Softimage SDK Programmer's Guide > Customizing Softimage using the SDK > Custom Events >

# What is an Event?

In Softimage, user actions such as creating new scenes, rendering frames, and pressing keys trigger events. For example, when a user creates a new scene, the OnBeginNewScene and OnEndNewScene events are triggered.

You can write special functions to handle events, and register these functions with Softimage as event handlers. Whenever an event is triggered, Softimage calls the event handlers registered for that event.

For example, the following demonstrates how to launch a custom file importer when a file matching a specific type (file format/extension) is dropped in the scene. This is done by using a drag and drop event to call the custom importer command when the correct file extension is detected (see the siOnDragAndDropEvent_OnEvent callback below):

## Python Example: Self-installing drag-and-drop event handler

    #
    # Drag and drop events are intentionally disabled by default for performance, so the
    # drag portion of the event gives you the opportunity to enable drop detection while
    # the drop portion is where you can perform the desired action on the item.
    #
    import win32com.client
    from win32com.client import constants as c	# to use Softimage enums and constants
    import re					# for regular expressions

    # Registration
    def XSILoadPlugin( in_reg ):
    	in_reg.Author = "SDK Doc"
    	in_reg.Name = "ImportBooFile Plug-in"
    	in_reg.RegisterCommand("ImportBoo","ImportBoo")
    	in_reg.RegisterEvent("siOnDragAndDropEvent",c.siOnDragAndDrop)
    	return 1

    # Set up custom importer command
    def ImportBoo_Init( in_ctxt ):
    	oCmd = in_ctxt.Source
    	oCmd.ReturnValue = 1
    	oArgs = oCmd.Arguments
    	oArgs.Add("in_filename",c.siArgumentInput)
    	return 1

    # Implementation of the importer
    def ImportBoo_Execute( in_filename ):
    	Application.LogMessage( "Importing " + in_filename )
    	#
    	# This is where you either implement the importer or call the implementation
    	#
    	return 1

    # Callback for the siOnDragAndDropEvent event. The important thing to remember is that
    # the drag and drop event is a two-stage action: dragging and dropping. When the item
    # is being dragged, you can check to see whether it is something you want to pay
    # attention to after it's dropped (ie., if it's the right kind of file). If it is, you
    # enable the DragSourceSupported attribute so that when the file is actually dropped,
    # the siSourceDropAction is fired and you can call the importer.
    def siOnDragAndDropEvent_OnEvent( in_ctxt ):
    	action = in_ctxt.GetAttribute("DragAndDropAction")
    	file = in_ctxt.GetAttribute("DragSource")

    	if ( action == c.siSourceDragAction ) :
    		# When the file is dragged, check to see if it's got the right extension
    		pattrn = re.compile( "\.boo$", re.I ) # equivalent to JScript's /\.boo$/i
    		if ( pattrn.search(file) ) :
    			# Enable the drop action via the DragSourceSupported
    			# context attribute if it's got the right extension
    			in_ctxt.SetAttribute( "DragSourceSupported", 1 )
    		else :
    			# Otherwise disable the drop action
    			in_ctxt.SetAttribute( "DragSourceSupported", 0 )
    	else : # action == c.siSourceDropAction
    		# When file is , dropped, run your custom importer command
    		ImportBoo_Execute( file )

         return 1

    # Output:
    # INFO : Importing <user_location>\Application\Plugins\test.boo

You can also see the Project Selector example that shows how to use the change project event (siOnChangeProject). This example is located in the examples folder of the Softimage SDK installation directory.