Added feature to align title of the block

examples/block.rs

@@ -6,7 +6,7 @@ use std::{error::Error, io};
 use termion::{event::Key, input::MouseTerminal, raw::IntoRawMode, screen::AlternateScreen};
 use tui::{
     backend::TermionBackend,
-    layout::{Constraint, Direction, Layout},
+    layout::{Alignment, Constraint, Direction, Layout},
     style::{Color, Modifier, Style},
     text::Span,
     widgets::{Block, BorderType, Borders},
@@ -30,21 +30,28 @@ fn main() -> Result<(), Box<dyn Error>> {
             // Just draw the block and the group on the same area and build the group
             // with at least a margin of 1
             let size = f.size();
+
+            // Surounding block
             let block = Block::default()
                 .borders(Borders::ALL)
                 .title("Main block with round corners")
+                .title_alignment(Alignment::Center)
                 .border_type(BorderType::Rounded);
             f.render_widget(block, size);
+
             let chunks = Layout::default()
                 .direction(Direction::Vertical)
                 .margin(4)
                 .constraints([Constraint::Percentage(50), Constraint::Percentage(50)].as_ref())
                 .split(f.size());
 
+            // Top two inner blocks
             let top_chunks = Layout::default()
                 .direction(Direction::Horizontal)
                 .constraints([Constraint::Percentage(50), Constraint::Percentage(50)].as_ref())
                 .split(chunks[0]);
+
+            // Top left inner block with green background
             let block = Block::default()
                 .title(vec![
                     Span::styled("With", Style::default().fg(Color::Yellow)),
@@ -53,21 +60,29 @@ fn main() -> Result<(), Box<dyn Error>> {
                 .style(Style::default().bg(Color::Green));
             f.render_widget(block, top_chunks[0]);
 
-            let block = Block::default().title(Span::styled(
-                "Styled title",
-                Style::default()
-                    .fg(Color::White)
-                    .bg(Color::Red)
-                    .add_modifier(Modifier::BOLD),
-            ));
+            // Top right inner block with styled title aligned to the right
+            let block = Block::default()
+                .title(Span::styled(
+                    "Styled title",
+                    Style::default()
+                        .fg(Color::White)
+                        .bg(Color::Red)
+                        .add_modifier(Modifier::BOLD),
+                ))
+                .title_alignment(Alignment::Right);
             f.render_widget(block, top_chunks[1]);
 
+            // Bottom two inner blocks
             let bottom_chunks = Layout::default()
                 .direction(Direction::Horizontal)
                 .constraints([Constraint::Percentage(50), Constraint::Percentage(50)].as_ref())
                 .split(chunks[1]);
+
+            // Bottom left block with all default borders
             let block = Block::default().title("With borders").borders(Borders::ALL);
             f.render_widget(block, bottom_chunks[0]);
+
+            // Bottom right block with styled left and right border
             let block = Block::default()
                 .title("With styled borders and doubled borders")
                 .border_style(Style::default().fg(Color::Cyan))

src/widgets/block.rs

@@ -1,6 +1,6 @@
 use crate::{
     buffer::Buffer,
-    layout::Rect,
+    layout::{Alignment, Rect},
     style::Style,
     symbols::line,
     text::{Span, Spans},
@@ -45,6 +45,9 @@ impl BorderType {
 pub struct Block<'a> {
     /// Optional title place on the upper left of the block
     title: Option<Spans<'a>>,
+    /// Title alignment. The default is top left of the block, but one can choose to place
+    /// title in the top middle, or top right of the block
+    title_alignment: Alignment,
     /// Visible borders
     borders: Borders,
     /// Border style
@@ -60,6 +63,7 @@ impl<'a> Default for Block<'a> {
     fn default() -> Block<'a> {
         Block {
             title: None,
+            title_alignment: Alignment::Left,
             borders: Borders::NONE,
             border_style: Default::default(),
             border_type: BorderType::Plain,
@@ -89,6 +93,11 @@ impl<'a> Block<'a> {
         self
     }
 
+    pub fn title_alignment(mut self, alignment: Alignment) -> Block<'a> {
+        self.title_alignment = alignment;
+        self
+    }
+
     pub fn border_style(mut self, style: Style) -> Block<'a> {
         self.border_style = style;
         self
@@ -192,19 +201,38 @@ impl<'a> Widget for Block<'a> {
                 .set_style(self.border_style);
         }
 
+        // Title
         if let Some(title) = self.title {
-            let lx = if self.borders.intersects(Borders::LEFT) {
+            let left_border_dx = if self.borders.intersects(Borders::LEFT) {
                 1
             } else {
                 0
             };
-            let rx = if self.borders.intersects(Borders::RIGHT) {
+
+            let right_border_dx = if self.borders.intersects(Borders::RIGHT) {
                 1
             } else {
                 0
             };
-            let width = area.width.saturating_sub(lx).saturating_sub(rx);
-            buf.set_spans(area.left() + lx, area.top(), &title, width);
+
+            let title_area_width = area
+                .width
+                .saturating_sub(left_border_dx)
+                .saturating_sub(right_border_dx);
+
+            let title_dx = match self.title_alignment {
+                Alignment::Left => left_border_dx,
+                Alignment::Center => area.width.saturating_sub(title.width() as u16) / 2,
+                Alignment::Right => area
+                    .width
+                    .saturating_sub(title.width() as u16)
+                    .saturating_sub(right_border_dx),
+            };
+
+            let title_x = area.left() + title_dx;
+            let title_y = area.top();
+
+            buf.set_spans(title_x, title_y, &title, title_area_width);
         }
     }
 }
@@ -507,5 +535,39 @@ mod tests {
                 height: 0,
             },
         );
+        assert_eq!(
+            Block::default()
+                .title("Test")
+                .title_alignment(Alignment::Center)
+                .inner(Rect {
+                    x: 0,
+                    y: 0,
+                    width: 0,
+                    height: 1,
+                }),
+            Rect {
+                x: 0,
+                y: 1,
+                width: 0,
+                height: 0,
+            },
+        );
+        assert_eq!(
+            Block::default()
+                .title("Test")
+                .title_alignment(Alignment::Right)
+                .inner(Rect {
+                    x: 0,
+                    y: 0,
+                    width: 0,
+                    height: 1,
+                }),
+            Rect {
+                x: 0,
+                y: 1,
+                width: 0,
+                height: 0,
+            },
+        );
     }
 }

