PDF support (#97)

* Add vl-convert-pdf crate that builds on svg2pdf to add text overlays

* Add PDF functions to converter, add vl2pdf and vg2pdf CLI subcommands

* Compute metrics on base PDF fonts, choose and scale

* Python PDF conversion functions

* skip text without fill

* Handle multiple spans within single text chunk

* Comments, add basic right-to-left support

* Add pdf scale to CLI

* Add Python PDF tests

* Add VlConvert as PDF creator

* Update thirdparty_rust.yaml

* Add show-warnings for vl2pdf

* Update README.md

* update to svg2pdf 0.7.0

* Fix chunk coordinate conversion

* Add README and example for vl-convert-pdf

.github/workflows/CI.yml

@@ -161,7 +161,7 @@ jobs:
           python-version: ${{ matrix.options[1] }}
       - name: install Python dependencies
         run: |
-          python -m pip install pytest maturin scikit-image
+          python -m pip install pytest maturin scikit-image pypdfium2
       - name: Build development wheel
         run: |
           maturin develop -m vl-convert-python/Cargo.toml

Cargo.toml

@@ -6,6 +6,7 @@ members = [
     "vl-convert",
     "vl-convert-python",
     "vl-convert-vendor",
+    "vl-convert-pdf",
 ]
 
 [profile.release]

README.md

@@ -23,8 +23,12 @@ Commands:
   vl2vg      Convert a Vega-Lite specification to a Vega specification
   vl2svg     Convert a Vega-Lite specification to an SVG image
   vl2png     Convert a Vega-Lite specification to an PNG image
+  vl2jpeg    Convert a Vega-Lite specification to an JPEG image
+  vl2pdf     Convert a Vega-Lite specification to a PDF image
   vg2svg     Convert a Vega specification to an SVG image
   vg2png     Convert a Vega specification to an PNG image
+  vg2jpeg    Convert a Vega specification to an JPEG image
+  vg2pdf     Convert a Vega specification to an PDF image
   ls-themes  List available themes
   cat-theme  Print the config JSON for a theme
   help       Print this message or the help of the given subcommand(s)
@@ -99,6 +103,9 @@ The Vega JavaScript library supports exporting chart specifications directly to
 
 VlConvert generates PNG images by first exporting charts to SVG as described above, then converting the SVG image to a PNG image using the `resvg` crate.
 
+## Vega(-Lite) to PDF
+VlConvert generates PDF images by first exporting charts to SVG as described above, then converting them to PDF with a combination of the `svg2pdf` crate and custom text layout and font embedding logic. Font embedding currently supports TrueType fonts only.
+
 ## Limitations
 ### PNG Performance
 VlConvert relies on the [`resvg`](https://github.com/RazrFalcon/resvg) Rust library for rendering PNG images from the SVG produced by Vega. resvg is a very accurate implementation of SVG rendering, but it is not GPU accelerated and can be somewhat slow when asked to render charts with many individual marks (e.g. large scatter plots).  For a single pane scatter plot, the performance is on the order of 1 second per 1000 points.

vl-convert-pdf/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "vl-convert-pdf"
+version = "0.13.1"
+edition = "2021"
+license = "BSD-3-Clause"
+readme = "README.md"
+homepage = "https://github.com/jonmmease/vl-convert"
+repository = "https://github.com/jonmmease/vl-convert"
+
+[dependencies]
+svg2pdf = "0.7.0"
+pdf-writer = "0.8.1"
+usvg = "0.35.0"
+anyhow = "1.0.71"
+ttf-parser = "0.19.1"
+subsetter = "0.1.1"
+miniz_oxide = "0.7.1"
+siphasher = "0.3.10"
+itertools = "0.11.0"
+unicode-bidi = "0.3.13"

vl-convert-pdf/LICENSE

@@ -0,0 +1,11 @@
+Copyright 2023 Jon Mease
+
+Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vl-convert-pdf/README.md

@@ -0,0 +1,11 @@
+## vl-convert-pdf
+This crate builds on top of the excellent [svg2pdf](https://github.com/typst/svg2pdf) project (created by the [typst](https://typst.app/) team) to convert SVG images to PDF files with embedded text. svg2pdf supports converting text into geometric paths using the [usvg](https://github.com/RazrFalcon/resvg) library, but it doesn't yet support embedding text (which is required for text selection, text copying, screen readers, etc.).
+
+This project uses svg2pdf to handle everything in the SVG image except text, and then adds an embedded text layer on top using the [pdf-writer](https://github.com/typst/pdf-writer) library (also created by the typst team). The text embedding logic handles TrueType fonts and is heavily inspired by the implementation in the [typst](https://github.com/typst/typst) typesetting project.
+
+In the future, it would be great if the text embedding logic in typst could be extracted and used by svg2pdf (making this crate unnecessary), but in the meantime this crate will maintain an independent implementation of text embedding.
+
+Many thanks to the typst team for their support in https://github.com/typst/svg2pdf/issues/21.
+
+## Example
+See examples/pdf_conversion.rs for example usage

vl-convert-pdf/examples/pdf_conversion.rs

@@ -0,0 +1,21 @@
+use std::fs;
+use usvg::fontdb::Database;
+use usvg::TreeParsing;
+use vl_convert_pdf::svg_to_pdf;
+
+fn main() {
+    let tree = usvg::Tree::from_str(r#"
+<svg width="200" height="200" viewBox="0 0 200 200" xmlns="http://www.w3.org/2000/svg">
+    <text id="text1" x="100" y="100" text-anchor="middle" font-family="Arial" font-size="20" fill="black">
+        Hello, World!
+    </text>
+    <rect id="frame" x="1" y="1" width="198" height="198" fill="none" stroke="black"/>
+</svg>
+    "#, &Default::default()).unwrap();
+
+    let mut font_db = Database::new();
+    font_db.load_system_fonts();
+
+    let pdf_bytes = svg_to_pdf(&tree, &font_db, 1.0).unwrap();
+    fs::write("target/hello.pdf".to_string(), pdf_bytes).unwrap();
+}