Debug Overlays: Log Overlay
osu! framework provides in-picture debugging overlays, defined in osu.Framework.Input.FrameworkActionContainer. One of these overlays is the Log Overlay.
Control-F10 toggles the Log Overlay, which displays events logged by osu.Framework.Logging.Logger. Invoking Logger.Log will log messages that are able to be displayed in this stream.
By default, messages are logged using the logger level Verbose, which get omitted from the log overlay unless building with the DEBUG preprocessor flag. Any level higher than verbose will result in the messages being displayed through this overlay regardless.