feat: import Rnote notebooks (Issue #47)

The import (menu entry and drag & drop) now also accepts .rnote files
from Rnote 0.5.10 on, including the transformation and document config
layouts that changed in 0.13 and 0.15. Taken over: brush strokes with
their pressure curve, shapes as outlines, texts, bitmap images and SVG
images, which are rasterized with resvg (Rnote stores imported PDF
pages as SVG). Fixed-size and continuous documents keep their pages;
infinite ones become an endless notebook.

The parts shared with the Xournal++ import moved to src/import.rs.
resvg and its dependencies were added to the Flatpak cargo sources.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/import.rs

@@ -0,0 +1,257 @@
+//! Import of other formats as a new notebook (Issue #47): PDF (`storage`), Xournal++
+//! (`xopp`) and Rnote (`rnote`). This module holds what the importers share: building
+//! strokes, texts and images in the stored format and creating the notebook.
+
+use std::io::Read;
+use std::path::{Path, PathBuf};
+
+use crate::document::{Notebook, Page, PageBackground, StrokeTool};
+use crate::storage::{self, NotebookLayout, NotebookManifest, SampleData, StrokeData};
+use crate::t;
+use crate::text::{TextBox, TextFont};
+
+/// Largest accepted file after decompression (guards against gzip bombs).
+const MAX_UNCOMPRESSED_BYTES: u64 = 512 * 1024 * 1024;
+
+/// Alpha of imported highlighter strokes that are stored opaque (as the app's highlighters).
+pub const HIGHLIGHTER_ALPHA: f32 = 0.35;
+
+/// What could not be taken over.
+#[derive(Debug, Clone, Default, PartialEq)]
+pub struct ImportReport {
+    pub skipped: usize,
+    /// The PDF background was referenced but not found or unreadable
+    pub missing_pdf: Option<String>,
+}
+
+/// Result of an importer: pages, the next free stroke id, the layout (`None`: default).
+pub struct Imported {
+    pub pages: Vec<Page>,
+    pub next_stroke_id: u64,
+    pub layout: Option<NotebookLayout>,
+    pub report: ImportReport,
+}
+
+/// Can the file be imported (by its name)?
+pub fn is_importable_path(path: &Path) -> bool {
+    crate::file_picker::is_pdf_path(path)
+        || crate::xopp::is_xopp_path(path)
+        || crate::rnote::is_rnote_path(path)
+}
+
+/// Imports a PDF, Xournal++ or Rnote file as a new notebook titled `title`.
+pub fn import_file(
+    base_dir: &Path,
+    title: &str,
+    path: &Path,
+) -> Result<(Notebook, NotebookManifest, PathBuf, ImportReport), String> {
+    if crate::xopp::is_xopp_path(path) {
+        crate::xopp::create_notebook_from_xopp(base_dir, title, path)
+    } else if crate::rnote::is_rnote_path(path) {
+        crate::rnote::create_notebook_from_rnote(base_dir, title, path)
+    } else {
+        let bytes = std::fs::read(path).map_err(|e| e.to_string())?;
+        storage::create_notebook_from_pdf(base_dir, title, bytes)
+            .map(|(nb, manifest, dir)| (nb, manifest, dir, ImportReport::default()))
+    }
+}
+
+/// Decompresses gzip data; other data is returned unchanged.
+pub fn gunzip(bytes: &[u8]) -> Result<Vec<u8>, String> {
+    if !bytes.starts_with(&[0x1f, 0x8b]) {
+        return Ok(bytes.to_vec());
+    }
+    let mut data = Vec::new();
+    flate2::read::MultiGzDecoder::new(bytes)
+        .take(MAX_UNCOMPRESSED_BYTES)
+        .read_to_end(&mut data)
+        .map_err(|e| t!("Datei nicht lesbar: {err}", err = e))?;
+    Ok(data)
+}
+
+/// Creates a new notebook and fills it with the pages `build` creates in its folder (images
+/// and PDFs go to its asset folder). On failure nothing is left behind.
+pub fn create_notebook(
+    base_dir: &Path,
+    title: &str,
+    build: impl FnOnce(&Path) -> Result<Imported, String>,
+) -> Result<(Notebook, NotebookManifest, PathBuf, ImportReport), String> {
+    let (_, _, dir) = storage::create_new_notebook(base_dir, title).map_err(|e| e.to_string())?;
+    let result = (|| {
+        let imported = build(&dir)?;
+        let page_count = imported.pages.len() as u64;
+        let notebook =
+            Notebook::from_pages(imported.pages, 0, imported.next_stroke_id, page_count + 1);
+        let mut manifest = storage::load_manifest(&dir).map_err(|e| e.to_string())?;
+        if imported.layout.is_some() {
+            manifest.layout = imported.layout;
+        }
+        storage::save_notebook(&dir, &notebook, &mut manifest).map_err(|e| e.to_string())?;
+        Ok((notebook, manifest, imported.report))
+    })();
+    match result {
+        Ok((notebook, manifest, report)) => Ok((notebook, manifest, dir, report)),
+        Err(err) => {
