.

2 files changed, 23 insertions, 1133 deletions

diff --git a/apps/ex13.mu b/apps/ex13.mu
new file mode 100644
index 00000000..3e890785
--- /dev/null
+++ b/apps/ex13.mu
@@ -0,0 +1,23 @@
+# Load an image from disk and display it on screen.
+#
+# Build the code disk:
+#   $ ./translate apps/ex13.mu                       # generates code.img
+# Load a pbm, pgm or ppm image (no more than 255 levels) in the data disk
+#   $ dd if=/dev/zero of=data.img count=20160
+#   $ dd if=___ of=data.img conv=notrunc
+# Run:
+#   $ qemu-system-i386 -hda code.img -hdb data.img
+
+fn main screen: (addr screen), keyboard: (addr keyboard), data-disk: (addr disk) {
+  var img-storage: image
+  var img/esi: (addr image) <- address img-storage
+  load-image img, data-disk
+  render-image screen, img, 0/x, 0/y, 0x300/width, 0x300/height
+}
+
+fn load-image self: (addr image), data-disk: (addr disk) {
+  var s-storage: (stream byte 0x200000)  # 512* 0x1000 sectors
+  var s/ebx: (addr stream byte) <- address s-storage
+  load-sectors data-disk, 0/lba, 0x1000/sectors, s
+  initialize-image self, s
+}
diff --git a/apps/img.mu b/apps/img.mu
deleted file mode 100644
index 9606bd43..00000000
--- a/apps/img.mu
+++ /dev/null
@@ -1,1133 +0,0 @@
-# load an image from disk and display it on screen
-#
-# To build:
-#   $ ./translate apps/img.mu                       # generates code.img
-# Load a pbm, pgm or ppm image (no more than 255 levels) in the data disk
-#   $ dd if=/dev/zero of=data.img count=20160
-#   $ dd if=x.pbm of=data.img conv=notrunc
-# or
-#   $ dd if=t.pgm of=data.img conv=notrunc
-# or
-#   $ dd if=snail.ppm of=data.img conv=notrunc
-# To run:
-#   $ qemu-system-i386 -hda code.img -hdb data.img
-
-type image {
-  type: int  # supported types:
-             #  1: portable bitmap (P1) - pixels 0 or 1
-             #  2: portable greymap (P2) - pixels 1-byte greyscale values
-             #  3: portable pixmap (P3) - pixels 3-byte rgb values
-  max: int
-  width: int
-  height: int
-  data: (handle array byte)
-}
-
-fn main screen: (addr screen), keyboard: (addr keyboard), data-disk: (addr disk) {
-  var img-storage: image
-  var img/esi: (addr image) <- address img-storage
-  load-image img, data-disk
-  render-image screen, img, 0/x, 0/y, 0x300/width, 0x300/height
-}
-
-fn load-image self: (addr image), data-disk: (addr disk) {
-  # data-disk -> stream
-  var s-storage: (stream byte 0x200000)  # 512* 0x1000 sectors
-  var s/ebx: (addr stream byte) <- address s-storage
-  draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, "loading sectors from data disk", 3/fg, 0/bg
-  move-cursor-to-left-margin-of-next-line 0/screen
-  load-sectors data-disk, 0/lba, 0x1000/sectors, s
-  draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, "parsing", 3/fg, 0/bg
-  move-cursor-to-left-margin-of-next-line 0/screen
-  initialize-image self, s
-}
-
-fn initialize-image _self: (addr image), in: (addr stream byte) {
-  var self/esi: (addr image) <- copy _self
-  var mode-storage: slice
-  var mode/ecx: (addr slice) <- address mode-storage
-  next-word in, mode
-  {
-    var P1?/eax: boolean <- slice-equal? mode, "P1"
-    compare P1?, 0/false
-    break-if-=
-    var type-a/eax: (addr int) <- get self, type
-    copy-to *type-a, 1/ppm
-    initialize-image-from-pbm self, in
-    return
-  }
-  {
-    var P2?/eax: boolean <- slice-equal? mode, "P2"
-    compare P2?, 0/false
-    break-if-=
-    var type-a/eax: (addr int) <- get self, type
-    copy-to *type-a, 2/pgm
-    initialize-image-from-pgm self, in
-    return
-  }
-  {
-    var P3?/eax: boolean <- slice-equal? mode, "P3"
-    compare P3?, 0/false
-    break-if-=
-    var type-a/eax: (addr int) <- get self, type
-    copy-to *type-a, 3/ppm
-    initialize-image-from-ppm self, in
-    return
-  }
-  abort "initialize-image: unrecognized image type"
-}
-
-# dispatch to a few variants with mostly identical boilerplate
-fn render-image screen: (addr screen), _img: (addr image), xmin: int, ymin: int, width: int, height: int {
-  var img/esi: (addr image) <- copy _img
-  var type-a/eax: (addr int) <- get img, type
-  {
-    compare *type-a, 1/pbm
-    break-if-!=
-    render-pbm-image screen, img, xmin, ymin, width, height
-    return
-  }
-  {
-    compare *type-a, 2/pgm
-    break-if-!=
-    var img2-storage: image
-    var img2/edi: (addr image) <- address img2-storage
-    dither-pgm-unordered img, img2
-    render-raw-image screen, img2, xmin, ymin, width, height
-    return
-  }
-  {
-    compare *type-a, 3/ppm
-    break-if-!=
-    var img2-storage: image
-    var img2/edi: (addr image) <- address img2-storage
-    dither-ppm-unordered img, img2
-    render-raw-image screen, img2, xmin, ymin, width, height
-    return
-  }
-  abort "render-image: unrecognized image type"
-}
-
-## helpers
-
-# import a black-and-white ascii bitmap (each pixel is 0 or 1)
