ÄnyImageImporter: recognize BMP header magic.

I needed to know the signature for a StbImageConverter test, so why not
add it here as well now that I managed to figure that out.

doc/changelog.dox

@@ -342,7 +342,7 @@ See also:
     @relativeref{Trade::AbstractImageConverter,doConvertToData()}, for example
     when the implementation only neeeds to do a format detection based on file
     extension
--   Recognizing TIFF file header magic in @ref Trade::AnyImageImporter "AnyImageImporter"
+-   Recognizing BMP and TIFF file header magic in @relativeref{Trade,AnyImageImporter}
 -   @ref Audio::AnyImporter "AnyAudioImporter",
     @relativeref{Trade,AnyImageImporter}, @relativeref{Trade,AnyImageConverter},
     @relativeref{Trade,AnySceneImporter}, @relativeref{Trade,AnySceneConverter}

src/MagnumPlugins/AnyImageImporter/AnyImageImporter.cpp

@@ -162,6 +162,9 @@ void AnyImageImporter::doOpenData(Containers::ArrayView<const char> data) {
     /* https://github.com/BinomialLLC/basis_universal/blob/7d784c728844c007d8c95d63231f7adcc0f65364/transcoder/basisu_file_headers.h#L78 */
     if(dataString.hasPrefix("sB"_s))
         plugin = "BasisImporter";
+    /* https://en.wikipedia.org/wiki/BMP_file_format#Bitmap_file_header */
+    else if(dataString.hasPrefix("BM"_s))
+        plugin = "BmpImporter";
     /* https://docs.microsoft.com/cs-cz/windows/desktop/direct3ddds/dx-graphics-dds-pguide */
     else if(dataString.hasPrefix("DDS "_s))
         plugin = "DdsImporter";

src/MagnumPlugins/AnyImageImporter/AnyImageImporter.h

@@ -58,7 +58,8 @@ tries to open the file with it. Supported formats:
 
 -   Basis Universal (`*.basis` or data with corresponding signature), loaded
     with @ref BasisImporter or any other plugin that provides it
--   Windows Bitmap (`*.bmp`), loaded with any plugin that provides `BmpImporter`
+-   Windows Bitmap (`*.bmp` or data with corresponding signature), loaded with
+    any plugin that provides `BmpImporter`
 -   DirectDraw Surface (`*.dds` or data with corresponding signature), loaded
     with @ref DdsImporter or any other plugin that provides it
 -   Graphics Interchange Format (`*.gif`), loaded with any plugin that provides

src/MagnumPlugins/AnyImageImporter/Test/AnyImageImporterTest.cpp

@@ -96,7 +96,8 @@ constexpr struct {
     {"ICO", "pngs.ico", nullptr, "IcoImporter"},
     {"DDS", "rgba_dxt1.dds", nullptr, "DdsImporter"},
     {"DDS data", "rgba_dxt1.dds", fileCallback, "DdsImporter"},
-    {"BMP", "image.bmp", nullptr, "BmpImporter"},
+    {"BMP", "rgb.bmp", nullptr, "BmpImporter"},
+    {"BMP data", "rgb.bmp", fileCallback, "BmpImporter"},
     {"GIF", "image.gif", nullptr, "GifImporter"},
     {"PSD", "image.psd", nullptr, "PsdImporter"},
     {"TIFF", "image.tiff", nullptr, "TiffImporter"},

src/MagnumPlugins/AnyImageImporter/Test/CMakeLists.txt

@@ -59,6 +59,7 @@ corrade_add_test(AnyImageImporterTest AnyImageImporterTest.cpp
         image.tiff
         pngs.ico
         rgb.basis
+        rgb.bmp
         rgb.hdr
         rgb.png
         rgb.tga