0. Introduction to game programming

The main loop

• How do video games and other computer software run?
• When we execute a simple script, the computer runs it, and then stops execution
• Thus, to keep the program running, we need an infinite loop
  • This is known as the main loop

Main loop: A simplified example

• An extremely simplified version looks something like this

  while (true)
  {
    processInput();
    update();
    render();
  }
  

• first we poll the user for input: were any buttons pressed?
• then we update all the game objects
  • Player moves according to input, enemies move on their own, etc.
• then we draw, or render everything on screen
• one round inside the main loop is said to take one frame

Unity main loop

• In Unity, we can create scripts inside GameObjects
  • if a script includes an update method, it is executed inside that main loop every frame
• Also btw, the main loop is in reality much more complicated
• Manual: Order of execution for event functions

Runtime vs. compile time

• two important concepts:
• Before a program can be executed, it has to be converted into machine code, i.e, compiled
  • the time this process takes is called compile time
  • every time you save a C# script file and return to Unity, Unity will compile the scripts for its use
• after compiling, the application can be run
  • this time period is called runtime