-fn initialize-image-from-pbm _self: (addr image), in: (addr stream byte) {
-  var self/esi: (addr image) <- copy _self
-  var curr-word-storage: slice
-  var curr-word/ecx: (addr slice) <- address curr-word-storage
-  # load width, height
-  next-word in, curr-word
-  var tmp/eax: int <- parse-decimal-int-from-slice curr-word
-  var width/edx: int <- copy tmp
-  next-word in, curr-word
-  tmp <- parse-decimal-int-from-slice curr-word
-  var height/ebx: int <- copy tmp
-  # save width, height
-  var dest/eax: (addr int) <- get self, width
-  copy-to *dest, width
-  dest <- get self, height
-  copy-to *dest, height
-  # initialize data
-  var capacity/edx: int <- copy width
-  capacity <- multiply height
-  var data-ah/edi: (addr handle array byte) <- get self, data
-  populate data-ah, capacity
-  var _data/eax: (addr array byte) <- lookup *data-ah
-  var data/edi: (addr array byte) <- copy _data
-  var i/ebx: int <- copy 0
-  {
-    compare i, capacity
-    break-if->=
-    next-word in, curr-word
-    var src/eax: int <- parse-decimal-int-from-slice curr-word
-    {
-      var dest/ecx: (addr byte) <- index data, i
-      copy-byte-to *dest, src
-    }
-    i <- increment
-    loop
-  }
-}
-
-# render a black-and-white ascii bitmap (each pixel is 0 or 1)
-fn render-pbm-image screen: (addr screen), _img: (addr image), xmin: int, ymin: int, width: int, height: int {
-  var img/esi: (addr image) <- copy _img
-  # yratio = height/img->height
-  var img-height-a/eax: (addr int) <- get img, height
-  var img-height/xmm0: float <- convert *img-height-a
-  var yratio/xmm1: float <- convert height
-  yratio <- divide img-height
-  # xratio = width/img->width
-  var img-width-a/eax: (addr int) <- get img, width
-  var img-width/ebx: int <- copy *img-width-a
-  var img-width-f/xmm0: float <- convert img-width
-  var xratio/xmm2: float <- convert width
-  xratio <- divide img-width-f
-  # esi = img->data
-  var img-data-ah/eax: (addr handle array byte) <- get img, data
-  var _img-data/eax: (addr array byte) <- lookup *img-data-ah
-  var img-data/esi: (addr array byte) <- copy _img-data
-  var len/edi: int <- length img-data
-  #
-  var one/eax: int <- copy 1
-  var one-f/xmm3: float <- convert one
-  var width-f/xmm4: float <- convert width
-  var height-f/xmm5: float <- convert height
-  var zero/eax: int <- copy 0
-  var zero-f/xmm0: float <- convert zero
-  var y/xmm6: float <- copy zero-f
-  {
-    compare y, height-f
-    break-if-float>=
-    var imgy-f/xmm5: float <- copy y
-    imgy-f <- divide yratio
-    var imgy/edx: int <- truncate imgy-f
-    var x/xmm7: float <- copy zero-f
-    {
-      compare x, width-f
-      break-if-float>=
-      var imgx-f/xmm5: float <- copy x
-      imgx-f <- divide xratio
-      var imgx/ecx: int <- truncate imgx-f
-      var idx/eax: int <- copy imgy
-      idx <- multiply img-width
-      idx <- add imgx
-      # error info in case we rounded wrong and 'index' will fail bounds-check
-      compare idx, len
-      {
-        break-if-<
-        set-cursor-position 0/screen, 0x20/x 0x20/y
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgx, 3/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgy, 4/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, idx, 5/fg 0/bg
-      }
-      var src-a/eax: (addr byte) <- index img-data, idx
-      var src/eax: byte <- copy-byte *src-a
-      var color-int/eax: int <- copy src
-      {
-        compare color-int, 0/black
-        break-if-=
-        color-int <- copy 0xf/white
-      }
-      var screenx/ecx: int <- convert x
-      screenx <- add xmin
-      var screeny/edx: int <- convert y
-      screeny <- add ymin
-      pixel screen, screenx, screeny, color-int
-      x <- add one-f
-      loop
-    }
-    y <- add one-f
-    loop
-  }
-}
-
-# import a greyscale ascii "greymap" (each pixel is a shade of grey from 0 to 255)
-fn initialize-image-from-pgm _self: (addr image), in: (addr stream byte) {
-  var self/esi: (addr image) <- copy _self
-  var curr-word-storage: slice
-  var curr-word/ecx: (addr slice) <- address curr-word-storage
-  # load width, height
-  next-word in, curr-word
-  var tmp/eax: int <- parse-decimal-int-from-slice curr-word
-  var width/edx: int <- copy tmp
-  next-word in, curr-word
-  tmp <- parse-decimal-int-from-slice curr-word
-  var height/ebx: int <- copy tmp
-  # check and save color levels
-  next-word in, curr-word
-  {
-    tmp <- parse-decimal-int-from-slice curr-word
-    compare tmp, 0xff
-    break-if-=
-    draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, "levels of grey is not 255; continuing and hoping for the best", 0x2b/fg 0/bg
-  }
-  var dest/edi: (addr int) <- get self, max
-  copy-to *dest, tmp
-  # save width, height
-  dest <- get self, width
-  copy-to *dest, width
-  dest <- get self, height
-  copy-to *dest, height
