Introduce ImageFlags to annotate cube map and array images.

With the intention that those will eventually contain also things like
YUp / YDown, PremultipliedAlpha and such.

This commit is mostly just busywork, wiring this into [Compressed]Image,
[Compressed]ImageView and Trade::ImageData and ensuring the flags get
correctly propagated during moves and conversions. Unfortunately in case
of Trade::ImageData it meant deprecating the current set of constructor
in order to insert an ImageFlags parameter before the importer state
pointer.

The only non-trivial piece of logic is when a 2D
[Compressed]ImageView gets converted to a 3D one, then the Array bit is
implicitly dropped, as 2D arrays of 1D images are not really a thing.
Instead, it's now possible to add new flags when doing the conversion --
for example to turn a 2D image to a (single-layer) 2D array image.

doc/changelog.dox

@@ -335,6 +335,9 @@ See also:
     @ref CompressedImageView::size() as well as @ref Trade::ImageData::size()
     now return a @cpp const& @ce instead of a value to allow creating a
     @relativeref{Corrade,Containers::StridedArrayView} slice onto this member.
+-   @ref Image, @ref CompressedImage, @ref ImageView, @ref CompressedImageView
+    as well as @ref Trade::ImageData are now able to annotate array, cube map
+    and cube map array images using @ref ImageFlags
 
 @subsubsection changelog-latest-changes-debugtools DebugTools library
 
@@ -916,6 +919,11 @@ See also:
     changed to have input first and output second, for consistency with other
     interfaces, together with a switch to @ref Containers::StringView. The
     original signature is marked as deprecated.
+-   Due to introduction of @ref ImageFlags, @ref Trade::ImageData constructors
+    that were taking @cpp const void* importerState @ce as the last parameter
+    are now deprecated in favor of constructors that take @ref ImageFlags *and*
+    `importerState`. Code that wasn't passing the `importerState` parameter
+    isn't affected by this change.
 -   @cpp Trade::TextureData::Type @ce was deprecated in favor of
     @ref Trade::TextureType that is much less annoying to type, in addition
     @cpp Trade::TextureData::Type::Cube @ce was deprecated in favor of

src/Magnum/CMakeLists.txt

@@ -74,6 +74,7 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/version.h.cmake
 # Files shared between main library and unit test library
 set(Magnum_SRCS
     FileCallback.cpp
+    ImageFlags.cpp
     PixelStorage.cpp
     Resource.cpp
     Sampler.cpp
@@ -95,6 +96,7 @@ set(Magnum_HEADERS
     DimensionTraits.h
     FileCallback.h
     Image.h
+    ImageFlags.h
     ImageView.h
     Magnum.h
     Mesh.h

src/Magnum/Image.cpp

@@ -31,12 +31,15 @@
 
 namespace Magnum {
 
-template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const PixelFormat format, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data) noexcept: Image{storage, format, {}, pixelFormatSize(format), size, std::move(data)} {}
+template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const PixelFormat format, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data, const ImageFlags<dimensions> flags) noexcept: Image{storage, format, {}, pixelFormatSize(format), size, std::move(data), flags} {}
 
-template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const UnsignedInt format, const UnsignedInt formatExtra, const UnsignedInt pixelSize, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data) noexcept: Image{storage, pixelFormatWrap(format), formatExtra, pixelSize, size, std::move(data)} {}
+template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const UnsignedInt format, const UnsignedInt formatExtra, const UnsignedInt pixelSize, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data, const ImageFlags<dimensions> flags) noexcept: Image{storage, pixelFormatWrap(format), formatExtra, pixelSize, size, std::move(data), flags} {}
 
-template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const PixelFormat format, const UnsignedInt formatExtra, const UnsignedInt pixelSize, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data) noexcept: _storage{storage}, _format{format}, _formatExtra{formatExtra}, _pixelSize{pixelSize}, _size{size}, _data{std::move(data)} {
+template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const PixelFormat format, const UnsignedInt formatExtra, const UnsignedInt pixelSize, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data, const ImageFlags<dimensions> flags) noexcept: _storage{storage}, _format{format}, _formatExtra{formatExtra}, _pixelSize{pixelSize}, _flags{flags}, _size{size}, _data{std::move(data)} {
     CORRADE_ASSERT(Implementation::imageDataSize(*this) <= _data.size(), "Image: data too small, got" << _data.size() << "but expected at least" << Implementation::imageDataSize(*this) << "bytes", );
+    #ifndef CORRADE_NO_ASSERT
+    Implementation::checkImageFlagsForSize("Image:", flags, size);
+    #endif
 }
 
 template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const PixelFormat format) noexcept: Image{storage, format, {}, pixelFormatSize(format)} {}
@@ -45,7 +48,7 @@ template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage sto
 
 template<UnsignedInt dimensions> Image<dimensions>::Image(const PixelStorage storage, const PixelFormat format, const UnsignedInt formatExtra, const UnsignedInt pixelSize) noexcept: _storage{storage}, _format{format}, _formatExtra{formatExtra}, _pixelSize{pixelSize}, _data{} {}
 
