[WIP] DdsImporter: Refactor to accomodate for more usecases.

Primary usecase is load one image from all. I would be a shame to have to
wait for all images being possibly converted from BGRA to RGBA when loading
only one single image.

Also, calling `imageData2D/3D` twice was not possible up to now.

The strategy now is to do everything which has to be done at least once
anyway in `doImageData()` and create the images themselves from stored
offsets lazily in `doImageData*D()`.

Signed-off-by: Squareys <Squareys@googlemail.com>

src/MagnumPlugins/DdsImporter/DdsImporter.h

@@ -31,9 +31,17 @@
  */
 #include <vector>
 #include <Magnum/Trade/AbstractImporter.h>
+#include <Magnum/Math/Vector3.h>
+#include <Corrade/Containers/Array.h>
+#include <Corrade/Containers/ArrayView.h>
 
 namespace Magnum { namespace Trade {
 
+struct ImageDataOffset {
+    Vector3i _dimensions;
+    Containers::ArrayView<char> _data;
+};
+
 /**
 @brief DDS importer plugin
 
@@ -61,15 +69,21 @@ class DdsImporter: public AbstractImporter {
         std::optional<ImageData3D> doImage3D(UnsignedInt id) override;
 
     private:
-        void loadUncompressedImageData(ColorFormat format, const Vector3i& dims, UnsignedInt components,
-            UnsignedByte numDimensions);
-        void loadCompressedImageData(CompressedColorFormat format, const Vector3i& dims,
-            UnsignedByte numDimensions);
+        size_t addImageDataOffset(const Vector3i& dims, size_t offset);
+
+        Containers::Array<char> _in;
+
+        bool _compressed;
+        bool _volume;
 
-        std::istream* _in;
+        /* components per pixel */
+        UnsignedInt _components;
+        union {
+            ColorFormat uncompressed;
+            CompressedColorFormat compressed;
+        } _colorFormat;
 
-        std::vector<ImageData2D> _imageData2D;
-        std::vector<ImageData3D> _imageData3D;
+        std::vector<ImageDataOffset> _imageData;
 };
 
 }}