From 81309f083d51e33bd24dc63e3698c6a39f31f4f7 Mon Sep 17 00:00:00 2001
From: Paul Cornett <paulcor@users.noreply.github.com>
Date: Wed, 11 Mar 2020 22:10:22 -0700
Subject: [PATCH] Ensure that scrollbar GtkRange page increment is set to a
 positive value

It should not be less than the step increment, which is always one.
See #18688
---
 src/gtk/scrolbar.cpp | 5 ++++-
 src/gtk/scrolwin.cpp | 2 ++
 src/gtk/window.cpp   | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/gtk/scrolbar.cpp b/src/gtk/scrolbar.cpp
index 3838510e77..f9fc488838 100644
--- a/src/gtk/scrolbar.cpp
+++ b/src/gtk/scrolbar.cpp
@@ -201,12 +201,15 @@ void wxScrollBar::SetThumbPosition( int viewStart )
 
 void wxScrollBar::SetScrollbar(int position, int thumbSize, int range, int pageSize, bool)
 {
-    if (range == 0)
+    if (range <= 0)
     {
         // GtkRange requires upper > lower
         range =
+        pageSize =
         thumbSize = 1;
     }
+    else if (pageSize <= 0)
+        pageSize = 1;
     g_signal_handlers_block_by_func(m_widget, (void*)gtk_value_changed, this);
     GtkRange* widget = GTK_RANGE(m_widget);
     GtkAdjustment* adj = gtk_range_get_adjustment(widget);
diff --git a/src/gtk/scrolwin.cpp b/src/gtk/scrolwin.cpp
index 95765bf0c7..54ed62a9c6 100644
--- a/src/gtk/scrolwin.cpp
+++ b/src/gtk/scrolwin.cpp
@@ -54,6 +54,8 @@ void wxScrollHelper::DoAdjustScrollbar(GtkRange* range,
     {
         upper = (virtSize + pixelsPerLine - 1) / pixelsPerLine;
         page_size = winSize / pixelsPerLine;
+        if (page_size == 0)
+            page_size = 1;
         *lines = upper;
         *linesPerPage = page_size;
     }
diff --git a/src/gtk/window.cpp b/src/gtk/window.cpp
index c00031bbb5..80d331716c 100644
--- a/src/gtk/window.cpp
+++ b/src/gtk/window.cpp
@@ -6011,6 +6011,8 @@ void wxWindowGTK::SetScrollbar(int orient,
         range =
         thumbVisible = 1;
     }
+    else if (thumbVisible <= 0)
+        thumbVisible = 1;
 
     g_signal_handlers_block_by_func(
         sb, (void*)gtk_scrollbar_value_changed, this);