setTrackbarPos

setTrackbarPos is a function in OpenCV used to set the position of a trackbar that has been created in a window. It provides a way to change the trackbar value programmatically to reflect data or user interface changes without requiring user interaction.

The function typically takes three parameters: the name of the trackbar, the name of the window that owns the trackbar, and the desired position value. The position must lie within the trackbar’s defined range, usually from 0 to the maximum value set when the trackbar was created with createTrackbar. The effect is that the trackbar’s displayed position and its internal value are updated accordingly.

One important behavioral note is that setTrackbarPos does not automatically invoke the trackbar’s callback function. If a callback was supplied when creating the trackbar and you need it to run after programmatic changes, you must call the callback manually or trigger the related logic separately.

Returnwise, setTrackbarPos is a void function, and it silently does nothing if the specified trackbar or window does not exist or if the position is outside the allowed range (though out-of-range values should normally be avoided by proper range management).

In usage terms, setTrackbarPos is commonly used after loading data or applying filters to synchronize the UI with the current state of the program. Related functions include createTrackbar to create a trackbar and getTrackbarPos to query its current value.

See also: createTrackbar, getTrackbarPos, cv::setTrackbarPos in C++ bindings.