feat(block): add option to center and right align the title (#462)

* Added ability to set title alignment, added tests, modified blocks example to show the feature

* Added test for inner with title in block

* Updated block example to show center alignment

* Formatting fixed

* Updated tests to use lamdas and be more concise. Updated title alignmnet code to be more straightforward and have correct behavior when placing title in the center without left border

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 ", "               "]),
+    );
+}