hills tweetcart from https://twitter.com/lucatron_/status/1461514152459993092

hills.lua

-- Color palette.
pal({131,3,139,11,138},1)

-- Set dither pattern.
-- `▒` is a global variable inserted by PICO-8 that has the value 23130.5.
-- The value corresponds to a fillp pattern that looks like the glyph itself.
-- We need to floor ▒ to remove the .5, which signifies the pattern should be transparent.
-- (`\` is PICO-8's integer divison operator. So `x\1` floors the left operand.)
fillp(▒\1)

-- Get a random number. Passing -1 will generate nearly any PICO-8 number.
r=rnd(-1)

-- Make short alias for sin.
f=sin

-- Render 151 frames.
-- Once this loop ends, we call `run()` to restart the application, which will
-- generate a new point of view thanks the previous `rnd` call.
for i=0,150 do
  -- Camera rotation. Use random initial offset and increase over time.
  -- ▤ is a PICO-8 global with the value 3855.5.
  a=r+i/▤

  -- To maximise performance need to use local variables rather than globals.
  -- (Globals use a table lookup.)
  -- `c` and `s` save the `cos(a)` and `sin(a)` values.
  -- `u` and `v` will be used for world space coordinates.
  -- `h` will be used for terrain height.
  local c,s,u,v,h = cos(a),f(a)

  -- Iterate pixels on the screen.
  -- Each pixel will be transformed into world space, and we'll draw each point
  -- as a section of terrain.
  --
  -- Note we extend past the bottom of the screen to ensure we render terrain
  -- that originates from below the screen and is still visible.
  for y=4,156 do
    -- It's not possible to render 152*127 points in one frame, so we split them
    -- over 6 frames. We render every 6th column, and change the offset by 1
    -- every frame.
    -- This causes some ghosting, but a slow camera hides most of it.
    -- (This also causes the nice Windows Movie Maker transition between runs!)
    for x=i%6,127,6 do
      -- Convert screen space to world space (orthographic).
      -- Note: x/5-13 ≈≈ (x-64)/5  (tilts the camera up)
      u=x/5-13
      v=y-90
      u,v = (c*u - s*v+r)/5,(s*u + c*v)/5  -- Rotate and scale!

      -- Get terrain height from world (u, v).
      -- I found that frequency-modulation (using sin inside of sin) was a nice
      -- simple way to get varied terrain.
      -- The `3.2` was chosen so that `h` can be used directly as a color value.
      h=3.2
       +f(u/8 + f(u/9 - v/7)/3)
       +f(u/8 - v/9 + f(v/7)/3)
      
      -- Draw terrain point as vertical line.
      -- `h + .5` is the first dithered color value (offset by half).
      -- `h\1*16` is the second ditherd color value (shift right by 2 and no offset).
      -- Note: h\1*16 == (h\1)*16 == flr(h)*16
      line(
        x, y,
        x, y - h*7,
        h + .5 + h\1*16
      )
    end
  end

  flip()
end

run()