Ability to check that extension is supported in particular version.

Will be used in shader compilation when we need to decide based on
both GLSL version used *and* extension support.

src/Context.h

@@ -317,8 +317,9 @@ class MAGNUM_EXPORT Context {
          * @endcode
          *
          * If no version from the list is supported, returns lowest available
-         * OpenGL version (@ref Version::GL210 for desktop OpenGL, @ref Version::GLES200
-         * for OpenGL ES).
+         * OpenGL version (@ref Version::GL210 for desktop OpenGL,
+         * @ref Version::GLES200 for OpenGL ES).
+         * @see @ref isExtensionSupported(Version)
          */
         Version supportedVersion(std::initializer_list<Version> versions) const;
 
@@ -342,6 +343,25 @@ class MAGNUM_EXPORT Context {
             return isVersionSupported(T::coreVersion()) || (isVersionSupported(T::requiredVersion()) && extensionStatus[T::Index]);
         }
 
+        /**
+         * @brief Whether given extension is supported in given version
+         *
+         * Similar to @ref isExtensionSupported(), but checks also that the
+         * minimal required version of the extension is larger or equal to
+         * @p version. Useful mainly in shader compilation when the decisions
+         * depend on selected GLSL version, for example:
+         * @code
+         * const Version version = Context::current()->supportedVersion({Version::GL320, Version::GL300, Version::GL210});
+         * if(Context::current()->isExtensionSupported<Extensions::GL::ARB::explicit_attrib_location>(version)) {
+         *     // Called only if ARB_explicit_attrib_location is supported
+         *     // *and* version is higher than GL 3.1
+         * }
+         * @endcode
+         */
+        template<class T> bool isExtensionSupported(Version version) const {
+            return T::coreVersion() <= version || (T::requiredVersion() <= version && extensionStatus[T::Index]);
+        }
+
         /**
          * @brief Whether given extension is supported
          *

src/Test/ContextTest.cpp

@@ -37,6 +37,7 @@ class ContextTest: public AbstractOpenGLTester {
         void supportedExtension();
         void unsupportedExtension();
         void pastExtension();
+        void versionDependentExtension();
 };
 
 ContextTest::ContextTest() {
@@ -44,7 +45,8 @@ ContextTest::ContextTest() {
               &ContextTest::versionList,
               &ContextTest::supportedExtension,
               &ContextTest::unsupportedExtension,
-              &ContextTest::pastExtension});
+              &ContextTest::pastExtension,
+              &ContextTest::versionDependentExtension});
 }
 
 void ContextTest::version() {
@@ -114,6 +116,19 @@ void ContextTest::pastExtension() {
     #endif
 }
 
+void ContextTest::versionDependentExtension() {
+    #ifndef MAGNUM_TARGET_GLES
+    CORRADE_COMPARE(Extensions::GL::ARB::get_program_binary::requiredVersion(), Version::GL300);
+    if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::get_program_binary>())
+        CORRADE_SKIP(Extensions::GL::ARB::get_program_binary::string() + std::string("extension isn't supported, can't test"));
+
+    CORRADE_VERIFY(Context::current()->isExtensionSupported<Extensions::GL::ARB::get_program_binary>(Context::current()->version()));
+    CORRADE_VERIFY(!Context::current()->isExtensionSupported<Extensions::GL::ARB::get_program_binary>(Version::GL210));
+    #else
+    CORRADE_SKIP("No OpenGL ES 3.0-only extensions exist yet");
+    #endif
+}
+
 }}
 
 CORRADE_TEST_MAIN(Magnum::Test::ContextTest)