about summary refs log tree commit diff stats
path: root/500fake-screen.mu
blob: c34beeaa1a7e1e569037dc7f0df2d548a6e6ecd9 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
# Testable primitives for writing to screen.
#
# Mu mostly uses the screen for text, but it builds it out of pixel graphics
# and a bitmap font. There is no support for a blinking cursor, scrolling and
# so on.
#
# Fake screens are primarily for testing text-mode prints. However, they do
# support some rudimentary pixel operations as well. Caveats:
#
# - Drawing pixels atop text or vice versa is not supported. Results in a fake
#   screen will not mimic real screens in these situations.
# - Fake screens currently also assume a fixed-width 8x16 font.
# - Combining characters don't render like in a real screen (which itself
#   isn't ideal).

type screen {
  # text mode
  width: int
  height: int
  data: (handle array screen-cell)
  cursor-x: int  # [0..width)
  cursor-y: int  # [0..height)
  # pixel graphics
  pixels: (handle array byte)
}

type screen-cell {
  data: code-point
  color: int
  background-color: int
  unused?: boolean
}

fn initialize-screen _screen: (addr screen), width: int, height: int, pixel-graphics?: boolean {
  var screen/esi: (addr screen) <- copy _screen
  var tmp/eax: int <- copy 0
  var dest/edi: (addr int) <- copy 0
  # screen->width = width
  dest <- get screen, width
  tmp <- copy width
  copy-to *dest, tmp
  # screen->height = height
  dest <- get screen, height
  tmp <- copy height
  copy-to *dest, tmp
  # populate screen->data
  {
    var data-ah/edi: (addr handle array screen-cell) <- get screen, data
    var capacity/eax: int <- copy width
    capacity <- multiply height
    #
    populate data-ah, capacity
  }
  # if necessary, populate screen->pixels
  {
    compare pixel-graphics?, 0/false
    break-if-=
    var pixels-ah/edi: (addr handle array byte) <- get screen, pixels
    var capacity/eax: int <- copy width
    capacity <- shift-left 3/log2-font-width
    capacity <- multiply height
    capacity <- shift-left 4/log2-font-height
    #
    populate pixels-ah, capacity
  }
  # screen->cursor-x = 0
  dest <- get screen, cursor-x
  copy-to *dest, 0
  # screen->cursor-y = 0
  dest <- get screen, cursor-y
  copy-to *dest, 0
}

# in graphemes
fn screen-size _screen: (addr screen) -> _/eax: int, _/ecx: int {
  var screen/esi: (addr screen) <- copy _screen
  var width/eax: int <- copy 0
  var height/ecx: int <- copy 0
  compare screen, 0
  {
    break-if-!=
    return 0x80/128, 0x30/48
  }
  # fake screen
  var tmp/edx: (addr int) <- get screen, width
  width <- copy *tmp
  tmp <- get screen, height
  height <- copy *tmp
  return width, height
}

# testable screen primitive
# return number of 8x16 units drawn
fn draw-code-point _screen: (addr screen), c: code-point, x: int, y: int, color: int, background-color: int -> _/eax: int {
  var screen/esi: (addr screen) <- copy _screen
  {
    compare screen, 0
    break-if-!=
    var result/eax: int <- draw-code-point-on-real-screen c, x, y, color, background-color
    return result
  }
  # fake screen
  var wide?/eax: boolean <- wide-code-point? c
  compare wide?, 0/false
  {
    break-if-=
    draw-wide-code-point-on-fake-screen screen, c, x, y, color, background-color
    return 2
  }
  draw-narrow-code-point-on-fake-screen screen, c, x, y, color, background-color
  return 1
}

