Render text + fix transforms (#26)

Fixes #16

This enables naive text rendering support using usvg's support for
flattening text into paths. It also fixes application of transform for
nested SVGs.

With this patch, `vello_svg` can now render the "badges" from the Xilem
README:

<img width="726" alt="Screenshot 2024-07-29 at 11 14 21"
src="https://github.com/user-attachments/assets/4ddea064-7ea6-42ff-9570-0c138e76529e">

CHANGELOG.md

@@ -12,6 +12,14 @@ Subheadings to categorize changes are `added, changed, deprecated, removed, fixe
 
 This release has an [MSRV][] of 1.75.
 
+### Added
+
+- Support for rendering basic text
+
+### Fixed
+
+- Transform of nested SVGs
+
 ## 0.3.0
 
 This release has an [MSRV][] of 1.75.

src/lib.rs

@@ -35,6 +35,7 @@ pub use vello;
 
 /// Re-export usvg.
 pub use usvg;
+use vello::kurbo::Affine;
 
 /// Render a [`Scene`] from an SVG string, with default error handling.
 ///
@@ -95,5 +96,5 @@ pub fn append_tree_with<F: FnMut(&mut vello::Scene, &usvg::Node)>(
     svg: &usvg::Tree,
     error_handler: &mut F,
 ) {
-    render::render_group(scene, svg.root(), error_handler);
+    render::render_group(scene, svg.root(), Affine::IDENTITY, error_handler);
 }

src/render.rs

@@ -2,16 +2,18 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
 use crate::util;
+use vello::kurbo::Affine;
 use vello::peniko::{BlendMode, Fill};
 use vello::Scene;
 
 pub(crate) fn render_group<F: FnMut(&mut Scene, &usvg::Node)>(
     scene: &mut Scene,
     group: &usvg::Group,
+    transform: Affine,
     error_handler: &mut F,
 ) {
     for node in group.children() {
-        let transform = util::to_affine(&node.abs_transform());
+        let transform = transform * util::to_affine(&node.abs_transform());
         match node {
             usvg::Node::Group(g) => {
                 let mut pushed_clip = false;
@@ -32,7 +34,7 @@ pub(crate) fn render_group<F: FnMut(&mut Scene, &usvg::Node)>(
                     }
                 }
 
-                render_group(scene, g, error_handler);
+                render_group(scene, g, Affine::IDENTITY, error_handler);
 
                 if pushed_clip {
                     scene.pop_layer();
@@ -110,12 +112,12 @@ pub(crate) fn render_group<F: FnMut(&mut Scene, &usvg::Node)>(
                         scene.draw_image(&image, image_ts);
                     }
                     usvg::ImageKind::SVG(svg) => {
-                        render_group(scene, svg.root(), error_handler);
+                        render_group(scene, svg.root(), transform, error_handler);
                     }
                 }
             }
-            usvg::Node::Text(_) => {
-                error_handler(scene, node);
+            usvg::Node::Text(text) => {
+                render_group(scene, text.flattened(), transform, error_handler);
             }
         }
     }