fbui v0.4.0

Changed

• Breaking for default-features = false users: fbui-render and
  fbui-widgets gain a default std feature (and fbui-widgets a
  default all-widgets). A dependent that already turned default
  features off must now list std (plus all-widgets, and harness as
  before) to keep the API it had. Default builds are unchanged.

Added

• fbui with no operating system — the no_std track (NOSTD.md).
  • fbui-render and fbui-widgets build #![no_std] + alloc with
    default-features = false. A new default std feature keeps the
    hosted build exactly as it was; without it the image-crate codecs, PNG
    export, file paths, Ui::request_screenshot, the flow harness and
    profile are unavailable. fbui_render::math::F32Ext supplies the f32
    math API from libm (inherent methods still win under std).
  • Minimal widget set: fbui-widgets without the new all-widgets
    feature (on by default) compiles only Label, Button, Container,
    Stack, ScrollView, List, ImageView and ProgressBar.
  • fbui-bare (new crate): the bare-metal runner. A board supplies a
    Framebuffer (info/pixels/flush) and a Board (poll_input,
    now_ms, wait); fbui_bare::run is the main loop, keeping the idle
    rule (no damage, no animation → wait(None)). Runner steps it for
    tests. A footprint test gates a 320×240 UI under 2 MiB of heap
    (measured: 875 KiB peak).
  • fbui-doc (new crate, always no_std): PNG/JPEG decoding to
    tiny-skia pixmaps and a PDF subset renderer — xref tables/streams,
    object streams, a reconstructing fallback; Flate/LZW/ASCII85/ASCIIHex/
    RunLength/DCT; paths, clipping, shadings, tiling patterns, images with
    soft masks; embedded TrueType/OpenType/CFF/Type 1/Type 3 fonts, Type 0
    with Identity-H, and a fallback face for non-embedded fonts. Fixtures
    from reportlab, fpdf2 and pikepdf, and a no-panic mutation test.
  • fbui_render::Image::from_pixmap wraps a premultiplied tiny-skia
    pixmap without a copy.
  • apps/doc-viewer: a no_std PDF/PNG/JPEG viewer app (library,
    paging, zoom, pan) on fbui-bare, built from the minimal widgets plus a
    custom PageView; apps/doc-viewer-rpi3 boots it on a Raspberry Pi
    3 with no OS (MMU, mailbox framebuffer, UART keys, wfi idle), verified
    in QEMU raspi3b by scripts/qemu_drive.py.
  • CI gains a nostd job: thumbv7em-none-eabihf builds, host no_std
    tests, the Pi 3 image, and a scripted QEMU session.

Fixed

• FontContext::layout no longer panics when the font database is empty
  (it lays out nothing) — a no_std target that loaded no font shows no
  text instead of crashing.