set_content_update_callback — Sets the callback for content updates in buffer window.
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.
Callback for content updates.
Parameter to CallbackFunction.
If the window exists and is a buffer window, set_content_update_callback returns 2 (H_MSG_TRUE).