set_content_update_callback — Sets the callback for content updates in buffer window.
set_content_update_callback( : : WindowHandle, CallbackFunction, CallbackContext : )
set_content_update_callback sets a callback CallbackFunction,
which is called whenever the contents of the buffer window
WindowHandle change.
The parameter CallbackContext is always passed to the
callback.
The type of CallbackFunction is: Herror callback(void *context)
On Windows systems, the __stdcall calling convention is used: Herror __stdcall callback(void *context)
The callback function must not call a HALCON operator. Doing so is undefined behavior. It is advised to perform only computationally inexpensive tasks in the callback, e.g., setting a flag or triggering an asynchronous operation.
In combination with the operators send_mouse_down_event,
send_mouse_up_event, and send_mouse_double_click_event,
set_content_update_callback can be used to create a buffer based
control for a GUI Toolkit (such as Qt), where the control passes mouse
events to the buffer, while the buffer notifies the control on changes by
calling the function CallbackFunction.
The control then can obtain the contents of the buffer with
dump_window_image and display them.
set_content_update_callback depends on the library libcanvas, which
might not be available on embedded systems.
WindowHandle (input_control) window → (handle)
Window handle.
CallbackFunction (input_control) pointer → (integer)
Callback for content updates.
CallbackContext (input_control) pointer → (integer / handle)
Parameter to CallbackFunction.
If the window exists and is a buffer window,
set_content_update_callback returns 2 (H_MSG_TRUE).
Foundation