gl: don't do direct rendering below OpenGL 3.0

See comments.

modules/video_output/opengl/converters.c

@@ -1125,7 +1125,14 @@ generic_init(opengl_tex_converter_t *tc, bool allow_dr)
         const bool has_bs =
             HasExtension(tc->glexts, "GL_ARB_buffer_storage") ||
             HasExtension(tc->glexts, "GL_EXT_buffer_storage");
-        supports_map_persistent = has_pbo && has_bs && tc->api->BufferStorage
+
+        /* Ensure we do direct rendering with OpenGL 3.0 or higher. Indeed,
+         * persistent mapped buffers seems to be slow with OpenGL 2.1 drivers
+         * and bellow. This may be caused by OpenGL compatibility layer. */
+        const unsigned char *ogl_version = glGetString(GL_VERSION);
+        const bool glver_ok = strverscmp((const char *)ogl_version, "3.0") >= 0;
+
+        supports_map_persistent = glver_ok && has_pbo && has_bs && tc->api->BufferStorage
             && tc->api->MapBufferRange && tc->api->FlushMappedBufferRange
             && tc->api->UnmapBuffer && tc->api->FenceSync && tc->api->DeleteSync
             && tc->api->ClientWaitSync;