Trade: tighten AbstractImageConverter input requirements.

The multi-level APIs still don't check anything regarding level sizes
and order since for example *.ico has no restrictions at all. But the
rest (like non-zero size) is a restriction for all file formats I'm
aware of.

TgaImageConverter test had to be adapted, I expect a lot of breakages in
plugins tests as well. But user code should be fine I think. Also
reduced the rather excessive dimensions in AbstractImageConverterTest,
since the allocation requirement now made the default Emscripten heap
OOM.

doc/changelog.dox

@@ -733,6 +733,11 @@ See also:
     interfaces, which are also @cpp const @ce and can't fail. Documentation of
     each function was expanded to suggest a recommended place for potential
     error handling.
+-   @ref Trade::AbstractImageConverter::convertToData() and
+    @relativeref{Trade::AbstractImageConverter,convertToFile()} now expect
+    image views to not be @cpp nullptr @ce and to have a non-zero size in all
+    dimensions. This used to fail for all existing plugin implementations
+    anyway, but now it's treated as a programmer error and thus asserted on.
 -   @ref Trade::TextureData constructor was not @cpp explicit @ce by mistake,
     now it is
 -   @ref Trade::TextureData::image() used to document that cube map images are

src/Magnum/Trade/AbstractImageConverter.cpp

@@ -36,6 +36,7 @@
 
 #include "Magnum/Image.h"
 #include "Magnum/ImageView.h"
+#include "Magnum/PixelFormat.h"
 #include "Magnum/Trade/ImageData.h"
 
 #ifndef CORRADE_PLUGINMANAGER_NO_DYNAMIC_PLUGIN_SUPPORT
@@ -99,6 +100,24 @@ Containers::Optional<ImageData1D> AbstractImageConverter::convert(const ImageVie
     CORRADE_ASSERT(features() & ImageConverterFeature::Convert1D,
         "Trade::AbstractImageConverter::convert(): 1D image conversion not supported", {});
 
+    /* Unlike with convertToData() / convertToFile(), where images are checked
+       for having a non-zero size and being non-null, here it's explicitly
+       allowed:
+
+        -   Usual format conversions / resamplings are a loop that "just works"
+            with zero-sized dimensions.
+        -   Nullptr views could be potentially useful for converters that fill
+            an image of desired format and size with data, such as generating a
+            noise image or some test pattern. While it could be implemented as
+            an importer plugin as well, the size/format would have to be passed
+            manually through plugin-specific configuration there, which is
+            rather annoying compared to having an API prepared directly for
+            that.
+
+       Plugin implementations that can't work with these have to do this check
+       themselves, and since that's then a plugin-specific behavior, it should
+       be a runtime error, not an assert. */
+
     Containers::Optional<ImageData1D> out = doConvert(image);
     CORRADE_ASSERT(!out || !out->_data.deleter(), "Trade::AbstractImageConverter::convert(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -112,6 +131,9 @@ Containers::Optional<ImageData2D> AbstractImageConverter::convert(const ImageVie
     CORRADE_ASSERT(features() & ImageConverterFeature::Convert2D,
         "Trade::AbstractImageConverter::convert(): 2D image conversion not supported", {});
 
+    /* No zero size / nullptr checks here, see convert(const ImageView1D&) for
+       reasons why */
+
     Containers::Optional<ImageData2D> out = doConvert(image);
     CORRADE_ASSERT(!out || !out->_data.deleter(), "Trade::AbstractImageConverter::convert(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -157,6 +179,9 @@ Containers::Optional<ImageData3D> AbstractImageConverter::convert(const ImageVie
     CORRADE_ASSERT(features() & ImageConverterFeature::Convert3D,
         "Trade::AbstractImageConverter::convert(): 3D image conversion not supported", {});
 
