Make View::draw take a &self (instead of a &mut self)

TrackedView, the only user of the mutability, now uses internal
mutability with a Cell.

src/printer.rs

@@ -173,7 +173,7 @@ impl Printer {
     }
 
     /// Returns a printer on a subset of this one's area.
-    pub fn sub_printer<S: Into<Vec2>>(&self, offset: S, size: S, focused: bool)
+    pub fn sub_printer<S: Into<Vec2>, T: Into<Vec2>>(&self, offset: S, size: T, focused: bool)
                                       -> Printer {
         let offset = offset.into().or_min(self.size);
         Printer {
@@ -184,4 +184,9 @@ impl Printer {
             theme: self.theme.clone(),
         }
     }
+
+    /// Returns a sub-printer with the given offset.
+    pub fn offset<S: Into<Vec2>>(&self, offset: S, focused: bool) -> Printer {
+        self.sub_printer(offset, self.size, focused)
+    }
 }

src/view/button.rs

@@ -29,7 +29,7 @@ impl Button {
 }
 
 impl View for Button {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
         let style = if !printer.focused {
             ColorStyle::Primary
         } else {

src/view/dialog.rs

@@ -111,7 +111,7 @@ impl Dialog {
 }
 
 impl View for Dialog {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
 
         // This will be the buttons_height used by the buttons.
         let mut buttons_height = 0;
@@ -133,7 +133,7 @@ impl View for Dialog {
             .get_offset(width, printer.size.x - overhead.horizontal());
         let y = printer.size.y - self.padding.bottom - self.borders.bottom - 1;
 
-        for (i, button) in self.buttons.iter_mut().enumerate() {
+        for (i, button) in self.buttons.iter().enumerate() {
             let size = button.size;
             // Add some special effect to the focused button
             button.draw(&printer.sub_printer(Vec2::new(offset, y),

src/view/edit_view.rs

@@ -79,7 +79,7 @@ impl EditView {
 }
 
 impl View for EditView {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
         assert!(printer.size.x == self.last_length);
 
         let width = self.content.width();

src/view/linear_layout.rs

@@ -162,10 +162,10 @@ fn try_focus((i, child): (usize, &mut Child), source: direction::Direction)
 }
 
 impl View for LinearLayout {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
         // Use pre-computed sizes
         let mut offset = Vec2::zero();
-        for (i, child) in self.children.iter_mut().enumerate() {
+        for (i, child) in self.children.iter().enumerate() {
             let printer =
                 &printer.sub_printer(offset, child.size, i == self.focus);
             child.view.draw(printer);

src/view/menu_popup.rs

@@ -133,7 +133,7 @@ impl MenuPopup {
 }
 
 impl View for MenuPopup {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
         let h = self.menu.len();
         let offset = self.align.v.get_offset(h, printer.size.y);
         let printer =

src/view/mod.rs

@@ -127,7 +127,7 @@ pub trait View {
     fn layout(&mut self, Vec2) {}
 
     /// Draws the view with the given printer (includes bounds) and focus.
-    fn draw(&mut self, printer: &Printer);
+    fn draw(&self, printer: &Printer);
 
     /// Finds the view pointed to by the given path.
     ///

src/view/select_view.rs

@@ -132,7 +132,7 @@ impl SelectView<String> {
 }
 
 impl<T: 'static> View for SelectView<T> {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
 
         let h = self.items.len();
         let offset = self.align.v.get_offset(h, printer.size.y);

src/view/shadow_view.rs

@@ -56,7 +56,7 @@ impl<T: View> ViewWrapper for ShadowView<T> {
         self.view.layout(size - offset);
     }
 
-    fn wrap_draw(&mut self, printer: &Printer) {
+    fn wrap_draw(&self, printer: &Printer) {
 
         // Skip the first row/column
         let printer =

src/view/stack_view.rs

@@ -61,11 +61,11 @@ impl StackView {
 }
 
 impl View for StackView {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
         let last = self.layers.len();
         let mut previous = Vec2::zero();
         printer.with_color(ColorStyle::Primary, |printer| {
-            for (i, v) in self.layers.iter_mut().enumerate() {
+            for (i, v) in self.layers.iter().enumerate() {
                 // Place the view
                 // Center the view
                 let offset = v.position

src/view/text_view.rs

@@ -194,7 +194,7 @@ impl<'a> Iterator for LinesIterator<'a> {
 }
 
 impl View for TextView {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
 
         let h = self.rows.len();
         let offset = self.align.v.get_offset(h, printer.size.y);

src/view/tracked_view.rs

@@ -1,3 +1,5 @@
+use std::cell::Cell;
+
 use view::{IdView, View, ViewWrapper};
 use Printer;
 use vec::Vec2;
@@ -7,7 +9,14 @@ pub struct TrackedView<T: View> {
     /// Wrapped view.
     pub view: T,
     /// Last position the view was located.
-    pub offset: Vec2,
+    offset: Cell<Vec2>,
+}
+
+impl<T: View> TrackedView<T> {
+    /// Return the last offset at which the view was drawn.
+    pub fn offset(&self) -> Vec2 {
+        self.offset.get()
+    }
 }
 
 impl<T: View> TrackedView<T> {
@@ -15,7 +24,7 @@ impl<T: View> TrackedView<T> {
     pub fn new(view: T) -> Self {
         TrackedView {
             view: view,
-            offset: Vec2::zero(),
+            offset: Cell::new(Vec2::zero()),
         }
     }
 
@@ -28,8 +37,8 @@ impl<T: View> TrackedView<T> {
 impl<T: View> ViewWrapper for TrackedView<T> {
     wrap_impl!(&self.view);
 
-    fn wrap_draw(&mut self, printer: &Printer) {
-        self.offset = printer.offset;
+    fn wrap_draw(&self, printer: &Printer) {
+        self.offset.set(printer.offset);
         self.view.draw(printer);
     }
 }

src/view/view_wrapper.rs

@@ -18,8 +18,8 @@ pub trait ViewWrapper {
     fn get_view_mut(&mut self) -> &mut View;
 
     /// Wraps the `draw` method.
-    fn wrap_draw(&mut self, printer: &Printer) {
-        self.get_view_mut().draw(printer);
+    fn wrap_draw(&self, printer: &Printer) {
+        self.get_view().draw(printer);
     }
 
     /// Wraps the `get_min_size` method.
@@ -54,7 +54,7 @@ pub trait ViewWrapper {
 }
 
 impl<T: ViewWrapper> View for T {
-    fn draw(&mut self, printer: &Printer) {
+    fn draw(&self, printer: &Printer) {
         self.wrap_draw(printer);
     }