Add a helper function to check if an extension is supported by file transform

include/OpenColorIO/OpenColorTransforms.h

@@ -1070,6 +1070,13 @@ class OCIOEXPORT FileTransform : public Transform
     static const char * GetFormatNameByIndex(int index);
     /// Get the LUT reader extension at index, return empty string if an invalid index is specified.
     static const char * GetFormatExtensionByIndex(int index);
+    /// Returns true if the extension corresponds to a format supported by FileTransform.
+    /// The argument is case-insensitive, and a leading dot, if present, is ignored.
+    /// Note that FileTransform will attempt all format readers on a given file until it is
+    /// successful, even files that contain an unsupported extension or no extension.
+    /// However, this function is useful for applications that want to know which files are likely
+    /// to be LUT files, based on their extension.
+    static bool IsFormatExtensionSupported(const char * extension);
 
     FileTransform & operator=(const FileTransform &) = delete;
     /// Do not use (needed only for pybind11).

src/OpenColorIO/transforms/FileTransform.cpp

@@ -158,6 +158,11 @@ const char * FileTransform::GetFormatExtensionByIndex(int index)
     return FormatRegistry::GetInstance().getFormatExtensionByIndex(FORMAT_CAPABILITY_READ, index);
 }
 
+bool FileTransform::IsFormatExtensionSupported(const char * extension)
+{
+    return FormatRegistry::GetInstance().isFormatExtensionSupported(extension);
+}
+
 std::ostream& operator<< (std::ostream& os, const FileTransform& t)
 {
     os << "<FileTransform ";
@@ -522,6 +527,32 @@ const char * FormatRegistry::getFormatExtensionByIndex(int capability, int index
     return "";
 }
 
+bool FormatRegistry::isFormatExtensionSupported(const char * extension) const
+{
+    // Early return false with an input of just the dot or invalid pointer.
+    if (!extension || !*extension || 0 == strcmp(extension, "."))
+    {
+        return false;
+    }
+
+    // If dot is present at the start, pointer arithmetic increment up by one to ignore that dot.
+    FileFormatVectorMap::const_iterator iter;
+    if (extension[0] == '.')
+    {
+        iter = m_formatsByExtension.find(StringUtils::Lower(extension + 1));
+    }
+    else
+    {
+        iter = m_formatsByExtension.find(StringUtils::Lower(extension));
+    }
+
+    if (iter != m_formatsByExtension.end())
+    {
+        return true;
+    }
+    return false;
+}
+
 ///////////////////////////////////////////////////////////////////////////
 
 FileFormat::~FileFormat()

src/OpenColorIO/transforms/FileTransform.h

@@ -137,6 +137,7 @@ class FormatRegistry
     int getNumFormats(int capability) const noexcept;
     const char * getFormatNameByIndex(int capability, int index) const noexcept;
     const char * getFormatExtensionByIndex(int capability, int index) const noexcept;
+    bool isFormatExtensionSupported(const char * extension) const;
 private:
     FormatRegistry();
     ~FormatRegistry();

src/bindings/python/transforms/PyFileTransform.cpp

@@ -72,7 +72,9 @@ void bindPyFileTransform(py::module & m)
         .def("getInterpolation", &FileTransform::getInterpolation, 
              DOC(FileTransform, getInterpolation))
         .def("setInterpolation", &FileTransform::setInterpolation, "interpolation"_a, 
-             DOC(FileTransform, setInterpolation));
+             DOC(FileTransform, setInterpolation))
+        .def_static("IsFormatExtensionSupported", &FileTransform::IsFormatExtensionSupported, "extension"_a,
+             DOC(FileTransform, IsFormatExtensionSupported));
 
     defRepr(clsFileTransform);
 

tests/cpu/transforms/FileTransform_tests.cpp

@@ -290,6 +290,20 @@ OCIO_ADD_TEST(FileTransform, format_by_index)
     ValidateFormatByIndex(formatRegistry, OCIO::FORMAT_CAPABILITY_READ);
 }
 
+OCIO_ADD_TEST(FileTransform, is_format_extension_supported)
+{
+    OCIO::FormatRegistry & formatRegistry = OCIO::FormatRegistry::GetInstance();
+    OCIO_CHECK_EQUAL(formatRegistry.isFormatExtensionSupported("foo"), false);
+    OCIO_CHECK_EQUAL(formatRegistry.isFormatExtensionSupported("bar"), false);
+    OCIO_CHECK_EQUAL(formatRegistry.isFormatExtensionSupported("."), false);
+    OCIO_CHECK_ASSERT(formatRegistry.isFormatExtensionSupported("cdl"));
+    OCIO_CHECK_ASSERT(formatRegistry.isFormatExtensionSupported(".cdl"));
+    OCIO_CHECK_ASSERT(formatRegistry.isFormatExtensionSupported("Cdl"));
+    OCIO_CHECK_ASSERT(formatRegistry.isFormatExtensionSupported(".Cdl"));
+    OCIO_CHECK_ASSERT(formatRegistry.isFormatExtensionSupported("3dl"));
+    OCIO_CHECK_ASSERT(formatRegistry.isFormatExtensionSupported(".3dl"));
+}
+
 OCIO_ADD_TEST(FileTransform, validate)
 {
     OCIO::FileTransformRcPtr tr = OCIO::FileTransform::Create();

tests/python/FileTransformTest.py

@@ -85,6 +85,20 @@ def test_cdlstyle(self):
             with self.assertRaises(TypeError):
                 self.tr.setCDLStyle(invalid)
 
+    def test_is_format_extension_supported(self):
+        """
+        Test the IsFormatExtensionSupported() method.
+        """
+        self.assertFalse(self.tr.IsFormatExtensionSupported('foo'))
+        self.assertFalse(self.tr.IsFormatExtensionSupported('bar'))
+        self.assertFalse(self.tr.IsFormatExtensionSupported('.'))
+        self.assertTrue(self.tr.IsFormatExtensionSupported('cdl'))
+        self.assertTrue(self.tr.IsFormatExtensionSupported('.cdl'))
+        self.assertTrue(self.tr.IsFormatExtensionSupported('Cdl'))
+        self.assertTrue(self.tr.IsFormatExtensionSupported('.Cdl'))
+        self.assertTrue(self.tr.IsFormatExtensionSupported('3dl'))
+        self.assertTrue(self.tr.IsFormatExtensionSupported('.3dl'))
+
     def test_getformats(self):
         """
         Test the getFormats() method.