DebugTools: make CommpareImage usable with CORRADE_COMPARE_AS().

doc/changelog.dox

@@ -59,6 +59,13 @@ See also:
     recognizes also uppercase file extensions (see
     [mosra/magnum#312](https://github.com/mosra/magnum/pull/312))
 
+@subsubsection changelog-latest-changes-debugtools DebugTools library
+
+-   @ref DebugTools::CompareImage, @ref DebugTools::CompareImageToFile and
+    other variants are now usable directly through @ref CORRADE_COMPARE_AS(),
+    no need to pass an explicit instance to @ref CORRADE_COMPARE_WITH() when
+    just the default parameters are needed
+
 @subsubsection changelog-latest-changes-platform Platform libraries
 
 -   On OpenGL ES builds, @ref Platform::Sdl2Application now tells SDL whether

src/Magnum/DebugTools/CompareImage.h

@@ -100,6 +100,8 @@ template<> class MAGNUM_DEBUGTOOLS_EXPORT Comparator<Magnum::DebugTools::Compare
     public:
         explicit Comparator(Magnum::Float maxThreshold, Magnum::Float meanThreshold): Magnum::DebugTools::Implementation::ImageComparatorBase{nullptr, maxThreshold, meanThreshold} {}
 
+        /*implicit*/ Comparator(): Comparator{0.0f, 0.0f} {}
+
         bool operator()(const Magnum::ImageView2D& actual, const Magnum::ImageView2D& expected) {
             return Magnum::DebugTools::Implementation::ImageComparatorBase::operator()(actual, expected);
         }
@@ -120,6 +122,8 @@ template<> class MAGNUM_DEBUGTOOLS_EXPORT Comparator<Magnum::DebugTools::Compare
     public:
         explicit Comparator(PluginManager::Manager<Magnum::Trade::AbstractImporter>* manager, Magnum::Float maxThreshold, Magnum::Float meanThreshold): Magnum::DebugTools::Implementation::ImageComparatorBase{manager, maxThreshold, meanThreshold} {}
 
+        /*implicit*/ Comparator(): Comparator{nullptr, 0.0f, 0.0f} {}
+
         bool operator()(const Magnum::ImageView2D& actual, const std::string& expected) {
             return Magnum::DebugTools::Implementation::ImageComparatorBase::operator()(actual, expected);
         }
@@ -129,6 +133,8 @@ template<> class MAGNUM_DEBUGTOOLS_EXPORT Comparator<Magnum::DebugTools::Compare
     public:
         explicit Comparator(PluginManager::Manager<Magnum::Trade::AbstractImporter>* manager, Magnum::Float maxThreshold, Magnum::Float meanThreshold): Magnum::DebugTools::Implementation::ImageComparatorBase{manager, maxThreshold, meanThreshold} {}
 
+        /*implicit*/ Comparator(): Comparator{nullptr, 0.0f, 0.0f} {}
+
         bool operator()(const std::string& actual, const Magnum::ImageView2D& expected) {
             return Magnum::DebugTools::Implementation::ImageComparatorBase::operator()(actual, expected);
         }