improve scrolling with middle click drag (fixes #4529)

sumatrapdfreader · Sep 15, 2024 · e53e193 · e53e193
1 parent 116c512
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diff --git a/docs/md/Version-history.md b/docs/md/Version-history.md
@@ -50,6 +50,7 @@ Changes in [pre-release builds](https://www.sumatrapdfreader.org/prerelease):
 - closing a current tab now behaves like in Chrome: selects next tab (to the right). We used to select previously active tab, but that's unpredicable and we prefer to align SumatraPDF behavior with other popular apps.
 - swapped key bindings: 'i' is now CmdTogglePageInfo, 'I' is CmdInvertColors. Several people were confused by accidentally typing 'i' to invert colors, is less likely to type it accidentally
 - allow creating custom themes in advanced settings in `Themes` section. [See docs](https://www.sumatrapdfreader.org/docs/Customize-theme-colors).
+- improve scrolling with middle click drag [#4529](https://github.com/sumatrapdfreader/sumatrapdf/issues/4529)
 
 ### 3.5.2 (2023-10-25)
 

diff --git a/src/Canvas.cpp b/src/Canvas.cpp
@@ -677,6 +677,7 @@ static void OnMouseMiddleButtonDown(MainWindow* win, int x, int y, WPARAM) {
         case MouseAction::None:
             win->mouseAction = MouseAction::Scrolling;
 
+            win->dragStartPending = true;
             // record current mouse position, the farther the mouse is moved
             // from this position, the faster we scroll the document
             win->dragStart = Point(x, y);
@@ -689,6 +690,17 @@ static void OnMouseMiddleButtonDown(MainWindow* win, int x, int y, WPARAM) {
     }
 }
 
+static void OnMouseMiddleButtonUp(MainWindow* win, int x, int y, WPARAM) {
+    switch (win->mouseAction) {
+        case MouseAction::Scrolling:
+            if (!win->dragStartPending) {
+                win->mouseAction = MouseAction::None;
+                SetCursorCached(IDC_ARROW);
+                break;
+            }
+    }
+}
+
 static void OnMouseRightButtonDown(MainWindow* win, int x, int y) {
     // lf("Right button clicked on %d %d", x, y);
     if (MouseAction::Scrolling == win->mouseAction) {
@@ -1632,6 +1644,10 @@ static LRESULT WndProcCanvasFixedPageUI(MainWindow* win, HWND hwnd, UINT msg, WP
             OnMouseMiddleButtonDown(win, x, y, wp);
             return 0;
 
+        case WM_MBUTTONUP:
+            OnMouseMiddleButtonUp(win, x, y, wp);
+            return 0;
+
         case WM_RBUTTONDOWN:
             OnMouseRightButtonDown(win, x, y);
             return 0;