity);
  
  shipVelocity.y += GRAVITY;
  
  angle += angularVelocity;
  
  // Keep the ship on the screen
  if(shipPosition.x > width) shipPosition.x = 0;
  if(shipPosition.x < 0) shipPosition.x = width;
  if(shipPosition.y > height - ground.height * 1.5) shipPosition.y = height - ground.height * 1.5;
  
  pushMatrix();
  translate(shipPosition.x, shipPosition.y);
  rotate(radians(angle));
  image(ship.getFrame(ship_frame), 0, 0);
  popMatrix();
}

void keyPressed(){
  if(key == CODED){
     if(keyCode == LEFT){
       leftKeyDown = true;
     }
     if(keyCode == RIGHT){
       rightKeyDown = true;
     }
     if(keyCode == UP){
       upKeyDown = true;
     }
  }
}

void keyReleased(){
  if(key == CODED){
     if(keyCode == LEFT || keyCode == RIGHT){
        leftKeyDown = rightKeyDown = false;
     }
     if(keyCode == UP){
       upKeyDown = false;
     }
  }
}

class Spritesheet{
 PImage[] frames;
 
 Spritesheet(PImage img, int noFrames){
  int frameHeight = img.height / noFrames;
  frames = new PImage[noFrames];
  for(int i = 0; i < frames.length; i++){
    frames[i] = img.get(0, frameHeight * i, img.width, frameHeight);
  }
 }
 
 PImage getFrame(int frame){
   if(frame < frames.length)
     return frames[frame];
   return null;
 }
}