Moving Windows in StackView (#200)

* Inital draft of reposition code.

* throwing it all in git so I can show @gycos the mess I made

* Cleaning up the example and removing that garbage getter function from StackView. More thought needs to be applied to that API.

* modified stackview to locally draw background, currently every frame. Adjusted surrounding elements to mirror this change.

* fixed dirty flag on stackView to use a cell. Also added dirty events on window resize.

* Final code cleanup.

* Fixed all highlighted issues in PR #200

examples/position.rs

@@ -0,0 +1,56 @@
+extern crate cursive;
+
+use cursive::Cursive;
+use cursive::view::Position;
+use cursive::views::LayerPosition;
+use cursive::views::TextView;
+
+/// Moves top layer by the specified amount
+fn move_top(c: &mut Cursive, x_in: isize, y_in: isize) {
+    // Step 1. Get the current position of the layer.
+    let s = c.screen_mut();
+    let l = LayerPosition::FromFront(0);
+
+    let (x, y) = s.offset().pair();
+
+    // Step 2. add the specifed amount
+    // (unsigned math in Rust is a mess.)
+    let x = if x_in < 0 {
+        x - (-x_in) as usize
+    } else {
+        x + x_in as usize
+    };
+    let y = if y_in < 0 {
+        y - (-y_in) as usize
+    } else {
+        y + y_in as usize
+    };
+
+    // convert the new x and y into a position
+    let p = Position::absolute((x, y));
+
+    // Step 3. Apply the new position
+    s.reposition_layer(l, p);
+}
+
+fn main() {
+    let mut siv = Cursive::new();
+    siv.set_fps(60);
+
+    // We can quit by pressing `q`
+    siv.add_global_callback('q', Cursive::quit);
+    // Next Gen FPS Controls.
+    siv.add_global_callback('w', |s| move_top(s, 0, -1));
+    siv.add_global_callback('a', |s| move_top(s, -1, 0));
+    siv.add_global_callback('s', |s| move_top(s, 0, 1));
+    siv.add_global_callback('d', |s| move_top(s, 1, 0));
+
+    // Add window to fly around.
+    siv.add_layer(TextView::new(
+        "Press w,a,s,d to move the window.\n\
+         Press q to quit the application.",
+    ));
+
+    // Run the event loop
+    siv.run();
+}

src/cursive.rs

@@ -9,8 +9,8 @@ use std::path::Path;
 use std::sync::mpsc;
 use theme;
 use vec::Vec2;
-use view::{self, AnyView, Finder, View};
-use views;
+use view::{self, AnyView, Finder, Position, View};
+use views::{self, LayerPosition};
 
 /// Identifies a screen in the cursive root.
 pub type ScreenId = usize;
@@ -416,9 +416,14 @@ impl Cursive {
 
     /// Convenient method to remove a layer from the current screen.
     pub fn pop_layer(&mut self) -> Option<Box<AnyView>> {
-        let result = self.screen_mut().pop_layer();
-        self.clear();
-        result
+        self.screen_mut().pop_layer()
+    }
+
+    /// Convenient stub forwarding layer repositioning.
+    pub fn reposition_layer(
+        &mut self, layer: LayerPosition, position: Position
+    ) {
+        self.screen_mut().reposition_layer(layer, position);
     }
 
     // Handles a key event when it was ignored by the current view
@@ -460,6 +465,15 @@ impl Cursive {
         let printer =
             Printer::new(self.screen_size(), &self.theme, &self.backend);
 
+        let selected = self.menubar.receive_events();
+
+        // Print the stackview background before the menubar
+        let offset = if self.menubar.autohide { 0 } else { 1 };
+        let id = self.active_screen;
+        let sv_printer = printer.offset((0, offset), !selected);
+
+        self.screens[id].draw_bg(&sv_printer);
+
         // Draw the currently active screen
         // If the menubar is active, nothing else can be.
         // Draw the menubar?
@@ -472,12 +486,9 @@ impl Cursive {
             self.menubar.draw(&printer);
         }
 
-        let selected = self.menubar.receive_events();
-
-        let offset = if self.menubar.autohide { 0 } else { 1 };
-        let printer = printer.offset((0, offset), !selected);
-        let id = self.active_screen;
-        self.screens[id].draw(&printer);
+        // finally draw stackview layers
+        // using variables from above
+        self.screens[id].draw_fg(&sv_printer);
     }
 
     /// Returns `true` until [`quit(&mut self)`] is called.