+    /* No zero size / nullptr checks here, see convert(const ImageView1D&) for
+       reasons why */
+
     Containers::Optional<ImageData3D> out = doConvert(image);
     CORRADE_ASSERT(!out || !out->_data.deleter(), "Trade::AbstractImageConverter::convert(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -170,6 +195,9 @@ Containers::Optional<ImageData1D> AbstractImageConverter::convert(const Compress
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressed1D,
         "Trade::AbstractImageConverter::convert(): compressed 1D image conversion not supported", {});
 
+    /* No zero size / nullptr checks here, see convert(const ImageView1D&) for
+       reasons why */
+
     Containers::Optional<ImageData1D> out = doConvert(image);
     CORRADE_ASSERT(!out || !out->_data.deleter(), "Trade::AbstractImageConverter::convert(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -183,6 +211,9 @@ Containers::Optional<ImageData2D> AbstractImageConverter::convert(const Compress
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressed2D,
         "Trade::AbstractImageConverter::convert(): compressed 2D image conversion not supported", {});
 
+    /* No zero size / nullptr checks here, see convert(const ImageView1D&) for
+       reasons why */
+
     Containers::Optional<ImageData2D> out = doConvert(image);
     CORRADE_ASSERT(!out || !out->_data.deleter(), "Trade::AbstractImageConverter::convert(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -196,6 +227,9 @@ Containers::Optional<ImageData3D> AbstractImageConverter::convert(const Compress
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressed3D,
         "Trade::AbstractImageConverter::convert(): compressed 3D image conversion not supported", {});
 
+    /* No zero size / nullptr checks here, see convert(const ImageView1D&) for
+       reasons why */
+
     Containers::Optional<ImageData3D> out = doConvert(image);
     CORRADE_ASSERT(!out || !out->_data.deleter(), "Trade::AbstractImageConverter::convert(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -217,10 +251,37 @@ Containers::Optional<ImageData3D> AbstractImageConverter::convert(const ImageDat
     return image.isCompressed() ? convert(CompressedImageView3D(image)) : convert(ImageView3D(image));
 }
 
+#ifndef CORRADE_NO_ASSERT
+namespace {
+
+template<UnsignedInt dimensions, template<UnsignedInt, class> class View> bool checkImageValidity(const char* const messagePrefix, const View<dimensions, const char>& image) {
+    /* At some point there might be a file format that allows zero-sized
+       images, but so far I don't know about any. When such format appears,
+       this check will get moved to plugin implementations that can't work with
+       zero-sized images.
+
+       Also note that this check isn't done for the Image->Image conversion
+       above, there zero-sized images and nullptr *could* make sense. */
+    CORRADE_ASSERT(image.size().product(),
+        messagePrefix << "can't convert image with a zero size:" << image.size(), false);
+    CORRADE_ASSERT(image.data(),
+        messagePrefix << "can't convert image with a nullptr view", false);
+    return true;
+}
+
+}
+#endif
+
 Containers::Array<char> AbstractImageConverter::convertToData(const ImageView1D& image) {
     CORRADE_ASSERT(features() >= ImageConverterFeature::Convert1DToData,
         "Trade::AbstractImageConverter::convertToData(): 1D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", image))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(image);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -237,6 +298,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const ImageView2D&
     CORRADE_ASSERT(features() >= ImageConverterFeature::Convert2DToData,
         "Trade::AbstractImageConverter::convertToData(): 2D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", image))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(image);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -259,6 +326,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const ImageView3D&
     CORRADE_ASSERT(features() >= ImageConverterFeature::Convert3DToData,
         "Trade::AbstractImageConverter::convertToData(): 3D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", image))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(image);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -275,6 +348,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const CompressedIm
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertCompressed1DToData,
         "Trade::AbstractImageConverter::convertToData(): compressed 1D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", image))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(image);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -291,6 +370,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const CompressedIm
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertCompressed2DToData,
         "Trade::AbstractImageConverter::convertToData(): compressed 2D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", image))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(image);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -313,6 +398,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const CompressedIm
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertCompressed3DToData,
         "Trade::AbstractImageConverter::convertToData(): compressed 3D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", image))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(image);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -343,10 +434,65 @@ Containers::Array<char> AbstractImageConverter::convertToData(const ImageData3D&
     return image.isCompressed() ? convertToData(CompressedImageView3D(image)) : convertToData(ImageView3D(image));
 }
 
