# ============================================================================
# image.ludic — PNG decoding, images and sprites, written in Ludic.
#
# Replaces the C runtime's image half. Reads a real .png off disk, inflates the
# IDAT stream with the Ludic DEFLATE decoder next door, reverses the per-scanline
# filters, and expands whatever colour type the file uses into 0xAARRGGBB.
#
# Supported: 8/4/2/1-bit greyscale, 8-bit truecolour, indexed with PLTE/tRNS,
# greyscale+alpha and RGBA — the same set the C runtime handled.
# ============================================================================

const IMG_MAX: int = 32
const SPR_MAX: int = 160
const SPR_SZ:  int = 16

var img_px:   pointers = null     # IMG_MAX pointers to RGBA buffers
var img_w:    words = null
var img_h:    words = null
var img_n:    int = 0

var spr_px:   words = null     # SPR_MAX * 16 * 16 RGBA pixels, one block
var spr_n:    int = 0

function rt_image_init() -> void {
  img_px = bytes(IMG_MAX * 8)
  img_w = words(IMG_MAX)
  img_h = words(IMG_MAX)
  spr_px = words(SPR_MAX * SPR_SZ * SPR_SZ)
  fill(spr_px, 0, SPR_MAX * SPR_SZ * SPR_SZ * 4)
}

# ---- decoding -------------------------------------------------------------
function png_be32(b: pointer, at: int) -> int {
  return (b[at] << 24) | (b[at + 1] << 16) | (b[at + 2] << 8) | b[at + 3]
}

function png_tag(b: pointer, at: int, a: int, c: int, d: int, e: int) -> bool {
  if b[at] != a { return false }
  if b[at + 1] != c { return false }
  if b[at + 2] != d { return false }
  if b[at + 3] != e { return false }
  return true
}

function rt_read_file(path: string) -> pointer {
  let f = file_open(path, "rb")
  if (f == null) { return null }
  file_seek(f, 0, 2)
  let n = file_tell(f)
  file_seek(f, 0, 0)
  if n <= 0 { file_close(f); return null }
  let buf = bytes(n + 8)
  file_read(f, buf, n)
  file_close(f)
  rt_file_len = n
  return buf
}
var rt_file_len: int = 0

# decoded image is left in these; -1 width means failure
var png_w:  int = 0
var png_h:  int = 0
var png_px: words = null

function rt_decode_png(path: string) -> bool {
  png_w = 0
  png_h = 0
  png_px = null
  let d = rt_read_file(path)
  if (d == null) { return false }
  let size = rt_file_len
  if size < 8 { free(d); return false }
  if d[0] != 137 { free(d); return false }
  if d[1] != 80 { free(d); return false }

  var w = 0
  var h = 0
  var bd = 0
  var ct = 0
  let plte = bytes(768)
  let trns = bytes(256)
  var ntrns = 0
  let idat = bytes(size)
  var idlen = 0
  var i = 8
  var done = 0

  while done == 0 {
    if i + 8 > size { done = 1 }
    if done == 0 {
      let ln = png_be32(d, i)
      let typ = i + 4
      let body = i + 8
      if ln < 0 { done = 1 }
      if body + ln > size { done = 1 }
      if done == 0 {
        if png_tag(d, typ, 73, 72, 68, 82) {          # IHDR
          w = png_be32(d, body)
          h = png_be32(d, body + 4)
          bd = d[body + 8]
          ct = d[body + 9]
        }
        if png_tag(d, typ, 80, 76, 84, 69) {          # PLTE
          let m = min(ln, 768)
          for k in 0 .. m { plte[k] = d[body + k] }
        }
        if png_tag(d, typ, 116, 82, 78, 83) {         # tRNS
          ntrns = min(ln, 256)
          for k in 0 .. ntrns { trns[k] = d[body + k] }
        }
        if png_tag(d, typ, 73, 68, 65, 84) {          # IDAT
          for k in 0 .. ln { idat[idlen + k] = d[body + k] }
          idlen = idlen + ln
        }
        if png_tag(d, typ, 73, 69, 78, 68) { done = 1 }   # IEND
        i = i + 12 + ln
      }
    }
  }

  if w <= 0 { free(d); return false }
  if h <= 0 { free(d); return false }

  var channels = 1
  if ct == 2 { channels = 3 }
  if ct == 6 { channels = 4 }
  if ct == 4 { channels = 2 }
  let bppbits = bd * channels
  var fbpp = (bppbits + 7) / 8
  if fbpp < 1 { fbpp = 1 }
  let stride = (w * bppbits + 7) / 8
  let rawlen = h * (stride + 1)
  let raw = bytes(rawlen + 8)
  if z_uncompress(idat, idlen, raw, rawlen) < 0 {
    free(d); free(raw); free(idat)
    return false
  }

