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* Lesson 10: Keyboard input

** Getting set up

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[[file:images/lesson01-ticblank.png]]

You can either edit over your existing code, or start a new program.
If you want to start a new program, press *ESCAPE* until you get to
the main prompt:

Then type in =new lua=, hit *ENTER*, then =save GAMENAME.LUA=, hit
*ENTER*. (Replace "GAMENAME" with whatever you want.)

#+BEGIN_SRC terminal
  > new lua
  new cart has been created

  > save GAMENAME.lua
  cart GAMENAME.lua saved!
#+END_SRC

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--

** Draw two sprites

[[file:images/lesson-keymove-sprites.png]]

Draw two sprites for this program. I have a fish that the player
will control and a bubble that will move automatically.


** Editing the code

In the code editor we're going to write our setup code. We want to
have a player (x,y) so we're creating variables =px= and =py=, and a
bubble (x,y) so that's =bx= and =by=. You can set the number values
to whatever you'd like.

Within the TIC() function I'm just clearing the screen and
displaying the fish and the bubble sprites at their coordinates.

#+BEGIN_SRC lua
  -- Setup
  px = 120; py = 70             -- Player coordinates
  bx = 80;  by = 136            -- Bubble coordinates

  -- Game loop
  function TIC()
    cls(11)                     -- Clear screen
    spr(0,px,py)                -- Draw fish
    spr(1,bx,by)                -- Draw bubble
  end
#+END_SRC

Next, let's update the buble to move automatically. The bubble is
/not/ player-controlled, it just moves up each game cycle. Once it
is off the screen (at the top), we give it a new random horizontal
position and then move it back to the bottom of the screen.

#+BEGIN_SRC lua
  -- Bubble
  by=by-1                       -- Move bubble up
  if by < -8 then               -- Check if bubble is off-screen
   bx = math.random(0,230)      -- Set random x
   by = 136                     -- Put under screen
  end
#+END_SRC

[[file:images/lesson-keymove-animation1.gif]]

Next we want to check for button presses. TIC-80 has the following
button codes:

[[file:images/tic80-buttons.png]]

So UP is 0, DOWN is 1, LEFT is 2, and RIGHT is 3.

#+BEGIN_SRC lua
  -- Move player
  if btn(0) then py=py-1 end -- UP
  if btn(1) then py=py+1 end -- DOWN
  if btn(2) then px=px-1 end -- LEFT
  if btn(3) then px=px+1 end -- RIGHT
#+END_SRC

** Testing

[[file:images/lesson-keymove-animation2.gif]]

Now when we run the program we can move the fish around, and the
bubble moves on its own. They currently don't interact, but that
will be for later. We /could/ add the Distance function into the
program, and add some logic, but we will put it all together later.

** Save your work

Make sure to press the *CTRL+S* key, or press *ESC* to go to the
prompt and type =save= to save your work! If you want to access the
folder with your code, type =folder=.

If you have a USB flash drive, make sure to copy your file over so
you don't lose it when the computer resets!

** Back to the course page!

[[../index.org][⬅️ Once you're all done, go back to the course homepage!]]