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docs: extract rendering spikes into docs/spikes.md

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Spikes 8-14 are a cross-release display/UX bench batch, not part of the
v0.1 integration gate — only 8 and 9 feed v0.1. Move them out of the v0.1
technical doc into their own log (with a feeds-table and dependency notes),
leaving a pointer behind; link it from the README layout map.
This commit is contained in:
Julien Calixte
2026-07-05 17:27:34 +02:00
parent a848c05afa
commit ac56bc4aec
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# Rendering & UX spikes
> Scope: bench experiments that retire **display/UX** risk, run after the v0.1
> hardware bring-up spikes (1–7) in
> [`v0.1-mvp-technical.md`](v0.1-mvp-technical.md#hardware-bring-up-order).
> Unlike 1–7, these are **not** a v0.1 integration gate, and each feeds a
> different release (noted per spike).
>
> They ride on the `epd::Frame` `DrawTarget` and the Spike 5 partial-refresh
> path. Project overview: [`../README.md`](../README.md). Vocabulary:
> [`../CONTEXT.md`](../CONTEXT.md). Release sequence: [`roadmap.md`](roadmap.md).
These prove display/UX risks, not stack risks, so they sit outside the 1–7
"prove before integration" gate. **Run Spike 8 first:** it partitions the panel
into the writing column and the side panel that the later spikes (scrollbar,
line-number gutter, status readouts) draw within and around. Each feeds a
different release, but the bench experiment is worth running now to retire the
risk early.
| Spike | Feeds |
| ----------------------------------------- | ---------------------------------------------------- |
| 8 — Layout: side panel + writing column | v0.1 |
| 9 — Boot splash bitmap | v0.1 |
| 10 — Dark / light theme | v1.0 |
| 11 — Transient panel (help / config) | v0.4 `:` · v0.5 palette · v0.9 settings (mechanism) |
| 12 — Scroll position indicator | reading / `View`-mode UX |
| 13 — Line-number gutter | v0.2 |
| 14 — Multi-file navigation | v0.5 |
8. **Spike 8 — Layout: side panel + writing column.** Split the 792×272 landscape
into a full-height **writing column** (~60 cols, left) and an always-visible
**side panel** (~150 px / ~20 cols, right), per the
[Screen layout](v0.1-mvp-product.md#screen-layout). Today the editor fills the
full 79-col width with text and a cramped 12 px bottom status
([`firmware/src/editor.rs`](../firmware/src/editor.rs), `COLS`/`ROWS` +
`draw_status`); this spike narrows the text to a legible measure and moves all
metadata into the panel, retiring the header/status bands entirely. Two driver
facts shape it. First, narrowing does *not* speed up typing: `update_part`
already drives both controllers full width, windowed only in Y, because "the
waveform time dominates, not the data clock-out"
([`firmware/src/epd.rs`](../firmware/src/epd.rs)) — the win is line length and
persistent info, not latency. Second, since every partial refresh spans the full
width, a keystroke's windowed-Y band repaints the panel's pixels on that row
*for free* (redrawn identically), but a panel field that changes on a *different*
row than the cursor costs a **second** windowed-Y band — burning the "20 partials
→ forced full refresh" ghosting counter twice as fast (render module). That sorts
what the panel may hold: static (filename, dirty), event-driven (mode, Wi-Fi,
keyboard-disconnect, publish state), and throttled (clock, word count, session)
fields only — nothing that repaints per keystroke, so no live cursor *column*.
The panel sits entirely in the master half (right of the `x = 396` seam), so its
glyphs never split the seam; the writing column still straddles it, as today.
Prove: render column + panel; type and confirm the windowed-Y refresh stays a
single band (panel redraws in place, no second region); then update a throttled
field (word count on a typing pause) and a discrete one (mode flip) and confirm
each is one isolated band that forces no extra full refresh. Decides the
column/panel split in pixels, the panel's field layout and update cadence, and
whether the ghosting counter needs per-region accounting. (Feeds v0.1's screen
layout — the writing column + side panel the product doc now draws.)
9. **Spike 9 — Boot splash bitmap.** Embed the Typoena logo as a 1-bit asset and
blit it, with the build tag, at boot before the editor opens. Spike 2 already
proved vector + font rendering, so the only new risk is the image-asset
pipeline (embedding + blit) and that a large near-full-frame image takes a
clean full refresh. Mostly a feature — kept as a spike only to prove the
asset path. (Feeds v0.1's "e-ink shows Typoena splash + boot log".)
10. **Spike 10 — Dark / light theme.** Invert the 1-bit framebuffer (white on
black) and refresh. The invert is trivial (XOR at blit); the real unknowns
are (a) ghosting and refresh time on a predominantly-black panel — full-black
waveforms stress the panel differently — and (b) whether partial-refresh
ghosting accumulates faster in dark mode, forcing a more frequent full
refresh. Prove: legible inverted text, acceptable ghosting, and
partial-refresh latency unchanged from Spike 5. (Feeds v1.0's light/dark
theme.)
