hologram.lua

--This code uses the following RGB trick
--https://gist.github.com/lucatronica/6dc7fae058440ab208d99584fe314e5c

--Setting up the RGB colors.
--Unlike the above example, we're using all 16 colors now!
--That's because we're now using the 4th bit of the color index.
--We use this bit (color 8) for the background text color.
pal({
     8,11,10,140,14,12,7,
 129,8,11,10,140,14,12,7,
},1)

--frame count
n=0

function _draw()
  cls()

  --Draw the background text.
  --Seeding random makes the random pattern consistent across frames.
  srand()
  --Iterate the lines from top to bottom.
  for y=0,127,7 do
    --'d' is the direction the text should move: -1 or +1.
    local d=sgn(y%14-7)

    --Only the third line should be in English.
    if y==14 then
      --Iterate the characters.
      --We wrap X in a 150 range to prevent "teleporting" at the edges of the screen.
      --(150 was chosen since it's a multiple of 6 and 5)
      for x=0,149,6 do
        --The character index.
        local i=1+(x/6)%5
        --Draw one character.
        ?sub("pico8 ",i,i),(x+n*d)%150-11,y,8
      end
    else
      for x=0,143,8 do
        --2 new features here!
        --  chr() - convert a byte to a character
        --  Native kana (indexes between 154 and 253).
        --
        --'2.5*max(sin(rnd()+t()/3)))' is used vary each character over time:
        --max() is called with a single argument as the second arg defaults to 0.
        --This creates the following pattern
        --https://commons.wikimedia.org/wiki/File:Simple_half-wave_rectified_sine.svg
        --Note how it stays still for half the time!
        ?chr(154+rnd(99)+2.5*max(sin(rnd()+t()/3))),(x+n*d)%144-8,y,8
      end
    end
  end
  
  --Powers of 2.
  local p={[0]=1,2,4}
  
  --Pre-calculate hologram rotation parameters.
  --'q' is the rotation amount.
  local q=t()/12
  local c=cos(q)
  local s=sin(q)
  
  --Iterate over pixels in the text we just draw (just the top left corner).
  for y=0,31.5,.5 do
    for x=0,31.5,.5 do
      --New operator '&' (binary AND)!
      --We're checking if the 4th bit is set (that it's a text pixel).
      if pget(x,y)&8==8 then
        --'u' and 'v' X and Y coordinates.
        --Rotation and perspective are relative to (0,0), so we need to shift
        --'x' and 'y' by 16 pixels to center them around (0,0).
        local x2=x-16
        
        --Iterate the 3 RGB layers.
        for i=0,2 do
          --The z position. We now have a 3D coordinate ('x','y','z')!
          local z2=(i-1)*1.65
          
          --Rotate the coordinate around the Y axis.
          --i.e. rotate (X,Z)=('u','z') around (0,0). 
          local x3=x2*c-z2*s
          local z3=x2*s+z2*c
          
          --Apply perspective.
          local k=.54-z3/72
          local u=64+x3/k
          local v=64+(y-16)/k
          
          --New operator '|' (binary OR)!
          --p[i] is the color of the current layer.
          pset(u,v,pget(u,v)|p[i])
        end
      end
    end
  end
  
  n+=1
end