I wrote this patch because I missed a visual feedback when changing the volume with the multimedia keys of my keyboard.
The patch adds the commands "raisevolume", "lowervolume" and "mute" to the lxpanelctl tool. With these commands lxpanelctl can be used in the openbox configuration file instead of amixer to handle the multimedia keys.
If invoked by lxpanelctl, the commands are passed on by the panel to the volumealsa plugin, which then changes the volume and shows its popup window for three seconds. To achieve the possibility of sending commands from the panel to external plugins, I added a function pointer called "handle_command(int cmd, void *p)" to the Plugin structure (with p being the plugin itself). This function pointer might also be used by other plugins to deal with external events.
I hope this feature is useful for other people out there.