Make width measuring optional and disabled by default

examples/hello_world.rs

@@ -1,7 +1,7 @@
 use crossterm::event::Event;
 use crossterm::style::{ContentStyle, Stylize};
 use toss::frame::{Frame, Pos};
-use toss::terminal::{Redraw, Terminal};
+use toss::terminal::Terminal;
 
 fn draw(f: &mut Frame) {
     f.write(
@@ -24,8 +24,11 @@ fn render_frame(term: &mut Terminal) {
         term.autoresize().unwrap();
 
         draw(term.frame());
+        term.present().unwrap();
 
-        if term.present().unwrap() == Redraw::NotRequired {
+        if term.measuring_required() {
+            term.measure_widths().unwrap();
+        } else {
             break;
         }
     }
@@ -34,6 +37,7 @@ fn render_frame(term: &mut Terminal) {
 fn main() {
     // Automatically enters alternate screen and enables raw mode
     let mut term = Terminal::new().unwrap();
+    term.set_measuring(true);
 
     loop {
         // Render and display a frame. A full frame is displayed on the terminal

examples/overlapping_graphemes.rs

@@ -1,7 +1,7 @@
 use crossterm::event::Event;
 use crossterm::style::{ContentStyle, Stylize};
 use toss::frame::{Frame, Pos};
-use toss::terminal::{Redraw, Terminal};
+use toss::terminal::Terminal;
 
 fn draw(f: &mut Frame) {
     f.write(
@@ -65,7 +65,9 @@ fn render_frame(term: &mut Terminal) {
 
         draw(term.frame());
 
-        if term.present().unwrap() == Redraw::NotRequired {
+        if term.measuring_required() {
+            term.measure_widths().unwrap();
+        } else {
             break;
         }
     }
@@ -74,6 +76,7 @@ fn render_frame(term: &mut Terminal) {
 fn main() {
     // Automatically enters alternate screen and enables raw mode
     let mut term = Terminal::new().unwrap();
+    term.set_measuring(true);
 
     loop {
         // Render and display a frame. A full frame is displayed on the terminal

examples/text_wrapping.rs

@@ -1,7 +1,7 @@
 use crossterm::event::Event;
 use crossterm::style::ContentStyle;
 use toss::frame::{Frame, Pos};
-use toss::terminal::{Redraw, Terminal};
+use toss::terminal::Terminal;
 
 fn draw(f: &mut Frame) {
     let text = concat!(
@@ -36,7 +36,9 @@ fn render_frame(term: &mut Terminal) {
 
         draw(term.frame());
 
-        if term.present().unwrap() == Redraw::NotRequired {
+        if term.measuring_required() {
+            term.measure_widths().unwrap();
+        } else {
             break;
         }
     }
@@ -45,6 +47,7 @@ fn render_frame(term: &mut Terminal) {
 fn main() {
     // Automatically enters alternate screen and enables raw mode
     let mut term = Terminal::new().unwrap();
+    term.set_measuring(true);
 
     loop {
         // Render and display a frame. A full frame is displayed on the terminal

src/terminal.rs

@@ -11,12 +11,6 @@ use crossterm::{ExecutableCommand, QueueableCommand};
 use crate::buffer::{Buffer, Size};
 use crate::frame::Frame;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum Redraw {
-    Required,
-    NotRequired,
-}
-
 pub struct Terminal {
     /// Render target.
     out: Box<dyn Write>,
@@ -54,6 +48,24 @@ impl Terminal {
         Ok(result)
     }
 
+    pub fn set_measuring(&mut self, active: bool) {
+        self.frame.widthdb.active = active;
+    }
+
+    pub fn measuring(&self) -> bool {
+        self.frame.widthdb.active
+    }
+
+    pub fn measuring_required(&self) -> bool {
+        self.frame.widthdb.measuring_required()
+    }
+
+    pub fn measure_widths(&mut self) -> io::Result<()> {
+        self.frame.widthdb.measure_widths(&mut self.out)?;
+        self.full_redraw = true;
+        Ok(())
+    }
+
     /// Resize the frame and other internal buffers if the terminal size has
     /// changed.
     pub fn autoresize(&mut self) -> io::Result<()> {
@@ -77,19 +89,7 @@ impl Terminal {
     ///
     /// After calling this function, the frame returned by [`Self::frame`] will
     /// be empty again and have no cursor position.
-    pub fn present(&mut self) -> io::Result<Redraw> {
+    pub fn present(&mut self) -> io::Result<()> {
-        if self.frame.widthdb.measuring_required() {
-            self.frame.widthdb.measure_widths(&mut self.out)?;
-            // Since we messed up the screen by measuring widths, we'll need to
-            // do a full redraw the next time around.
-            self.full_redraw = true;
-            // Throwing away the current frame because its content were rendered
-            // with unconfirmed width data. Also, this function guarantees that
-            // after it is called, the frame is empty.
-            self.frame.reset();
-            return Ok(Redraw::Required);
-        }
-
         if self.full_redraw {
             io::stdout().queue(Clear(ClearType::All))?;
             self.prev_frame_buffer.reset(); // Because the screen is now empty
@@ -103,7 +103,7 @@ impl Terminal {
         mem::swap(&mut self.prev_frame_buffer, &mut self.frame.buffer);
         self.frame.reset();
 
-        Ok(Redraw::NotRequired)
+        Ok(())
     }
 
     fn draw_differences(&mut self) -> io::Result<()> {

src/widthdb.rs

@@ -11,6 +11,7 @@ use unicode_width::UnicodeWidthStr;
 /// Measures and stores the with (in terminal coordinates) of graphemes.
 #[derive(Debug, Default)]
 pub struct WidthDB {
+    pub active: bool,
     known: HashMap<String, u8>,
     requested: HashSet<String>,
 }
@@ -22,6 +23,9 @@ impl WidthDB {
     /// Unicode Standard Annex #11.
     pub fn grapheme_width(&mut self, grapheme: &str) -> u8 {
         assert_eq!(Some(grapheme), grapheme.graphemes(true).next());
+        if !self.active {
+            return grapheme.width() as u8;
+        }
         if let Some(width) = self.known.get(grapheme) {
             *width
         } else {
@@ -35,6 +39,9 @@ impl WidthDB {
     /// If the width of a grapheme has not been measured yet, it is estimated
     /// using the Unicode Standard Annex #11.
     pub fn width(&mut self, s: &str) -> usize {
+        if !self.active {
+            return s.width();
+        }
         let mut total: usize = 0;
         for grapheme in s.graphemes(true) {
             total += if let Some(width) = self.known.get(grapheme) {
@@ -50,7 +57,7 @@ impl WidthDB {
     /// Whether any new graphemes have been seen since the last time
     /// [`Self::measure_widths`] was called.
     pub fn measuring_required(&self) -> bool {
-        !self.requested.is_empty()
+        self.active && !self.requested.is_empty()
     }
 
     /// Measure the width of all new graphemes that have been seen since the
@@ -60,6 +67,9 @@ impl WidthDB {
     /// the terminal. After it finishes, the terminal's contents should be
     /// assumed to be garbage and a full redraw should be performed.
     pub fn measure_widths(&mut self, out: &mut impl Write) -> io::Result<()> {
+        if !self.active {
+            return Ok(());
+        }
         for grapheme in self.requested.drain() {
             out.queue(Clear(ClearType::All))?
                 .queue(MoveTo(0, 0))?