From d87abd132e037ff836e9744e1a79c265abd86b6b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Br=C3=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Fri, 31 Jul 2020 16:36:50 +0200
Subject: [PATCH 1/3] Do not try to create bitmap for default constructed Caret

If a Caret is default-constructed, the width and height are still 0,
and the wxBitmap::Create implementations expect valid sizes.

The same applies for the bitmap after a size change.
---
 src/generic/caret.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/generic/caret.cpp b/src/generic/caret.cpp
index 0f5aa7ac51..603888570b 100644
--- a/src/generic/caret.cpp
+++ b/src/generic/caret.cpp
@@ -103,7 +103,8 @@ void wxCaret::InitGeneric()
 #ifndef wxHAS_CARET_USING_OVERLAYS
     m_xOld =
     m_yOld = -1;
-    m_bmpUnderCaret.Create(m_width, m_height);
+    if (m_width && m_height)
+        m_bmpUnderCaret.Create(m_width, m_height);
 #endif
 }
 
@@ -174,7 +175,10 @@ void wxCaret::DoSize()
     m_overlay.Reset();
 #else
     // Change bitmap size
-    m_bmpUnderCaret = wxBitmap(m_width, m_height);
+    if (m_width && m_height)
+        m_bmpUnderCaret = wxBitmap(m_width, m_height);
+    else
+        m_bmpUnderCaret = wxBitmap();
 #endif
     if (countVisible > 0)
     {

From b8a4b96243a3fe992c6c4840c69c16fbc3b07a9f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Br=C3=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Mon, 31 Aug 2020 16:45:20 +0200
Subject: [PATCH 2/3] Create underlying bitmap for caret when it is explicitly
 created

wxCaret::Create implies a size change, so call DoSize to initialize
the underlying wxBitmap.
---
 include/wx/caret.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/wx/caret.h b/include/wx/caret.h
index e6e9728ff8..b625b5f0ac 100644
--- a/include/wx/caret.h
+++ b/include/wx/caret.h
@@ -153,6 +153,7 @@ protected:
         m_window = window;
         m_width = width;
         m_height = height;
+        DoSize();
 
         return true;
     }

From 88f808e303c1649a4ffdeb7044b1a5dd96e6e1d3 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Thu, 1 Oct 2020 02:28:42 +0200
Subject: [PATCH 3/3] Add a unit test for wxCaret::Create()

Verify that constructing wxCaret using its default ctor and Create()
works too, now that it does -- previously it uses to result in a GTK
warning and a crash in wxGTK.
---
 tests/controls/windowtest.cpp | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/tests/controls/windowtest.cpp b/tests/controls/windowtest.cpp
index 372317e67b..cfcc4a0f6d 100644
--- a/tests/controls/windowtest.cpp
+++ b/tests/controls/windowtest.cpp
@@ -136,10 +136,22 @@ TEST_CASE_METHOD(WindowTestCase, "Window::Mouse", "[window]")
     CHECK(m_window->GetCursor().IsOk());
 
 #if wxUSE_CARET
-    //A plain window doesn't have a caret
     CHECK(!m_window->GetCaret());
 
-    wxCaret* caret = new wxCaret(m_window, 16, 16);
+    wxCaret* caret;
+
+    // Try creating the caret in two different, but normally equivalent, ways.
+    SECTION("Caret 1-step")
+    {
+        caret = new wxCaret(m_window, 16, 16);
+    }
+
+    SECTION("Caret 2-step")
+    {
+        caret = new wxCaret();
+        caret->Create(m_window, 16, 16);
+    }
+
     m_window->SetCaret(caret);
 
     CHECK(m_window->GetCaret()->IsOk());