  # reverse the per-scanline filters, in place
  for y in 0 .. h {
    let line = y * (stride + 1)
    let ft = raw[line]
    let cur = line + 1
    let prev = cur - (stride + 1)
    for x in 0 .. stride {
      var a = 0
      var b = 0
      var c = 0
      if x >= fbpp { a = raw[cur + x - fbpp] }
      if y > 0 { b = raw[prev + x] }
      if x >= fbpp { if y > 0 { c = raw[prev + x - fbpp] } }
      var v = raw[cur + x]
      if ft == 1 { v = v + a }
      if ft == 2 { v = v + b }
      if ft == 3 { v = v + (a + b) / 2 }
      if ft == 4 {
        let p = a + b - c
        let pa = abs(p - a)
        let pb = abs(p - b)
        let pc = abs(p - c)
        var pick = c
        if pb <= pc { pick = b }
        if pa <= pb { if pa <= pc { pick = a } }
        v = v + pick
      }
      raw[cur + x] = (v & 255)
    }
  }

  # expand to 0xAARRGGBB
  let out: words = words(w * h)
  let maxv = (1 << bd) - 1
  for y in 0 .. h {
    let row = y * (stride + 1) + 1
    for x in 0 .. w {
      var R = 0
      var G = 0
      var B = 0
      var A = 255
      if ct == 6 {
        R = raw[row + x * 4]
        G = raw[row + x * 4 + 1]
        B = raw[row + x * 4 + 2]
        A = raw[row + x * 4 + 3]
      }
      if ct == 2 {
        R = raw[row + x * 3]
        G = raw[row + x * 3 + 1]
        B = raw[row + x * 3 + 2]
      }
      if ct == 4 {
        R = raw[row + x * 2]
        G = R
        B = R
        A = raw[row + x * 2 + 1]
      }
      if ct == 3 {
        let bp = x * bd
        let idx = ((raw[row + bp / 8] >> (8 - bd - bp % 8)) & maxv)
        R = plte[idx * 3]
        G = plte[idx * 3 + 1]
        B = plte[idx * 3 + 2]
        if idx < ntrns { A = trns[idx] }
      }
      if ct == 0 {
        let bp = x * bd
        let s = ((raw[row + bp / 8] >> (8 - bd - bp % 8)) & maxv)
        var g = s
        if bd != 8 { g = s * 255 / maxv }
        R = g
        G = g
        B = g
      }
      out[y * w + x] = (((A << 24) | (R << 16)) | ((G << 8) | B))
    }
  }

  free(d)
  free(idat)
  free(raw)
  free(plte)
  free(trns)
  png_w = w
  png_h = h
  png_px = out
  return true
}

# ---- images ---------------------------------------------------------------
function rt_image_load(path: string) -> int {
  if img_n >= IMG_MAX { return 0 - 1 }
  if rt_decode_png(path) == false { return 0 - 1 }
  let id = img_n
  img_n = img_n + 1
  img_px[id] = png_px
  img_w[id] = png_w
  img_h[id] = png_h
  return id
}

function rt_blend_px(x: int, y: int, argb: int) -> void {
  let a = ((argb >> 24) & 255)
  if a == 0 { return }
  if x < 0 { return }
  if y < 0 { return }
  if x >= rt_fbw { return }
  if y >= rt_fbh { return }
  var r = ((argb >> 16) & 255)
  var g = ((argb >> 8) & 255)
  var b = (argb & 255)
  if a != 255 {
    let dst = rt_fb[y * rt_fbw + x]
    let dr = ((dst >> 16) & 255)
    let dg = ((dst >> 8) & 255)
    let db = (dst & 255)
    r = (r * a + dr * (255 - a)) / 255
    g = (g * a + dg * (255 - a)) / 255
    b = (b * a + db * (255 - a)) / 255
  }
  rt_fb[y * rt_fbw + x] = (((r << 16) | (g << 8)) | b)
}

function rt_draw_image(id: int, dx: int, dy: int) -> void {
  if id < 0 { return }
  if id >= img_n { return }
  let w = img_w[id]
  let h = img_h[id]
  let s: words = img_px[id]
  for y in 0 .. h {
    for x in 0 .. w {
      rt_blend_px(dx + x, dy + y, s[y * w + x])
    }
  }
}

function rt_draw_image_scaled(id: int, dx: int, dy: int, dw: int, dh: int) -> void {
  if id < 0 { return }
  if id >= img_n { return }
  if dw <= 0 { return }
  if dh <= 0 { return }
  let w = img_w[id]
  let h = img_h[id]
  let s: words = img_px[id]
  for y in 0 .. dh {
    for x in 0 .. dw {
      rt_blend_px(dx + x, dy + y, s[(y * h / dh) * w + x * w / dw])
    }
  }
}