tests/widgets_block.rs

@@ -1,7 +1,7 @@
 use tui::{
     backend::TestBackend,
     buffer::Buffer,
-    layout::Rect,
+    layout::{Alignment, Rect},
     style::{Color, Style},
     text::Span,
     widgets::{Block, Borders},
@@ -211,3 +211,136 @@ fn widgets_block_renders_on_small_areas() {
         Buffer::with_lines(vec!["┌Test─"]),
     );
 }
+
+#[test]
+fn widgets_block_title_alignment() {
+    let test_case = |alignment, borders, expected| {
+        let backend = TestBackend::new(15, 2);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        let block = Block::default()
+            .title(Span::styled("Title", Style::default()))
+            .title_alignment(alignment)
+            .borders(borders);
+
+        let area = Rect {
+            x: 1,
+            y: 0,
+            width: 13,
+            height: 2,
+        };
+
+        terminal
+            .draw(|f| {
+                f.render_widget(block, area);
+            })
+            .unwrap();
+
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    // title top-left with all borders
+    test_case(
+        Alignment::Left,
+        Borders::ALL,
+        Buffer::with_lines(vec![" ┌Title──────┐ ", " └───────────┘ "]),
+    );
+
+    // title top-left without top border
+    test_case(
+        Alignment::Left,
+        Borders::LEFT | Borders::BOTTOM | Borders::RIGHT,
+        Buffer::with_lines(vec![" │Title      │ ", " └───────────┘ "]),
+    );
+
+    // title top-left with no left border
+    test_case(
+        Alignment::Left,
+        Borders::TOP | Borders::RIGHT | Borders::BOTTOM,
+        Buffer::with_lines(vec![" Title───────┐ ", " ────────────┘ "]),
+    );
+
+    // title top-left without right border
+    test_case(
+        Alignment::Left,
+        Borders::LEFT | Borders::TOP | Borders::BOTTOM,
+        Buffer::with_lines(vec![" ┌Title─────── ", " └──────────── "]),
+    );
+
+    // title top-left without borders
+    test_case(
+        Alignment::Left,
+        Borders::NONE,
+        Buffer::with_lines(vec![" Title         ", "               "]),
+    );
+
+    // title center with all borders
+    test_case(
+        Alignment::Center,
+        Borders::ALL,
+        Buffer::with_lines(vec![" ┌───Title───┐ ", " └───────────┘ "]),
+    );
+
+    // title center without top border
+    test_case(
+        Alignment::Center,
+        Borders::LEFT | Borders::BOTTOM | Borders::RIGHT,
+        Buffer::with_lines(vec![" │   Title   │ ", " └───────────┘ "]),
+    );
+
+    // title center with no left border
+    test_case(
+        Alignment::Center,
+        Borders::TOP | Borders::RIGHT | Borders::BOTTOM,
+        Buffer::with_lines(vec![" ────Title───┐ ", " ────────────┘ "]),
+    );
+
+    // title center without right border
+    test_case(
+        Alignment::Center,
+        Borders::LEFT | Borders::TOP | Borders::BOTTOM,
+        Buffer::with_lines(vec![" ┌───Title──── ", " └──────────── "]),
+    );
+
+    // title center without borders
+    test_case(
+        Alignment::Center,
+        Borders::NONE,
+        Buffer::with_lines(vec!["     Title     ", "               "]),
+    );
+
+    // title top-right with all borders
+    test_case(
+        Alignment::Right,
+        Borders::ALL,
+        Buffer::with_lines(vec![" ┌──────Title┐ ", " └───────────┘ "]),
+    );
+
+    // title top-right without top border
+    test_case(
+        Alignment::Right,
+        Borders::LEFT | Borders::BOTTOM | Borders::RIGHT,
+        Buffer::with_lines(vec![" │      Title│ ", " └───────────┘ "]),
+    );
+
+    // title top-right with no left border
+    test_case(
+        Alignment::Right,
+        Borders::TOP | Borders::RIGHT | Borders::BOTTOM,
+        Buffer::with_lines(vec![" ───────Title┐ ", " ────────────┘ "]),
+    );
+
+    // title top-right without right border
+    test_case(
+        Alignment::Right,
+        Borders::LEFT | Borders::TOP | Borders::BOTTOM,
+        Buffer::with_lines(vec![" ┌───────Title ", " └──────────── "]),
+    );
+
+    // title top-right without borders
+    test_case(
+        Alignment::Right,
+        Borders::NONE,
+        Buffer::with_lines(vec!["         Title ", "               "]),
+    );
+}