Reintroduce damage tracking for `iced_tiny_skia`

4 files changed, 156 insertions, 0 deletions

diff --git a/graphics/src/damage.rs b/graphics/src/damage.rs
new file mode 100644
index 00000000..ff8edaf5
--- /dev/null
+++ b/graphics/src/damage.rs
@@ -0,0 +1,80 @@
+//! Compute the damage between frames.
+use crate::core::Rectangle;
+
+/// Diffs the damage regions given some previous and current primitives.
+pub fn diff<T>(
+    previous: &[T],
+    current: &[T],
+    bounds: impl Fn(&T) -> Vec<Rectangle>,
+    diff: impl Fn(&T, &T) -> Vec<Rectangle>,
+) -> Vec<Rectangle> {
+    let damage = previous.iter().zip(current).flat_map(|(a, b)| diff(a, b));
+
+    if previous.len() == current.len() {
+        damage.collect()
+    } else {
+        let (smaller, bigger) = if previous.len() < current.len() {
+            (previous, current)
+        } else {
+            (current, previous)
+        };
+
+        // Extend damage by the added/removed primitives
+        damage
+            .chain(bigger[smaller.len()..].iter().flat_map(bounds))
+            .collect()
+    }
+}
+
+/// Computes the damage regions given some previous and current primitives.
+pub fn list<T>(
+    previous: &[T],
+    current: &[T],
+    bounds: impl Fn(&T) -> Vec<Rectangle>,
+    are_equal: impl Fn(&T, &T) -> bool,
+) -> Vec<Rectangle> {
+    diff(previous, current, &bounds, |a, b| {
+        if are_equal(a, b) {
+            vec![]
+        } else {
+            bounds(a).into_iter().chain(bounds(b)).collect()
+        }
+    })
+}
+
+/// Groups the given damage regions that are close together inside the given
+/// bounds.
+pub fn group(mut damage: Vec<Rectangle>, bounds: Rectangle) -> Vec<Rectangle> {
+    use std::cmp::Ordering;
+
+    const AREA_THRESHOLD: f32 = 20_000.0;
+
+    damage.sort_by(|a, b| {
+        a.x.partial_cmp(&b.x)
+            .unwrap_or(Ordering::Equal)
+            .then_with(|| a.y.partial_cmp(&b.y).unwrap_or(Ordering::Equal))
+    });
+
+    let mut output = Vec::new();
+    let mut scaled = damage
+        .into_iter()
+        .filter_map(|region| region.intersection(&bounds))
+        .filter(|region| region.width >= 1.0 && region.height >= 1.0);
+
+    if let Some(mut current) = scaled.next() {
+        for region in scaled {
+            let union = current.union(&region);
+
+            if union.area() - current.area() - region.area() <= AREA_THRESHOLD {
+                current = union;
+            } else {
+                output.push(current);
+                current = region;
+            }
+        }
+
+        output.push(current);
+    }
+
+    output
+}
diff --git a/graphics/src/layer.rs b/graphics/src/layer.rs
index 0187cc59..c9a818fb 100644
--- a/graphics/src/layer.rs
+++ b/graphics/src/layer.rs
@@ -113,6 +113,11 @@ impl<T: Layer> Stack<T> {
         self.layers[..self.active_count].iter()
     }
 
+    /// Returns the slice of layers in the [`Stack`].
+    pub fn as_slice(&self) -> &[T] {
+        &self.layers[..self.active_count]
+    }
+
     /// Flushes and settles any primitives in the current layer of the [`Stack`].
     pub fn flush(&mut self) {
         self.layers[self.current].flush();
diff --git a/graphics/src/lib.rs b/graphics/src/lib.rs
index a9649c6e..865ebd97 100644
--- a/graphics/src/lib.rs
+++ b/graphics/src/lib.rs
@@ -15,6 +15,7 @@ mod viewport;
 
 pub mod color;
 pub mod compositor;
+pub mod damage;
 pub mod error;
 pub mod gradient;
 pub mod image;
diff --git a/graphics/src/text.rs b/graphics/src/text.rs
index c204c850..31b6de28 100644
--- a/graphics/src/text.rs
+++ b/graphics/src/text.rs
@@ -70,6 +70,76 @@ pub enum Text {
     },
 }
 
+impl Text {
+    /// Returns the visible bounds of the [`Text`].
+    pub fn visible_bounds(&self) -> Option<Rectangle> {
+        let (bounds, horizontal_alignment, vertical_alignment) = match self {
+            Text::Paragraph {
+                position,
+                paragraph,
+                clip_bounds,
+                ..
+            } => (
+                Rectangle::new(*position, paragraph.min_bounds)
+                    .intersection(clip_bounds),
+                Some(paragraph.horizontal_alignment),
+                Some(paragraph.vertical_alignment),
+            ),
+            Text::Editor {
+                editor,
+                position,
+                clip_bounds,
+                ..
+            } => (
+                Rectangle::new(*position, editor.bounds)
+                    .intersection(clip_bounds),
+                None,
+                None,
+            ),
+            Text::Cached {
+                bounds,
+                clip_bounds,
+                horizontal_alignment,
+                vertical_alignment,
+                ..
+            } => (
+                bounds.intersection(clip_bounds),
+                Some(*horizontal_alignment),
+                Some(*vertical_alignment),
+            ),
+            Text::Raw { raw, .. } => (Some(raw.clip_bounds), None, None),
+        };
+
+        let mut bounds = bounds?;
+
+        if let Some(alignment) = horizontal_alignment {
+            match alignment {
+                alignment::Horizontal::Left => {}
+                alignment::Horizontal::Center => {
+                    bounds.x -= bounds.width / 2.0;
+                }
+                alignment::Horizontal::Right => {
+                    bounds.x -= bounds.width;
+                }
+            }
+        }
+
+        if let Some(alignment) = vertical_alignment {
+            match alignment {
+                alignment::Vertical::Top => {}
+                alignment::Vertical::Center => {
+                    bounds.y -= bounds.height / 2.0;
+                }
+                alignment::Vertical::Bottom => {
+                    bounds.y -= bounds.height;
+                }
+            }
+        }
+
+        Some(bounds)
+    }
+}
+
 /// The regular variant of the [Fira Sans] font.
 ///
 /// It is loaded as part of the default fonts in Wasm builds.