AnyImageImporter: fall back to BasisImporter if KtxImporter isn't found.

Final piece of the KTX2/Basis delegation chain that I somehow forgot to
implement.

src/MagnumPlugins/AnyImageImporter/AnyImageImporter.cpp

@@ -94,9 +94,31 @@ void AnyImageImporter::doOpenFile(const Containers::StringView filename) {
         plugin = "JpegImporter"_s;
     else if(normalizedExtension == ".jp2"_s)
         plugin = "Jpeg2000Importer"_s;
-    else if(normalizedExtension == ".ktx2"_s)
+    else if(normalizedExtension == ".ktx2"_s) {
         plugin = "KtxImporter"_s;
-    else if(normalizedExtension == ".mng"_s)
+
+        /* KtxImporter delegates to BasisImporter in case the file is
+           Basis-compressed, so that's a good default choice. However, if it
+           isn't available, we should try delegating to BasisImporter instead,
+           so people that have just Basis-compressed KTX files don't need to
+           have KtxImporter as well.
+
+           BasisImporter unfortunately can't handle non-Basis-compressed KTX
+           files, so in case people have just BasisImporter and not
+           KtxImporter, it'll fail, but with a clear message suggesting to use
+           KtxImporter. If neither BasisImporter would be available, it'd fail
+           too (complaining that KtxImporter isn't available), so the behavior
+           is roughly the same.
+
+           Further discussion and reasoning here:
+           https://github.com/mosra/magnum-plugins/pull/112#discussion_r734976174 */
+        if(manager()->loadState("KtxImporter"_s) == PluginManager::LoadState::NotFound &&
+           manager()->loadState("BasisImporter"_s) != PluginManager::LoadState::NotFound) {
+            if(flags() & ImporterFlag::Verbose)
+                Debug{} << "Trade::AnyImageImporter::openFile(): KtxImporter not found, trying a fallback";
+            plugin = "BasisImporter"_s;
+        }
+    } else if(normalizedExtension == ".mng"_s)
         plugin = "MngImporter"_s;
     else if(normalizedExtension == ".pbm"_s)
         plugin = "PbmImporter"_s;
@@ -200,10 +222,19 @@ void AnyImageImporter::doOpenData(Containers::Array<char>&& data, DataFlags) {
     else if(dataString.hasPrefix("\xff\xd8\xff"_s))
         plugin = "JpegImporter"_s;
     /* https://github.khronos.org/KTX-Specification/#_identifier */
-    else if(dataString.hasPrefix("\xabKTX 20\xbb\r\n\x1a\n"_s))
+    else if(dataString.hasPrefix("\xabKTX 20\xbb\r\n\x1a\n"_s)) {
         plugin = "KtxImporter"_s;
+
+        /* Same logic as in doOpenFile() for *.ktx2 files, see above for more
+           information */
+        if(manager()->loadState("KtxImporter"_s) == PluginManager::LoadState::NotFound &&
+           manager()->loadState("BasisImporter"_s) != PluginManager::LoadState::NotFound) {
+            if(flags() & ImporterFlag::Verbose)
+                Debug{} << "Trade::AnyImageImporter::openData(): KtxImporter not found, trying a fallback";
+            plugin = "BasisImporter"_s;
+        }
     /* https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_header */
-    else if(dataString.hasPrefix("\x89PNG\x0d\x0a\x1a\x0a"_s))
+    } else if(dataString.hasPrefix("\x89PNG\x0d\x0a\x1a\x0a"_s))
         plugin = "PngImporter"_s;
     /* http://paulbourke.net/dataformats/tiff/,
        http://paulbourke.net/dataformats/tiff/tiff_summary.pdf */

src/MagnumPlugins/AnyImageImporter/AnyImageImporter.h

@@ -79,7 +79,8 @@ Supported formats:
 -   JPEG 2000 (`*.jp2`), loaded with any plugin that provides
     `Jpeg2000Importer`
 -   KTX2 (`*.ktx2` or data with corresponding signature), loaded with
-    @ref KtxImporter or any other plugin that provides it
+    @ref KtxImporter or any other plugin that provides it. If not found,
+    @ref BasisImporter is tried as a fallback.
 -   Multiple-image Network Graphics (`*.mng`), loaded with any plugin that
     provides `MngImporter`
 -   Portable Bitmap (`*.pbm`), loaded with any plugin that provides `PbmImporter`