+#ifndef CORRADE_NO_ASSERT
+namespace {
+
+template<UnsignedInt dimensions> bool checkImageValidity(const char* const messagePrefix, const Containers::ArrayView<const BasicImageView<dimensions>> imageLevels) {
+    CORRADE_ASSERT(!imageLevels.empty(),
+        messagePrefix << "at least one image has to be specified", false);
+
+    const PixelFormat format = imageLevels[0].format();
+    const UnsignedInt formatExtra = imageLevels[0].formatExtra();
+    /* Going through *all* levels although the format assertion is never fired
+       in the first iteration in order to properly check also the first one for
+       zero size / nullptr. */
+    for(std::size_t i = 0; i != imageLevels.size(); ++i) {
+        CORRADE_ASSERT(imageLevels[i].size().product(),
+            messagePrefix << "can't convert image" << i << "with a zero size:" << imageLevels[i].size(), false);
+        CORRADE_ASSERT(imageLevels[i].data(),
+            messagePrefix << "can't convert image" << i << "with a nullptr view", false);
+        CORRADE_ASSERT(imageLevels[i].format() == format,
+            messagePrefix << "levels don't have the same format, expected" << format << "but got" << imageLevels[i].format() << "for image" << i, false);
+        CORRADE_ASSERT(imageLevels[i].formatExtra() == formatExtra,
+            messagePrefix << "levels don't have the same extra format field, expected" << formatExtra << "but got" << imageLevels[i].formatExtra() << "for image" << i, false);
+    }
+
+    return true;
+}
+
+template<UnsignedInt dimensions> bool checkImageValidity(const char* const messagePrefix, const Containers::ArrayView<const BasicCompressedImageView<dimensions>> imageLevels) {
+    CORRADE_ASSERT(!imageLevels.empty(),
+        messagePrefix << "at least one image has to be specified", false);
+
+    const CompressedPixelFormat format = imageLevels[0].format();
+    /* Going through *all* levels although the format assertion is never fired
+       in the first iteration in order to properly check also the first one for
+       zero size / nullptr. */
+    for(std::size_t i = 0; i != imageLevels.size(); ++i) {
+        CORRADE_ASSERT(imageLevels[i].size().product(),
+            messagePrefix << "can't convert image" << i << "with a zero size:" << imageLevels[i].size(), false);
+        CORRADE_ASSERT(imageLevels[i].data(),
+            messagePrefix << "can't convert image" << i << "with a nullptr view", false);
+        CORRADE_ASSERT(imageLevels[i].format() == format,
+            messagePrefix << "levels don't have the same format, expected" << format << "but got" << imageLevels[i].format() << "for image" << i, false);
+    }
+
+    return true;
+}
+
+}
+#endif
+
 Containers::Array<char> AbstractImageConverter::convertToData(const Containers::ArrayView<const ImageView1D> imageLevels) {
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertLevels1DToData,
         "Trade::AbstractImageConverter::convertToData(): multi-level 1D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", imageLevels))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(imageLevels);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -364,6 +510,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const Containers::
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertLevels2DToData,
         "Trade::AbstractImageConverter::convertToData(): multi-level 2D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", imageLevels))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(imageLevels);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -381,6 +533,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const Containers::
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertLevels3DToData,
         "Trade::AbstractImageConverter::convertToData(): multi-level 3D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", imageLevels))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(imageLevels);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -398,6 +556,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const Containers::
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertCompressedLevels1DToData,
         "Trade::AbstractImageConverter::convertToData(): multi-level compressed 1D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", imageLevels))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(imageLevels);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -415,6 +579,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const Containers::
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertCompressedLevels2DToData,
         "Trade::AbstractImageConverter::convertToData(): multi-level compressed 2D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", imageLevels))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(imageLevels);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -432,6 +602,12 @@ Containers::Array<char> AbstractImageConverter::convertToData(const Containers::
     CORRADE_ASSERT(features() >= ImageConverterFeature::ConvertCompressedLevels3DToData,
         "Trade::AbstractImageConverter::convertToData(): multi-level compressed 3D image conversion not supported", nullptr);
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToData():", imageLevels))
+        return {};
+    #endif
+
     Containers::Array<char> out = doConvertToData(imageLevels);
     CORRADE_ASSERT(!out.deleter(), "Trade::AbstractImageConverter::convertToData(): implementation is not allowed to use a custom Array deleter", {});
     return out;
@@ -449,6 +625,12 @@ bool AbstractImageConverter::convertToFile(const ImageView1D& image, const Conta
     CORRADE_ASSERT(features() & ImageConverterFeature::Convert1DToFile,
         "Trade::AbstractImageConverter::convertToFile(): 1D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", image))
+        return {};
+    #endif
+
     return doConvertToFile(image, filename);
 }
 
