From 590ee199ccaf16ab12bbbb23c302cbd0e2ccd254 Mon Sep 17 00:00:00 2001
From: rfranke <rfranke@users.noreply.github.com>
Date: Sun, 12 Jan 2020 16:09:11 +0100
Subject: [PATCH] Fix scrolling in thumb browser under macOS, see #5599

The Quartz backend emits adjusted GdkEventScroll delta values.
This is why the RT thumb browser scrolls several hundred times too fast
if the deltas are additionally multiplied by thumb size under macOS.

See use of scroll_unit and GDK_WINDOWING_QUARTZ for Gtk scrollbars:
https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-24/gtk/gtkrange.c#L3080
---
 rtgui/thumbbrowserbase.cc | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/rtgui/thumbbrowserbase.cc b/rtgui/thumbbrowserbase.cc
index 5f75ab413..c611b252d 100644
--- a/rtgui/thumbbrowserbase.cc
+++ b/rtgui/thumbbrowserbase.cc
@@ -87,7 +87,16 @@ void ThumbBrowserBase::scroll (int direction, double deltaX, double deltaY)
     }
     //GDK_SCROLL_SMOOTH can come in as many events with small deltas, don't quantize these to +/-1.0 so trackpads work well
     double coef;
+    double scroll_unit;
+    if (arrangement == TB_Vertical) {
+        scroll_unit = vscroll.get_adjustment()->get_step_increment();
+    } else {
+        scroll_unit = hscroll.get_adjustment()->get_step_increment();
+    }
     if(direction == GDK_SCROLL_SMOOTH) {
+#ifdef GDK_WINDOWING_QUARTZ
+        scroll_unit = 1.0;
+#endif
         coef = delta;
     } else if (direction == GDK_SCROLL_DOWN) {
         coef = +1.0;
@@ -99,7 +108,7 @@ void ThumbBrowserBase::scroll (int direction, double deltaX, double deltaY)
     if (direction == GDK_SCROLL_UP || direction == GDK_SCROLL_DOWN || direction == GDK_SCROLL_SMOOTH) {
         if (arrangement == TB_Vertical) {
             double currValue = vscroll.get_value();
-            double newValue = rtengine::LIM<double>(currValue + coef * vscroll.get_adjustment()->get_step_increment(),
+            double newValue = rtengine::LIM<double>(currValue + coef * scroll_unit,
                                                     vscroll.get_adjustment()->get_lower (),
                                                     vscroll.get_adjustment()->get_upper());
             if (newValue != currValue) {
@@ -107,7 +116,7 @@ void ThumbBrowserBase::scroll (int direction, double deltaX, double deltaY)
             }
         } else {
             double currValue = hscroll.get_value();
-            double newValue = rtengine::LIM<double>(currValue + coef * hscroll.get_adjustment()->get_step_increment(),
+            double newValue = rtengine::LIM<double>(currValue + coef * scroll_unit,
                                                     hscroll.get_adjustment()->get_lower(),
                                                     hscroll.get_adjustment()->get_upper());
             if (newValue != currValue) {