Fix crash in StelTexture destructor on exit

On deletion of StelApp StelTextureMgr is deleted, after which some
instances of StelTexture are deleted. But StelTexture destructor logs
VRAM usage via StelTextureMgr, accessing a no longer existing object.

This commit turns the nonstatic raw pointer to texture manager into a
static weak pointer (QPointer), so that it was possible to check whether
texture manager still exists before trying to access it. Making it
static is supposed to prevent useless copying of this smart pointer
while the texture manager is effectively a singleton.

Fixes #3427

src/core/StelTexture.cpp

@@ -39,13 +39,19 @@
 # define GL_TEXTURE_MAX_ANISOTROPY 0x84FE
 #endif
 
-StelTexture::StelTexture(StelTextureMgr *mgr)
-	: textureMgr(mgr)
+QPointer<StelTextureMgr> StelTexture::textureMgr;
+
+StelTexture::StelTexture()
 {
 }
 
 StelTexture::~StelTexture()
 {
+	// Don't try to access texture manager or OpenGL context if texture
+	// manager has been deleted, because at this point we are shutting
+	// down, and the OpenGL context may have also been deleted.
+	if (!textureMgr) return;
+
 	if (id != 0)
 	{
 		/// FS: make sure the correct GL context is bound!
@@ -228,6 +234,7 @@ template <typename T, typename...Params, typename...Args>
 void StelTexture::startAsyncLoader(T (*functionPointer)(Params...), Args&&...args)
 {
 	Q_ASSERT(loader==Q_NULLPTR);
+	if (!textureMgr) return;
 	//own thread pool supported with Qt 5.4+
 	loader = new QFuture<GLData>(QtConcurrent::run(textureMgr->loaderThreadPool,
 	                                               functionPointer, std::forward<Args>(args)...));
@@ -379,6 +386,11 @@ QByteArray StelTexture::convertToGLFormat(QImage image, GLint& format, GLint& ty
 
 bool StelTexture::glLoad(const GLData& data)
 {
+	// Don't try to access texture manager or OpenGL context if texture
+	// manager has been deleted, because at this point we are shutting
+	// down, and the OpenGL context may have also been deleted.
+	if (!textureMgr) return false;
+
 	if (data.data.isEmpty())
 	{
 		reportError(data.loaderError.isEmpty() ? "Unknown error" : data.loaderError);

src/core/StelTexture.hpp

@@ -22,6 +22,7 @@
 
 #include <QOpenGLFunctions>
 #include <QSharedPointer>
+#include <QPointer>
 #include <QObject>
 #include <QImage>
 
@@ -143,7 +144,7 @@ private slots:
 	static GLData loadFromData( const QByteArray &data, const int decimateBy);
 
 	//! Private constructor
-	StelTexture(StelTextureMgr* mgr);
+	StelTexture();
 
 	//! Wrap an existing GL texture with this object
 	void wrapGLTexture(GLuint texId);
@@ -173,7 +174,7 @@ private slots:
 	void startAsyncLoader(T (*functionPointer)(Params...), Args&&...args);
 
 	//! The parent texture manager
-	StelTextureMgr* textureMgr = nullptr;
+	static QPointer<StelTextureMgr> textureMgr;
 
 	QOpenGLFunctions* gl = nullptr;
 	StelTextureParams loadParams;

src/core/StelTextureMgr.cpp

@@ -46,6 +46,7 @@ StelTextureMgr::StelTextureMgr(QObject *parent)
 	ctx->functions()->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &maxTexSize);
 	if (maxTexSize<8192)
 		qDebug() << "Max texture size:" << maxTexSize;
+	StelTexture::textureMgr = this;
 }
 
 StelTextureSP StelTextureMgr::createTexture(const QString& afilename, const StelTexture::StelTextureParams& params)
@@ -67,7 +68,7 @@ StelTextureSP StelTextureMgr::createTexture(const QString& afilename, const Stel
 	StelTextureSP cache = lookupCache(canPath);
 	if(!cache.isNull()) return cache;
 
-	StelTextureSP tex = StelTextureSP(new StelTexture(this));
+	StelTextureSP tex = StelTextureSP(new StelTexture);
 	tex->fullPath = canPath;
 
 	QImage image(tex->fullPath);
@@ -159,7 +160,7 @@ StelTextureSP StelTextureMgr::createTextureThread(const QString& url, const Stel
 	StelTextureSP cache = lookupCache(canPath);
 	if(!cache.isNull()) return cache;
 
-	StelTextureSP tex = StelTextureSP(new StelTexture(this));
+	StelTextureSP tex = StelTextureSP(new StelTexture);
 	tex->loadParams = params;
 	tex->fullPath = canPath;
 	if (!lazyLoading)
@@ -175,7 +176,7 @@ StelTextureSP StelTextureMgr::createTextureThread(const QString& url, const Stel
 //! Create a texture from a QImage.
 StelTextureSP StelTextureMgr::createTexture(const QImage &image, const StelTexture::StelTextureParams& params)
 {
-	StelTextureSP tex = StelTextureSP(new StelTexture(this));
+	StelTextureSP tex = StelTextureSP(new StelTexture);
 	tex->loadParams = params;
 	bool r = tex->glLoad(image);
 	Q_ASSERT(r);
@@ -202,7 +203,7 @@ StelTextureSP StelTextureMgr::wrapperForGLTexture(GLuint texId)
 
 
 	//no existing tex with this ID found, create a new wrapper
-	StelTextureSP newTex(new StelTexture(this));
+	StelTextureSP newTex(new StelTexture);
 	newTex->wrapGLTexture(texId);
 	if(!newTex->errorOccured)
 	{
@@ -230,7 +231,7 @@ StelTextureSP StelTextureMgr::getDitheringTexture(const int samplerToBindTo)
 
 	const auto texId = ForTextureMgr::makeDitherPatternTexture(gl);
 
-	ditheringTexture.reset(new StelTexture(this));
+	ditheringTexture.reset(new StelTexture);
 	ditheringTexture->wrapGLTexture(texId);
 	if(!ditheringTexture->errorOccured)
 	{

src/core/StelTextureMgr.hpp

@@ -34,7 +34,7 @@ class QThreadPool;
 //! @class StelTextureMgr
 //! Manage textures loading.
 //! It provides method for loading images in a separate thread.
-class StelTextureMgr : QObject
+class StelTextureMgr : public QObject
 {
 	Q_OBJECT
 public: