From 584d6b35c0fba11dfe0b100499dc478c525510aa Mon Sep 17 00:00:00 2001
From: Scott Mohekey <smohekey@insightful.co.nz>
Date: Fri, 31 Jul 2026 08:50:07 +1200
Subject: [PATCH] fix: correct SGR mouse-wheel button codes (64/65/66/67, not
 68/69/70/71)
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The wheel buttons were encoded as `64 + <button number>` (4/5/6/7), producing
68/69/70/71. In the X10/SGR mouse protocol the four wheel buttons are 64/65/66/67
— bit 6 set with the button number in the low two bits — so the surplus bits read
as a spurious Shift modifier (`64 + 5` = 69 = wheel-down + shift).

Applications that validate the button field reject the modified report as an
invalid wheel event and don't scroll; lenient ones mask the modifier and happen
to still work. Encode the wheel buttons as `64 + (0/1/2/3)` to match the spec and
xterm, so both SGR (`ESC[<…M`) and normal-encoding (`ESC[M`) reports carry the
correct code.
---
 lib/src/core/mouse/button.dart | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/lib/src/core/mouse/button.dart b/lib/src/core/mouse/button.dart
index 53dd08b0..f4a2d6a4 100644
--- a/lib/src/core/mouse/button.dart
+++ b/lib/src/core/mouse/button.dart
@@ -5,21 +5,23 @@ enum TerminalMouseButton {
 
   right(id: 2),
 
-  wheelUp(id: 64 + 4, isWheel: true),
+  wheelUp(id: 64 + 0, isWheel: true),
 
-  wheelDown(id: 64 + 5, isWheel: true),
+  wheelDown(id: 64 + 1, isWheel: true),
 
-  wheelLeft(id: 64 + 6, isWheel: true),
+  wheelLeft(id: 64 + 2, isWheel: true),
 
-  wheelRight(id: 64 + 7, isWheel: true),
+  wheelRight(id: 64 + 3, isWheel: true),
   ;
 
   /// The id that is used to report a button press or release to the terminal.
   ///
-  /// Mouse wheel up / down use button IDs 4 = 0100 (binary) and 5 = 0101 (binary).
-  /// The bits three and four of the button are transposed by 64 and 128
-  /// respectively, when reporting the id of the button and have have to be
-  /// adjusted correspondingly.
+  /// Wheel buttons 4–7 are encoded with bit 6 set (add 64) and the button number
+  /// in the low two bits, giving 64 (up), 65 (down), 66 (left), 67 (right). The
+  /// button number is transposed into that bit — it is *not* added on top of 64,
+  /// or the extra bits read as spurious shift/meta modifiers (e.g. 64+5 = 69 =
+  /// wheel-down **+ shift**), which strict applications reject as an invalid wheel
+  /// event and ignore — the whole scroll then does nothing.
   final int id;
 
   /// Whether this button is a mouse wheel button.