-  # initialize data
-  var capacity/edx: int <- copy width
-  capacity <- multiply height
-  var data-ah/edi: (addr handle array byte) <- get self, data
-  populate data-ah, capacity
-  var _data/eax: (addr array byte) <- lookup *data-ah
-  var data/edi: (addr array byte) <- copy _data
-  var i/ebx: int <- copy 0
-  {
-    compare i, capacity
-    break-if->=
-    next-word in, curr-word
-    var src/eax: int <- parse-decimal-int-from-slice curr-word
-    {
-      var dest/ecx: (addr byte) <- index data, i
-      copy-byte-to *dest, src
-    }
-    i <- increment
-    loop
-  }
-}
-
-# render a greyscale ascii "greymap" (each pixel is a shade of grey from 0 to 255) by quantizing the shades
-fn render-pgm-image screen: (addr screen), _img: (addr image), xmin: int, ymin: int, width: int, height: int {
-  var img/esi: (addr image) <- copy _img
-  # yratio = height/img->height
-  var img-height-a/eax: (addr int) <- get img, height
-  var img-height/xmm0: float <- convert *img-height-a
-  var yratio/xmm1: float <- convert height
-  yratio <- divide img-height
-  # xratio = width/img->width
-  var img-width-a/eax: (addr int) <- get img, width
-  var img-width/ebx: int <- copy *img-width-a
-  var img-width-f/xmm0: float <- convert img-width
-  var xratio/xmm2: float <- convert width
-  xratio <- divide img-width-f
-  # esi = img->data
-  var img-data-ah/eax: (addr handle array byte) <- get img, data
-  var _img-data/eax: (addr array byte) <- lookup *img-data-ah
-  var img-data/esi: (addr array byte) <- copy _img-data
-  var len/edi: int <- length img-data
-  #
-  var one/eax: int <- copy 1
-  var one-f/xmm3: float <- convert one
-  var width-f/xmm4: float <- convert width
-  var height-f/xmm5: float <- convert height
-  var zero/eax: int <- copy 0
-  var zero-f/xmm0: float <- convert zero
-  var y/xmm6: float <- copy zero-f
-  {
-    compare y, height-f
-    break-if-float>=
-    var imgy-f/xmm5: float <- copy y
-    imgy-f <- divide yratio
-    var imgy/edx: int <- truncate imgy-f
-    var x/xmm7: float <- copy zero-f
-    {
-      compare x, width-f
-      break-if-float>=
-      var imgx-f/xmm5: float <- copy x
-      imgx-f <- divide xratio
-      var imgx/ecx: int <- truncate imgx-f
-      var idx/eax: int <- copy imgy
-      idx <- multiply img-width
-      idx <- add imgx
-      # error info in case we rounded wrong and 'index' will fail bounds-check
-      compare idx, len
-      {
-        break-if-<
-        set-cursor-position 0/screen, 0x20/x 0x20/y
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgx, 3/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgy, 4/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, idx, 5/fg 0/bg
-      }
-      var src-a/eax: (addr byte) <- index img-data, idx
-      var src/eax: byte <- copy-byte *src-a
-      var color-int/eax: int <- nearest-grey src
-      var screenx/ecx: int <- convert x
-      screenx <- add xmin
-      var screeny/edx: int <- convert y
-      screeny <- add ymin
-      pixel screen, screenx, screeny, color-int
-      x <- add one-f
-      loop
-    }
-    y <- add one-f
-    loop
-  }
-}
-
-fn nearest-grey level-255: byte -> _/eax: int {
-  var result/eax: int <- copy level-255
-  result <- shift-right 4
-  result <- add 0x10
-  return result
-}
-
-fn dither-pgm-unordered-monochrome _src: (addr image), _dest: (addr image) {
-  var src/esi: (addr image) <- copy _src
-  var dest/edi: (addr image) <- copy _dest
-  # copy 'width'
-  var src-width-a/eax: (addr int) <- get src, width
-  var tmp/eax: int <- copy *src-width-a
-  var src-width: int
-  copy-to src-width, tmp
-  {
-    var dest-width-a/edx: (addr int) <- get dest, width
-    copy-to *dest-width-a, tmp
-  }
-  # copy 'height'
-  var src-height-a/eax: (addr int) <- get src, height
-  var tmp/eax: int <- copy *src-height-a
-  var src-height: int
-  copy-to src-height, tmp
-  {
-    var dest-height-a/ecx: (addr int) <- get dest, height
-    copy-to *dest-height-a, tmp
-  }
-  # transform 'data'
-  var capacity/ebx: int <- copy src-width
-  capacity <- multiply src-height
-  var dest/edi: (addr image) <- copy _dest
-  var dest-data-ah/eax: (addr handle array byte) <- get dest, data
-  populate dest-data-ah, capacity
-  var _dest-data/eax: (addr array byte) <- lookup *dest-data-ah
-  var dest-data/edi: (addr array byte) <- copy _dest-data
-  # needs a buffer to temporarily hold more than 256 levels of precision
-  var errors-storage: (array int 0xc0000)
-  var errors/ebx: (addr array int) <- address errors-storage
-  var src-data-ah/eax: (addr handle array byte) <- get src, data
-  var _src-data/eax: (addr array byte) <- lookup *src-data-ah
-  var src-data/esi: (addr array byte) <- copy _src-data
-  var y/edx: int <- copy 0
-  {
-    compare y, src-height
-    break-if->=
-    var x/ecx: int <- copy 0
-    {
-      compare x, src-width
