Use Layout::full_width instead of calculating for alignment

This does require line breaking to have happened, but that is already a
requirement, as otherwise `Layout::lines` is empty.

Author: tomcur

parley/src/layout/alignment.rs

@@ -15,15 +15,7 @@ pub(crate) fn align<B: Brush>(
 ) {
     // Whether the text base direction is right-to-left.
     let is_rtl = layout.base_level & 1 == 1;
-    let alignment_width = alignment_width.unwrap_or_else(|| {
-        let max_line_length = layout
-            .lines
-            .iter()
-            .map(|line| line.metrics.advance)
-            .max_by(f32::total_cmp)
-            .unwrap_or(0.0);
-        max_line_length.min(max_line_length)
-    });
+    let alignment_width = alignment_width.unwrap_or_else(|| layout.full_width);
 
     // Apply alignment to line items
     for line in &mut layout.lines {

parley/src/layout/mod.rs

@@ -156,12 +156,16 @@ impl<B: Brush> Layout<B> {
             .break_remaining(max_advance.unwrap_or(f32::MAX));
     }
 
-    // Apply to alignment to layout relative to the specified container width. If container_width is not
-    // specified then the max line length is used.
-    //
-    // If `align_when_overflowing` is set to `true` then `Center` and `End` alignment will apply even if
-    // the line contents are wider than the `container_width`. If it is set to `false` then all overflowing
-    // lines will be `Start` aligned.
+    /// Apply alignment to the layout relative to the specified container width or full layout
+    /// width.
+    ///
+    /// You must perform line breaking prior to aligning, through [`Layout::break_lines`] or
+    /// [`Layout::break_all_lines`]. If `container_width` is not specified, the layout's
+    /// [`Layout::full_width`] is used.
+    ///
+    /// If `align_when_overflowing` is set to `true`, alignment will apply even if the line
+    /// contents are wider than the alignment width. If it is set to `false`, all overflowing lines
+    /// will be [`Alignment::Start`] aligned.
     pub fn align(
         &mut self,
         container_width: Option<f32>,