-template<UnsignedInt dimensions> Image<dimensions>::Image(Image<dimensions>&& other) noexcept: _storage{std::move(other._storage)}, _format{std::move(other._format)}, _formatExtra{std::move(other._formatExtra)}, _pixelSize{std::move(other._pixelSize)}, _size{std::move(other._size)}, _data{std::move(other._data)} {
+template<UnsignedInt dimensions> Image<dimensions>::Image(Image<dimensions>&& other) noexcept: _storage{std::move(other._storage)}, _format{std::move(other._format)}, _formatExtra{std::move(other._formatExtra)}, _pixelSize{std::move(other._pixelSize)}, _flags{std::move(other._flags)}, _size{std::move(other._size)}, _data{std::move(other._data)} {
     other._size = {};
 }
 
@@ -55,17 +58,18 @@ template<UnsignedInt dimensions> Image<dimensions>& Image<dimensions>::operator=
     swap(_format, other._format);
     swap(_formatExtra, other._formatExtra);
     swap(_pixelSize, other._pixelSize);
+    swap(_flags, other._flags);
     swap(_size, other._size);
     swap(_data, other._data);
     return *this;
 }
 
 template<UnsignedInt dimensions> Image<dimensions>::operator BasicMutableImageView<dimensions>() {
-    return BasicMutableImageView<dimensions>{_storage, _format, _formatExtra, _pixelSize, _size, _data};
+    return BasicMutableImageView<dimensions>{_storage, _format, _formatExtra, _pixelSize, _size, _data, _flags};
 }
 
 template<UnsignedInt dimensions> Image<dimensions>::operator BasicImageView<dimensions>() const {
-    return BasicImageView<dimensions>{_storage, _format, _formatExtra, _pixelSize, _size, _data};
+    return BasicImageView<dimensions>{_storage, _format, _formatExtra, _pixelSize, _size, _data, _flags};
 }
 
 template<UnsignedInt dimensions> std::pair<VectorTypeFor<dimensions, std::size_t>, VectorTypeFor<dimensions, std::size_t>> Image<dimensions>::dataProperties() const {
@@ -86,13 +90,17 @@ template<UnsignedInt dimensions> Containers::Array<char> Image<dimensions>::rele
     return data;
 }
 
-template<UnsignedInt dimensions> CompressedImage<dimensions>::CompressedImage(const CompressedPixelStorage storage, const CompressedPixelFormat format, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data) noexcept: _storage{storage}, _format{format}, _size{size}, _data{std::move(data)} {}
+template<UnsignedInt dimensions> CompressedImage<dimensions>::CompressedImage(const CompressedPixelStorage storage, const CompressedPixelFormat format, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data, const ImageFlags<dimensions> flags) noexcept: _storage{storage}, _format{format}, _flags{flags}, _size{size}, _data{std::move(data)} {
+    #ifndef CORRADE_NO_ASSERT
+    Implementation::checkImageFlagsForSize("CompressedImage:", flags, size);
+    #endif
+}
 
-template<UnsignedInt dimensions> CompressedImage<dimensions>::CompressedImage(const CompressedPixelStorage storage, const UnsignedInt format, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data) noexcept: CompressedImage{storage, compressedPixelFormatWrap(format), size, std::move(data)} {}
+template<UnsignedInt dimensions> CompressedImage<dimensions>::CompressedImage(const CompressedPixelStorage storage, const UnsignedInt format, const VectorTypeFor<dimensions, Int>& size, Containers::Array<char>&& data, const ImageFlags<dimensions> flags) noexcept: CompressedImage{storage, compressedPixelFormatWrap(format), size, std::move(data), flags} {}
 
 template<UnsignedInt dimensions> CompressedImage<dimensions>::CompressedImage(const CompressedPixelStorage storage) noexcept: _storage{storage}, _format{} {}
 
-template<UnsignedInt dimensions> CompressedImage<dimensions>::CompressedImage(CompressedImage<dimensions>&& other) noexcept: _storage{std::move(other._storage)}, _format{std::move(other._format)}, _size{std::move(other._size)}, _data{std::move(other._data)}
+template<UnsignedInt dimensions> CompressedImage<dimensions>::CompressedImage(CompressedImage<dimensions>&& other) noexcept: _storage{std::move(other._storage)}, _format{std::move(other._format)}, _flags{other._flags}, _size{std::move(other._size)}, _data{std::move(other._data)}
 {
     other._size = {};
 }
@@ -101,17 +109,18 @@ template<UnsignedInt dimensions> CompressedImage<dimensions>& CompressedImage<di
     using std::swap;
     swap(_storage, other._storage);
     swap(_format, other._format);
+    swap(_flags, other._flags);
     swap(_size, other._size);
     swap(_data, other._data);
     return *this;
 }
 
 template<UnsignedInt dimensions> CompressedImage<dimensions>::operator BasicMutableCompressedImageView<dimensions>() {
-    return BasicMutableCompressedImageView<dimensions>{_storage, _format, _size, _data};
+    return BasicMutableCompressedImageView<dimensions>{_storage, _format, _size, _data, _flags};
 }
 
 template<UnsignedInt dimensions> CompressedImage<dimensions>::operator BasicCompressedImageView<dimensions>() const {
-    return BasicCompressedImageView<dimensions>{_storage, _format, _size, _data};
+    return BasicCompressedImageView<dimensions>{_storage, _format, _size, _data, _flags};
 }
 
 template<UnsignedInt dimensions> std::pair<VectorTypeFor<dimensions, std::size_t>, VectorTypeFor<dimensions, std::size_t>> CompressedImage<dimensions>::dataProperties() const {