10.6 Positioning objects in the Gantt plot

Bars and Milestones need both a vertical position and a horizontal position. The horizontal start position is specified as a date, e.g. "2001-06-23", and the vertical positions are specified as a number [0,1,2,3,...]. This vertical number indicates the position from the top where the object should be placed. To understand this you might imagine a number of "invisible" horizontal bands with a certain height. If you specify 0 as the vertical position the bar will be placed in the first band, specify 3 and the bar will be placed in the fourth band and so on.

It is perfectly legal, and perhaps even desirable to leave "gaps" when laying out bands to group related activities. So, for example you could have three activities/bars at positions 1,2,3 and then another 2 bars at position 6,7 leaving band 0,4,5 empty.

All these "invisible bands" have the same height (equ-spaced). The height of each band is automatically determined and depends on both the method of layout ( as specified by (GanttChart::SetLayout()) and the individual heights of the individual bars and titles. The rules are quite simple:

• If you use layout=GANTT_FROMTOP (the default and most common) the height will equal the height (+ a margin) of the highest gantt bar. The height calculation of each bar takes into account both the actual bar, the title, and any left- right-marks (more about that later) that may be present. The name "fromtop" refers to that when you have explicitly specified a height the bars will usually be added from band 0 and onwards and hence being added from the top. (This might leave empty space at the bottom of the plot area in the graph if the height of the graph has been explicitly specified).
• If you use layout=GANTT_EVEN the bars are evenly (hence the name) spread out over the available height in the gantt chart and no consideration is taken of the individual bars heights. Note that if you use automatic sizing you cant use even layout. It just doesn't make sense. Even layout is for those cases when you deliberately specify a very large image and want the bars evenly distributed using the full height.