Workaround for EGL_BAD_SURFACE segfaults introduced with Plasma 5.26+

KDE Plasma 5.26 introduced a change whereby an EGL_BAD_SURFACE error
would result in a segfault when using Klassy when opening certain
applications (mainly those applications with custom colour schemes).

The EGL_BAD_SURFACE was caused by a shadow being created at the same
time as the paint() function execution, due to a paletteChanged
signal.

This workaround checks if paint() is under execution before shadow
creation, and aborts the shadow update if this is the case.

CMakeLists.txt

@@ -3,7 +3,7 @@ project(breeze)
 set(PROJECT_VERSION "4.1.breeze5.25.80")
 set(PROJECT_VERSION_MAJOR 5)
 
-add_definitions( -DKLASSY_VERSION="${PROJECT_VERSION}" -DKLASSY_GIT_MASTER=1)
+add_definitions( -DKLASSY_VERSION="${PROJECT_VERSION}" -DKLASSY_GIT_MASTER=0)
 
 set(KF5_MIN_VERSION "5.94")
 set(KDE_COMPILERSETTINGS_LEVEL "5.82")

README.md

@@ -14,8 +14,6 @@
 <a name="overview"/>
 
 ## Overview
-**WARNING: KDE Plasma 5.26 introduced a change which induces segfaults. Please do not use Klassy with Plasma 5.26. Development of Klassy will continue only once Plasma developers fix their bug.**
-
 _Klassy_ (formerly _ClassiK_/_ClassikStyles_) is a highly customizable binary Window Decoration and Application Style plugin for recent versions of the KDE Plasma desktop. [Initially taking inspiration from the iconography of KDE 1](https://forum.kde.org/viewtopic.php?f=285&t=138602?raw=true), the _Klassy_ defaults are an attempt to create a usable and appealing look for the modern Plasma desktop. Install with the instructions below, and then enable in System Settings -> Appearance -> Window Decorations, and also in System Settings -> Appearance -> Application Style.
 
 ![Screenshot of Button icons menu](screenshots/button_icon_menu.png?raw=true "Screenshot of Button icons menu")

kdecoration/breezedecoration.cpp

@@ -918,6 +918,8 @@ void Decoration::updateButtonsGeometry()
 //________________________________________________________________
 void Decoration::paint(QPainter *painter, const QRect &repaintRegion)
 {
+    m_painting = true;
+
     // TODO: optimize based on repaintRegion
     auto c = client().toStrongRef();
     Q_ASSERT(c);
@@ -985,6 +987,8 @@ void Decoration::paint(QPainter *painter, const QRect &repaintRegion)
         painter->drawRect(rect().adjusted(0, 0, -1, -1));
         painter->restore();
     }
+
+    m_painting = false;
 }
 
 void Decoration::calculateWindowAndTitleBarShapes(const bool windowShapeOnly)
@@ -1270,6 +1274,15 @@ void Decoration::updateShadow(const bool force, const bool noCache, const bool i
     auto s = settings();
     auto c = client().toStrongRef();
     Q_ASSERT(c);
+
+    // if the decoration is painting, abandon setting the shadow.
+    // Setting the shadow at the same time as paint() being executed causes a EGL_BAD_SURFACE error and a SEGFAULT from Plasma 5.26 onwards.
+    if (m_painting) {
+        qWarning("Klassy: paint() occuring at same time as shadow creation for \"%s\" - abandonning setting shadow to prevent EGL_BAD_SURFACE.",
+                 c->caption().toLatin1().data());
+        return;
+    }
+
     // Animated case, no cached shadow object
     if ((m_shadowAnimation->state() == QAbstractAnimation::Running) && (m_shadowOpacity != 0.0) && (m_shadowOpacity != 1.0)) {
         setShadow(createShadowObject(0.5 + m_shadowOpacity * 0.5, isThinWindowOutlineOverride));

kdecoration/breezedecoration.h

@@ -217,6 +217,9 @@ private Q_SLOTS:
     KDecoration2::DecorationButtonGroup *m_leftButtons = nullptr;
     KDecoration2::DecorationButtonGroup *m_rightButtons = nullptr;
 
+    //* Whether the paint() method is active
+    bool m_painting = false;
+
     //* size grip widget
     SizeGrip *m_sizeGrip = nullptr;