GL: clean up Framebuffer constructors.

The AbstractFramebuffer constructor is now constexpr, but that doesn't
mean we can have GL::defaultFramebuffer constexpr -- all member
functions are (by design) non-const and we also need to modify its
viewport value quite often. So this has to stay as-is.

src/Magnum/GL/AbstractFramebuffer.h

@@ -707,11 +707,26 @@ class MAGNUM_GL_EXPORT AbstractFramebuffer {
     #else
     protected:
     #endif
-        explicit AbstractFramebuffer(): _flags{ObjectFlag::DeleteOnDestruction} {}
+        /* Used by the (constexpr) DefaultFramebuffer constructor and both
-        explicit AbstractFramebuffer(GLuint id, const Range2Di& viewport, ObjectFlags flags) noexcept: _id{id}, _viewport{viewport}, _flags{flags} {}
+           the NoCreate and normal constructor of Framebuffer */
+        constexpr explicit AbstractFramebuffer(GLuint id, const Range2Di& viewport, ObjectFlags flags) noexcept: _id{id}, _viewport{viewport}, _flags{flags} {}
 
         ~AbstractFramebuffer() = default;
 
+        AbstractFramebuffer(const AbstractFramebuffer&) = delete;
+        AbstractFramebuffer(AbstractFramebuffer&& other) noexcept: _id{other._id}, _viewport{other._viewport}, _flags{other._flags} {
+            other._id = 0;
+            other._viewport = {};
+        }
+        AbstractFramebuffer& operator=(const AbstractFramebuffer&) = delete;
+        AbstractFramebuffer& operator=(AbstractFramebuffer&& other) noexcept {
+            using std::swap;
+            swap(_id, other._id);
+            swap(_viewport, other._viewport);
+            swap(_flags, other._flags);
+            return *this;
+        }
+
         void MAGNUM_GL_LOCAL createIfNotAlready();
 
         void MAGNUM_GL_LOCAL bindInternal(FramebufferTarget target);

src/Magnum/GL/DefaultFramebuffer.cpp

@@ -46,11 +46,6 @@ namespace GL {
 
 DefaultFramebuffer defaultFramebuffer;
 
-DefaultFramebuffer::DefaultFramebuffer() {
-    _id = 0;
-    _flags |= ObjectFlag::Created;
-}
-
 DefaultFramebuffer::Status DefaultFramebuffer::checkStatus(const FramebufferTarget target) {
     return Status((this->*Context::current().state().framebuffer->checkStatusImplementation)(target));
 }

src/Magnum/GL/DefaultFramebuffer.h

@@ -306,7 +306,13 @@ class MAGNUM_GL_EXPORT DefaultFramebuffer: public AbstractFramebuffer {
         };
         #endif
 
-        explicit MAGNUM_GL_LOCAL DefaultFramebuffer();
+        /**
+         * @brief Constructor
+         *
+         * Not meant to be constructed on the application side, use the
+         * @ref GL::defaultFramebuffer instance directly.
+         */
+        constexpr explicit DefaultFramebuffer(): AbstractFramebuffer{0, {}, ObjectFlag::Created|ObjectFlag::DeleteOnDestruction} {}
 
         /** @brief Copying is not allowed */
         DefaultFramebuffer(const DefaultFramebuffer&) = delete;
@@ -504,6 +510,9 @@ class MAGNUM_GL_EXPORT DefaultFramebuffer: public AbstractFramebuffer {
 };
 
 /** @brief Default framebuffer instance */
+/* Even though the constructor is constexpr, this variable can't -- all
+   framebuffer APIs are non-const since they modify global GL state and besides
+   that we also need to modify its private _viewport member quite a lot */
 extern DefaultFramebuffer MAGNUM_GL_EXPORT defaultFramebuffer;
 
 /** @debugoperatorclassenum{DefaultFramebuffer,DefaultFramebuffer::Status} */

src/Magnum/GL/Framebuffer.cpp

@@ -97,7 +97,7 @@ Int Framebuffer::maxColorAttachments() {
     return value;
 }
 
-Framebuffer::Framebuffer(const Range2Di& viewport) {
+Framebuffer::Framebuffer(const Range2Di& viewport): AbstractFramebuffer{0, viewport, ObjectFlag::DeleteOnDestruction} {
     CORRADE_INTERNAL_ASSERT(viewport != Implementation::FramebufferState::DisengagedViewport);
     _viewport = viewport;
     (this->*Context::current().state().framebuffer->createImplementation)();

src/Magnum/GL/Framebuffer.h

@@ -361,14 +361,13 @@ class MAGNUM_GL_EXPORT Framebuffer: public AbstractFramebuffer, public AbstractO
          * destructing) objects even without any OpenGL context being active.
          * @see @ref Framebuffer(const Range2Di&), @ref wrap()
          */
-        explicit Framebuffer(NoCreateT) noexcept { _id = 0; }
+        explicit Framebuffer(NoCreateT) noexcept: AbstractFramebuffer{{}, {}, {}} {}
 
         /** @brief Copying is not allowed */
         Framebuffer(const Framebuffer&) = delete;
 
         /** @brief Move constructor */
-        /* MinGW complains loudly if the declaration doesn't also have inline */
+        Framebuffer(Framebuffer&&) noexcept = default;
-        inline Framebuffer(Framebuffer&& other) noexcept;
 
         /**
          * @brief Destructor
@@ -382,8 +381,7 @@ class MAGNUM_GL_EXPORT Framebuffer: public AbstractFramebuffer, public AbstractO
         Framebuffer& operator=(const Framebuffer&) = delete;
 
         /** @brief Move assignment */
-        /* MinGW complains loudly if the declaration doesn't also have inline */
+        Framebuffer& operator=(Framebuffer&&) noexcept = default;
-        inline Framebuffer& operator=(Framebuffer&& other) noexcept;
 
         /** @brief OpenGL framebuffer ID */
         GLuint id() const { return _id; }
@@ -939,22 +937,6 @@ class MAGNUM_GL_EXPORT Framebuffer: public AbstractFramebuffer, public AbstractO
 /** @debugoperatorclassenum{Framebuffer,Framebuffer::Status} */
 MAGNUM_GL_EXPORT Debug& operator<<(Debug& debug, Framebuffer::Status value);
 
-inline Framebuffer::Framebuffer(Framebuffer&& other) noexcept {
-    _id = other._id;
-    _viewport = other._viewport;
-    _flags = other._flags;
-    other._id = 0;
-    other._viewport = {};
-}
-
-inline Framebuffer& Framebuffer::operator=(Framebuffer&& other) noexcept {
-    using std::swap;
-    swap(_id, other._id);
-    swap(_viewport, other._viewport);
-    swap(_flags, other._flags);
-    return *this;
-}
-
 inline GLuint Framebuffer::release() {
     const GLuint id = _id;
     _id = 0;