fn overlay-code-point _screen: (addr screen), c: code-point, x: int, y: int, color: int, background-color: int -> _/eax: int {
  var screen/esi: (addr screen) <- copy _screen
  {
    compare screen, 0
    break-if-!=
    var result/eax: int <- overlay-code-point-on-real-screen c, x, y, color, background-color
    return result
  }
  # fake screen
  # TODO: support overlays in fake screen
  var wide?/eax: boolean <- wide-code-point? c
  compare wide?, 0/false
  {
    break-if-=
    draw-wide-code-point-on-fake-screen screen, c, x, y, color, background-color
    return 2
  }
  draw-narrow-code-point-on-fake-screen screen, c, x, y, color, background-color
  return 1
}

fn draw-narrow-code-point-on-fake-screen _screen: (addr screen), c: code-point, x: int, y: int, color: int, background-color: int {
  var screen/esi: (addr screen) <- copy _screen
  # ignore if out of bounds
  {
    compare x, 0
    break-if->=
    return
  }
  {
    var xmax-addr/eax: (addr int) <- get screen, width
    var xmax/eax: int <- copy *xmax-addr
    compare x, xmax
    break-if-<
    {
      loop
    }
    return
  }
  {
    compare y, 0
    break-if->=
    return
  }
  {
    var ymax-addr/eax: (addr int) <- get screen, height
    var ymax/eax: int <- copy *ymax-addr
    compare y, ymax
    break-if-<
    return
  }
  #
  var index/ecx: int <- screen-cell-index screen, x, y
  var data-ah/eax: (addr handle array screen-cell) <- get screen, data
  var data/eax: (addr array screen-cell) <- lookup *data-ah
  var offset/ecx: (offset screen-cell) <- compute-offset data, index
  var dest-cell/ecx: (addr screen-cell) <- index data, offset
  var dest-code-point/eax: (addr code-point) <- get dest-cell, data
  var c2/edx: code-point <- copy c
  copy-to *dest-code-point, c2
  var dest-color/eax: (addr int) <- get dest-cell, color
  var src-color/edx: int <- copy color
  copy-to *dest-color, src-color
  dest-color <- get dest-cell, background-color
  src-color <- copy background-color
  copy-to *dest-color, src-color
  var dest/eax: (addr boolean) <- get dest-cell, unused?
  copy-to *dest, 0/false
}

fn draw-wide-code-point-on-fake-screen _screen: (addr screen), c: code-point, x: int, y: int, color: int, background-color: int {
  var screen/esi: (addr screen) <- copy _screen
  # ignore if out of bounds
  {
    compare x, 0
    break-if->=
    return
  }
  {
    var xmax-addr/eax: (addr int) <- get screen, width
    var xmax/eax: int <- copy *xmax-addr
    xmax <- decrement  # wide code-points need an extra unit
    compare x, xmax
    break-if-<
    return
  }
  {
    compare y, 0
    break-if->=
    return
  }
  {
    var ymax-addr/eax: (addr int) <- get screen, height
    var ymax/eax: int <- copy *ymax-addr
    compare y, ymax
    break-if-<
    return
  }
  #
  var index/ecx: int <- screen-cell-index screen, x, y
  {
    var data-ah/eax: (addr handle array screen-cell) <- get screen, data
    var data/eax: (addr array screen-cell) <- lookup *data-ah
    var offset/ecx: (offset screen-cell) <- compute-offset data, index
    var dest-cell/ecx: (addr screen-cell) <- index data, offset
    var dest-code-point/eax: (addr code-point) <- get dest-cell, data
    var c2/edx: code-point <- copy c
    copy-to *dest-code-point, c2
    var dest-color/eax: (addr int) <- get dest-cell, color
    var src-color/edx: int <- copy color
    copy-to *dest-color, src-color
    dest-color <- get dest-cell, background-color
    src-color <- copy background-color
    copy-to *dest-color, src-color
    var dest/eax: (addr boolean) <- get dest-cell, unused?
    copy-to *dest, 0/false
  }
  # set next screen-cell to unused
  index <- increment
  {
    var data-ah/eax: (addr handle array screen-cell) <- get screen, data
    var data/eax: (addr array screen-cell) <- lookup *data-ah
    var offset/ecx: (offset screen-cell) <- compute-offset data, index
    var dest-cell/ecx: (addr screen-cell) <- index data, offset
    var dest/eax: (addr boolean) <- get dest-cell, unused?
    copy-to *dest, 1/true
  }
}

