How can I get the height of a timeitem? or the height of a treeitem?
And how can I get the count from all visible treeitems?
You can use the IphGantRow3.GetRect method to get the rectangle of the GanttRow, to get the x-coordinates you must use the DateToPixel on Start and stop.
To get all visible tree items; Iterate thru Gantt.RowList and get the IphGantRow3.GetRect for each item check if the rectangle is -1,-1,-1,-1 then that row is not on screen.