It is common to group activities. We have used this feature in the examples of constrains. There is no special type for activity bars that are used to illustrate grouping. The common way of illustrating this (as have been used above) is to add "half" a triangle marker at both ends of the bar. The special provision that JpGraph does is that if you add a left or right marker of type MARK_LEFTTRIANGLE or MARK_RIGHTTRIANGLE those triangles will be drawn under the bars to give the effect as show in the examples above. In the example above we also have made the grouping bars have slightly less heigh since the end triangles will visually "grow" the bar.
So to get the effect we want for a group bar we have to use the two lines:
$groupbar->
leftMark->
SetType(
"MARK_LEFTTRIANGLE");
$groupbar
->rightMark->SetType(
"MARK_RIGHTTRIANGLE")
As of the current version There is not yet any formatting support to accomplish the effect of indentation for the titles so this is accomplished by using a fixed width font and adding spaces in front of the title.