11. **Spike 11 — Transient panel (help / config).** Prove a modal full-screen
view that swaps in over the editor and restores the buffer exactly on exit —
the shared primitive behind a help screen, the v0.9 settings screen, the v0.5
file palette (`Ctrl-P`), and the v0.4 `:` command line. The risk is
e-ink-specific: entering/leaving with partial refresh leaves ghosting, and
the editor viewport underneath must return artifact-free. Prove with a static
help screen (trivial content): a full refresh on enter and on exit restores
the prior text exactly; measure in/out latency. Decides overlay-box vs.
full-screen swap — recommend the swap, since a dimmed partial overlay is both
slow and ghost-prone at ~630 ms. Panel *content* (which config keys, help
text) is feature work deferred to the owning release; this spike proves only
the mechanism.
12. **Spike 12 — Scroll position indicator.** The buffer already scrolls (`View`
mode `j`/`k`/`space`); this spike proves how to *show* position without
wrecking latency. Measure two affordances on the bench: (a) a right-edge
scrollbar repainted each scroll step, and (b) a compact side-panel readout
(`34/128` or `27%`). Risk: the scrollbar is a tall pixel column repainted on
every scroll — measure its partial-refresh cost against the small
side-panel field, on the windowed-Y path, during held-key scroll. Prove:
pick the affordance whose refresh cost is acceptable and confirm it forces no
extra full refreshes. (Feeds the reading/`View`-mode UX; the a-vs-b choice is
a design decision this spike hands data to.)
13. **Spike 13 — Line-number gutter.** Draw a fixed-width digit column left of
the text area. The v0.2 spec is the hard case: **relative** numbers in
Normal mode (current line as its absolute number), **absolute** in Insert.
The naive part — reserving columns and drawing digits — is trivial; the
e-ink risk is churn. Relative numbering renumbers the *entire visible gutter
on every `j`/`k`*, so a single cursor move becomes a partial refresh of a
tall digit column, straight into the Spike 5 windowed-Y path and the "20
partials → forced full refresh" ghosting counter
([`firmware/src/epd.rs`](../firmware/src/epd.rs), render module). Absolute
numbering is cheap by comparison — only the rows below an inserted/deleted
line renumber. Two more interactions: the gutter steals horizontal columns
from the render-time soft-wrap, and wrapped continuation rows have no number
(blank vs. tilde — a layout decision). Prove: measure gutter partial-refresh
cost for (a) a held-`j` scan that renumbers the whole relative gutter vs.
(b) a single-line absolute edit, and confirm neither blows the ghosting
budget or forces extra full refreshes. Decides whether relative numbering is
viable on this panel or must be gated (absolute-only, or a batched/coalesced
gutter repaint). (Feeds v0.2's line-number gutter; genuine new e-ink risk.)
14. **Spike 14 — Multi-file navigation (open / switch / new / delete).** The
panel *mechanism* is already Spike 11 (which names this v0.5 file palette),
and filename entry reuses the v0.4 `:` command line — so this spike proves
neither, and depends on both. What is genuinely new is **persistence and
buffer lifecycle**, not rendering: enumerate a FAT directory across *both*
`/sd/repo` and `/sd/local`, keep ≤ 3 ropes resident, and on switch swap the
active rope + cursor + soft-wrap after an atomic save-of-current
(persistence module). Two sharp edges. **New file** (`:enew`) must prompt
for scope — tracked (`/sd/repo`, pushed) vs. local (`/sd/local`, `Ctrl-G`
disabled). **Delete** extends v0.5 scope (the roadmap lists `:enew` but not
delete): removing the currently-open buffer must close it and fall back to
another resident buffer or an empty one, and — the load-bearing check — the
FAT unlink must reach the next Publish's *staged* set, which the git
module's `git add .`-equivalent staging may not catch for removals (needs
`git rm` / `add -A` semantics —
[`git` module](v0.1-mvp-technical.md#git--commit--push)). Prove:
open/switch/new/delete across both roots with a correct ≤ 3-buffer
lifecycle, a delete that propagates into the following commit, and an
artifact-free full-refresh swap on every buffer change (leaning on Spike
11). Latency is not the risk here; buffer-state and git-staging correctness
are. (Feeds v0.5 multi-file, delete included — now authorized in
[roadmap](roadmap.md#v05--file-palette--multi-file--) v0.5.)

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@@ -103,6 +103,15 @@ spike 4 is the gate for
Only after spike 7 do we start integration. Any spike that fails forces a
stack decision (e.g. fall back to libgit2; switch to a separate SD SPI bus).
### Rendering spikes (post-bring-up)
The display/UX spikes (8–14) — panel layout, boot splash, theme, transient
panel, scroll indicator, line-number gutter, multi-file navigation — are **not**
part of the v0.1 integration gate and span several releases, so they live in
their own log: [`spikes.md`](spikes.md). Spikes **8 (layout)** and **9 (splash)**
feed v0.1; the rest feed later releases. Run Spike 8 first — it partitions the
panel into the writing column and side panel the others draw within.
## Module breakdown
### `editor` — text buffer + cursor