Don't use constexpr in AbstractImage subclasses.

AbstractImage has virtual destructor, thus it is not possible to
instantiate it in constant expression.

src/BufferedImage.h

@@ -53,7 +53,7 @@ template<std::uint8_t dimensions> class BufferedImage: public AbstractImage {
         }
 
         /** @brief %Image size */
-        inline constexpr typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
+        inline typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
 
         /**
          * @brief Data

src/Image.h

@@ -76,11 +76,11 @@ template<std::uint8_t dimensions> class Image: public AbstractImage {
         inline ~Image() { delete[] _data; }
 
         /** @brief %Image size */
-        inline constexpr typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
+        inline typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
 
         /** @brief Pointer to raw data */
         inline void* data() { return _data; }
-        inline constexpr const void* data() const { return _data; } /**< @overload */
+        inline const void* data() const { return _data; } /**< @overload */
 
         /**
          * @brief Set image data

src/ImageWrapper.h

@@ -80,11 +80,11 @@ template<std::uint8_t dimensions> class ImageWrapper: public AbstractImage {
         inline ImageWrapper(const typename DimensionTraits<Dimensions, GLsizei>::VectorType& size, Components components, ComponentType type): AbstractImage(components, type), _size(size), _data(nullptr) {}
 
         /** @brief %Image size */
-        inline constexpr typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
+        inline typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
 
         /** @brief Pointer to raw data */
         inline void* data() { return _data; }
-        inline constexpr const void* data() const { return _data; } /**< @overload */
+        inline const void* data() const { return _data; } /**< @overload */
 
         /**
          * @brief Set image data

src/Trade/ImageData.h

@@ -69,11 +69,11 @@ template<std::uint8_t dimensions> class ImageData: public AbstractImage {
         inline std::string name() const { return _name; }
 
         /** @brief %Image size */
-        inline constexpr typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
+        inline typename DimensionTraits<Dimensions, GLsizei>::VectorType size() const { return _size; }
 
         /** @brief Pointer to raw data */
         inline void* data() { return _data; }
-        inline constexpr const void* data() const { return _data; } /**< @overload */
+        inline const void* data() const { return _data; } /**< @overload */
 
     private:
         std::string _name;