src/views/stack_view.rs

@@ -3,6 +3,7 @@ use With;
 use direction::Direction;
 use event::{Event, EventResult};
 use std::any::Any;
+use std::cell;
 use std::ops::Deref;
 use theme::ColorStyle;
 use vec::Vec2;
@@ -15,6 +16,9 @@ pub struct StackView {
     // Store layers from back to front.
     layers: Vec<Child>,
     last_size: Vec2,
+    // Flag indicates if undrawn areas of the background are exposed
+    // and therefore need redrawing.
+    bg_dirty: cell::Cell<bool>,
 }
 
 enum Placement {
@@ -147,6 +151,7 @@ impl StackView {
         StackView {
             layers: Vec::new(),
             last_size: Vec2::zero(),
+            bg_dirty: cell::Cell::new(true),
         }
     }
 
@@ -225,6 +230,7 @@ impl StackView {
 
     /// Remove the top-most layer.
     pub fn pop_layer(&mut self) -> Option<Box<AnyView>> {
+        self.bg_dirty.set(true);
         self.layers.pop().map(|child| child.view.unwrap())
     }
 
@@ -280,6 +286,65 @@ impl StackView {
     pub fn move_to_back(&mut self, layer: LayerPosition) {
         self.move_layer(layer, LayerPosition::FromBack(0));
     }
+
+    /// Moves a layer to a new position on the screen.
+    ///
+    /// Has no effect on fullscreen layers
+    /// Has no effect if layer is not found
+    pub fn reposition_layer(
+        &mut self, layer: LayerPosition, position: Position
+    ) {
+        let i = self.get_index(layer);
+        let child = match self.layers.get_mut(i) {
+            Some(i) => i,
+            None => return,
+        };
+        match child.placement {
+            Placement::Floating(_) => {
+                child.placement = Placement::Floating(position);
+                self.bg_dirty.set(true);
+            }
+            Placement::Fullscreen => (),
+        }
+    }
+
+    /// Background drawing
+    /// Drawing functions are split into forground and background to
+    /// ease inserting layers under the stackview but above it's background
+    /// you probably just want to call draw()
+    pub fn draw_bg(&self, printer: &Printer) {
+        // If the background is dirty draw a new background
+        if self.bg_dirty.get() {
+            for y in 0..printer.size.y {
+                printer.with_color(ColorStyle::background(), |printer| {
+                    printer.print_hline((0, y), printer.size.x, " ");
+                });
+            }
+
+            // set background as clean, so we don't need to do this every frame
+            self.bg_dirty.set(false);
+        }
+    }
+
+    /// Forground drawing
+    /// Drawing functions are split into forground and background to
+    /// ease inserting layers under the stackview but above it's background
+    /// you probably just want to call draw()
+    pub fn draw_fg(&self, printer: &Printer) {
+        let last = self.layers.len();
+        printer.with_color(ColorStyle::primary(), |printer| {
+            for (i, (v, offset)) in
+                StackPositionIterator::new(self.layers.iter(), printer.size)
+                    .enumerate()
+            {
+                v.view.draw(&printer.sub_printer(
+                    offset,
+                    v.size,
+                    i + 1 == last,
+                ));
+            }
+        });
+    }
 }
 
 struct StackPositionIterator<R: Deref<Target = Child>, I: Iterator<Item = R>> {
@@ -325,22 +390,17 @@ impl<R: Deref<Target = Child>, I: Iterator<Item = R>> Iterator
 
 impl View for StackView {
     fn draw(&self, printer: &Printer) {
-        let last = self.layers.len();
-        printer.with_color(ColorStyle::primary(), |printer| {
-            for (i, (v, offset)) in
-                StackPositionIterator::new(self.layers.iter(), printer.size)
-                    .enumerate()
-            {
-                v.view.draw(&printer.sub_printer(
-                    offset,
-                    v.size,
-                    i + 1 == last,
-                ));
-            }
-        });
+        // This function is included for compat with the view trait,
+        // it should behave the same as calling them seperately, but does
+        // not pause to let you insert in between the layers.
+        self.draw_bg(printer);
+        self.draw_fg(printer);
     }
 
     fn on_event(&mut self, event: Event) -> EventResult {
+        if event == Event::WindowResize {
+            self.bg_dirty.set(true);
+        }
         // Use the stack position iterator to get the offset of the top layer.
         // TODO: save it instead when drawing?
         match StackPositionIterator::new(