From a053e71ee6569d5e5dde163948c159d556705b06 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Thu, 18 May 2023 00:31:15 +0200
Subject: [PATCH] Fix lack of unsharing in wxImage::Clear()

Calling Clear() wrongly modified any other wxImage objects reusing the
same data.

Fix this by adding the missing call to AllocExclusive() to this function
and also add a check for the image validity which was missing there as
well ever since this function was added back in fc3762b5fc (add
wxImage::Clear (patch by troelsk); closes #10141, 2009-01-09).

Also add a unit test.

See #23553.

(cherry picked from commit 92664881fed59ffe3650886d6ea215e75d262981)
---
 docs/changes.txt      |  1 +
 src/common/image.cpp  |  4 ++++
 tests/image/image.cpp | 28 ++++++++++++++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/docs/changes.txt b/docs/changes.txt
index baa5eafe5f..258363eb35 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -253,6 +253,7 @@ All (GUI):
 - Fix entering dates in wxGenericDatePicker in nb_NO and other locales
   using names for the months in short date format (#23310).
 - Fix wx-config output when using NanoSVG library (#23373).
+- Fix bug modifying shared images in wxImage::Clear() (#23555).
 
 wxGTK:
 
diff --git a/src/common/image.cpp b/src/common/image.cpp
index a449b60930..321578412f 100644
--- a/src/common/image.cpp
+++ b/src/common/image.cpp
@@ -227,6 +227,10 @@ void wxImage::Destroy()
 
 void wxImage::Clear(unsigned char value)
 {
+    wxCHECK_RET( IsOk(), wxT("invalid image") );
+
+    AllocExclusive();
+
     memset(M_IMGDATA->m_data, value, M_IMGDATA->m_width*M_IMGDATA->m_height*3);
 }
 
diff --git a/tests/image/image.cpp b/tests/image/image.cpp
index 56929d3956..c0480811c5 100644
--- a/tests/image/image.cpp
+++ b/tests/image/image.cpp
@@ -2305,6 +2305,34 @@ TEST_CASE("wxImage::ChangeColours", "[image]")
     CHECK_THAT(test, RGBSameAs(expected));
 }
 
+TEST_CASE("wxImage::Clear", "[image]")
+{
+    wxImage image(2, 2);
+    image.SetRGB(0, 0, 0xff, 0x00, 0x00);
+    image.SetRGB(0, 1, 0x00, 0xff, 0x00);
+    image.SetRGB(1, 0, 0x00, 0x00, 0xff);
+    image.SetRGB(1, 1, 0xff, 0xff, 0xff);
+
+    wxImage image2(image);
+
+    // Check that the image has the expected red component values initially.
+    CHECK( image2.GetRed(0, 0) == 0xff );
+    CHECK( image2.GetRed(0, 1) == 0x00 );
+    CHECK( image2.GetRed(1, 0) == 0x00 );
+    CHECK( image2.GetRed(1, 1) == 0xff );
+
+    // Check that the image got cleared.
+    image2.Clear();
+    CHECK( image2.GetRed(0, 0) == 0x00 );
+    CHECK( image2.GetRed(0, 1) == 0x00 );
+    CHECK( image2.GetRed(1, 0) == 0x00 );
+    CHECK( image2.GetRed(1, 1) == 0x00 );
+
+    // Check that the original image didn't change (see #23553).
+    CHECK( image.GetRed(0, 0) == 0xff );
+    CHECK( image.GetRed(1, 1) == 0xff );
+}
+
 TEST_CASE("wxImage::SizeLimits", "[image]")
 {
 #if SIZEOF_VOID_P == 8