# fake screens only
fn screen-cell-index _screen: (addr screen), x: int, y: int -> _/ecx: int {
  var screen/esi: (addr screen) <- copy _screen
  var width-addr/eax: (addr int) <- get screen, width
  var result/ecx: int <- copy y
  result <- multiply *width-addr
  result <- add x
  return result
}

fn cursor-position _screen: (addr screen) -> _/eax: int, _/ecx: int {
  var screen/esi: (addr screen) <- copy _screen
  {
    compare screen, 0
    break-if-!=
    var x/eax: int <- copy 0
    var y/ecx: int <- copy 0
    x, y <- cursor-position-on-real-screen
    return x, y
  }
  # fake screen
  var cursor-x-addr/eax: (addr int) <- get screen, cursor-x
  var cursor-y-addr/ecx: (addr int) <- get screen, cursor-y
  return *cursor-x-addr, *cursor-y-addr
}

fn set-cursor-position _screen: (addr screen), x: int, y: int {
  var screen/esi: (addr screen) <- copy _screen
  {
    compare screen, 0
    break-if-!=
    set-cursor-position-on-real-screen x, y
    return
  }
  # fake screen
  # ignore x < 0
  {
    compare x, 0
    break-if->=
    return
  }
  # ignore x >= width
  {
    var width-addr/eax: (addr int) <- get screen, width
    var width/eax: int <- copy *width-addr
    compare x, width
    break-if-<=
    return
  }
  # ignore y < 0
  {
    compare y, 0
    break-if->=
    return
  }
  # ignore y >= height
  {
    var height-addr/eax: (addr int) <- get screen, height
    var height/eax: int <- copy *height-addr
    compare y, height
    break-if-<
    return
  }
  # screen->cursor-x = x
  var dest/edi: (addr int) <- get screen, cursor-x
  var src/eax: int <- copy x
  copy-to *dest, src
  # screen->cursor-y = y
  dest <- get screen, cursor-y
  src <- copy y
  copy-to *dest, src
}

fn draw-cursor screen: (addr screen), c: code-point {
  {
    compare screen, 0
    break-if-!=
    draw-cursor-on-real-screen c
    return
  }
  # fake screen
  var cursor-x/eax: int <- copy 0
  var cursor-y/ecx: int <- copy 0
  cursor-x, cursor-y <- cursor-position screen
  var dummy/eax: int <- draw-code-point screen, c, cursor-x, cursor-y, 0/fg, 7/bg
}

fn clear-screen _screen: (addr screen) {
  var screen/esi: (addr screen) <- copy _screen
  {
    compare screen, 0
    break-if-!=
    clear-real-screen
    return
  }
  # fake screen
  set-cursor-position screen, 0, 0
  var y/eax: int <- copy 0
  var height/ecx: (addr int) <- get screen, height
  {
    compare y, *height
    break-if->=
    var x/edx: int <- copy 0
    var width/ebx: (addr int) <- get screen, width
    {
      compare x, *width
      break-if->=
      var dummy/eax: int <- draw-code-point screen, 0/nul, x, y, 0/fg=black, 0/bg=black
      x <- increment
      loop
    }
    y <- increment
    loop
  }
  set-cursor-position screen, 0, 0
  var pixels-ah/eax: (addr handle array byte) <- get screen, pixels
  var pixels/eax: (addr array byte) <- lookup *pixels-ah
  var i/ecx: int <- copy 0
  var max/edx: int <- length pixels
  {
    compare i, max
    break-if->=
    var curr/eax: (addr byte) <- index pixels, i
    var zero/ebx: byte <- copy 0
    copy-byte-to *curr, zero
    i <- increment
    loop
  }
}

