From 03ba1a98f04d24d7526c068f0efcb941ef289f8f Mon Sep 17 00:00:00 2001
From: Wez Furlong <wez@wezfurlong.org>
Date: Thu, 4 Jun 2020 20:39:51 -0700
Subject: [PATCH] wezterm: scroll the viewport when dragging to select text

closes https://github.com/wez/wezterm/issues/8
---
 src/frontend/gui/termwindow.rs | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/frontend/gui/termwindow.rs b/src/frontend/gui/termwindow.rs
index 70397f961bb..3253852e26e 100644
--- a/src/frontend/gui/termwindow.rs
+++ b/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();
     }