-      break-if->=
-      var curr/eax: byte <- _read-pgm-buffer src-data, x, y, src-width
-      var curr-int/eax: int <- copy curr
-      curr-int <- shift-left 0x10  # we have 32 bits; we'll use 16 bits for the fraction and leave 8 for unanticipated overflow
-      var error/esi: int <- _read-dithering-error errors, x, y, src-width
-      error <- add curr-int
-      $_dither-pgm-unordered-monochrome:update-error: {
-        compare error, 0x800000
-        {
-          break-if->=
-          _write-raw-buffer dest-data, x, y, src-width, 0/black
-          break $_dither-pgm-unordered-monochrome:update-error
-        }
-        _write-raw-buffer dest-data, x, y, src-width, 1/white
-        error <- subtract 0xff0000
-      }
-      _diffuse-dithering-error-floyd-steinberg errors, x, y, src-width, src-height, error
-      x <- increment
-      loop
-    }
-    move-cursor-to-left-margin-of-next-line 0/screen
-    y <- increment
-    loop
-  }
-}
-
-fn dither-pgm-unordered _src: (addr image), _dest: (addr image) {
-  var src/esi: (addr image) <- copy _src
-  var dest/edi: (addr image) <- copy _dest
-  # copy 'width'
-  var src-width-a/eax: (addr int) <- get src, width
-  var tmp/eax: int <- copy *src-width-a
-  var src-width: int
-  copy-to src-width, tmp
-  {
-    var dest-width-a/edx: (addr int) <- get dest, width
-    copy-to *dest-width-a, tmp
-  }
-  # copy 'height'
-  var src-height-a/eax: (addr int) <- get src, height
-  var tmp/eax: int <- copy *src-height-a
-  var src-height: int
-  copy-to src-height, tmp
-  {
-    var dest-height-a/ecx: (addr int) <- get dest, height
-    copy-to *dest-height-a, tmp
-  }
-  # compute scaling factor 255/max
-  var target-scale/eax: int <- copy 0xff
-  var scale-f/xmm7: float <- convert target-scale
-  var src-max-a/eax: (addr int) <- get src, max
-  var tmp-f/xmm0: float <- convert *src-max-a
-  scale-f <- divide tmp-f
-  # transform 'data'
-  var capacity/ebx: int <- copy src-width
-  capacity <- multiply src-height
-  var dest/edi: (addr image) <- copy _dest
-  var dest-data-ah/eax: (addr handle array byte) <- get dest, data
-  populate dest-data-ah, capacity
-  var _dest-data/eax: (addr array byte) <- lookup *dest-data-ah
-  var dest-data/edi: (addr array byte) <- copy _dest-data
-  # needs a buffer to temporarily hold more than 256 levels of precision
-  var errors-storage: (array int 0xc0000)
-  var errors/ebx: (addr array int) <- address errors-storage
-  var src-data-ah/eax: (addr handle array byte) <- get src, data
-  var _src-data/eax: (addr array byte) <- lookup *src-data-ah
-  var src-data/esi: (addr array byte) <- copy _src-data
-  var y/edx: int <- copy 0
-  {
-    compare y, src-height
-    break-if->=
-    var x/ecx: int <- copy 0
-    {
-      compare x, src-width
-      break-if->=
-      var initial-color/eax: byte <- _read-pgm-buffer src-data, x, y, src-width
-      # . scale to 255 levels
-      var initial-color-int/eax: int <- copy initial-color
-      var initial-color-f/xmm0: float <- convert initial-color-int
-      initial-color-f <- multiply scale-f
-      initial-color-int <- convert initial-color-f
-      var error/esi: int <- _read-dithering-error errors, x, y, src-width
-      # error += (initial-color << 16)
-      {
-        var tmp/eax: int <- copy initial-color-int
-        tmp <- shift-left 0x10  # we have 32 bits; we'll use 16 bits for the fraction and leave 8 for unanticipated overflow
-        error <- add tmp
-      }
-      # nearest-color = nearest(error >> 16)
-      var nearest-color/eax: int <- copy error
-      nearest-color <- shift-right-signed 0x10
-      {
-        compare nearest-color, 0
-        break-if->=
-        nearest-color <- copy 0
-      }
-      {
-        compare nearest-color, 0xf0
-        break-if-<=
-        nearest-color <- copy 0xf0
-      }
-      # . truncate last 4 bits
-      nearest-color <- and 0xf0
-      # error -= (nearest-color << 16)
-      {
-        var tmp/eax: int <- copy nearest-color
-        tmp <- shift-left 0x10
-        error <- subtract tmp
-      }
-      # color-index = (nearest-color >> 4 + 16)
-      var color-index/eax: int <- copy nearest-color
-      color-index <- shift-right 4
-      color-index <- add 0x10
-      var color-index-byte/eax: byte <- copy-byte color-index
-      _write-raw-buffer dest-data, x, y, src-width, color-index-byte
-      _diffuse-dithering-error-floyd-steinberg errors, x, y, src-width, src-height, error
-      x <- increment
-      loop
-    }
-    y <- increment
-    loop
-  }
-}
-
-# Use Floyd-Steinberg algorithm for diffusing error at x, y in a 2D grid of
-# dimensions (width, height)
-#
-# https://tannerhelland.com/2012/12/28/dithering-eleven-algorithms-source-code.html
-#
-# Error is currently a fixed-point number with 16-bit fraction. But
-# interestingly this function doesn't care about that.
