Measure automatically in Terminal::present

src/terminal.rs

@@ -91,16 +91,6 @@ impl Terminal {
         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<()> {
@@ -124,11 +114,27 @@ impl Terminal {
     }
 
     /// Display the current frame on the screen and prepare the next frame.
-    /// Returns `true` if an immediate redraw is required.
+    ///
+    /// Before drawing and presenting a frame, [`Self::autoresize`] should be
+    /// called. [`Self::present`] does **not** call it automatically.
+    ///
+    /// If width measurements are turned on, any new graphemes encountered since
+    /// the last [`Self::present`] call will be measured. This can lead to the
+    /// screen flickering or being mostly blank until measurements complete.
+    ///
+    /// Returns `true` if any new graphemes were measured. Since their widths
+    /// may have changed because of the measurements, the application using this
+    /// [`Terminal`] should re-draw and re-present the current frame.
     ///
     /// 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<()> {
+    pub fn present(&mut self) -> io::Result<bool> {
+        let measure = self.frame.widthdb.measuring_required();
+        if measure {
+            self.frame.widthdb.measure_widths(&mut self.out)?;
+            self.full_redraw = true;
+        }
+
         if self.full_redraw {
             io::stdout().queue(Clear(ClearType::All))?;
             self.prev_frame_buffer.reset(); // Because the screen is now empty
@@ -142,7 +148,7 @@ impl Terminal {
         mem::swap(&mut self.prev_frame_buffer, &mut self.frame.buffer);
         self.frame.reset();
 
-        Ok(())
+        Ok(measure)
     }
 
     fn draw_differences(&mut self) -> io::Result<()> {