ctrl|cmd +/- to manipulate font size with glutin backend

Simliar code needs to be added to the x11 backend in a follow on
commit.

Refs: #2

src/gliumwindows.rs

@@ -109,6 +109,24 @@ impl term::TerminalHost for Host {
             .request_spawn_tab(self.display.gl_window().id())
             .ok();
     }
+
+    fn increase_font_size(&mut self) {
+        self.event_loop
+            .request_increase_font_size(self.display.gl_window().id())
+            .ok();
+    }
+
+    fn decrease_font_size(&mut self) {
+        self.event_loop
+            .request_decrease_font_size(self.display.gl_window().id())
+            .ok();
+    }
+
+    fn reset_font_size(&mut self) {
+        self.event_loop
+            .request_reset_font_size(self.display.gl_window().id())
+            .ok();
+    }
 }
 
 pub struct TerminalWindow {
@@ -620,7 +638,7 @@ impl TerminalWindow {
 
     /// Called in response to either the screen dpi changing,
     /// or the font scaling factor changing
-    fn scaling_changed(&mut self, font_scale: Option<f64>) -> Result<(), Error> {
+    pub fn scaling_changed(&mut self, font_scale: Option<f64>) -> Result<(), Error> {
         let dpi_scale = self.host.display.gl_window().get_hidpi_factor();
         let font_scale = font_scale.unwrap_or_else(|| self.fonts.get_font_scale());
         eprintln!(

src/guiloop/glutinloop.rs

@@ -71,6 +71,9 @@ struct Windows {
 enum SpawnRequest {
     Window,
     Tab(WindowId),
+    FontLarger(WindowId),
+    FontSmaller(WindowId),
+    FontReset(WindowId),
 }
 
 /// The `GuiEventLoop` represents the combined gui event processor,
@@ -116,6 +119,41 @@ impl GlutinGuiSystem {
                 Ok(SpawnRequest::Tab(_window_id)) => {
                     eprintln!("Spawning tabs is not yet implemented for glutin");
                 }
+                Ok(SpawnRequest::FontLarger(window_id)) => {
+                    let scale = fonts.get_font_scale() * 1.1;
+                    if let Some(window) = self
+                        .event_loop
+                        .windows
+                        .borrow_mut()
+                        .by_id
+                        .get_mut(&window_id)
+                    {
+                        window.scaling_changed(Some(scale)).ok();
+                    }
+                }
+                Ok(SpawnRequest::FontSmaller(window_id)) => {
+                    let scale = fonts.get_font_scale() * 0.9;
+                    if let Some(window) = self
+                        .event_loop
+                        .windows
+                        .borrow_mut()
+                        .by_id
+                        .get_mut(&window_id)
+                    {
+                        window.scaling_changed(Some(scale)).ok();
+                    }
+                }
+                Ok(SpawnRequest::FontReset(window_id)) => {
+                    if let Some(window) = self
+                        .event_loop
+                        .windows
+                        .borrow_mut()
+                        .by_id
+                        .get_mut(&window_id)
+                    {
+                        window.scaling_changed(Some(1.0)).ok();
+                    }
+                }
                 Err(TryRecvError::Empty) => return Ok(()),
                 Err(err) => bail!("spawn_rx disconnected {:?}", err),
             }
@@ -206,6 +244,16 @@ impl GuiEventLoop {
         })
     }
 
+    pub fn request_increase_font_size(&self, window_id: WindowId) -> Result<(), Error> {
+        self.spawn_tx.send(SpawnRequest::FontLarger(window_id))
+    }
+    pub fn request_decrease_font_size(&self, window_id: WindowId) -> Result<(), Error> {
+        self.spawn_tx.send(SpawnRequest::FontSmaller(window_id))
+    }
+    pub fn request_reset_font_size(&self, window_id: WindowId) -> Result<(), Error> {
+        self.spawn_tx.send(SpawnRequest::FontReset(window_id))
+    }
+
     pub fn request_spawn_window(&self) -> Result<(), Error> {
         self.spawn_tx.send(SpawnRequest::Window)
     }

term/src/terminal.rs

@@ -36,6 +36,15 @@ pub trait TerminalHost {
 
     /// Toggle full-screen mode
     fn toggle_full_screen(&mut self) {}
+
+    /// Increase font size by one step
+    fn increase_font_size(&mut self) {}
+
+    /// Decrease font size by one step
+    fn decrease_font_size(&mut self) {}
+
+    /// Reset font size
+    fn reset_font_size(&mut self) {}
 }
 
 pub struct Terminal {

term/src/terminalstate.rs

@@ -706,6 +706,22 @@ impl TerminalState {
             return Ok(());
         }
 
+        if (mods == KeyModifiers::SUPER || mods == KeyModifiers::CTRL) && key == KeyCode::Char('-')
+        {
+            host.decrease_font_size();
+            return Ok(());
+        }
+        if (mods == KeyModifiers::SUPER || mods == KeyModifiers::CTRL) && key == KeyCode::Char('=')
+        {
+            host.increase_font_size();
+            return Ok(());
+        }
+        if (mods == KeyModifiers::SUPER || mods == KeyModifiers::CTRL) && key == KeyCode::Char('0')
+        {
+            host.reset_font_size();
+            return Ok(());
+        }
+
         if mods == KeyModifiers::SUPER {
             if let Char(c) = key {
                 if c >= '0' && c <= '9' {