Porting notes

Refr is a port of PdfSpace by Wiesław Šoltés, from C#, Uno Platform, SkiaSharp and PdfPig to Rust, GPUI and PDFium. It keeps PdfSpace's workspace model, tools, layout and file format, and changes the platform layer underneath.

Where things went

PdfSpace	Refr
`PdfSpace.Core`: models and validated JSON	`refr-core`: `model.rs`, `geometry.rs`, `workspace_json.rs`
`PdfSpace.Layout`: page layouts and transforms	`refr-core`: `layout.rs`
`PdfSpace.Editing`: transactions, undo/redo, page operations	`refr-core`: `editor.rs`
`PdfSpace.Documents`: import, words, search, page ranges	`refr-pdf`: `lib.rs`, plus `refr-core`: `page_range.rs`
`PdfSpace.Skia`: rendering, annotation painting, export, sample	`refr-pdf`: `lib.rs`, `draw.rs`, `frame.rs`, `sample.rs`
`PdfSpace.Controls`: buttons, icons, panels, theme	`refr`: `theme.rs`, `text_input.rs`, `assets/icons/`
`PdfSpace.Viewer`: viewport and thumbnails	`refr`: `document.rs`, `viewport.rs`, `panels.rs`
`PdfSpace.Storage`: files, recovery, clipboard, print	`refr`: `storage.rs`, `workbench.rs`
`PdfSpace.Workbench`: shell, tools, panels, workflows	`refr`: `workbench.rs`, `shell.rs`, `panels.rs`, `about.rs`

As in PdfSpace, the document model has no UI dependencies. refr-core doesn't depend on GPUI or PDFium, so a WebAssembly host (for example Svelte with wasm-bindgen) could reuse it and put its own renderer on top.

What stayed the same

The .pdfspace format. PascalCase names, numeric enums, base64 sources and the same validation limits. Computed properties that PdfSpace writes are accepted and ignored. See The .pdfspace format.
The editing model. Immutable snapshots, one validated transaction per command, named history entries, 100 undo steps, and dirty state tracked by snapshot identity.
The workbench. Eight tabs, the All tools, Edit, Convert, E-Sign and Organize modes, floating quick tools, the navigation rail, the five side panels and the Home view.
Honesty about limits. No simulated OCR, protection or redaction, and the same wording about crops and drawn signatures.
The sample. The generated six-page "Circular futures" report.
The icons. PdfSpace's original vector paths (MIT).

What's different

Area	PdfSpace	Refr
Platform	Browser (WebAssembly) and desktop, through Uno	Native macOS app
PDF engine	PdfPig for parsing and text, Skia for rendering	PDFium for parsing, text, rendering and writing
PDF export	A new, flattened visual PDF drawn through Skia	Original pages copied with PDFium. Text stays selectable and searchable, rotation and crop become page properties, annotations become vector content, and comments become PDF text annotations.
Threading	.NET tasks	PDFium isn't thread-safe, so it runs on one dedicated thread that owns every parsed document. The app calls it from GPUI's background executor.
Page images	Cached Skia pictures	Bitmaps rendered in eighth-zoom steps, with the nearest cached image shown while a sharper one renders. Images leaving the cache are freed from GPUI's atlas.
Rotated annotation text	Skia rotates text	GPUI can't rotate text, so on rotated pages Refr fills Helvetica glyph outlines as paths.
Printing	Browser print or the platform print dialog	Opens a printable PDF in the default PDF viewer
Storage	Browser local storage or files	Files, with atomic writes and a recovery copy in Application Support
Keyboard	Uno key routing	GPUI key contexts. Viewport shortcuts use `Viewport && !TextInput` so tool letters never steal typing.

Coordinate systems

PdfSpace and Refr both store annotation geometry in top-left page points. Refr defines them precisely as logical page space: the page's effective box (media box ∩ crop box) turned by its own /Rotate. refr-pdf::PageFrame maps it to PDF user space, so workspaces made in either app put marks in the same place on pages with an intrinsic rotation or an offset media box. See Coordinate spaces.