+            let _ = std::fs::remove_dir_all(&dir);
+            Err(err)
+        }
+    }
+}
+
+/// Builds a page from stored-format strokes.
+pub fn page(
+    id: u64,
+    size: glam::Vec2,
+    background: PageBackground,
+    pdf_background: Option<crate::document::PdfBackground>,
+    strokes: Vec<StrokeData>,
+) -> Page {
+    storage::PageData {
+        format_version: storage::CURRENT_FORMAT_VERSION,
+        id,
+        background,
+        pdf_background,
+        title: None,
+        size: (size != crate::document::A4_SIZE).then(|| size.to_array()),
+        strokes,
+    }
+    .to_page()
+}
+
+/// Our stroke width and the sample pressures for absolute widths per point (page units):
+/// we draw a diameter of `width · (0.5 + p)`, so the widest point gets p = 1 and thinner
+/// ones less (down to a third of the widest).
+pub fn fit_widths(widths: &[f32]) -> (f32, Vec<f32>) {
+    let widest = widths.iter().copied().fold(0.0, f32::max).max(0.01);
+    let width = widest / 1.5;
+    let pressures = widths
+        .iter()
+        .map(|w| (w / width - 0.5).clamp(0.0, 1.0))
+        .collect();
+    (width, pressures)
+}
+
+/// Pen or highlighter stroke through `points` (page units) with the given widths per point.
+pub fn ink_stroke(
+    id: u64,
+    mut color: [f32; 4],
+    highlighter: bool,
+    points: &[glam::Vec2],
+    width: f32,
+    pressures: &[f32],
+) -> StrokeData {
+    let tool = if highlighter {
+        if color[3] >= 0.99 {
+            color[3] = HIGHLIGHTER_ALPHA;
+        }
+        StrokeTool::Highlighter
+    } else {
+        // Pens are always opaque (translucent pens are read as highlighters)
+        color[3] = 1.0;
+        StrokeTool::Pen
+    };
+    let samples = points
+        .iter()
+        .zip(pressures)
+        .enumerate()
+        .map(|(i, (p, &pressure))| SampleData {
+            x: p.x,
+            y: p.y,
+            p: pressure,
+            t: i as f64 * 0.005,
+        })
+        .collect();
+    StrokeData {
+        id,
+        color,
+        samples,
+        shape: None,
+        tool,
+        width,
+        finalized: true,
+        image: None,
+        text: None,
+    }
+}
+
+/// Text field with its upper left corner at `origin` and the axes (page vector per unit to
+/// the right and down). Without `wrap_width` it is as wide as its longest line.
+#[allow(clippy::too_many_arguments)]
+pub fn text_stroke(
+    id: u64,
+    content: &str,
+    size: f32,
+    font: TextFont,
+    origin: glam::Vec2,
+    axes: [glam::Vec2; 2],
+    wrap_width: Option<f32>,
+    mut color: [f32; 4],
+) -> StrokeData {
+    let wrap_width = wrap_width.unwrap_or_else(|| {
+        let unwrapped = TextBox::new(content.to_string(), size, font, f32::MAX / 4.0);
+        let widest = unwrapped
+            .layout()
+            .lines
+            .iter()
+            .map(|line| line.width)
+            .fold(0.0, f32::max);
+        widest + size
+    });
+    let text = TextBox::new(content.to_string(), size, font, wrap_width);
+    let corners = crate::text::frame_corners(origin, axes, text.box_size());
+    color[3] = 1.0;
+    StrokeData {
+        id,
+        color,
+        samples: corner_samples(corners),
+        shape: None,
+        tool: StrokeTool::Pen,
+        width: 0.0,
+        finalized: true,
+        image: None,
+        text: Some(text),
+    }
+}
+
+/// Image with the corners upper left, upper right, lower right, lower left.
+pub fn image_stroke(id: u64, asset: String, corners: [glam::Vec2; 4]) -> StrokeData {
+    StrokeData {
+        id,
+        color: [1.0, 1.0, 1.0, 1.0],
+        samples: corner_samples(corners),
+        shape: None,
+        tool: StrokeTool::Pen,
+        width: 0.0,
+        finalized: true,
+        image: Some(asset),
+        text: None,
+    }
+}
+
+fn corner_samples(corners: [glam::Vec2; 4]) -> Vec<SampleData> {
+    corners
+        .iter()
+        .map(|c| SampleData {
+            x: c.x,
+            y: c.y,
+            p: 1.0,
+            t: 0.0,
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_fit_widths_keeps_the_drawn_widths() {
+        let (width, pressures) = fit_widths(&[30.0, 15.0, 10.0, 2.0]);
+        let drawn: Vec<f32> = pressures.iter().map(|p| width * (0.5 + p)).collect();
+        assert!((drawn[0] - 30.0).abs() < 1e-3);
+        assert!((drawn[1] - 15.0).abs() < 1e-3);
+        assert!((drawn[2] - 10.0).abs() < 1e-3);
+        // Thinner than a third of the widest point is not possible
+        assert!((drawn[3] - 10.0).abs() < 1e-3);
+    }
+}