Installer splash generation

setup-banner.gif and setup-banner-dev.gif (one directory up) are the splash screens shown by the Squirrel.Windows installer while it extracts the app (loadingGif in electron-forge/forge.config.ts). Squirrel only accepts GIF, shows it at native pixel size in a borderless window, and provides no progress bar — the animation is the user's only feedback that the install is running.

Both files are generated from splash.html in this directory. Do not edit the GIFs by hand; change the HTML/timeline and regenerate:

pnpm --filter desktop generate-setup-banners

Run it on Windows so the wordmark renders in Segoe UI (the font is rasterized into the GIF).

How it works

• splash.html is a deterministic frame source: window.renderFrame(t) computes every element's opacity/transform at absolute time t seconds (no CSS animations), so output is reproducible. window.SPLASH_TIMELINE is the [{ t, delay }] frame schedule. ?variant=nightly switches to the purple palette and shows the NIGHTLY badge.
• generate.mts walks the timeline in headless Chromium (via the repo's @playwright/test), screenshots each frame, and encodes an animated GIF with gifenc — no external binaries needed.

Timeline

• The reveal plays once (0–1.5 s at 10 fps), then a steady tail pulses the dots out to 20 s at 5 fps. The GIF loops, so the reveal replays every ~20 s — long enough that a normal install finishes during the first pass and effectively sees it once. Adjust REVEAL_DURATION / LOOP_DURATION / STEADY_FPS in splash.html.
• Keep the frame count modest. Squirrel's Update.exe renders the GIF with WpfAnimatedGif, which pre-decodes every frame to a full-size (640×480) bitmap held in memory, in a 32-bit process (verified: electron-winstaller's vendored Squirrel.exe is x86). Memory scales with frame count, not file size — ~1.2 MiB per frame. The current 108 frames ≈ 127 MiB; a 100 s / 1000- frame GIF would be ~1.2 GiB and risks an OutOfMemoryException. The low-fps steady tail exists to hold the count down.

Framing

• The window has no chrome and no drop shadow (Squirrel's Update.exe is WindowStyle.None + transparent). The splash is a flat dark surface with a 1px hairline. The surface is dark on purpose: the installer ships one baked GIF that can't follow the user's Windows theme, and no opaque surface is theme-neutral — a dark surface degrades more gracefully than a light one (gentle on a dark desktop, unremarkable on a light one, whereas a light one is a harsh bright flash for dark-mode users). The colorful trillium also pops on it. The one cost is that the mark's white "starburst" (the surface showing through the leaf gaps) becomes dark.
• The hairline does the work a drop shadow can't: on a dark desktop the dark surface nearly matches the background, so the hairline is what gives the splash a defined edge; on a light desktop the dark fill already contrasts and the hairline just reads as a crisp border. (An earlier card-on-tray framing was dropped once the surface went dark — the tray collapsed into an invisible margin and the shadow stopped showing, leaving the hairline as the only thing earning its keep.)

Encoding

• Frames are delta-encoded: one global palette, and pixels unchanged from the previous frame are written as a transparent index over the kept canvas (dispose: 1). This shrinks the mostly-static steady tail to almost nothing (~140 KiB total). It saves file size only — not Update.exe memory, which re-expands every frame to full size regardless.
• The flat colors (surface, hairline, wordmark) are pinned into the palette: gifenc's applyPalette nearest-color search is approximate, so without pinning a big flat area drifts (the white card, in an earlier light design, used to go warm). deriveAnchorColors() reads the surface and hairline from the first rendered frame — so changing the surface tone in splash.html needs no change here — and pins the wordmark colour explicitly (update it there if the wordmark changes).

Output contract

• 640 × 480, opaque; flat dark surface (#26292f) + 1px hairline (#484d57). Transparency is used only for delta frames — frame 0 is a full opaque frame, so the loop resets cleanly with no reliance on desktop show-through. 108 frames, ~20 s loop, infinite loop, 255-color global palette, ~140 KiB.
• The mark and wordmark are drawn larger than strictly needed: Squirrel's Update.exe is not DPI-aware, so on a HiDPI display the window is bilinear-stretched by the display scale factor (e.g. 1.5×) and there is no way to signal density through a GIF. Bolder artwork survives that stretch better — it cannot be made pixel-sharp from our side.
• The leaf geometry and the nine stable fill colors are taken verbatim from the app icon (icon-color.svg); the nightly variant remaps each leaf to a purple ramp.