Move damage tracking logic to `compositor` in `iced_tiny_skia`

1 files changed, 140 insertions, 0 deletions

diff --git a/graphics/src/damage.rs b/graphics/src/damage.rs
new file mode 100644
index 00000000..63604150
--- /dev/null
+++ b/graphics/src/damage.rs
@@ -0,0 +1,140 @@
+use crate::core::{Rectangle, Size};
+use crate::Primitive;
+
+use std::sync::Arc;
+
+pub fn regions(a: &Primitive, b: &Primitive) -> Vec<Rectangle> {
+    match (a, b) {
+        (
+            Primitive::Group {
+                primitives: primitives_a,
+            },
+            Primitive::Group {
+                primitives: primitives_b,
+            },
+        ) => return list(primitives_a, primitives_b),
+        (
+            Primitive::Clip {
+                bounds: bounds_a,
+                content: content_a,
+            },
+            Primitive::Clip {
+                bounds: bounds_b,
+                content: content_b,
+            },
+        ) => {
+            if bounds_a == bounds_b {
+                return regions(content_a, content_b)
+                    .into_iter()
+                    .filter_map(|r| r.intersection(bounds_a))
+                    .collect();
+            } else {
+                return vec![*bounds_a, *bounds_b];
+            }
+        }
+        (
+            Primitive::Translate {
+                translation: translation_a,
+                content: content_a,
+            },
+            Primitive::Translate {
+                translation: translation_b,
+                content: content_b,
+            },
+        ) => {
+            if translation_a == translation_b {
+                return regions(content_a, content_b)
+                    .into_iter()
+                    .map(|r| r + *translation_a)
+                    .collect();
+            }
+        }
+        (
+            Primitive::Cache { content: content_a },
+            Primitive::Cache { content: content_b },
+        ) => {
+            if Arc::ptr_eq(content_a, content_b) {
+                return vec![];
+            }
+        }
+        _ if a == b => return vec![],
+        _ => {}
+    }
+
+    let bounds_a = a.bounds();
+    let bounds_b = b.bounds();
+
+    if bounds_a == bounds_b {
+        vec![bounds_a]
+    } else {
+        vec![bounds_a, bounds_b]
+    }
+}
+
+pub fn list(previous: &[Primitive], current: &[Primitive]) -> Vec<Rectangle> {
+    let damage = previous
+        .iter()
+        .zip(current)
+        .flat_map(|(a, b)| regions(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().map(Primitive::bounds))
+            .collect()
+    }
+}
+
+pub fn group(
+    mut damage: Vec<Rectangle>,
+    scale_factor: f32,
+    bounds: Size<u32>,
+) -> Vec<Rectangle> {
+    use std::cmp::Ordering;
+
+    const AREA_THRESHOLD: f32 = 20_000.0;
+
+    let bounds = Rectangle {
+        x: 0.0,
+        y: 0.0,
+        width: bounds.width as f32,
+        height: bounds.height as f32,
+    };
+
+    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 * scale_factor).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
+}