-fn _diffuse-dithering-error-floyd-steinberg errors: (addr array int), x: int, y: int, width: int, height: int, error: int {
-  {
-    compare error, 0
-    break-if-!=
-    return
-  }
-  var width-1/esi: int <- copy width
-  width-1 <- decrement
-  var height-1/edi: int <- copy height
-  height-1 <- decrement
-  # delta = error/16
-#?   show-errors errors, width, height, x, y
-  var delta/ecx: int <- copy error
-  delta <- shift-right-signed 4
-  # In Floyd-Steinberg, each pixel X transmits its errors to surrounding
-  # pixels in the following proportion:
-  #           X     7/16
-  #     3/16  5/16  1/16
-  var x/edx: int <- copy x
-  {
-    compare x, width-1
-    break-if->=
-    var tmp/eax: int <- copy 7
-    tmp <- multiply delta
-    var xright/edx: int <- copy x
-    xright <- increment
-    _accumulate-dithering-error errors, xright, y, width, tmp
-  }
-  var y/ebx: int <- copy y
-  {
-    compare y, height-1
-    break-if-<
-    return
-  }
-  var ybelow: int
-  copy-to ybelow, y
-  increment ybelow
-  {
-    compare x, 0
-    break-if-<=
-    var tmp/eax: int <- copy 3
-    tmp <- multiply delta
-    var xleft/edx: int <- copy x
-    xleft <- decrement
-    _accumulate-dithering-error errors, xleft, ybelow, width, tmp
-  }
-  {
-    var tmp/eax: int <- copy 5
-    tmp <- multiply delta
-    _accumulate-dithering-error errors, x, ybelow, width, tmp
-  }
-  {
-    compare x, width-1
-    break-if->=
-    var xright/edx: int <- copy x
-    xright <- increment
-    _accumulate-dithering-error errors, xright, ybelow, width, delta
-  }
-#?   show-errors errors, width, height, x, y
-}
-
-fn _accumulate-dithering-error errors: (addr array int), x: int, y: int, width: int, error: int {
-  var curr/esi: int <- _read-dithering-error errors, x, y, width
-  curr <- add error
-  _write-dithering-error errors, x, y, width, curr
-}
-
-fn _read-dithering-error _errors: (addr array int), x: int, y: int, width: int -> _/esi: int {
-  var errors/esi: (addr array int) <- copy _errors
-  var idx/ecx: int <- copy y
-  idx <- multiply width
-  idx <- add x
-  var result-a/eax: (addr int) <- index errors, idx
-  return *result-a
-}
-
-fn _write-dithering-error _errors: (addr array int), x: int, y: int, width: int, val: int {
-  var errors/esi: (addr array int) <- copy _errors
-  var idx/ecx: int <- copy y
-  idx <- multiply width
-  idx <- add x
-#?   draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, idx, 7/fg 0/bg
-#?   move-cursor-to-left-margin-of-next-line 0/screen
-  var src/eax: int <- copy val
-  var dest-a/edi: (addr int) <- index errors, idx
-  copy-to *dest-a, src
-}
-
-fn _read-pgm-buffer _buf: (addr array byte), x: int, y: int, width: int -> _/eax: byte {
-  var buf/esi: (addr array byte) <- copy _buf
-  var idx/ecx: int <- copy y
-  idx <- multiply width
-  idx <- add x
-  var result-a/eax: (addr byte) <- index buf, idx
-  var result/eax: byte <- copy-byte *result-a
-  return result
-}
-
-fn _write-raw-buffer _buf: (addr array byte), x: int, y: int, width: int, val: byte {
-  var buf/esi: (addr array byte) <- copy _buf
-  var idx/ecx: int <- copy y
-  idx <- multiply width
-  idx <- add x
-  var src/eax: byte <- copy val
-  var dest-a/edi: (addr byte) <- index buf, idx
-  copy-byte-to *dest-a, src
-}
-
-# some debugging helpers
-fn show-errors errors: (addr array int), width: int, height: int, x: int, y: int {
-  compare y, 1
-  {
-    break-if-=
-    return
-  }
-  compare x, 0
-  {
-    break-if-=
-    return
-  }
-  var y/edx: int <- copy 0
-  {
-    compare y, height
-    break-if->=
-    var x/ecx: int <- copy 0
-    {
-      compare x, width
-      break-if->=
-      var error/esi: int <- _read-dithering-error errors, x, y, width
-      psd "e", error, 5/fg, x, y
-      x <- increment
-      loop
-    }
-    move-cursor-to-left-margin-of-next-line 0/screen
-    y <- increment
-    loop
-  }
-}
-
-fn psd s: (addr array byte), d: int, fg: int, x: int, y: int {
-  {
-    compare y, 0x18
-    break-if->=
-    return
-  }
-  {
-    compare y, 0x1c
-    break-if-<=
-    return
-  }
-  {
-    compare x, 0x40
-    break-if->=
-    return
-  }
-#?   {
-#?     compare x, 0x48
-#?     break-if-<=
-#?     return
-#?   }
-  draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, s, 7/fg 0/bg
-  draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, d, fg 0/bg
-}
-
-fn psx s: (addr array byte), d: int, fg: int, x: int, y: int {
-#?   {
-#?     compare y, 0x60
-#?     break-if->=
-#?     return
-#?   }
-#?   {
-#?     compare y, 0x6c
-#?     break-if-<=
-#?     return
-#?   }
-  {
-    compare x, 0x20
-    break-if->=
-    return
-  }
-#?   {
-#?     compare x, 0x6c
-#?     break-if-<=
-#?     return
-#?   }
-  draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, s, 7/fg 0/bg
-  draw-int32-hex-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, d, fg 0/bg
-}
-
-# import a color ascii "pixmap" (each pixel consists of 3 shades of r/g/b from 0 to 255)
