Make GL Context current when deleting lanczos textures in timer hander.

A timer could have fired at any time. We process mulitple QtQuickViews
on timers which change the GL context.

Deleting a kwin GLTexture calls glDeleteTextures/glDeleteFramebuffers.

Surprisingly I haven't seen a crash report from this, but it doesn't
look right.

plugins/scenes/opengl/lanczosfilter.cpp

@@ -32,7 +32,7 @@
 namespace KWin
 {
 
-LanczosFilter::LanczosFilter(QObject* parent)
+LanczosFilter::LanczosFilter(Scene *parent)
     : QObject(parent)
     , m_offscreenTex(nullptr)
     , m_offscreenTarget(nullptr)
@@ -40,6 +40,7 @@ LanczosFilter::LanczosFilter(QObject* parent)
     , m_shader(nullptr)
     , m_uOffsets(0)
     , m_uKernel(0)
+    , m_scene(parent)
 {
 }
 
@@ -379,6 +380,8 @@ void LanczosFilter::timerEvent(QTimerEvent *event)
     if (event->timerId() == m_timer.timerId()) {
         m_timer.stop();
 
+        m_scene->makeOpenGLContextCurrent();
+
         delete m_offscreenTarget;
         delete m_offscreenTex;
         m_offscreenTarget = nullptr;
@@ -387,6 +390,8 @@ void LanczosFilter::timerEvent(QTimerEvent *event)
         workspace()->forEachToplevel([this](Toplevel *toplevel) {
             discardCacheTexture(toplevel->effectWindow());
         });
+
+        m_scene->doneOpenGLContextCurrent();
     }
 }
 

plugins/scenes/opengl/lanczosfilter.h

@@ -26,13 +26,14 @@ class WindowPaintData;
 class GLTexture;
 class GLRenderTarget;
 class GLShader;
+class Scene;
 
 class LanczosFilter : public QObject
 {
     Q_OBJECT
 
 public:
-    explicit LanczosFilter(QObject* parent = nullptr);
+    explicit LanczosFilter(Scene *parent);
     ~LanczosFilter() override;
     void performPaint(EffectWindowImpl* w, int mask, QRegion region, WindowPaintData& data);
 
@@ -55,6 +56,7 @@ private:
     int m_uKernel;
     QVector2D m_offsets[16];
     QVector4D m_kernel[16];
+    Scene *m_scene;
 };
 
 } // namespace