[librsvg: 7/14] New functions to create a Path from a pango::Layout

[Marge Bot <marge-bot src gnome org>]

commit 84eeacece6b563725e779901c9221826b797f465
Author: Federico Mena Quintero <federico gnome org>
Date:   Fri Feb 4 20:23:56 2022 -0600

    New functions to create a Path from a pango::Layout
    
    Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/673>

 src/drawing_ctx.rs | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
---
diff --git a/src/drawing_ctx.rs b/src/drawing_ctx.rs
index 99096163d..11634e230 100644
--- a/src/drawing_ctx.rs
+++ b/src/drawing_ctx.rs
@@ -1827,6 +1827,50 @@ pub fn create_pango_context(font_options: &FontOptions, transform: &Transform) -
     context
 }
 
+/// Converts a Pango layout to a Cairo path on the specified cr starting at (x, y).
+/// Does not clear the current path first.
+fn pango_layout_to_cairo(
+    x: f64,
+    y: f64,
+    layout: &pango::Layout,
+    gravity: pango::Gravity,
+    cr: &cairo::Context,
+) {
+    let rotation_from_gravity = gravity.to_rotation();
+    let rotation = if !rotation_from_gravity.approx_eq_cairo(0.0) {
+        Some(-rotation_from_gravity)
+    } else {
+        None
+    };
+
+    cr.move_to(x, y);
+
+    let matrix = cr.matrix();
+    if let Some(rot) = rotation {
+        cr.rotate(rot);
+    }
+
+    pangocairo::functions::update_layout(cr, layout);
+    pangocairo::functions::layout_path(cr, layout);
+    cr.set_matrix(matrix);
+}
+
+/// Converts a Pango layout to a Path starting at (x, y).
+pub fn pango_layout_to_path(
+    x: f64,
+    y: f64,
+    layout: &pango::Layout,
+    gravity: pango::Gravity,
+) -> Result<Path, RenderingError> {
+    let surface = cairo::RecordingSurface::create(cairo::Content::ColorAlpha, None)?;
+    let cr = cairo::Context::new(&surface)?;
+
+    pango_layout_to_cairo(x, y, layout, gravity, &cr);
+
+    let cairo_path = cr.copy_path()?;
+    Ok(Path::from_cairo(cairo_path))
+}
+
 // https://www.w3.org/TR/css-masking-1/#ClipPathElement
 fn element_can_be_used_inside_clip_path(element: &Element) -> bool {
     matches!(
@@ -2295,4 +2339,29 @@ mod tests {
             ],
         );
     }
+
+    #[test]
+    fn empty_or_whitespace_text_yields_empty_path() {
+        let context = create_pango_context(
+            &FontOptions {
+                options: cairo::FontOptions::new().unwrap(),
+            },
+            &Transform::identity(),
+        );
+
+        // empty text
+
+        let layout = pango::Layout::new(&context);
+        layout.set_text("");
+
+        let path = pango_layout_to_path(0.0, 0.0, &layout, pango::Gravity::Auto).unwrap();
+        assert!(path.is_empty());
+
+        // only whitespace
+
+        layout.set_text(" ");
+
+        let path = pango_layout_to_path(0.0, 0.0, &layout, pango::Gravity::Auto).unwrap();
+        assert!(path.is_empty());
+    }
 }