-fn initialize-image-from-ppm _self: (addr image), in: (addr stream byte) {
-  var self/esi: (addr image) <- copy _self
-  var curr-word-storage: slice
-  var curr-word/ecx: (addr slice) <- address curr-word-storage
-  # load width, height
-  next-word in, curr-word
-  var tmp/eax: int <- parse-decimal-int-from-slice curr-word
-  var width/edx: int <- copy tmp
-  next-word in, curr-word
-  tmp <- parse-decimal-int-from-slice curr-word
-  var height/ebx: int <- copy tmp
-  next-word in, curr-word
-  # check color levels
-  {
-    tmp <- parse-decimal-int-from-slice curr-word
-    compare tmp, 0xff
-    break-if-=
-    abort "initialize-image-from-ppm: supports exactly 255 levels per rgb channel"
-  }
-  var dest/edi: (addr int) <- get self, max
-  copy-to *dest, tmp
-  # save width, height
-  dest <- get self, width
-  copy-to *dest, width
-  dest <- get self, height
-  copy-to *dest, height
-  # initialize data
-  var capacity/edx: int <- copy width
-  capacity <- multiply height
-  # . multiply by 3 for the r/g/b channels
-  var tmp/eax: int <- copy capacity
-  tmp <- shift-left 1
-  capacity <- add tmp
-  #
-  var data-ah/edi: (addr handle array byte) <- get self, data
-  populate data-ah, capacity
-  var _data/eax: (addr array byte) <- lookup *data-ah
-  var data/edi: (addr array byte) <- copy _data
-  var i/ebx: int <- copy 0
-  {
-    compare i, capacity
-    break-if->=
-    next-word in, curr-word
-    var src/eax: int <- parse-decimal-int-from-slice curr-word
-    {
-      var dest/ecx: (addr byte) <- index data, i
-      copy-byte-to *dest, src
-    }
-    i <- increment
-    loop
-  }
-}
-
-# import a color ascii "pixmap" (each pixel consists of 3 shades of r/g/b from 0 to 255)
-fn render-ppm-image screen: (addr screen), _img: (addr image), xmin: int, ymin: int, width: int, height: int {
-  var img/esi: (addr image) <- copy _img
-  # yratio = height/img->height
-  var img-height-a/eax: (addr int) <- get img, height
-  var img-height/xmm0: float <- convert *img-height-a
-  var yratio/xmm1: float <- convert height
-  yratio <- divide img-height
-  # xratio = width/img->width
-  var img-width-a/eax: (addr int) <- get img, width
-  var img-width/ebx: int <- copy *img-width-a
-  var img-width-f/xmm0: float <- convert img-width
-  var xratio/xmm2: float <- convert width
-  xratio <- divide img-width-f
-  # esi = img->data
-  var img-data-ah/eax: (addr handle array byte) <- get img, data
-  var _img-data/eax: (addr array byte) <- lookup *img-data-ah
-  var img-data/esi: (addr array byte) <- copy _img-data
-  var len/edi: int <- length img-data
-  #
-  var one/eax: int <- copy 1
-  var one-f/xmm3: float <- convert one
-  var width-f/xmm4: float <- convert width
-  var height-f/xmm5: float <- convert height
-  var zero/eax: int <- copy 0
-  var zero-f/xmm0: float <- convert zero
-  var y/xmm6: float <- copy zero-f
-  {
-    compare y, height-f
-    break-if-float>=
-    var imgy-f/xmm5: float <- copy y
-    imgy-f <- divide yratio
-    var imgy/edx: int <- truncate imgy-f
-    var x/xmm7: float <- copy zero-f
-    {
-      compare x, width-f
-      break-if-float>=
-      var imgx-f/xmm5: float <- copy x
-      imgx-f <- divide xratio
-      var imgx/ecx: int <- truncate imgx-f
-      var idx/eax: int <- copy imgy
-      idx <- multiply img-width
-      idx <- add imgx
-      # . multiply by 3 for the r/g/b channels
-      {
-        var tmp/ecx: int <- copy idx
-        tmp <- shift-left 1
-        idx <- add tmp
-      }
-      # error info in case we rounded wrong and 'index' will fail bounds-check
-      compare idx, len
-      {
-        break-if-<
-        set-cursor-position 0/screen, 0x20/x 0x20/y
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgx, 3/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgy, 4/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, idx, 5/fg 0/bg
-      }
-      # r channel
-      var r: int
-      {
-        var src-a/eax: (addr byte) <- index img-data, idx
-        var src/eax: byte <- copy-byte *src-a
-        copy-to r, src
-      }
-      idx <- increment
-      # g channel
-      var g: int
-      {
-        var src-a/eax: (addr byte) <- index img-data, idx
-        var src/eax: byte <- copy-byte *src-a
-        copy-to g, src
-      }
-      idx <- increment
-      # b channel
-      var b: int
-      {
-        var src-a/eax: (addr byte) <- index img-data, idx
-        var src/eax: byte <- copy-byte *src-a
-        copy-to b, src
-      }
-      idx <- increment
-      # plot nearest color
-      var color/eax: int <- nearest-color-euclidean r, g, b
-      var screenx/ecx: int <- convert x
-      screenx <- add xmin
-      var screeny/edx: int <- convert y
-      screeny <- add ymin
-      pixel screen, screenx, screeny, color
-      x <- add one-f
-      loop
-    }
-    y <- add one-f
-    loop
-  }
-}
-
-fn dither-ppm-unordered _src: (addr image), _dest: (addr image) {
-  var src/esi: (addr image) <- copy _src
