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  28  <H2><A NAME="10_15">10.15 Adding constrains between your activities</A></H2>
  29  <P> With Gantt charts there is often the need to illustrate constrains
  30   between one or several activities. One of the most common constrain is
  31   that on activity can't start before an other activity finish.</P>
  32  <P> JpGraph support visualizing the following types of constrains</P>
  33  <UL>
  34  <LI> Start to End</LI>
  35  <LI> Start to Start</LI>
  36  <LI> End to Start</LI>
  37  <LI> End to End</LI>
  38  </UL>
  39  <P> An example will clarify how to specify a constrain between two
  40   activities.</P>
  41  <P> Assume that we start with the Gantt schema as illustrated below<DIV class="example">
  42  <BR> <A href="exframes/frame_ganttconstrainex0.html" target="blank"><IMG border="0"
  43  HEIGHT="231"  src="img/ganttconstrainex0.png" WIDTH="523"></A>
  44  <BR><B>Figure 167:</B> The original Gantt schema we wich to add
  45   constrains to <A href="exframes/frame_ganttconstrainex0.html" target="blank">
  46  [src]</A>&nbsp;
  47  <P></P>
  48  </DIV></P>
  49  <P> We would now like to add the constrains that the activity &quot;Label 3&quot;
  50   cant start before activity &quot;Label 2&quot; has finished and that the
  51   milestone &quot;Phase 1 done&quot; is depending on when activity &quot;Label 3&quot; is
  52   done.</P>
  53  <P> The principle of adding constrains is that you for each activity you
  54   want to have a constrain you have to tell to what other activity this
  55   constrain should be to. That other activity is specified by telling on
  56   what row that activity lies. Depending on what type of constrain, e.g.
  57   Start-to-End, an arrow will now connect the two activities in correct
  58   way.</P>
  59  <P> The way to do this is to call the <A href="../ref/GanttPlotObject.html#_GANTTPLOTOBJECT_SETCONSTRAIN">
  60   SetConstrain()</A> method on the activity. In this method you specify
  61   the type of constrain as well as to what other activity this constrain
  62   should be to. If you read the class reference you can also see that you
  63   can specify the type and size of arrow used. For now we will just use
  64   the default sizes and type.</P>
  65  <P> So for example to add an End-To-Start constrain between &quot;Label 2&quot;
  66   and &quot;Label 3&quot; you could write<DIV class="phpscript"><CODE><FONT color="#000000">
  67   <FONT color="#0000BB">&nbsp;$bar2</FONT><FONT color="#007700">-&gt;</FONT><FONT color="#0000BB">
  68  SetConstrain</FONT><FONT color="#007700">(</FONT><FONT color="#0000BB">2</FONT><FONT
  69  color="#007700">,</FONT><FONT color="#0000BB">CONSTRAIN_ENDSTART</FONT><FONT
  70  color="#007700">)</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
  71  </P>
  72  <P> The first parameter in the call above &quot;2&quot; is the row of the target
  73   activity (i.e. the row where &quot;Label 3&quot;) activity is. In the example
  74   below we have added the constrains we wanted.<DIV class="example">
  75  <BR> <A href="exframes/frame_ganttconstrainex1.html" target="blank"><IMG border="0"
  76  HEIGHT="253"  src="img/ganttconstrainex1.png" WIDTH="523"></A>
  77  <BR><B>Figure 168:</B> Adding constrains to a gantt chart <A href="exframes/frame_ganttconstrainex1.html"
  78  target="blank">[src]</A>&nbsp;
  79  <P></P>
  80  </DIV></P>
  81  <P> A note: The actual path followed by the arrow is controlled by some
  82   heuristics to make it clear what the constrain is. It has been a design
  83   decision that in order to keep the API simple the user has no further
  84   detailed controlled on the actual path followed. However, in future
  85   version the heuristics may be extended and provide some
  86   user-controllable parameters.</P>
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