start of demo, palette type

pal_from_spr.p8

@@ -0,0 +1,101 @@
+pico-8 cartridge // http://www.pico-8.com
+version 41
+__lua__
+-- sprite-sampled palette
+-- kistaro@gmail.com
+
+function _init()
+ -- lock top 16 rows to default palette
+ pal({[0]=0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}, 2)
+ poke(0x5f5f, 0x10)
+ poke2(0x5f70, 0xffff)
+end
+
+function _update()
+end
+
+function _draw()
+ cls()
+ draw_hud()
+ draw_bars()
+end
+
+function draw_hud()
+end
+
+function draw_bars()
+ for i=0,15 do
+  local i7 = i * 7
+  rectfill(0,16+i7,128,i7+22,i)
+ end
+end
+-->8
+-- palette structure
+
+palette = {
+ -- cols: table. identical
+ --       format to table-type
+ --       pal call
+ 
+ --   tr: transparency table.
+ --       keys: [0]..[15]
+ --         (color indexes)
+ --       vals: true/false/nil
+ --         for transparency of
+ --         that color. false
+ --         sets opaque, nil
+ --         means "do not set".
+ --       tables with no absent
+ --       values can be compiled
+ --       for faster do_palt.
+
+ -- cpl_tr: compiled tr. set by
+ --       compile_palt iff all
+ --       tr values in range
+ --       are nonnil. do_palt
+ --       is faster this way
+}
+palette_mt = {__index=palette}
+
+function palette.new(x)
+ x = x or {}
+ if (not x.cols) x.cols = {}
+ if (not x.tr) x.tr = {}
+ setmetatable(x, palette_mt)
+end
+
+function palette:do_pal(p)
+ pal(self.cols, p)
+end
+
+function palette:do_palt()
+ if (self.cpl_tr) return palt(self.cpl_tr)
+ local tr = self.tr
+ for i=0,15 do
+  if (tr[i] ~= nil) palt(i, tr[i])
+ end
+end
+
+function palette:do_both(p)
+ self:do_palt()
+ self:do_pal(p)
+end
+
+function palette:compile_palt()
+ self.cpl_tr = nil
+ local bits, tr = 0, self.tr
+ for i = 15,0,-1 do
+  if (tr[i] == nil) return
+  bits <<= 1
+  if (tr[i]) bits += 1
+ end
+ self.cpl_tr = bits
+ return bits
+end
+__gfx__
+00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+00700700000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+00077000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+00077000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+00700700000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000