# map one destination axis onto the source for a 9-slice: the two insets are
# copied 1:1 and only the middle stretches
function rt_9map(d: int, dsz: int, ssz: int, inset: int) -> int {
  if inset * 2 >= dsz { return d * ssz / max(dsz, 1) }
  if inset * 2 >= ssz { return d * ssz / max(dsz, 1) }
  if d < inset { return d }
  if d >= dsz - inset { return ssz - (dsz - d) }
  return inset + (d - inset) * (ssz - 2 * inset) / (dsz - 2 * inset)
}

function rt_draw_9slice(id: int, dx: int, dy: int, dw: int, dh: int, inset: int) -> void {
  if id < 0 { return }
  if id >= img_n { return }
  if dw <= 0 { return }
  if dh <= 0 { return }
  let w = img_w[id]
  let h = img_h[id]
  let s: words = img_px[id]
  for y in 0 .. dh {
    let sy = rt_9map(y, dh, h, inset)
    for x in 0 .. dw {
      rt_blend_px(dx + x, dy + y, s[sy * w + rt_9map(x, dw, w, inset)])
    }
  }
}

# ---- sprites (16x16 art) --------------------------------------------------
function rt_png_load(path: string) -> int {
  if spr_n >= SPR_MAX { return 0 - 1 }
  if rt_decode_png(path) == false { return 0 - 1 }
  let id = spr_n
  spr_n = spr_n + 1
  let base = id * SPR_SZ * SPR_SZ
  for y in 0 .. SPR_SZ {
    for x in 0 .. SPR_SZ {
      var px = 0
      if x < png_w {
        if y < png_h {
          let c = png_px[y * png_w + x]
          if ((c >> 24) & 255) >= 128 { px = ((255 << 24) | (c & 16777215)) }
        }
      }
      spr_px[base + y * SPR_SZ + x] = px
    }
  }
  free(png_px)
  png_px = null
  return id
}

function rt_draw_sprite(id: int, px: int, py: int) -> void {
  if id < 0 { return }
  if id >= spr_n { return }
  let base = id * SPR_SZ * SPR_SZ
  for y in 0 .. SPR_SZ {
    for x in 0 .. SPR_SZ {
      let p = spr_px[base + y * SPR_SZ + x]
      if ((p >> 24) & 255) != 0 {
        rt_put_px(px + x, py + y, (p & 16777215))
      }
    }
  }
}

function rt_draw_sprite_scaled(id: int, px: int, py: int, sc: int) -> void {
  if id < 0 { return }
  if id >= spr_n { return }
  if sc < 1 { return }
  let base = id * SPR_SZ * SPR_SZ
  for y in 0 .. SPR_SZ {
    for x in 0 .. SPR_SZ {
      let p = spr_px[base + y * SPR_SZ + x]
      if ((p >> 24) & 255) != 0 {
        rt_fill_rect(px + x * sc, py + y * sc, sc, sc, (p & 16777215))
      }
    }
  }
}

# ---- .lspr sprite sheets (palette + ASCII rows) ---------------------------
function rt_hexval(c: int) -> int {
  if c >= 48 { if c <= 57 { return c - 48 } }
  if c >= 97 { if c <= 102 { return c - 87 } }
  if c >= 65 { if c <= 70 { return c - 55 } }
  return 0 - 1
}

function rt_sprites_load(path: string) -> void {
  let d = rt_read_file(path)
  if (d == null) { spr_n = 0; return }
  let size = rt_file_len
  let pal: words = words(128)
  fill(pal, 0, 128 * 4)
  var cur = 0 - 1
  var row = 0
  var i = 0
  while i < size {
    let start = i
    var len = 0
    var j = start
    while j < size {
      let ch = d[j]
      if ch == 10 { j = size } else { len = len + 1;  j = j + 1 }
    }
    let c0 = d[start]
    if c0 == 112 {                       # 'p' — "pal <char> <rrggbb>"
      let ch = d[start + 4]
      var v = 0
      for k in 0 .. 6 {
        let hv = rt_hexval(d[start + 6 + k])
        if hv >= 0 { v = v * 16 + hv }
      }
      if ch < 128 { pal[ch] = ((255 << 24) | v) }
    }
    if c0 == 115 {                       # 's' — "spr" starts a new sprite
      cur = 0 - 1
      if spr_n < SPR_MAX {
        cur = spr_n
        spr_n = spr_n + 1
        fill(offset(spr_px, cur * SPR_SZ * SPR_SZ * 4), 0, SPR_SZ * SPR_SZ * 4)
      }
      row = 0
    }
    if c0 != 112 {
      if c0 != 115 {
        if c0 != 35 {                    # '#' comment
          if cur >= 0 {
            if row < SPR_SZ {
              for x in 0 .. SPR_SZ {
                if x < len {
                  spr_px[cur * SPR_SZ * SPR_SZ + row * SPR_SZ + x] = pal[(d[start + x] & 127)]
                }
              }
              row = row + 1
            }
          }
        }
      }
    }
    i = start + len + 1
  }
  free(pal)
  free(d)
}