-  var dest/edi: (addr image) <- copy _dest
-  # copy 'width'
-  var src-width-a/eax: (addr int) <- get src, width
-  var tmp/eax: int <- copy *src-width-a
-  var src-width: int
-  copy-to src-width, tmp
-  {
-    var dest-width-a/edx: (addr int) <- get dest, width
-    copy-to *dest-width-a, tmp
-  }
-  # copy 'height'
-  var src-height-a/eax: (addr int) <- get src, height
-  var tmp/eax: int <- copy *src-height-a
-  var src-height: int
-  copy-to src-height, tmp
-  {
-    var dest-height-a/ecx: (addr int) <- get dest, height
-    copy-to *dest-height-a, tmp
-  }
-  # compute scaling factor 255/max
-  var target-scale/eax: int <- copy 0xff
-  var scale-f/xmm7: float <- convert target-scale
-  var src-max-a/eax: (addr int) <- get src, max
-  var tmp-f/xmm0: float <- convert *src-max-a
-  scale-f <- divide tmp-f
-  # allocate 'data'
-  var capacity/ebx: int <- copy src-width
-  capacity <- multiply src-height
-  var dest/edi: (addr image) <- copy _dest
-  var dest-data-ah/eax: (addr handle array byte) <- get dest, data
-  populate dest-data-ah, capacity
-  var _dest-data/eax: (addr array byte) <- lookup *dest-data-ah
-  var dest-data/edi: (addr array byte) <- copy _dest-data
-  # error buffers per r/g/b channel
-  var red-errors-storage: (array int 0xc0000)
-  var tmp/eax: (addr array int) <- address red-errors-storage
-  var red-errors: (addr array int)
-  copy-to red-errors, tmp
-  var green-errors-storage: (array int 0xc0000)
-  var tmp/eax: (addr array int) <- address green-errors-storage
-  var green-errors: (addr array int)
-  copy-to green-errors, tmp
-  var blue-errors-storage: (array int 0xc0000)
-  var tmp/eax: (addr array int) <- address blue-errors-storage
-  var blue-errors: (addr array int)
-  copy-to blue-errors, tmp
-  # transform 'data'
-  var src-data-ah/eax: (addr handle array byte) <- get src, data
-  var _src-data/eax: (addr array byte) <- lookup *src-data-ah
-  var src-data/esi: (addr array byte) <- copy _src-data
-  var y/edx: int <- copy 0
-  {
-    compare y, src-height
-    break-if->=
-    var x/ecx: int <- copy 0
-    {
-      compare x, src-width
-      break-if->=
-      # - update errors and compute color levels for current pixel in each channel
-      # update red-error with current image pixel
-      var red-error: int
-      {
-        var tmp/esi: int <- _read-dithering-error red-errors, x, y, src-width
-        copy-to red-error, tmp
-      }
-      {
-        var tmp/eax: int <- _ppm-error src-data, x, y, src-width, 0/red, scale-f
-        add-to red-error, tmp
-      }
-      # recompute red channel for current pixel
-      var red-level: int
-      {
-        var tmp/eax: int <- _error-to-ppm-channel red-error
-        copy-to red-level, tmp
-      }
-      # update green-error with current image pixel
-      var green-error: int
-      {
-        var tmp/esi: int <- _read-dithering-error green-errors, x, y, src-width
-        copy-to green-error, tmp
-      }
-      {
-        var tmp/eax: int <- _ppm-error src-data, x, y, src-width, 1/green, scale-f
-        add-to green-error, tmp
-      }
-      # recompute green channel for current pixel
-      var green-level: int
-      {
-        var tmp/eax: int <- _error-to-ppm-channel green-error
-        copy-to green-level, tmp
-      }
-      # update blue-error with current image pixel
-      var blue-error: int
-      {
-        var tmp/esi: int <- _read-dithering-error blue-errors, x, y, src-width
-        copy-to blue-error, tmp
-      }
-      {
-        var tmp/eax: int <- _ppm-error src-data, x, y, src-width, 2/blue, scale-f
-        add-to blue-error, tmp
-      }
-      # recompute blue channel for current pixel
-      var blue-level: int
-      {
-        var tmp/eax: int <- _error-to-ppm-channel blue-error
-        copy-to blue-level, tmp
-      }
-      # - figure out the nearest color
-#?       {
-#?         compare red-level, 0x80
-#?         break-if->
-#?         draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, red-level, 4/fg 0/bg
-#?         draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, green-level, 2/fg 0/bg
-#?         draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, blue-level, 9/fg 0/bg
-#?       }
-      var nearest-color-index/eax: int <- nearest-color-euclidean red-level, green-level, blue-level
-      {
-        var nearest-color-index-byte/eax: byte <- copy-byte nearest-color-index
-        _write-raw-buffer dest-data, x, y, src-width, nearest-color-index-byte
-      }
-      # - diffuse errors
-      var red-level: int
-      var green-level: int
-      var blue-level: int
-      {
-        var tmp-red-level/ecx: int <- copy 0
-        var tmp-green-level/edx: int <- copy 0
-        var tmp-blue-level/ebx: int <- copy 0
-        tmp-red-level, tmp-green-level, tmp-blue-level <- color-rgb nearest-color-index
-        copy-to red-level, tmp-red-level
-        copy-to green-level, tmp-green-level
-        copy-to blue-level, tmp-blue-level
