Use Frame for rendering instead of Buffer

src/buffer.rs

@@ -2,7 +2,7 @@ use crossterm::style::ContentStyle;
 use unicode_segmentation::UnicodeSegmentation;
 use unicode_width::UnicodeWidthStr;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
 pub struct Size {
     pub width: u16,
     pub height: u16,
@@ -48,22 +48,13 @@ impl Cell {
     }
 }
 
+#[derive(Debug, Default)]
 pub struct Buffer {
     size: Size,
     data: Vec<Cell>,
-    cursor: Option<Pos>,
 }
 
 impl Buffer {
-    #[allow(clippy::new_without_default)]
-    pub fn new() -> Self {
-        Self {
-            size: Size::ZERO,
-            data: vec![],
-            cursor: None,
-        }
-    }
-
     fn index(&self, x: u16, y: u16) -> usize {
         assert!(x < self.size.width);
         assert!(y < self.size.height);
@@ -86,7 +77,6 @@ impl Buffer {
     pub fn resize(&mut self, size: Size) {
         if size == self.size() {
             self.data.fill_with(Cell::empty);
-            self.cursor = None;
         } else {
             let width: usize = size.width.into();
             let height: usize = size.height.into();
@@ -95,7 +85,6 @@ impl Buffer {
             self.size = size;
             self.data.clear();
             self.data.resize_with(len, Cell::empty);
-            self.cursor = None;
         }
     }
 
@@ -104,7 +93,6 @@ impl Buffer {
     /// `buf.reset()` is equivalent to `buf.resize(buf.size())`.
     pub fn reset(&mut self) {
         self.data.fill_with(Cell::empty);
-        self.cursor = None;
     }
 
     pub fn write(&mut self, mut pos: Pos, content: &str, style: ContentStyle) {
@@ -133,14 +121,6 @@ impl Buffer {
         }
     }
 
-    pub fn cursor(&self) -> Option<Pos> {
-        self.cursor
-    }
-
-    pub fn set_cursor(&mut self, pos: Option<Pos>) {
-        self.cursor = pos;
-    }
-
     pub fn cells(&self) -> Cells<'_> {
         Cells {
             buffer: self,

src/frame.rs

@@ -0,0 +1,41 @@
+use crossterm::style::ContentStyle;
+
+use crate::buffer::Buffer;
+pub use crate::buffer::{Pos, Size};
+
+#[derive(Debug, Default)]
+pub struct Frame {
+    pub(crate) buffer: Buffer,
+    cursor: Option<Pos>,
+}
+
+impl Frame {
+    pub fn size(&self) -> Size {
+        self.buffer.size()
+    }
+
+    pub fn reset(&mut self) {
+        self.buffer.reset();
+        self.cursor = None;
+    }
+
+    pub fn cursor(&self) -> Option<Pos> {
+        self.cursor
+    }
+
+    pub fn set_cursor(&mut self, pos: Option<Pos>) {
+        self.cursor = pos;
+    }
+
+    pub fn show_cursor(&mut self, pos: Pos) {
+        self.set_cursor(Some(pos));
+    }
+
+    pub fn hide_cursor(&mut self) {
+        self.set_cursor(None);
+    }
+
+    pub fn write(&mut self, pos: Pos, content: &str, style: ContentStyle) {
+        self.buffer.write(pos, content, style);
+    }
+}

src/lib.rs

@@ -1,2 +1,3 @@
-pub mod buffer;
+mod buffer;
+pub mod frame;
 pub mod terminal;

src/terminal.rs

@@ -7,13 +7,15 @@ use crossterm::terminal::{Clear, ClearType, EnterAlternateScreen, LeaveAlternate
 use crossterm::{ExecutableCommand, QueueableCommand};
 
 use crate::buffer::{Buffer, Size};
+use crate::frame::Frame;
 
 pub struct Terminal {
+    /// Render target.
     out: Box<dyn Write>,
-    /// Currently visible on screen.
-    prev_buffer: Buffer,
-    /// Buffer to render to.
-    curr_buffer: Buffer,
+    /// The frame being currently rendered.
+    frame: Frame,
+    /// Buffer from the previous frame.
+    prev_frame_buffer: Buffer,
     /// When the screen is updated next, it must be cleared and redrawn fully
     /// instead of performing an incremental update.
     full_redraw: bool,
@@ -27,11 +29,15 @@ impl Drop for Terminal {
 }
 
 impl Terminal {
-    pub fn new(out: Box<dyn Write>) -> io::Result<Self> {
+    pub fn new() -> io::Result<Self> {
+        Self::with_target(Box::new(io::stdout()))
+    }
+
+    pub fn with_target(out: Box<dyn Write>) -> io::Result<Self> {
         let mut result = Self {
             out,
-            prev_buffer: Buffer::new(),
-            curr_buffer: Buffer::new(),
+            frame: Frame::default(),
+            prev_frame_buffer: Buffer::default(),
             full_redraw: true,
         };
         crossterm::terminal::enable_raw_mode()?;
@@ -39,28 +45,32 @@ impl Terminal {
         Ok(result)
     }
 
-    pub fn buffer(&mut self) -> &mut Buffer {
-        &mut self.curr_buffer
-    }
-
+    /// Resize the frame and other internal buffers if the terminal size has
+    /// changed.
     pub fn autoresize(&mut self) -> io::Result<()> {
         let (width, height) = crossterm::terminal::size()?;
         let size = Size { width, height };
-        if size != self.curr_buffer.size() {
-            self.prev_buffer.resize(size);
-            self.curr_buffer.resize(size);
+        if size != self.frame.size() {
+            self.frame.buffer.resize(size);
+            self.prev_frame_buffer.resize(size);
             self.full_redraw = true;
         }
 
         Ok(())
     }
 
-    /// Display the contents of the buffer on the screen and prepare rendering
-    /// the next frame.
+    pub fn frame(&mut self) -> &mut Frame {
+        &mut self.frame
+    }
+
+    /// Display the current frame on the screen and prepare the next 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<()> {
         if self.full_redraw {
             io::stdout().queue(Clear(ClearType::All))?;
-            self.prev_buffer.reset();
+            self.prev_frame_buffer.reset(); // Because the screen is now empty
             self.full_redraw = false;
         }
 
@@ -68,15 +78,15 @@ impl Terminal {
         self.update_cursor()?;
         self.out.flush()?;
 
-        mem::swap(&mut self.prev_buffer, &mut self.curr_buffer);
-        self.curr_buffer.reset();
+        mem::swap(&mut self.prev_frame_buffer, &mut self.frame.buffer);
+        self.frame.reset();
 
         Ok(())
     }
 
     fn draw_differences(&mut self) -> io::Result<()> {
         // TODO Only draw the differences
-        for (x, y, cell) in self.curr_buffer.cells() {
+        for (x, y, cell) in self.frame.buffer.cells() {
             let content = StyledContent::new(cell.style, &cell.content as &str);
             self.out
                 .queue(MoveTo(x, y))?
@@ -86,8 +96,8 @@ impl Terminal {
     }
 
     fn update_cursor(&mut self) -> io::Result<()> {
-        if let Some(pos) = self.curr_buffer.cursor() {
-            let size = self.curr_buffer.size();
+        if let Some(pos) = self.frame.cursor() {
+            let size = self.frame.size();
             let x_in_bounds = 0 <= pos.x && pos.x < size.width as i32;
             let y_in_bounds = 0 <= pos.y && pos.y < size.height as i32;
             if x_in_bounds && y_in_bounds {