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<H2><A NAME="9_15">9.15 Adding constrains between your activities</A></H2>
<P> With Gantt charts there is often the need to illustrate constrains
 between one or several activities. One of the most common constrain is
 that on activity can't start before an other activity finish.</P>
<P> JpGraph support visualizing the following types of constrains</P>
<UL>
<LI> Start to End</LI>
<LI> Start to Start</LI>
<LI> End to Start</LI>
<LI> End to End</LI>
</UL>
<P> An example will clarify how to specify a constrain between two
 activities.</P>
<P> Assume that we start with the Gantt schema as illustrated below<DIV class="example">
<BR> <A href="exframes/frame_ganttconstrainex0.html" target="blank"><IMG border="0"
HEIGHT="231"       src="img/img/img/img/img/img/ganttconstrainex0.png" WIDTH="523"></A>
<BR><B>Figure 171:</B> The original Gantt schema we wich to add
 constrains to <A href="exframes/frame_ganttconstrainex0.html" target="blank">
[src]</A>&nbsp;
<P></P>
</DIV></P>
<P> We would now like to add the constrains that the activity &quot;Label 3&quot;
 cant start before activity &quot;Label 2&quot; has finished and that the
 milestone &quot;Phase 1 done&quot; is depending on when activity &quot;Label 3&quot; is
 done.</P>
<P> The principle of adding constrains is that you for each activity you
 want to have a constrain you have to tell to what other activity this
 constrain should be to. That other activity is specified by telling on
 what row that activity lies. Depending on what type of constrain, e.g.
 Start-to-End, an arrow will now connect the two activities in correct
 way.</P>
<P> The way to do this is to call the <A href="../ref/GanttPlotObject.html#_GANTTPLOTOBJECT_SETCONSTRAIN">
 SetConstrain()</A> method on the activity. In this method you specify
 the type of constrain as well as to what other activity this constrain
 should be to. If you read the class reference you can also see that you
 can specify the type and size of arrow used. For now we will just use
 the default sizes and type.</P>
<P> So for example to add an End-To-Start constrain between &quot;Label 2&quot;
 and &quot;Label 3&quot; you could write<DIV class="phpscript"><CODE><FONT color="#000000">
 <FONT color="#0000BB">&nbsp;$bar2</FONT><FONT color="#007700">-&gt;</FONT><FONT color="#0000BB">
SetConstrain</FONT><FONT color="#007700">(</FONT><FONT color="#0000BB">2</FONT><FONT
color="#007700">,</FONT><FONT color="#0000BB">CONSTRAIN_ENDSTART</FONT><FONT
color="#007700">)</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
</P>
<P> The first parameter in the call above &quot;2&quot; is the row of the target
 activity (i.e. the row where &quot;Label 3&quot;) activity is. In the example
 below we have added the constrains we wanted.<DIV class="example">
<BR> <A href="exframes/frame_ganttconstrainex1.html" target="blank"><IMG border="0"
HEIGHT="253"       src="img/img/img/img/img/img/ganttconstrainex1.png" WIDTH="523"></A>
<BR><B>Figure 172:</B> Adding constrains to a gantt chart <A href="exframes/frame_ganttconstrainex1.html"
target="blank">[src]</A>&nbsp;
<P></P>
</DIV></P>
<P> A note: The actual path followed by the arrow is controlled by some
 heuristics to make it clear what the constrain is. It has been a design
 decision that in order to keep the API simple the user has no further
 detailed controlled on the actual path followed. However, in future
 version the heuristics may be extended and provide some
 user-controllable parameters.</P>
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