Ensure that the renderbuffer object is properly created before using it.

src/Magnum/Renderbuffer.cpp

@@ -64,7 +64,7 @@ Int Renderbuffer::maxSamples() {
     return value;
 }
 
-Renderbuffer::Renderbuffer() { glGenRenderbuffers(1, &_id); }
+Renderbuffer::Renderbuffer(): _created{false} { glGenRenderbuffers(1, &_id); }
 
 Renderbuffer::~Renderbuffer() {
     /* Moved out, nothing to do */
@@ -77,11 +77,24 @@ Renderbuffer::~Renderbuffer() {
     glDeleteRenderbuffers(1, &_id);
 }
 
-std::string Renderbuffer::label() const {
+inline void Renderbuffer::createIfNotAlready() {
+    if(_created) return;
+
+    /* glGen*() does not create the object, just reserves the name. Some
+       commands (such as glObjectLabel()) operate with IDs directly and they
+       require the object to be created. Binding the renderbuffer finally
+       creates it. Also all EXT DSA functions implicitly create it. */
+    bind();
+    CORRADE_INTERNAL_ASSERT(_created);
+}
+
+std::string Renderbuffer::label() {
+    createIfNotAlready();
     return Context::current()->state().debug->getLabelImplementation(GL_RENDERBUFFER, _id);
 }
 
 Renderbuffer& Renderbuffer::setLabelInternal(const Containers::ArrayReference<const char> label) {
+    createIfNotAlready();
     Context::current()->state().debug->labelImplementation(GL_RENDERBUFFER, _id, label);
     return *this;
 }
@@ -99,7 +112,9 @@ void Renderbuffer::bind() {
 
     if(binding == _id) return;
 
+    /* Binding the renderbuffer finally creates it */
     binding = _id;
+    _created = true;
     glBindRenderbuffer(GL_RENDERBUFFER, _id);
 }
 
@@ -110,6 +125,7 @@ void Renderbuffer::storageImplementationDefault(RenderbufferFormat internalForma
 
 #ifndef MAGNUM_TARGET_GLES
 void Renderbuffer::storageImplementationDSA(RenderbufferFormat internalFormat, const Vector2i& size) {
+    _created = true;
     glNamedRenderbufferStorageEXT(_id, GLenum(internalFormat), size.x(), size.y());
 }
 #endif
@@ -147,6 +163,7 @@ void Renderbuffer::storageMultisampleImplementationNV(const GLsizei samples, con
 
 #ifndef MAGNUM_TARGET_GLES
 void Renderbuffer::storageMultisampleImplementationDSA(GLsizei samples, RenderbufferFormat internalFormat, const Vector2i& size) {
+    _created = true;
     glNamedRenderbufferStorageMultisampleEXT(_id, samples, GLenum(internalFormat), size.x(), size.y());
 }
 #endif

src/Magnum/Renderbuffer.h

@@ -124,7 +124,7 @@ class MAGNUM_EXPORT Renderbuffer: public AbstractObject {
          *      @fn_gl_extension2{GetObjectLabel,EXT,debug_label} with
          *      @def_gl{RENDERBUFFER}
          */
-        std::string label() const;
+        std::string label();
 
         /**
          * @brief Set renderbuffer label
@@ -178,6 +178,8 @@ class MAGNUM_EXPORT Renderbuffer: public AbstractObject {
         void setStorageMultisample(Int samples, RenderbufferFormat internalFormat, const Vector2i& size);
 
     private:
+        void MAGNUM_LOCAL createIfNotAlready();
+
         Renderbuffer& setLabelInternal(Containers::ArrayReference<const char> label);
 
         void MAGNUM_LOCAL storageImplementationDefault(RenderbufferFormat internalFormat, const Vector2i& size);
@@ -198,14 +200,16 @@ class MAGNUM_EXPORT Renderbuffer: public AbstractObject {
         void MAGNUM_LOCAL bind();
 
         GLuint _id;
+        bool _created; /* see createIfNotAlready() for details */
 };
 
-inline Renderbuffer::Renderbuffer(Renderbuffer&& other) noexcept: _id(other._id) {
+inline Renderbuffer::Renderbuffer(Renderbuffer&& other) noexcept: _id{other._id}, _created{other._created} {
     other._id = 0;
 }
 
 inline Renderbuffer& Renderbuffer::operator=(Renderbuffer&& other) noexcept {
     std::swap(_id, other._id);
+    std::swap(_created, other._created);
     return *this;
 }
 

src/Magnum/Test/RenderbufferGLTest.cpp

@@ -111,29 +111,15 @@ void RenderbufferGLTest::label() {
         CORRADE_SKIP(Extensions::GL::ARB::framebuffer_object::string() + std::string(" is not available."));
     #endif
 
-    /* No-Op version is tested in AbstractObjectGLTest */
-    if(!Context::current()->isExtensionSupported<Extensions::GL::KHR::debug>() &&
-       !Context::current()->isExtensionSupported<Extensions::GL::EXT::debug_label>())
-        CORRADE_SKIP("Required extension is not available");
-
-    {
-        /** @todo Is this even legal optimization? */
-        CORRADE_EXPECT_FAIL("The object must be used at least once before setting/querying label.");
-        CORRADE_VERIFY(false);
-    }
     Renderbuffer renderbuffer;
-    #ifndef MAGNUM_TARGET_GLES2
-    renderbuffer.setStorage(RenderbufferFormat::RGBA8, {128, 128});
-    #else
-    renderbuffer.setStorage(RenderbufferFormat::RGBA4, {128, 128});
-    #endif
 
     CORRADE_COMPARE(renderbuffer.label(), "");
+    MAGNUM_VERIFY_NO_ERROR();
 
     renderbuffer.setLabel("MyRenderbuffer");
-    CORRADE_COMPARE(renderbuffer.label(), "MyRenderbuffer");
-
     MAGNUM_VERIFY_NO_ERROR();
+
+    CORRADE_COMPARE(renderbuffer.label(), "MyRenderbuffer");
 }
 
 void RenderbufferGLTest::setStorage() {