Snap the TextBox cursor to the pixel grid

This snaps the cursor of the TextBox to the grid to ensure it's always
rendered as sharp as possible.

druid/src/widget/textbox.rs

@@ -606,12 +606,16 @@ impl<T: TextStorage + EditableText> Widget<T> for TextBox<T> {
 
             let padding_offset = Vec2::new(textbox_insets.x0, textbox_insets.y0);
 
-            let cursor = if data.is_empty() {
+            let mut cursor = if data.is_empty() {
                 cursor_line + padding_offset
             } else {
                 cursor_line + padding_offset - self.inner.offset()
             };
 
+            // Snap the cursor to the pixel grid so it stays sharp.
+            cursor.p0.x = cursor.p0.x.trunc() + 0.5;
+            cursor.p1.x = cursor.p0.x;
+
             ctx.with_save(|ctx| {
                 ctx.clip(clip_rect);
                 ctx.stroke(cursor, &cursor_color, 1.);