fn fake-screen-empty? _screen: (addr screen) -> _/eax: boolean {
  var screen/esi: (addr screen) <- copy _screen
  var y/eax: int <- copy 0
  var height/ecx: (addr int) <- get screen, height
  {
    compare y, *height
    break-if->=
    var x/edx: int <- copy 0
    var width/ebx: (addr int) <- get screen, width
    {
      compare x, *width
      break-if->=
      var c/eax: code-point <- screen-code-point-at screen, x, y
      {
        compare c, 0
        break-if-=
        compare c, 0x20/space
        break-if-=
        return 0/false
      }
      x <- increment
      loop
    }
    y <- increment
    loop
  }
  var pixels-ah/eax: (addr handle array byte) <- get screen, pixels
  var pixels/eax: (addr array byte) <- lookup *pixels-ah
  var y/ebx: int <- copy 0
  var height-addr/edx: (addr int) <- get screen, height
  var height/edx: int <- copy *height-addr
  height <- shift-left 4/log2-font-height
  {
    compare y, height
    break-if->=
    var width-addr/edx: (addr int) <- get screen, width
    var width/edx: int <- copy *width-addr
    width <- shift-left 3/log2-font-width
    var x/edi: int <- copy 0
    {
      compare x, width
      break-if->=
      var index/ecx: int <- pixel-index screen, x, y
      var color-addr/ecx: (addr byte) <- index pixels, index
      var color/ecx: byte <- copy-byte *color-addr
      compare color, 0
      {
        break-if-=
        return 0/false
      }
      x <- increment
      loop
    }
    y <- increment
    loop
  }
  return 1/true
}

fn clear-rect _screen: (addr screen), xmin: int, ymin: int, xmax: int, ymax: int, background-color: int {
  var screen/esi: (addr screen) <- copy _screen
  {
    compare screen, 0
    break-if-!=
    clear-rect-on-real-screen xmin, ymin, xmax, ymax, background-color
    return
  }
  # fake screen
  set-cursor-position screen, 0, 0
  var y/eax: int <- copy ymin
  var ymax/ecx: int <- copy ymax
  {
    compare y, ymax
    break-if->=
    var x/edx: int <- copy xmin
    var xmax/ebx: int <- copy xmax
    {
      compare x, xmax
      break-if->=
      var dummy/eax: int <- draw-code-point screen, 0x20/space, x, y, 0/fg, background-color
      x <- increment
      loop
    }
    y <- increment
    loop
  }
  set-cursor-position screen, 0, 0
}

# there's no grapheme that guarantees to cover every pixel, so we'll bump down
# to pixels for a real screen
fn clear-real-screen {
  var y/eax: int <- copy 0
  {
    compare y, 0x300/screen-height=768
    break-if->=
    var x/edx: int <- copy 0
    {
      compare x, 0x400/screen-width=1024
      break-if->=
      pixel-on-real-screen x, y, 0/color=black
      x <- increment
      loop
    }
    y <- increment
    loop
  }
}

fn clear-rect-on-real-screen xmin: int, ymin: int, xmax: int, ymax: int, background-color: int {
  var y/eax: int <- copy ymin
  y <- shift-left 4/log2-font-height
  var ymax/ecx: int <- copy ymax
  ymax <- shift-left 4/log2-font-height
  {
    compare y, ymax
    break-if->=
    var x/edx: int <- copy xmin
    x <- shift-left 3/log2-font-width
    var xmax/ebx: int <- copy xmax
    xmax <- shift-left 3/log2-font-width
    {
      compare x, xmax
      break-if->=
      pixel-on-real-screen x, y, background-color
      x <- increment
      loop
    }
    y <- increment
    loop
  }
}

fn screen-cell-unused-at? _screen: (addr screen), x: int, y: int -> _/eax: boolean {
  var screen/esi: (addr screen) <- copy _screen
  var index/ecx: int <- screen-cell-index screen, x, y
  var result/eax: boolean <- screen-cell-unused-at-index? screen, index
  return result
}