@@ -477,6 +659,12 @@ bool AbstractImageConverter::convertToFile(const ImageView2D& image, const Conta
     CORRADE_ASSERT(features() & ImageConverterFeature::Convert2DToFile,
         "Trade::AbstractImageConverter::convertToFile(): 2D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", image))
+        return {};
+    #endif
+
     return doConvertToFile(image, filename);
 }
 
@@ -511,6 +699,12 @@ bool AbstractImageConverter::convertToFile(const ImageView3D& image, const Conta
     CORRADE_ASSERT(features() & ImageConverterFeature::Convert3DToFile,
         "Trade::AbstractImageConverter::convertToFile(): 3D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", image))
+        return {};
+    #endif
+
     return doConvertToFile(image, filename);
 }
 
@@ -539,6 +733,12 @@ bool AbstractImageConverter::convertToFile(const CompressedImageView1D& image, c
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressed1DToFile,
         "Trade::AbstractImageConverter::convertToFile(): compressed 1D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", image))
+        return {};
+    #endif
+
     return doConvertToFile(image, filename);
 }
 
@@ -567,6 +767,12 @@ bool AbstractImageConverter::convertToFile(const CompressedImageView2D& image, c
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressed2DToFile,
         "Trade::AbstractImageConverter::convertToFile(): compressed 2D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", image))
+        return {};
+    #endif
+
     return doConvertToFile(image, filename);
 }
 
@@ -601,6 +807,12 @@ bool AbstractImageConverter::convertToFile(const CompressedImageView3D& image, c
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressed3DToFile,
         "Trade::AbstractImageConverter::convertToFile(): compressed 3D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", image))
+        return {};
+    #endif
+
     return doConvertToFile(image, filename);
 }
 
@@ -647,6 +859,12 @@ bool AbstractImageConverter::convertToFile(const Containers::ArrayView<const Ima
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertLevels1DToFile,
         "Trade::AbstractImageConverter::convertToFile(): multi-level 1D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", imageLevels))
+        return {};
+    #endif
+
     return doConvertToFile(imageLevels, filename);
 }
 
@@ -673,6 +891,12 @@ bool AbstractImageConverter::convertToFile(const Containers::ArrayView<const Ima
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertLevels2DToFile,
         "Trade::AbstractImageConverter::convertToFile(): multi-level 2D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", imageLevels))
+        return {};
+    #endif
+
     return doConvertToFile(imageLevels, filename);
 }
 
@@ -699,6 +923,12 @@ bool AbstractImageConverter::convertToFile(const Containers::ArrayView<const Ima
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertLevels3DToFile,
         "Trade::AbstractImageConverter::convertToFile(): multi-level 3D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", imageLevels))
+        return {};
+    #endif
+
     return doConvertToFile(imageLevels, filename);
 }
 
