# Developing PdfCraft

Working instructions for agents and contributors are in `AGENTS.md` and `CLAUDE.md`. This page
collects what the desktop app reads from its environment and where it writes its diagnostics.

## Logs

The desktop app writes its `log` records to standard error and to `logs/pdfcraft.log` in its
settings folder, next to `app.ron`: Linux and FreeBSD `~/.local/share/pdfcraft/logs/` (or
`$XDG_DATA_HOME/pdfcraft/logs/`), macOS `~/Library/Application Support/PdfCraft/logs/`, Windows
`%APPDATA%\PdfCraft\data\logs\`. In portable mode (a `portable.txt` file next to the executable, as
the Windows portable zip ships) the settings folder is `PdfCraftData\` beside the executable, and
crash recovery and new digital IDs go there too. A start from a desktop menu, Finder or the Start
menu has no terminal, so this file is what to attach to a bug report: a failed autosave, a page that
would not render, a render worker that could not start and the report of an internal error all land
there.
Each launch moves the previous log to `pdfcraft.1.log` (and that one to `pdfcraft.2.log`), so the
log of a run that crashed survives the next start. The file stops growing at 16 MiB. `--version`
writes no file.

By default PdfCraft's own crates (`pdfcraft*`) log at `info` and everything else at `warn`.
`RUST_LOG` replaces that with env_logger-style directives, for example `RUST_LOG=debug`,
`RUST_LOG=warn,pdfcraft_render=trace` or `RUST_LOG=info,wgpu_core=warn`; a directive ending in `*`
covers every target starting with it (`pdfcraft*=debug`). The logger is
`apps/pdfcraft/src/logging.rs`. It never records the control-channel token or document passwords.

## GPU surface limits

The desktop renderer enables the selected adapter's supported 2D texture extent, while keeping
egui-wgpu's other device requirements. Restored windows on mixed-DPI monitors can exceed its
default 8192-pixel extent even when the GPU supports a larger surface (#577). The enabled extent
never exceeds the adapter's capability. A window larger than even that (restored at another
monitor's scale, or stretched across monitors) gets a surface fitted within the limit and is drawn
at a correspondingly lower scale instead of panicking in `Surface::configure` (vendored egui-wgpu,
`surface_fit`; see `vendor/README.md`). On DX12, PdfCraft's Windows default, the surface is
stretched over the window: softer, but complete and lined up with the pointer. wgpu's GL backend
copies it unscaled into a corner of the window instead.

## Renderer fallback

PdfCraft draws with wgpu, and starts again with eframe's own OpenGL renderer (glow) when wgpu fails
before the app is created: no adapter, no device, or a window surface the device can't configure.
The last of these was a panic, not an error, because wgpu's default error handler panics and
eframe configures the surface before any app code runs; a 2015 Intel GPU whose driver timed out in
`Surface::configure` on wgpu's GL backend closed PdfCraft at launch (#519). Vendored egui-wgpu
configures a new window's surface inside `winit::catch_errors` and returns a validation,
out-of-memory or internal error as `WgpuError::ConfigureSurface` (see `vendor/README.md`). Still a
panic, as upstream: an error in a later reconfigure (resizing, a lost surface); a device lost
during that first configure (wgpu reports it only to a callback, so the first frame panics, after
the app has started); and a window shown at zero size, which is first configured on resize. If
OpenGL can't start either, PdfCraft exits with both errors in the log. The fallback is logged at
`error`, with the wgpu error. `PDFCRAFT_RENDERER` skips it or chooses OpenGL from the start.

## Environment variables

| Variable | Effect |
|---|---|
| `RUST_LOG` | Log levels for standard error and the log file (see [Logs](#logs)) |
| `RUST_BACKTRACE` | `1` adds a backtrace to the report of an internal error |
| `XDG_DATA_HOME` | Linux/FreeBSD: base of the settings folder (`pdfcraft/`), the log folder and crash recovery |
| `WGPU_POWER_PREF` | GPU choice; by default PdfCraft prefers the low-power (integrated) GPU |
| `WGPU_BACKEND` | Graphics backend; by default Windows uses Direct3D 12, falling back to OpenGL |
| `PDFCRAFT_RENDERER` | `gl` starts with OpenGL (glow) and never loads wgpu; `wgpu` reports a wgpu failure instead of retrying with OpenGL; unset, wgpu is retried with OpenGL when it can't start (see [Renderer fallback](#renderer-fallback)) |
| `CRAFT_FONTS_DIR` | Build time: a [craft-fonts](https://github.com/storytold/craft-fonts) checkout to embed (Japanese fonts) |
| `PDFCRAFT_SYSTEM_FONTS` | `0` stops the desktop app from using an installed font for characters its embedded fonts lack (`cargo xtask screenshots` sets it) |