jellies.lua

::_::
cls()

--Iterate 6 jellies. The 0th one will be invisible, but we need it for pal().
for n=0,6 do
  --The x position of the Jelly.
  x=n*288%112
  
  --Scale of the jelly, from 0..1.
  k=n/6
  
  --The jelly fish movements are controlled by this angle.
  --The animation loops every q [0..1].
  q=k+t()/5
  
  --l determines the amount of horizontal stretch at the bottom of the body. 
  l=cos(q)
  
  --Each jelly uses an ellipse formula for the general shape.
  --h determines the radius of the ellipse. 
  h=k*(31+l*6)

  --Loop from the top of the jelly to the bottom, we'll fill it by drawing
  --horizintal lines.
  --".5" helps it look solid even when the jelly grows in height.
  for i=0,33*k,.5 do
   --y is the y position of the line:
   --  i-cos(q+.3)*i/5 -- Equivalent to (1-cos(q+.3)/5)*i. Shrinks the jelly
   --  vertically up and down over time, 1-cos(q+.3)/5 will oscilate [0.8..1.2].
   --  -t()*6*k -- Moves the jelly slowly upward. The ones in the BG move slower.
   --  %160-9 -- Wraps the y position from top to bottom.
    y=(i-cos(q+.3)*i/5-t()*6*k)%160-9
    
    --Half of the width of the ellipse at the current line.
    --  (h*h+9-(i-h)^2)^.5 -- Basically a weird circle equation/pythagoras: sqrt(h^2-(i-h)^2).
    --  The +9 makes the top of the ellipse smoother.
    --  l*max(i-29*k) -- The stretching at the bottom of the jelly.
    --  Note max(0,i-29*k) -> max(i-29*k) since parameters default to 0.
    r=(h*h+9-(i-h)^2)^.5+l*max(i-29*k)
    
    --Draw the line.
    line(x-r,y,x+r,y,4*k)
    
    --Set the color palette using hidden colours.
    --Note when n==0 you get pal(0,nil,1) -> pal(0,0,1).
    pal(n,({129,1,140,12})[n],1)
  end
  --Draw the little tentacles.
  for i=-r,r,r/9 do
    --  i*l/7 -- Gives the angling of the tentacles.
    --  y+7-l*l -- The -l*l shrinks y as the tentacle moves left or right,
    -- making it look like it's rotating.
    line(x+i,y+1,x+i+i*l/7,y+7-l*l,3*k)
  end
end
flip()goto _