From f76a56f7b9bc2075217840ca4e3b8434fdf80a0a Mon Sep 17 00:00:00 2001
From: Michael Sippel <micha@fragmental.art>
Date: Tue, 12 Jan 2021 22:33:47 +0100
Subject: [PATCH] add GridOffset

---
 src/grid_offset.rs | 99 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 src/grid_offset.rs

diff --git a/src/grid_offset.rs b/src/grid_offset.rs
new file mode 100644
index 0000000..f4ec661
--- /dev/null
+++ b/src/grid_offset.rs
@@ -0,0 +1,99 @@
+use {
+    std::{
+        sync::{Arc, RwLock},
+        ops::Range
+    },
+    cgmath::{Point2, Vector2},
+    crate::{
+        core::{
+            View,
+            Observer,
+            ObserverExt,
+            ObserverBroadcast,
+            InnerViewPort
+        },
+        view::{
+            index::{IndexView, ImplIndexView},
+            grid::{GridView, GridWindowIterator}
+        }
+    }
+};
+
+pub struct GridOffset<V: GridView + ?Sized> {
+    src: Option<Arc<V>>,
+    offset: Vector2<i16>,
+    cast: Arc<RwLock<ObserverBroadcast<dyn GridView<Item = V::Item>>>>
+}
+
+impl<V: 'static + GridView + ?Sized> GridOffset<V>
+where V::Item: Default {
+    pub fn new(port: InnerViewPort<dyn GridView<Item = V::Item>>) -> Arc<RwLock<Self>> {
+        let offset_view =
+            Arc::new(RwLock::new(
+                GridOffset::<V> {
+                    src: None,
+                    offset: Vector2::new(0, 0),
+                    cast: port.get_broadcast()
+                }
+            ));
+
+        port.set_view(Some(offset_view.clone()));
+        offset_view
+    }
+
+    pub fn set_offset(&mut self, new_offset: Vector2<i16>) {
+        let old_range = self.range();
+        self.offset = new_offset;
+        let new_range = self.range();
+
+        if let Some(old_range) = old_range {
+            self.cast.notify_each(GridWindowIterator::from(old_range));
+        }
+        if let Some(new_range) = new_range {
+            self.cast.notify_each(GridWindowIterator::from(new_range));
+        }
+    }
+}
+
+impl<V: GridView + ?Sized> View for GridOffset<V> {
+    type Msg = Point2<i16>;
+}
+
+impl<V: GridView + ?Sized> IndexView<Point2<i16>> for GridOffset<V>
+where V::Item: Default {
+    type Item = V::Item;
+
+    fn get(&self, pos: &Point2<i16>) -> Self::Item {
+        if let Some(src) = self.src.as_ref() {
+            src.get(&(pos - self.offset))
+        } else {
+            Self::Item::default()
+        }
+    }
+
+    fn range(&self) -> Option<Range<Point2<i16>>> {
+        let src_range = self.src.as_ref()?.range()?;
+        Some((src_range.start + self.offset) .. (src_range.end + self.offset))
+    }
+}
+
+impl<V: GridView + ?Sized> Observer<V> for GridOffset<V>
+where V::Item: Default {
+    fn reset(&mut self, view: Option<Arc<V>>) {
+        let old_range = self.range();
+        self.src = view;
+        let new_range = self.range();
+
+        if let Some(old_range) = old_range {
+            self.cast.notify_each(GridWindowIterator::from(old_range));
+        }
+        if let Some(new_range) = new_range {
+            self.cast.notify_each(GridWindowIterator::from(new_range));
+        }
+    }
+
+    fn notify(&self, msg: &Point2<i16>) {
+        self.cast.notify(&(msg + self.offset));
+    }
+}
+