fn screen-cell-unused-at-index? _screen: (addr screen), _index: int -> _/eax: boolean {
  var screen/esi: (addr screen) <- copy _screen
  var data-ah/eax: (addr handle array screen-cell) <- get screen, data
  var data/eax: (addr array screen-cell) <- lookup *data-ah
  var index/ecx: int <- copy _index
  var offset/ecx: (offset screen-cell) <- compute-offset data, index
  var cell/eax: (addr screen-cell) <- index data, offset
  var src/eax: (addr boolean) <- get cell, unused?
  return *src
}

fn screen-code-point-at _screen: (addr screen), x: int, y: int -> _/eax: code-point {
  var screen/esi: (addr screen) <- copy _screen
  var index/ecx: int <- screen-cell-index screen, x, y
  var result/eax: code-point <- screen-code-point-at-index screen, index
  return result
}

fn screen-code-point-at-index _screen: (addr screen), _index: int -> _/eax: code-point {
  var screen/esi: (addr screen) <- copy _screen
  var data-ah/eax: (addr handle array screen-cell) <- get screen, data
  var data/eax: (addr array screen-cell) <- lookup *data-ah
  var index/ecx: int <- copy _index
  var offset/ecx: (offset screen-cell) <- compute-offset data, index
  var cell/eax: (addr screen-cell) <- index data, offset
  var src/eax: (addr code-point) <- get cell, data
  return *src
}

fn screen-color-at _screen: (addr screen), x: int, y: int -> _/eax: int {
  var screen/esi: (addr screen) <- copy _screen
  var index/ecx: int <- screen-cell-index screen, x, y
  var result/eax: int <- screen-color-at-index screen, index
  return result
}

fn screen-color-at-index _screen: (addr screen), _index: int -> _/eax: int {
  var screen/esi: (addr screen) <- copy _screen
  var data-ah/eax: (addr handle array screen-cell) <- get screen, data
  var data/eax: (addr array screen-cell) <- lookup *data-ah
  var index/ecx: int <- copy _index
  var offset/ecx: (offset screen-cell) <- compute-offset data, index
  var cell/eax: (addr screen-cell) <- index data, offset
  var src/eax: (addr int) <- get cell, color
  var result/eax: int <- copy *src
  return result
}

fn screen-background-color-at _screen: (addr screen), x: int, y: int -> _/eax: int {
  var screen/esi: (addr screen) <- copy _screen
  var index/ecx: int <- screen-cell-index screen, x, y
  var result/eax: int <- screen-background-color-at-index screen, index
  return result
}

fn screen-background-color-at-index _screen: (addr screen), _index: int -> _/eax: int {
  var screen/esi: (addr screen) <- copy _screen
  var data-ah/eax: (addr handle array screen-cell) <- get screen, data
  var data/eax: (addr array screen-cell) <- lookup *data-ah
  var index/ecx: int <- copy _index
  var offset/ecx: (offset screen-cell) <- compute-offset data, index
  var cell/eax: (addr screen-cell) <- index data, offset
  var src/eax: (addr int) <- get cell, background-color
  var result/eax: int <- copy *src
  return result
}

fn pixel screen: (addr screen), x: int, y: int, color: int {
  {
    compare screen, 0
    break-if-!=
    pixel-on-real-screen x, y, color
    return
  }
  # fake screen
  var screen/esi: (addr screen) <- copy screen
  var pixels-ah/eax: (addr handle array byte) <- get screen, pixels
  var pixels/eax: (addr array byte) <- lookup *pixels-ah
  {
    compare pixels, 0
    break-if-!=
    abort "pixel graphics not enabled for this screen"
  }
  # ignore if out of bounds
  {
    compare x, 0
    break-if->=
    return
  }
  {
    var xmax-addr/eax: (addr int) <- get screen, width
    var xmax/eax: int <- copy *xmax-addr
    xmax <- shift-left 3/log2-font-width
    compare x, xmax
    break-if-<
    return
  }
  {
    compare y, 0
    break-if->=
    return
  }
  {
    var ymax-addr/eax: (addr int) <- get screen, height
    var ymax/eax: int <- copy *ymax-addr
    ymax <- shift-left 4/log2-font-height
    compare y, ymax
    break-if-<
    return
  }
  #
  var index/ecx: int <- pixel-index screen, x, y
  var dest/ecx: (addr byte) <- index pixels, index
  var src/eax: byte <- copy-byte color
  copy-byte-to *dest, src
}

fn pixel-index _screen: (addr screen), x: int, y: int -> _/ecx: int {
  var screen/esi: (addr screen) <- copy _screen
  var width-addr/eax: (addr int) <- get screen, width
  var result/ecx: int <- copy y
  result <- multiply *width-addr
  result <- shift-left 3/log2-font-width
  result <- add x
  return result
}

# double-buffering primitive
# 'screen' must be a fake screen. 'target-screen' is usually real.
# Both screens must have the same size.
fn copy-pixels _screen: (addr screen), target-screen: (addr screen) {
  var screen/esi: (addr screen) <- copy _screen
  var pixels-ah/eax: (addr handle array byte) <- get screen, pixels
  var _pixels/eax: (addr array byte) <- lookup *pixels-ah
  var pixels/edi: (addr array byte) <- copy _pixels
  var width-a/edx: (addr int) <- get screen, width
  var width/edx: int <- copy *width-a
  width <- shift-left 3/log2-font-width
  var height-a/ebx: (addr int) <- get screen, height
  var height/ebx: int <- copy *height-a
  height <- shift-left 4/log2-font-height
  var i/esi: int <- copy 0
  var y/ecx: int <- copy 0
  {
    # screen top left pixels x y width height
    compare y, height
    break-if->=
    var x/eax: int <- copy 0
    {
      compare x, width
      break-if->=
      {
        var color-addr/ebx: (addr byte) <- index pixels, i
        var color/ebx: byte <- copy-byte *color-addr
        var color2/ebx: int <- copy color
        pixel target-screen, x, y, color2
      }
      x <- increment
      i <- increment
      loop
    }
    y <- increment
    loop
  }
}

# It turns out double-buffering screen-cells is useless because rendering fonts
# takes too long. (At least under Qemu.)
# So we'll instead convert screen-cells to pixels when double-buffering.
# 'screen' must be a fake screen.
fn convert-screen-cells-to-pixels _screen: (addr screen) {
  var screen/esi: (addr screen) <- copy _screen
  var width-a/ebx: (addr int) <- get screen, width
  var height-a/edx: (addr int) <- get screen, height
  var data-ah/eax: (addr handle array byte) <- get screen, pixels
  var _data/eax: (addr array byte) <- lookup *data-ah
  var data: (addr array byte)
  copy-to data, _data
  var y/ecx: int <- copy 0
  {
    compare y, *height-a
    break-if->=
    var x/edi: int <- copy 0
    $convert-screen-cells-to-pixels:loop-x: {
      compare x, *width-a
      break-if->=
      {
        var tmp/eax: code-point <- screen-code-point-at screen, x, y
        # skip null code-points that only get created when clearing screen
        # there may be other pixels drawn there, and we don't want to clobber them
        # this is a situation where fake screens aren't faithful to real screens; we don't support overlap between screen-cells and raw pixels
        compare tmp, 0
        break-if-=
        var c: code-point
        copy-to c, tmp
        var tmp/eax: int <- screen-color-at screen, x, y
        var fg: int
        copy-to fg, tmp
        var bg/eax: int <- screen-background-color-at screen, x, y
        var offset/eax: int <- draw-code-point-on-screen-array data, c, x, y, fg, bg, *width-a, *height-a
        x <- add offset
        loop $convert-screen-cells-to-pixels:loop-x
      }
      x <- increment
      loop
    }
    y <- increment
    loop
  }
}