fix: allow canvas area to exceed u16::MAX (#1891)

This allows Canvas grids where the width * height exceeds u16::MAX by
converting values to usize earlier in several methods.

Fixes: https://github.com/ratatui/ratatui/issues/1449

ratatui-widgets/src/canvas.rs

@@ -128,7 +128,7 @@ impl BrailleGrid {
     /// Create a new `BrailleGrid` with the given width and height measured in terminal columns and
     /// rows respectively.
     fn new(width: u16, height: u16) -> Self {
-        let length = usize::from(width * height);
+        let length = usize::from(width) * usize::from(height);
         Self {
             width,
             height,
@@ -156,7 +156,10 @@ impl Grid for BrailleGrid {
     }
 
     fn paint(&mut self, x: usize, y: usize, color: Color) {
-        let index = y / 4 * self.width as usize + x / 2;
+        let index = y
+            .saturating_div(4)
+            .saturating_mul(self.width as usize)
+            .saturating_add(x.saturating_div(2));
         // using get_mut here because we are indexing the vector with usize values
         // and we want to make sure we don't panic if the index is out of bounds
         if let Some(c) = self.utf16_code_points.get_mut(index) {
@@ -190,7 +193,7 @@ impl CharGrid {
     /// Create a new `CharGrid` with the given width and height measured in terminal columns and
     /// rows respectively.
     fn new(width: u16, height: u16, cell_char: char) -> Self {
-        let length = usize::from(width * height);
+        let length = usize::from(width) * usize::from(height);
         Self {
             width,
             height,
@@ -219,7 +222,7 @@ impl Grid for CharGrid {
     }
 
     fn paint(&mut self, x: usize, y: usize, color: Color) {
-        let index = y * self.width as usize + x;
+        let index = y.saturating_mul(self.width as usize).saturating_add(x);
         // using get_mut here because we are indexing the vector with usize values
         // and we want to make sure we don't panic if the index is out of bounds
         if let Some(c) = self.cells.get_mut(index) {
@@ -261,7 +264,7 @@ impl HalfBlockGrid {
         Self {
             width,
             height,
-            pixels: vec![vec![Color::Reset; width as usize]; height as usize * 2],
+            pixels: vec![vec![Color::Reset; width as usize]; (height as usize) * 2],
         }
     }
 }
@@ -937,4 +940,40 @@ mod tests {
             ),
         );
     }
+
+    // The canvas methods work a lot with arithmetic so here we enter various width and height
+    // values to check if there are any integer overflows we just initialize the canvas painters
+    #[test]
+    fn check_canvas_paint_max() {
+        let mut b_grid = BrailleGrid::new(u16::MAX, 2);
+        let mut c_grid = CharGrid::new(u16::MAX, 2, 'd');
+
+        let max = u16::MAX as usize;
+
+        b_grid.paint(0, 0, Color::Red);
+        b_grid.paint(0, max, Color::Red);
+        b_grid.paint(max, 0, Color::Red);
+        b_grid.paint(max, max, Color::Red);
+
+        c_grid.paint(0, 0, Color::Red);
+        c_grid.paint(0, max, Color::Red);
+        c_grid.paint(max, 0, Color::Red);
+        c_grid.paint(max, max, Color::Red);
+    }
+
+    // We delibately cause integer overflow to check if we don't panic and don't get weird behavior
+    #[test]
+    fn check_canvas_paint_overflow() {
+        let mut b_grid = BrailleGrid::new(u16::MAX, 3);
+        let mut c_grid = CharGrid::new(u16::MAX, 3, 'd');
+
+        let max = u16::MAX as usize + 10;
+
+        // see if we can paint outside bounds
+        b_grid.paint(max, max, Color::Red);
+        c_grid.paint(max, max, Color::Red);
+        // see if we can paint usize max bounds
+        b_grid.paint(usize::MAX, usize::MAX, Color::Red);
+        c_grid.paint(usize::MAX, usize::MAX, Color::Red);
+    }
 }