@@ -725,6 +955,12 @@ bool AbstractImageConverter::convertToFile(const Containers::ArrayView<const Com
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressedLevels1DToFile,
         "Trade::AbstractImageConverter::convertToFile(): multi-level compressed 1D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", imageLevels))
+        return {};
+    #endif
+
     return doConvertToFile(imageLevels, filename);
 }
 
@@ -751,6 +987,12 @@ bool AbstractImageConverter::convertToFile(const Containers::ArrayView<const Com
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressedLevels2DToFile,
         "Trade::AbstractImageConverter::convertToFile(): multi-level compressed 2D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", imageLevels))
+        return {};
+    #endif
+
     return doConvertToFile(imageLevels, filename);
 }
 
@@ -777,6 +1019,12 @@ bool AbstractImageConverter::convertToFile(const Containers::ArrayView<const Com
     CORRADE_ASSERT(features() & ImageConverterFeature::ConvertCompressedLevels3DToFile,
         "Trade::AbstractImageConverter::convertToFile(): multi-level compressed 3D image conversion not supported", {});
 
+    #ifndef CORRADE_NO_ASSERT
+    /* Explicitly return if checks fail for CORRADE_GRACEFUL_ASSERT builds */
+    if(!checkImageValidity("Trade::AbstractImageConverter::convertToFile():", imageLevels))
+        return {};
+    #endif
+
     return doConvertToFile(imageLevels, filename);
 }
 

src/Magnum/Trade/AbstractImageConverter.h

@@ -565,6 +565,20 @@ checked by the implementation:
 -   The function @ref doConvertToFile(Containers::ArrayView<const CompressedImageView2D>, Containers::StringView)
     is called only if @ref ImageConverterFeature::ConvertCompressedLevels2DToFile
     is supported and equivalently for the 1D and 3D case.
+-   All @ref doConvertToData() and @ref doConvertToFile() functions taking a
+    single (compressed) image are called only if the image has a non-zero size
+    in all dimensions and the view is not @cpp nullptr @ce. Note that this does
+    not apply to @ref doConvert() --- there a zero-size image or a
+    @cpp nullptr @ce view may be a valid use case, and if the plugin
+    implementation doesn't work with any of those, it's expected to check that
+    on its own and produce a runtime error.
+-   All @ref doConvertToData() and @ref doConvertToFile() functions taking
+    multiple (compressed) images are called only the list has at least one
+    image, each of the images has a non-zero size, the views are not
+    @cpp nullptr @ce and additionally all views have the same pixel format.
+    Since file formats have varying requirements on image level sizes and their
+    order and some don't impose any requirements at all, the plugin
+    implementation is expected to check the sizes on its own.
 