src/MagnumPlugins/AnyImageImporter/Test/AnyImageImporterTest.cpp

@@ -29,6 +29,7 @@
 #include <Corrade/Containers/StringView.h>
 #include <Corrade/PluginManager/Manager.h>
 #include <Corrade/TestSuite/Tester.h>
+#include <Corrade/TestSuite/Compare/String.h>
 #include <Corrade/Utility/ConfigurationGroup.h>
 #include <Corrade/Utility/DebugStl.h>
 #include <Corrade/Utility/FormatStl.h>
@@ -51,6 +52,9 @@ struct AnyImageImporterTest: TestSuite::Tester {
     void load3D();
     void detect();
 
+    void ktxBasisFallbackFile();
+    void ktxBasisFallbackData();
+
     void unknownExtension();
     void unknownSignature();
     void emptyData();
@@ -129,6 +133,31 @@ constexpr struct {
     /* Not testing everything, just the most important ones */
 };
 
+const struct {
+    const char* name;
+    bool ktxImporterPresent;
+    bool basisImporterPresent;
+    bool verbose;
+    const char* expectedMessage;
+} KtxBasisFallbackData[]{
+    {"both KtxImporter and BasisImporter present", true, true, true,
+        "Trade::AnyImageImporter::{}(): using KtxImporter\n"},
+    {"only KtxImporter present", true, false, true,
+        "Trade::AnyImageImporter::{}(): using KtxImporter\n"},
+    {"only BasisImporter present", false, true, true,
+        "Trade::AnyImageImporter::{0}(): KtxImporter not found, trying a fallback\n"
+        "Trade::AnyImageImporter::{0}(): using BasisImporter\n"},
+    {"only BasisImporter present, verbose output disabled", false, true, false,
+        nullptr},
+    {"neither present", false, false, true,
+        #ifndef CORRADE_PLUGINMANAGER_NO_DYNAMIC_PLUGIN_SUPPORT
+        "PluginManager::Manager::load(): plugin KtxImporter is not static and was not found in nonexistent\n"
+        #else
+        "PluginManager::Manager::load(): plugin KtxImporter was not found\n"
+        #endif
+        "Trade::AnyImageImporter::{}(): cannot load the KtxImporter plugin"}
+};
+
 using namespace Containers::Literals;
 
 const struct {
@@ -173,6 +202,10 @@ AnyImageImporterTest::AnyImageImporterTest() {
     addInstancedTests({&AnyImageImporterTest::detect},
         Containers::arraySize(DetectData));
 
+    addInstancedTests({&AnyImageImporterTest::ktxBasisFallbackFile,
+                       &AnyImageImporterTest::ktxBasisFallbackData},
+        Containers::arraySize(KtxBasisFallbackData));
+
     addTests({&AnyImageImporterTest::unknownExtension});
 
     addInstancedTests({&AnyImageImporterTest::unknownSignature},
@@ -310,6 +343,85 @@ void AnyImageImporterTest::detect() {
     #endif
 }
 