-      }
-      # update red-error
-      var red-level-error/eax: int <- copy red-level
-      red-level-error <- shift-left 0x10
-      subtract-from red-error, red-level-error
-      _diffuse-dithering-error-floyd-steinberg red-errors, x, y, src-width, src-height, red-error
-      # update green-error
-      var green-level-error/eax: int <- copy green-level
-      green-level-error <- shift-left 0x10
-      subtract-from green-error, green-level-error
-      _diffuse-dithering-error-floyd-steinberg green-errors, x, y, src-width, src-height, green-error
-      # update blue-error
-      var blue-level-error/eax: int <- copy blue-level
-      blue-level-error <- shift-left 0x10
-      subtract-from blue-error, blue-level-error
-      _diffuse-dithering-error-floyd-steinberg blue-errors, x, y, src-width, src-height, blue-error
-      #
-      x <- increment
-      loop
-    }
-    y <- increment
-    loop
-  }
-}
-
-# convert a single channel for a single image pixel to error space
-fn _ppm-error buf: (addr array byte), x: int, y: int, width: int, channel: int, _scale-f: float -> _/eax: int {
-  # current image pixel
-  var initial-level/eax: byte <- _read-ppm-buffer buf, x, y, width, channel
-  # scale to 255 levels
-  var initial-level-int/eax: int <- copy initial-level
-  var initial-level-f/xmm0: float <- convert initial-level-int
-  var scale-f/xmm1: float <- copy _scale-f
-  initial-level-f <- multiply scale-f
-  initial-level-int <- convert initial-level-f
-  # switch to fixed-point with 16 bits of precision
-  initial-level-int <- shift-left 0x10
-  return initial-level-int
-}
-
-fn _error-to-ppm-channel error: int -> _/eax: int {
-  # clamp(error >> 16)
-  var result/esi: int <- copy error
-  result <- shift-right-signed 0x10
-  {
-    compare result, 0
-    break-if->=
-    result <- copy 0
-  }
-  {
-    compare result, 0xff
-    break-if-<=
-    result <- copy 0xff
-  }
-  return result
-}
-
-# read from a buffer containing alternating bytes from r/g/b channels
-fn _read-ppm-buffer _buf: (addr array byte), x: int, y: int, width: int, channel: int -> _/eax: byte {
-  var buf/esi: (addr array byte) <- copy _buf
-  var idx/ecx: int <- copy y
-  idx <- multiply width
-  idx <- add x
-  var byte-idx/edx: int <- copy 3
-  byte-idx <- multiply idx
-  byte-idx <- add channel
-  var result-a/eax: (addr byte) <- index buf, byte-idx
-  var result/eax: byte <- copy-byte *result-a
-  return result
-}
-
-# each byte in the image data is a color of the current palette
-fn render-raw-image screen: (addr screen), _img: (addr image), xmin: int, ymin: int, width: int, height: int {
-  var img/esi: (addr image) <- copy _img
-  # yratio = height/img->height
-  var img-height-a/eax: (addr int) <- get img, height
-  var img-height/xmm0: float <- convert *img-height-a
-  var yratio/xmm1: float <- convert height
-  yratio <- divide img-height
-  # xratio = width/img->width
-  var img-width-a/eax: (addr int) <- get img, width
-  var img-width/ebx: int <- copy *img-width-a
-  var img-width-f/xmm0: float <- convert img-width
-  var xratio/xmm2: float <- convert width
-  xratio <- divide img-width-f
-  # esi = img->data
-  var img-data-ah/eax: (addr handle array byte) <- get img, data
-  var _img-data/eax: (addr array byte) <- lookup *img-data-ah
-  var img-data/esi: (addr array byte) <- copy _img-data
-  var len/edi: int <- length img-data
-  #
-  var one/eax: int <- copy 1
-  var one-f/xmm3: float <- convert one
-  var width-f/xmm4: float <- convert width
-  var height-f/xmm5: float <- convert height
-  var zero/eax: int <- copy 0
-  var zero-f/xmm0: float <- convert zero
-  var y/xmm6: float <- copy zero-f
-  {
-    compare y, height-f
-    break-if-float>=
-    var imgy-f/xmm5: float <- copy y
-    imgy-f <- divide yratio
-    var imgy/edx: int <- truncate imgy-f
-    var x/xmm7: float <- copy zero-f
-    {
-      compare x, width-f
-      break-if-float>=
-      var imgx-f/xmm5: float <- copy x
-      imgx-f <- divide xratio
-      var imgx/ecx: int <- truncate imgx-f
-      var idx/eax: int <- copy imgy
-      idx <- multiply img-width
-      idx <- add imgx
-      # error info in case we rounded wrong and 'index' will fail bounds-check
-      compare idx, len
-      {
-        break-if-<
-        set-cursor-position 0/screen, 0x20/x 0x20/y
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgx, 3/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, imgy, 4/fg 0/bg
-        draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, idx, 5/fg 0/bg
-      }
-      var color-a/eax: (addr byte) <- index img-data, idx
-      var color/eax: byte <- copy-byte *color-a
-      var color-int/eax: int <- copy color
-      var screenx/ecx: int <- convert x
-      screenx <- add xmin
-      var screeny/edx: int <- convert y
-      screeny <- add ymin
-      pixel screen, screenx, screeny, color-int
-      x <- add one-f
-      loop
-    }
-    y <- add one-f
-    loop
-  }
-}