 @m_class{m-block m-warning}
 
@@ -826,8 +840,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::Convert1DToData or
-         * @ref ImageConverterFeature::ConvertLevels1DToData is supported.
+         * @ref ImageConverterFeature::ConvertLevels1DToData is supported. The
-         * Returns data on success, @cpp nullptr @ce otherwise.
+         * image view is expected to not be @cpp nullptr @ce and to have a
+         * non-zero size. Returns data on success, @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(const CompressedImageView1D&),
          *      @ref convertToData(const ImageData1D&), @ref convert(),
          *      @ref convertToFile()
@@ -839,8 +854,10 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::Convert2DToData or
-         * @ref ImageConverterFeature::ConvertLevels2DToData is supported.
+         * @ref ImageConverterFeature::ConvertLevels2DToData is supported. The
-         * Returns data on success, @cpp nullptr @ce otherwise.
+         * image view is expected to not be @cpp nullptr @ce and to have a
+         * non-zero size in all dimensions. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(const CompressedImageView2D&),
          *      @ref convertToData(const ImageData2D&), @ref convert(),
          *      @ref convertToFile()
@@ -861,8 +878,10 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::Convert3DToData or
-         * @ref ImageConverterFeature::ConvertLevels3DToData is supported.
+         * @ref ImageConverterFeature::ConvertLevels3DToData is supported. The
-         * Returns data on success, @cpp nullptr @ce otherwise.
+         * image view is expected to not be @cpp nullptr @ce and to have a
+         * non-zero size in all dimensions. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(const CompressedImageView3D&),
          *      @ref convertToData(const ImageData3D&), @ref convert(),
          *      @ref convertToFile()
@@ -875,7 +894,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressed1DToData
          * or @ref ImageConverterFeature::ConvertCompressedLevels1DToData is
-         * supported. Returns data on success, @cpp nullptr @ce otherwise.
+         * supported. The image view is expected to not be @cpp nullptr @ce and
+         * to have a non-zero size. Returns data on success, @cpp nullptr @ce
+         * otherwise.
          * @see @ref features(), @ref convertToData(const ImageView1D&),
          *      @ref convertToData(const ImageData1D&), @ref convert(),
          *      @ref convertToFile()
@@ -888,7 +909,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressed2DToData
          * or @ref ImageConverterFeature::ConvertCompressedLevels2DToData is
-         * supported. Returns data on success, @cpp nullptr @ce otherwise.
+         * supported. The image view is expected to not be @cpp nullptr @ce and
+         * to have a non-zero size in all dimensions. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(const ImageView2D&),
          *      @ref convertToData(const ImageData2D&), @ref convert(),
          *      @ref convertToFile()
@@ -910,7 +933,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressed3DToData
          * or @ref ImageConverterFeature::ConvertCompressedLevels3DToData is
-         * supported. Returns data on success, @cpp nullptr @ce otherwise.
+         * supported. The image view is expected to not be @cpp nullptr @ce and
+         * to have a non-zero size in all dimensions. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(const ImageView3D&),
          *      @ref convertToData(const ImageData3D&), @ref convert(),
          *      @ref convertToFile()
@@ -967,7 +992,10 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertLevels1DToData
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
+         * with each view expected to not be @cpp nullptr @ce, to have a
+         * non-zero size, and all of them sharing the same pixel format. Note
+         * that certain converters may impose additional size and order
          * restrictions on the images, see documentation of a particular plugin
          * for more information. Returns data on success, @cpp nullptr @ce
          * otherwise.
@@ -983,10 +1011,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertLevels2DToData
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns data on success, @cpp nullptr @ce
+         * non-zero size in all dimensions, and all views sharing the same
-         * otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(Containers::ArrayView<const CompressedImageView2D>),
          *      @ref convert(), @ref convertToFile()
          */
@@ -999,10 +1030,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertLevels3DToData
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns data on success, @cpp nullptr @ce
+         * non-zero size in all dimensions, and all views sharing the same
-         * otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(Containers::ArrayView<const CompressedImageView3D>),
          *      @ref convert(), @ref convertToFile()
          */
@@ -1015,7 +1049,10 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressedLevels1DToData