+void AnyImageImporterTest::ktxBasisFallbackFile() {
+    auto&& data = KtxBasisFallbackData[testCaseInstanceId()];
+    setTestCaseDescription(data.name);
+
+    PluginManager::Manager<AbstractImporter> manager{MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR};
+    #ifdef ANYIMAGEIMPORTER_PLUGIN_FILENAME
+    CORRADE_VERIFY(manager.load(ANYIMAGEIMPORTER_PLUGIN_FILENAME) & PluginManager::LoadState::Loaded);
+    #endif
+
+    /* Catch also ABI and interface mismatch errors */
+    if(data.ktxImporterPresent && !(manager.load("KtxImporter") & PluginManager::LoadState::Loaded))
+        CORRADE_SKIP("KtxImporter plugin can't be loaded.");
+    if(data.basisImporterPresent && !(manager.load("BasisImporter") & PluginManager::LoadState::Loaded))
+        CORRADE_SKIP("BasisImporter plugin can't be loaded.");
+
+    /* Set invalid plugin directory to ensure the remaining plugins don't get
+       loaded after this point */
+    #ifndef CORRADE_PLUGINMANAGER_NO_DYNAMIC_PLUGIN_SUPPORT
+    manager.setPluginDirectory("nonexistent");
+    #endif
+
+    Containers::Pointer<AbstractImporter> importer = manager.instantiate("AnyImageImporter");
+    if(data.verbose)
+        importer->setFlags(ImporterFlag::Verbose);
+
+    std::ostringstream out;
+    Debug redirectOutput{&out};
+    Error redirectError{&out};
+    /* We don't care if the file opens (it won't if BasisImporter isn't
+       present), just verifying if correct plugin got picked by checking the
+       message. */
+    importer->openFile(Utility::Path::join(ANYIMAGEIMPORTER_TEST_DIR, "basis.ktx2"));
+    if(data.expectedMessage) CORRADE_COMPARE_AS(out.str(),
+        Utility::formatString(data.expectedMessage, "openFile"),
+        TestSuite::Compare::StringHasPrefix);
+    else CORRADE_COMPARE(out.str(), "");
+}
+
+void AnyImageImporterTest::ktxBasisFallbackData() {
+    auto&& data = KtxBasisFallbackData[testCaseInstanceId()];
+    setTestCaseDescription(data.name);
+
+    PluginManager::Manager<AbstractImporter> manager{MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR};
+    #ifdef ANYIMAGEIMPORTER_PLUGIN_FILENAME
+    CORRADE_VERIFY(manager.load(ANYIMAGEIMPORTER_PLUGIN_FILENAME) & PluginManager::LoadState::Loaded);
+    #endif
+
+    /* Catch also ABI and interface mismatch errors */
+    if(data.ktxImporterPresent && !(manager.load("KtxImporter") & PluginManager::LoadState::Loaded))
+        CORRADE_SKIP("KtxImporter plugin can't be loaded.");
+    if(data.basisImporterPresent && !(manager.load("BasisImporter") & PluginManager::LoadState::Loaded))
+        CORRADE_SKIP("BasisImporter plugin can't be loaded.");
+
+    /* Set invalid plugin directory to ensure the remaining plugins don't get
+       loaded after this point */
+    #ifndef CORRADE_PLUGINMANAGER_NO_DYNAMIC_PLUGIN_SUPPORT
+    manager.setPluginDirectory("nonexistent");
+    #endif
+
+    Containers::Pointer<AbstractImporter> importer = manager.instantiate("AnyImageImporter");
+    if(data.verbose)
+        importer->setFlags(ImporterFlag::Verbose);
+
+    Containers::Optional<Containers::Array<char>> read = Utility::Path::read(Utility::Path::join(ANYIMAGEIMPORTER_TEST_DIR, "basis.ktx2"));
+    CORRADE_VERIFY(read);
+
+    std::ostringstream out;
+    Debug redirectOutput{&out};
+    Error redirectError{&out};
+    /* We don't care if the file opens (it won't if BasisImporter isn't
+       present), just verifying if correct plugin got picked by checking the
+       message. */
+    importer->openData(*read);
+    if(data.expectedMessage) CORRADE_COMPARE_AS(out.str(),
+        Utility::formatString(data.expectedMessage, "openData"),
+        TestSuite::Compare::StringHasPrefix);
+    else CORRADE_COMPARE(out.str(), "");
+}
+
 void AnyImageImporterTest::unknownExtension() {
     Containers::Pointer<AbstractImporter> importer = _manager.instantiate("AnyImageImporter");
 

src/MagnumPlugins/AnyImageImporter/Test/CMakeLists.txt

@@ -56,6 +56,8 @@ corrade_add_test(AnyImageImporterTest AnyImageImporterTest.cpp
         # Generated by AnyImageConverterTest::convert{1D,3D}()
         1d.ktx2
         3d.ktx2
+        # rgb.ktx2 from BasisImporter test data (in magnum-plugins), renamed
+        basis.ktx2
         gray.jpg
         image.exr
         image.tiff