honeylisp/ssc/iigs/graphics.fnl

; IIgs graphical architecture:
; PREMISE: All small-scale bitmapped graphics are encoded as code that pushes the graphics onto the stack,
; which has been aligned to the appropriate place to draw said graphics.
; Jump tables are stored in the main code segment so that eg. tiles can be easily calculated by index, and
; so we don't have to explicitly pass longs to a regular function.

(import-macros {:sss ! : compile} :ssc.macros)
(local lume (require :lib.lume))
(local {: countiter} (require :lib.util))

; Our bitmap compiler is based on MrSprite - http://brutaldeluxe.fr/products/crossdevtools/mrspritetech/
; sprite is a Lua string, where each byte is made up of two nibbles - the low nibble
; should be a 16-bit value representing the colour, and the high nibble should be
; 0 if the pixel is opaque, or f if the pixel is transparent.
; width should be a multiple of 4.
(fn preprocess-sprite [sprite w h]
  ; splits up each horizontal line into two kinds of "runs":
  ; :solid - each word can be directly written to memory; there is no transparency
  ; :masked - the word at this location must be bitwise ANDed by :mask and ORed by :word
  ; words containing nothing but transparent pixels are removed.
  ; Also determines the most frequently-occurring solid words and distributes them
  ; to registers.
  (let [rows [] frequencies {}]
    (var word 0)
    (var mask 0)
    (var isprite 1)
    (for [y 0 (- h 1)]
      (let [row []]
        (var solidrun nil)
        (for [x 0 (- w 1)]
          (let [b (string.byte (sprite:sub isprite isprite))
                pixcolour (bit.band b 0x0f)
                pixmask (bit.rshift (bit.band b 0xf0) 4)
                pixshift (match (% x 4) 0 4  1 0  2 12  3 8)]
            (set word (bit.bor word (bit.lshift pixcolour pixshift)))
            (set mask (bit.bor mask (bit.lshift pixmask pixshift)))
            (when (= (% x 4) 3)
              (when (not= mask 0) (set solidrun nil))
              (when (= mask 0) ; fully opaque word
                (when (= solidrun nil)
                  (set solidrun {:run :solid :x (/ (- x 3) 2) :words []})
                  (table.insert row solidrun))
                (table.insert solidrun.words word)
                (tset frequencies word (+ (or (. frequencies word) 0) 1)))
              (when (and (not= mask 0) (not= mask 0xffff))
                (table.insert row {:run :masked :x (/ (- x 3) 2) : word : mask}))
              (set word 0)
              (set mask 0))
            (set isprite (+ isprite 1))))
        (table.insert rows row)))
    (local top-frequencies (icollect [word freq (pairs frequencies)] {: word : freq}))
    (table.sort top-frequencies #(> $1.freq $2.freq))
    {: rows
     :registers {:x (?. top-frequencies 1 :word)
                 :y (?. top-frequencies 2 :word)
                 :d (?. top-frequencies 3 :word)}}))

(fn compile-row [block row registers]
  (each [_ run (ipairs row)]
    (match run.run
      :solid
      (let [s-target (+ run.x (* (length run.words) 2) -1)]
        (lume.push block [:tsc] [:adc (- s-target registers.s)] [:tcs])
        (set registers.s (- run.x 1))
        (for [iword (length run.words) 1 -1]
          (lume.push block
                     (match (. run.words iword)
                       registers.x [:phx]
                       registers.y [:phy]
                       registers.d [:phd]
                       word [:pea word]))))
      :masked
      (do (var s-offset (- run.x registers.s))
          (when (> s-offset 127)
            (lume.push block [:tsc] [:adc s-offset] [:tcs])
            (set registers.s run.x)
            (set s-offset 0))
          (lume.push block [:lda s-offset :s] [:and run.mask] [:ora run.word] [:sta s-offset :s])))))

(fn compile-sprite [sprite w h]
  (let [{: rows : registers} (preprocess-sprite sprite w h)
        block (lume.concat [:block]
                           (when registers.x [[:ldx registers.x]])
                           (when registers.y [[:ldy registers.y]])
                           (when registers.d [[:lda registers.d] [:tcd]]))]
    (set registers.s 0)
    (each [_ row (ipairs rows)]
      (compile-row block row registers)
      (set registers.s (- registers.s 160)))
    block))

#(compile $1
  (fn enable-shadow-writes ()  (set! (word-at (ref :0xc035)) (& (word-at (ref :0xc035)) 0xfff1)))
  (fn disable-shadow-writes () (set! (word-at (ref :0xc035)) (| (word-at (ref :0xc035)) 0x000e)))

  ; The fastest way to draw any graphics on the IIgs is to map the stack pointer to
  ; video memory, and use stack-pushing instructions to write values. draw-object
  ; takes a location in video memory and a pointer to a machine code routine called a "drawfn"
  ; that performs the drawing
  (global word draw-object-saved-stack 0)
  (fn draw-object (screen object)
    (asm (sei)  ; disable interrupts
         (lda object) (sta [{:abs #(+ ($1:lookup-addr :draw-object-current-object-jump) 1)}]) ; self-modifying code! rewrite the jump target
         (phd) ; save direct page register
         (tsc) (sta draw-object-saved-stack) ; save stack
         (lda screen 2) ; we offset by 2 because we just pushed a word onto the stack and the compiler doesn't know about it
           (tcs) ; drawfns expect the current screen pointer to be stored in the stack register
         (lda :0xc068) (ora 0x30) (sta :0xc068) ; move bank 1 to bank 0
         (clc) ; clear carry - all drawfns will add to the stack pointer and then walk it back
      draw-object-current-object-jump
         (jmp draw-object) ; will actually jump to "object"
      draw-object-finished (export draw-object-finished)
         (lda :0xc068) (and 0xffcf) (sta :0xc068) ; move bank 1 back to bank 1
         (lda draw-object-saved-stack) (tcs) ; restore the stack pointer
         (pld) ; restore direct page register
         (cli))) ; enable interrupts

  (macrobarrier drawfn)
  (form drawfn [(lambda [ssc name ...]
    (let [expr (lume.concat [:do ...] [[:asm [:jmp :draw-object-finished]]])]
      (ssc:define-fn name nil #(do
        (local fname (.. "<drawfn " name ">"))
        (local asm (ssc:expr-poly expr))
        (ssc:expr-poly [:form name (fn [ssc] (assert (= ssc.locals nil) (.. name " must be called from a drawfn")) [:jmp fname])])
        (ssc:expr-poly [:define name [:ref fname]])
        (ssc.org:append fname asm)))))])

  (drawfn pei-slam-tile
    (asm (tsc) (tcd) (adc 7) (tcs)
         [(lume.concat [:block] (icollect [_ (countiter 16)]
            [(! block (pei (:d6)) (pei (:d4)) (pei (:d2)) (pei (:d0))
                      (tsc) (adc 161) (tcd) (adc 7) (tcs))]))]))

  (drawfn pei-slam-scanline
    (asm (tsc) (tcd) (adc 159) (tcs)
         [(lume.concat [:block] (icollect [offset (countiter 158 0 -2)] [:pei [(.. :d offset)]]))]))

  (form compile-sprite [(lambda [ssc name sprite w h] (ssc:expr-poly [:drawfn name [:asm (compile-sprite sprite w h)]]))])
)