wezterm: scroll the viewport when dragging to select text

closes #8

src/frontend/gui/termwindow.rs

@@ -2945,6 +2945,32 @@ impl TermWindow {
  }
  }
 
+ // When the mouse gets close enough to the top or bottom then scroll
+ // the viewport so that we can see more in that direction and are able
+ // to select more than fits in the viewport.
+
+ // This is similar to the logic in the copy mode overlay, but the gap
+ // is smaller because it feels more natural for mouse selection to have
+ // a smaller gpa.
+ const VERTICAL_GAP: isize = 2;
+ let dims = tab.renderer().get_dimensions();
+ let top = self.get_viewport(tab.tab_id()).unwrap_or(dims.physical_top);
+ let vertical_gap = if dims.physical_top <= VERTICAL_GAP {
+ 1
+ } else {
+ VERTICAL_GAP
+ };
+ let top_gap = y - top;
+ if top_gap < vertical_gap {
+ // Increase the gap so we can "look ahead"
+ self.set_viewport(tab.tab_id(), Some(y.saturating_sub(vertical_gap)), dims);
+ } else {
+ let bottom_gap = (dims.viewport_rows as isize).saturating_sub(top_gap);
+ if bottom_gap < vertical_gap {
+ self.set_viewport(tab.tab_id(), Some(top + vertical_gap - bottom_gap), dims);
+ }
+ }
+
  self.window.as_ref().unwrap().invalidate();
  }