TgaImageConverter: warn if saving a 1D array image.

Future-proofing the test as instanced, as I expect there being more
cases -- especially when arbitrary key/value metadata come into place.

src/MagnumPlugins/TgaImageConverter/Test/TgaImageConverterTest.cpp

@@ -31,6 +31,7 @@
 #include <Corrade/TestSuite/Tester.h>
 #include <Corrade/TestSuite/Compare/Container.h>
 #include <Corrade/Utility/DebugStl.h>
+#include <Corrade/Utility/FormatStl.h>
 #include <Corrade/Utility/Path.h>
 
 #include "Magnum/ImageView.h"
@@ -51,6 +52,8 @@ struct TgaImageConverterTest: TestSuite::Tester {
     void rgb();
     void rgba();
 
+    void unsupportedMetadata();
+
     /* Explicitly forbid system-wide plugin dependencies */
     PluginManager::Manager<AbstractImageConverter> _converterManager{"nonexistent"};
     PluginManager::Manager<AbstractImporter> _importerManager{"nonexistent"};
@@ -68,6 +71,15 @@ constexpr struct {
         "Trade::TgaImageConverter::convertToData(): converting from RGBA to BGRA\n"}
 };
 
+const struct {
+    const char* name;
+    ImageFlags2D flags;
+    const char* message;
+} UnsupportedMetadataData[]{
+    {"1D array", ImageFlag2D::Array,
+        "1D array images are unrepresentable in TGA, saving as a regular 2D image"}
+};
+
 TgaImageConverterTest::TgaImageConverterTest() {
     addTests({&TgaImageConverterTest::wrongFormat});
 
@@ -76,6 +88,9 @@ TgaImageConverterTest::TgaImageConverterTest() {
         &TgaImageConverterTest::rgba},
         Containers::arraySize(VerboseData));
 
+    addInstancedTests({&TgaImageConverterTest::unsupportedMetadata},
+        Containers::arraySize(UnsupportedMetadataData));
+
     /* Load the plugin directly from the build tree. Otherwise it's static and
        already loaded. */
     #ifdef TGAIMAGECONVERTER_PLUGIN_FILENAME
@@ -184,6 +199,21 @@ void TgaImageConverterTest::rgba() {
     CORRADE_COMPARE(out.str(), data.message32);
 }
 
+void TgaImageConverterTest::unsupportedMetadata() {
+    auto&& data = UnsupportedMetadataData[testCaseInstanceId()];
+    setTestCaseDescription(data.name);
+
+    Containers::Pointer<AbstractImageConverter> converter = _converterManager.instantiate("TgaImageConverter");
+
+    const char imageData[4]{};
+    ImageView2D image{PixelFormat::RGBA8Unorm, {1, 1}, imageData, data.flags};
+
+    std::ostringstream out;
+    Warning redirectWarning{&out};
+    CORRADE_VERIFY(converter->convertToData(image));
+    CORRADE_COMPARE(out.str(), Utility::formatString("Trade::TgaImageConverter::convertToData(): {}\n", data.message));
+}
+
 }}}}
 
 CORRADE_TEST_MAIN(Magnum::Trade::Test::TgaImageConverterTest)

src/MagnumPlugins/TgaImageConverter/TgaImageConverter.cpp

@@ -47,6 +47,11 @@ TgaImageConverter::TgaImageConverter(PluginManager::AbstractManager& manager, co
 ImageConverterFeatures TgaImageConverter::doFeatures() const { return ImageConverterFeature::Convert2DToData; }
 
 Containers::Optional<Containers::Array<char>> TgaImageConverter::doConvertToData(const ImageView2D& image) {
+    /* Warn about lost metadata */
+    if(image.flags() & ImageFlag2D::Array) {
+        Warning{} << "Trade::TgaImageConverter::convertToData(): 1D array images are unrepresentable in TGA, saving as a regular 2D image";
+    }
+
     /* Initialize data buffer */
     const auto pixelSize = UnsignedByte(image.pixelSize());
     Containers::Array<char> data{ValueInit, sizeof(Implementation::TgaHeader) + pixelSize*image.size().product()};

src/MagnumPlugins/TgaImageConverter/TgaImageConverter.h

@@ -93,6 +93,10 @@ information.
 
 The output is always uncompressed. If you want to make use of RLE compression
 and have the files smaller, use the @ref StbImageConverter plugin instead.
+
+The TGA file format doesn't have a way to distinguish between 2D and 1D array
+images. If an image has @ref ImageFlag2D::Array set, a warning is printed and
+the file is saved as a regular 2D image.
 */
 class MAGNUM_TGAIMAGECONVERTER_EXPORT TgaImageConverter: public AbstractImageConverter {
     public: