Merge pull request #325 from hecrj/feature/canvas-interaction

Canvas interactivity and Game of Life example

1 files changed, 108 insertions, 0 deletions

diff --git a/wgpu/src/widget/canvas/cache.rs b/wgpu/src/widget/canvas/cache.rs
new file mode 100644
index 00000000..4b28d164
--- /dev/null
+++ b/wgpu/src/widget/canvas/cache.rs
@@ -0,0 +1,108 @@
+use crate::{
+    canvas::{Frame, Geometry},
+    Primitive,
+};
+
+use iced_native::Size;
+use std::{cell::RefCell, sync::Arc};
+
+enum State {
+    Empty,
+    Filled {
+        bounds: Size,
+        primitive: Arc<Primitive>,
+    },
+}
+
+impl Default for State {
+    fn default() -> Self {
+        State::Empty
+    }
+}
+/// A simple cache that stores generated [`Geometry`] to avoid recomputation.
+///
+/// A [`Cache`] will not redraw its geometry unless the dimensions of its layer
+/// change or it is explicitly cleared.
+///
+/// [`Layer`]: ../trait.Layer.html
+/// [`Cache`]: struct.Cache.html
+/// [`Geometry`]: struct.Geometry.html
+#[derive(Debug, Default)]
+pub struct Cache {
+    state: RefCell<State>,
+}
+
+impl Cache {
+    /// Creates a new empty [`Cache`].
+    ///
+    /// [`Cache`]: struct.Cache.html
+    pub fn new() -> Self {
+        Cache {
+            state: Default::default(),
+        }
+    }
+
+    /// Clears the [`Cache`], forcing a redraw the next time it is used.
+    ///
+    /// [`Cache`]: struct.Cache.html
+    pub fn clear(&mut self) {
+        *self.state.borrow_mut() = State::Empty;
+    }
+
+    /// Draws [`Geometry`] using the provided closure and stores it in the
+    /// [`Cache`].
+    ///
+    /// The closure will only be called when
+    /// - the bounds have changed since the previous draw call.
+    /// - the [`Cache`] is empty or has been explicitly cleared.
+    ///
+    /// Otherwise, the previously stored [`Geometry`] will be returned. The
+    /// [`Cache`] is not cleared in this case. In other words, it will keep
+    /// returning the stored [`Geometry`] if needed.
+    ///
+    /// [`Cache`]: struct.Cache.html
+    pub fn draw(&self, bounds: Size, draw_fn: impl Fn(&mut Frame)) -> Geometry {
+        use std::ops::Deref;
+
+        if let State::Filled {
+            bounds: cached_bounds,
+            primitive,
+        } = self.state.borrow().deref()
+        {
+            if *cached_bounds == bounds {
+                return Geometry::from_primitive(Primitive::Cached {
+                    cache: primitive.clone(),
+                });
+            }
+        }
+
+        let mut frame = Frame::new(bounds);
+        draw_fn(&mut frame);
+
+        let primitive = {
+            let geometry = frame.into_geometry();
+
+            Arc::new(geometry.into_primitive())
+        };
+
+        *self.state.borrow_mut() = State::Filled {
+            bounds,
+            primitive: primitive.clone(),
+        };
+
+        Geometry::from_primitive(Primitive::Cached { cache: primitive })
+    }
+}
+
+impl std::fmt::Debug for State {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            State::Empty => write!(f, "Empty"),
+            State::Filled { primitive, bounds } => f
+                .debug_struct("Filled")
+                .field("primitive", primitive)
+                .field("bounds", bounds)
+                .finish(),
+        }
+    }
+}