Python Callback Systemedit

The CallbackExt extension provides Python callback functionality to custom components. All callbacks will be passed a single argument containing an info dictionary. Callbacks can be defined in the DAT named in the Callback DAT parameter. To report all callbacks to the textport, turn on the Print Callbacks toggle parameter. The Callback DAT and Print Callbacks parameters are often found on the Callbacks parameter page, but their location can be customized.

The info dictionary always contains an "ownerComp" key. It will also have a "callbackName" key holding the callback name. It will sometimes contain an "about" key, describing the callback, and should always contain this key if a return value is expected. Generally, callbacks are called AFTER the internal method they are associated with, to allow over-riding of whatever that method does.

TouchDesigner's Python callback system uses the CallbacksExt Extension.

Adding CallbackExt to a Componentedit

The standard way to add CallbackExt to a component is to use the palette:callbacksHelper component.

Methodsedit

DoCallback(callbackName, callbackInfo=None, callbackOrDat=None) → callbackInfo | None

If it exists, call the named callback in ownerComp.par.Callbackdat and return callbackInfo with the callback's return value placed in callbackInfo['returnValue'].

If a user callback was found, returns callbackInfo with the callback return value in callbackInfo['returnValue']. If no callback found, this returns None.

If ownerComp has a parameter called Printcallbacks, and that parameter is True, callback debug info will be printed to textport.

DoCallbacks is the main function you will use when implementing a callback system with CallbacksExt.

• callbackName - Name of callback to be called
• callbackInfo - (Optional) an object that will be passed to the callback as its sole argument. Default is a dictionary with ownerComp and callbackName keys. This object can be of any type. If a dictionary is passed and it doesn't contain "ownerComp" or "callbackName" keys, those keys will be added automatically..
• callbackOrDat - (Optional) a DAT or function to pass callbacks to. If this is a DAT, the callback will be called from the named callback in the DAT. If this is a function, the callback will be called directly. If this is None (default) the callback will be called from the callback DAT set in ownercomp's callbackDAT parameter.

EditCallbackDAT()

Edit the Callback DAT in default editor

SetAssignedCallback(callbackName, callback, details=None)

Note: This is an expert feature, not for general use.

An assigned callback sets the callback system up to call a specified python method rather than searching a callback DAT. When this is set, <callback> will be called by default when DoCallback(<callbackName>) is called.

• callbackName - Name of callback to be called
• callback - The callback or None to remove the assigned callback
• details - Optional extra info to be passed in the ['details'] key of infoDict when callback is called.

PassCallbacksTo(passTarget)

Note: This is an expert feature, not for general use.

Set a target DAT or function for passing callbacks that are not found in the callback DAT. This allows you to set up a backup behavior for when callbacks are not found in the callback DAT.

• passTarget - a DAT or function

PassOnCallback(info)

Note: This is an expert feature, not for general use.

Pass this callback to PassTarget. This is meant to be called from within a callback to intentionally pass it on. Use PassCallbacksTo to set PassTarget.

• info - the callback's info object

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Membersedit

CallbackDat

Get or set the dat containing user callbacks. This will set the value of the Callbackdat parameter as well, if it exists.

PrintCallbacks

Get or set whether to print callback info to the Textport

PassTarget

The backup DAT or function assigned in the PassTargetTo method above.