Store both the rounded and unrounded node size in Node (bevyengine#9923)

# Objective

Text bounds are computed by the layout algorithm using the text's
measurefunc so that text will only wrap after it's used the maximum
amount of available horizontal space.

When the layout size is returned the layout coordinates are rounded and
this sometimes results in the final size of the Node not matching the
size computed with the measurefunc. This means that the text may no
longer fit the horizontal available space and instead wrap onto a new
line. However, no glyphs will be generated for this new line because no
vertical space for the extra line was allocated.

fixes bevyengine#9874

## Solution

Store both the rounded and unrounded node sizes in `Node`.

Rounding is used to eliminate pixel-wide gaps between nodes that should
be touching edge to edge, but this isn't necessary for text nodes as
they don't have solid edges.

## Changelog

* Added the `rounded_size: Vec2` field to `Node`.
* `text_system` uses the unrounded node size when computing a text
layout.

---------

Co-authored-by: Rob Parrett <[email protected]>

crates/bevy_ui/src/layout/mod.rs

@@ -342,14 +342,17 @@ pub fn ui_layout_system(
                 inverse_target_scale_factor * Vec2::new(layout.location.x, layout.location.y);
 
             absolute_location += layout_location;
+
             let rounded_size = round_layout_coords(absolute_location + layout_size)
                 - round_layout_coords(absolute_location);
+
             let rounded_location =
                 round_layout_coords(layout_location) + 0.5 * (rounded_size - parent_size);
 
             // only trigger change detection when the new values are different
-            if node.calculated_size != rounded_size {
+            if node.calculated_size != rounded_size || node.unrounded_size != layout_size {
                 node.calculated_size = rounded_size;
+                node.unrounded_size = layout_size;
             }
             if transform.translation.truncate() != rounded_location {
                 transform.translation = rounded_location.extend(0.);

crates/bevy_ui/src/ui_node.rs

@@ -17,6 +17,9 @@ pub struct Node {
     /// The size of the node as width and height in logical pixels
     /// automatically calculated by [`super::layout::ui_layout_system`]
     pub(crate) calculated_size: Vec2,
+    /// The unrounded size of the node as width and height in logical pixels
+    /// automatically calculated by [`super::layout::ui_layout_system`]
+    pub(crate) unrounded_size: Vec2,
 }
 
 impl Node {
@@ -26,6 +29,12 @@ impl Node {
         self.calculated_size
     }
 
+    /// The calculated node size as width and height in logical pixels before rounding
+    /// automatically calculated by [`super::layout::ui_layout_system`]
+    pub const fn unrounded_size(&self) -> Vec2 {
+        self.unrounded_size
+    }
+
     /// Returns the size of the node in physical pixels based on the given scale factor and `UiScale`.
     #[inline]
     pub fn physical_size(&self, scale_factor: f64, ui_scale: f64) -> Vec2 {
@@ -66,6 +75,7 @@ impl Node {
 impl Node {
     pub const DEFAULT: Self = Self {
         calculated_size: Vec2::ZERO,
+        unrounded_size: Vec2::ZERO,
     };
 }
 

crates/bevy_ui/src/widget/text.rs

@@ -166,7 +166,10 @@ fn queue_text(
             Vec2::splat(f32::INFINITY)
         } else {
             // `scale_factor` is already multiplied by `UiScale`
-            node.physical_size(scale_factor, 1.)
+            Vec2::new(
+                (node.unrounded_size.x as f64 * scale_factor) as f32,
+                (node.unrounded_size.y as f64 * scale_factor) as f32,
+            )
         };
 
         match text_pipeline.queue_text(