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
+         * with each view expected to not be @cpp nullptr @ce, to have a
+         * non-zero size, and all views sharing the same pixel format. Note
+         * that certain converters may impose additional size and order
          * restrictions on the images, see documentation of a particular plugin
          * for more information. Returns data on success, @cpp nullptr @ce
          * otherwise.
@@ -1031,10 +1068,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressedLevels2DToData
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns data on success, @cpp nullptr @ce
+         * non-zero size in all dimensions, and all views sharing the same
-         * otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(Containers::ArrayView<const ImageView2D>),
          *      @ref convert(), @ref convertToFile()
          */
@@ -1047,10 +1087,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressedLevels3DToData
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns data on success, @cpp nullptr @ce
+         * non-zero size in all dimensions, and all views sharing the same
-         * otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns data on success,
+         * @cpp nullptr @ce otherwise.
          * @see @ref features(), @ref convertToData(Containers::ArrayView<const ImageView3D>),
          *      @ref convert(), @ref convertToFile()
          */
@@ -1063,8 +1106,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::Convert1DToFile or
-         * @ref ImageConverterFeature::Convert1DToData is supported. Returns
+         * @ref ImageConverterFeature::Convert1DToData is supported. The image
-         * @cpp true @ce on success, @cpp false @ce otherwise.
+         * view is expected to not be @cpp nullptr @ce and to have a non-zero
+         * size. Returns @cpp true @ce on success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(const CompressedImageView1D&, Containers::StringView),
          *      @ref convertToFile(const ImageData1D&, Containers::StringView),
          *      @ref convert(), @ref convertToData()
@@ -1076,8 +1120,10 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::Convert2DToFile or
-         * @ref ImageConverterFeature::Convert2DToData is supported. Returns
+         * @ref ImageConverterFeature::Convert2DToData is supported. The image
-         * @cpp true @ce on success, @cpp false @ce otherwise.
+         * view is expected to not be @cpp nullptr @ce and to have a non-zero
+         * size in all dimensions. Returns @cpp true @ce on success,
+         * @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(const CompressedImageView2D&, Containers::StringView),
          *      @ref convertToFile(const ImageData2D&, Containers::StringView),
          *      @ref convert(), @ref convertToData()
@@ -1099,8 +1145,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::Convert3DToFile or
-         * @ref ImageConverterFeature::Convert3DToData is supported. Returns
+         * @ref ImageConverterFeature::Convert3DToData is supported. The image
-         * @cpp true @ce on success, @cpp false @ce otherwise.
+         * view is expected to not be @cpp nullptr @ce and to have a non-zero
+         * size. Returns @cpp true @ce on success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(const CompressedImageView3D&, Containers::StringView),
          *      @ref convertToFile(const ImageData3D&, Containers::StringView),
          *      @ref convert(), @ref convertToData()
@@ -1113,8 +1160,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressed1DToFile
          * or @ref ImageConverterFeature::ConvertCompressed1DToData is
-         * supported. Returns @cpp true @ce on success, @cpp false @ce
+         * supported. The image view is expected to not be @cpp nullptr @ce and
-         * otherwise.
+         * to have a non-zero size in all dimensions. Returns @cpp true @ce on
+         * success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(const ImageView1D&, Containers::StringView),
          *      @ref convertToFile(const ImageData1D&, Containers::StringView),
          *      @ref convert(), @ref convertToData()
@@ -1127,8 +1175,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressed2DToFile
          * or @ref ImageConverterFeature::ConvertCompressed2DToData is
-         * supported. Returns @cpp true @ce on success, @cpp false @ce
+         * supported. The image view is expected to not be @cpp nullptr @ce and
-         * otherwise.
+         * to have a non-zero size in all dimensions. Returns @cpp true @ce on
+         * success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(const ImageView2D&, Containers::StringView),
          *      @ref convertToFile(const ImageData2D&, Containers::StringView),
          *      @ref convert(), @ref convertToData()
@@ -1151,8 +1200,9 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressed3DToFile
          * or @ref ImageConverterFeature::ConvertCompressed3DToData is
-         * supported. Returns @cpp true @ce on success, @cpp false @ce
+         * supported. The image view is expected to not be @cpp nullptr @ce and
-         * otherwise.
