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FABRIC.md: item 4.4n -- CANVAS rectangle computed, per architecture

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Pure geometry, no code change. Gap chosen at 16px, within 4.4m's
flagged <=24px ceiling for the 600px-tall architectures, leaving 8px
of margin rather than cutting to the exact limit.

amd64 (1280x800): CANVAS top-left (0,0), 1280x688, strip at (0,704)
96px tall.
aarch64/riscv64 (800x600): CANVAS top-left (0,0), 800x488, strip at
(0,504) 96px tall.

Checked against 4.4o's 480px scroll-box requirement: 488px clears it
with exactly the 8px margin the gap choice was picked to preserve.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Robert Allan James
2026-08-11 20:19:21 -04:00
co-authored by Claude Sonnet 5
parent a4afecb656
commit 2b4d426e37
1 changed files with 27 additions and 1 deletions
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@@ -5489,13 +5489,39 @@ document and committing that amendment as its own item.*
> flagged here explicitly so it isn't discovered as a surprise failure two items later. amd64 > flagged here explicitly so it isn't discovered as a surprise failure two items later. amd64
> (800px tall) has no such pressure (`800 − 96 = 704px` for CANVAS + gap). > (800px tall) has no such pressure (`800 − 96 = 704px` for CANVAS + gap).
- [ ] **4.4n — CANVAS rectangle definition, per architecture.** Screen height (4.4l) minus REPL - [x] **4.4n — CANVAS rectangle definition, per architecture.** Screen height (4.4l) minus REPL
strip height (4.4m) minus the small fixed gap (exact pixel value chosen here) between CANVAS strip height (4.4m) minus the small fixed gap (exact pixel value chosen here) between CANVAS
and the strip. and the strip.
*Done when:* a CANVAS rectangle (top-left, width, height) is computed and recorded for each *Done when:* a CANVAS rectangle (top-left, width, height) is computed and recorded for each
architecture. architecture.
*Refs:* §27.8. *Refs:* §27.8.
> **Done 2026-08-11.** Pure geometry, no code change. Layout follows §27.6's reviewed
> mockup (REPL strip fixed at the bottom of the screen, CANVAS the region above it) and
> uses standard top-down raster coordinates (top-left/width/height) to match this item's own
> phrasing and how `fb_fill_rect()`/`vt100.c` already address pixels — not TTF-TEXT's
> separate bottom-left-origin Cartesian convention, which is a FORTH-word-level API choice
> for its own callers, not a general framebuffer-addressing convention.
>
> **Gap: 16px.** Chosen within 4.4m's flagged `≤24px` ceiling for the small architectures,
> leaving 8px of margin rather than cutting it exactly to the limit; matches the codebase's
> existing small-spacing conventions (`TTF_CACHE_MARGIN`=8, TTF cell leading=4).
>
> **amd64 (1280×800, per 4.4l):**
> - REPL strip: top-left (0, 704), 1280×96
> - Gap: 688–704 (16px)
> - **CANVAS: top-left (0, 0), 1280×688**
>
> **aarch64 / riscv64 (800×600, per 4.4l — identical, same resolution both):**
> - REPL strip: top-left (0, 504), 800×96
> - Gap: 488–504 (16px)
> - **CANVAS: top-left (0, 0), 800×488**
>
> **Checked against 4.4o's 480px requirement, not assumed:** 488px ≥ 480px on the small
> architectures — passes, with exactly the 8px margin the 16px gap choice was picked to
> preserve. Any larger gap than 4.4m's ceiling would have failed this; recorded as
> confirmation the earlier warning held, not a new finding.
- [ ] **4.4o — 640×480 scroll-box centering math within CANVAS.** Layout math computed on top - [ ] **4.4o — 640×480 scroll-box centering math within CANVAS.** Layout math computed on top
of `TTF-TEXT`'s own coordinate primitive, which is simpler and already fixed: Cartesian, of `TTF-TEXT`'s own coordinate primitive, which is simpler and already fixed: Cartesian,
origin at the bottom-left of the **physical framebuffer** (not CANVAS-relative — resolved origin at the bottom-left of the **physical framebuffer** (not CANVAS-relative — resolved