--make four 1-bit 8x8 pictures
trgt="00111100"
   .."01000010"
   .."10000001"
   .."10011001"
   .."10011001"
   .."10000001"
   .."01000010"
   .."00111100"

sqre="11111111"
   .."10000001"
   .."10000001"
   .."10000001"
   .."10000001"
   .."10000001"
   .."10000001"
   .."11111111"

crss="10000001"
   .."01000010"
   .."00100100"
   .."00011000"
   .."00011000"
   .."00100100"
   .."01000010"
   .."10000001"

dith="10101010"
   .."01010101"
   .."10101010"
   .."01010101"
   .."10101010"
   .."01010101"
   .."10101010"
   .."01010101"


--sets bit at (x,y,layer) of
--sprite sheet to 1
function ssetb(x,y,layer)

 col=bor(sget(x,y),
         shl(0b00000001,layer)
        )

 sset(x,y,col)
end

--func to write binary pic to
--the sprite sheet:
--  picture string
--  layer (0-3)
--  sprite pos
--  sprite size
function bspradd(p,layer,x,y,w,h)
 i=1
 for sx=x,x+w-1 do for sy=y,y+h-1 do

  if sub(p,i,i) == "1" then
   ssetb(sx,sy,layer)
  end
  i+=1

 end end
end

--clear first sprite in map
for x=0,7 do for y=0,7 do
 sset(x,y,0)
end end

--write each 1-bit picture to
--sprite map at 0,0
bspradd(trgt,0,0,0,8,8)
bspradd(sqre,1,0,0,8,8)
bspradd(crss,2,0,0,8,8)
bspradd(dith,3,0,0,8,8)


--palette binary mask
--  layer to draw
--  colour 1
--  [colour 0]
function palb(layer,c1,c0)
 for c=0,15 do

  b=shl(0b00000001,layer)
  col=band(c,b)
  if col==b then
   --draw colour 1
   palt(c,false)
   pal(c,c1)
  else
   --draw colour 0 (or dont)
   if c0 then
    palt(c,false)
    pal(c,c0)
   else
    --draw transparent
    palt(c,true)
   end
  end

 end
end


--do some drawing now :)
cls()
pal()
print("4-bit sprite:",20,3)
spr(0,20,10)

pal()
print("layer 0:",20,23)
palb(0,7)
spr(0,20,30)

pal()
print("layer 1:",20,43)
palb(1,7)
spr(0,20,50)

pal()
print("layer 2:",20,63)
palb(2,7)
spr(0,20,70)

pal()
print("layer 3:",20,83)
palb(3,7)
spr(0,20,90)

print("done!",20,115)