+         * to have a non-zero size in all dimensions. Returns @cpp true @ce on
+         * success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(const ImageView3D&, Containers::StringView),
          *      @ref convertToFile(const ImageData3D&, Containers::StringView),
          *      @ref convert(), @ref convertToData()
@@ -1222,7 +1272,10 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertLevels1DToFile
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
+         * with each view expected to not be @cpp nullptr @ce, to have a
+         * non-zero size, and all views sharing the same pixel format. Note
+         * that certain converters may impose additional size and order
          * restrictions on the images, see documentation of a particular plugin
          * for more information. Returns @cpp true @ce on success,
          * @cpp false @ce otherwise.
@@ -1238,10 +1291,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertLevels2DToFile
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns @cpp true @ce on success,
+         * non-zero size in all dimensions, and all views sharing the same
-         * @cpp false @ce otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns @cpp true @ce on
+         * success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(Containers::ArrayView<const CompressedImageView2D>, Containers::StringView),
          *      @ref convert(), @ref convertToData()
          */
@@ -1254,10 +1310,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertLevels3DToFile
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns @cpp true @ce on success,
+         * non-zero size in all dimensions, and all views sharing the same
-         * @cpp false @ce otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns @cpp true @ce on
+         * success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(Containers::ArrayView<const CompressedImageView3D>, Containers::StringView),
          *      @ref convert(), @ref convertToData()
          */
@@ -1270,7 +1329,10 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressedLevels1DToFile
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
+         * with each view expected to not be @cpp nullptr @ce, to have a
+         * non-zero size, and all views sharing the same pixel format. Note
+         * that certain converters may impose additional size and order
          * restrictions on the images, see documentation of a particular plugin
          * for more information. Returns @cpp true @ce on success,
          * @cpp false @ce otherwise.
@@ -1286,10 +1348,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressedLevels2DToFile
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns @cpp true @ce on success,
+         * non-zero size in all dimensions, and all views sharing the same
-         * @cpp false @ce otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns @cpp true @ce on
+         * success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(Containers::ArrayView<const ImageView2D>, Containers::StringView),
          *      @ref convert(), @ref convertToData()
          */
@@ -1302,10 +1367,13 @@ class MAGNUM_TRADE_EXPORT AbstractImageConverter: public PluginManager::Abstract
          * @m_since_latest
          *
          * Available only if @ref ImageConverterFeature::ConvertCompressedLevels3DToFile
-         * is supported. Note that certain converters may impose size and order
+         * is supported. The function expects at least one image to be passed,
-         * restrictions on the images, see documentation of a particular plugin
+         * with each view expected to not be @cpp nullptr @ce, to have a
-         * for more information. Returns @cpp true @ce on success,
+         * non-zero size in all dimensions, and all views sharing the same
-         * @cpp false @ce otherwise.
+         * pixel format. Note that certain converters may impose additional
+         * size and order restrictions on the images, see documentation of a
+         * particular plugin for more information. Returns @cpp true @ce on
+         * success, @cpp false @ce otherwise.
          * @see @ref features(), @ref convertToFile(Containers::ArrayView<const ImageView3D>, Containers::StringView),
          *      @ref convert(), @ref convertToData()
          */

src/MagnumPlugins/TgaImageConverter/Test/TgaImageConverterTest.cpp

@@ -112,14 +112,12 @@ TgaImageConverterTest::TgaImageConverterTest() {
 }
 
 void TgaImageConverterTest::wrongFormat() {
-    ImageView2D image{PixelFormat::RG8Unorm, {}, nullptr};
+    Containers::Pointer<AbstractImageConverter> converter = _converterManager.instantiate("TgaImageConverter");
 
+    const char data[4]{};
     std::ostringstream out;
     Error redirectError{&out};
-
+    CORRADE_VERIFY(!converter->convertToData(ImageView2D{PixelFormat::RG8Unorm, {1, 1}, data}));
-    Containers::Pointer<AbstractImageConverter> converter = _converterManager.instantiate("TgaImageConverter");
-    const auto data = converter->convertToData(image);
-    CORRADE_VERIFY(!data);
     CORRADE_COMPARE(out.str(), "Trade::TgaImageConverter::convertToData(): unsupported pixel format PixelFormat::RG8Unorm\n");
 }