[Sommaire] [Imprimer]

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  27  <HR NOSHADE>
  28  <H2><A NAME="9_19">9.19 Rotating the graphs</A></H2>
  29  <P> JpGraph provide the possibility for you to rotate the generated
  30   graph an arbitrary angle. This will only affect the actual graph (axis,
  31   axis titles, labels and so on) and not fixed elements on the graph like
  32   title or footer.</P>
  33  <P> Rotation is probably most used to rotate a graph 90 degrees, for
  34   example a bar graph to get the effect of horizontal bars.</P>
  35  <P></P>
  36  <HR> <SMALL>
  37  <P><STRONG> Performance note:</STRONG> Adding a rotation transformation
  38   will make the graph generation slightly slower since each point of the
  39   graph as to go through a transformation step before being stroked on to
  40   the image. JpGraph optimizes this by using a pre-calculated
  41   transformation matric and also optimizes the special case 90 degrees.</P>
  42  </SMALL>
  43  <HR>
  44  <P> By default the center of the rotation will be the center of the plot
  45   area, which may or may not coincide with the center of the entire
  46   image.</P>
  47  <P> To control the rotation you use the two methods</P>
  48  <UL>
  49  <LI> <A href="../ref/RotImage.html#_ROTIMAGE_SETANGLE">
  50  Graph::image::SetAngle()</A>, Specify rotation angle in degrees.</LI>
  51  <LI> <A href="../ref/RotImage.html#_ROTIMAGE_SETCENTER">
  52  Graph::image::SetCenter()</A>, Specify center of rotation in absolute
  53   image pixels</LI>
  54  </UL>
  55  <P> For example<DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
  56  &nbsp;$graph</FONT><FONT color="#007700">-&gt;</FONT><FONT color="#0000BB">image</FONT><FONT
  57  color="#007700">-&gt;</FONT><FONT color="#0000BB">SetAngle</FONT><FONT color="#007700">
  58  (</FONT><FONT color="#0000BB">45</FONT><FONT color="#007700">);</FONT><FONT
  59  color="#0000BB"></FONT></FONT></CODE></DIV></P>
  60  <P></P>
  61  <P> There is actually a third method that you could use, adding a
  62   translation to the graph<STRONG> after</STRONG> the rotation. Since
  63   this probably a very little used method we don't discuss it further but
  64   refer the reader to the class reference instead <A href="../ref/RotImage.html#_ROTIMAGE_SETTRANSLATION">
  65   Graph:image::SetTranslation()</A></P>
  66  <P> When you rotate an image you should be aware of that the individual
  67   labels on the axis are not rotated. The design decision behind this is
  68  <BR><STRONG> a)</STRONG> Bit mapped font can't be rotated
  69  <BR><STRONG> b)</STRONG> Maintain readability</P>
  70  <P> Please remember that you may still rotate the labels by calling the <A
  71  href="../ref/Axis.html#_AXIS_SETLABELANGLE"> Axis::SetLabelAngle()</A>
  72   method.</P>
  73  <P> Since the anchor point for labels is by default the optimum for
  74   graph at 0 degree you might want to adjust the anchor point and
  75   alignment for the labels on the axis to get a better visual appearance
  76   on you rotated graph. This is accomplished by the method <A href="../ref/Axis.html#_AXIS_SETLABELALIGN">
  77   Axis::SetLabelAlign()</A> For a detailed discussion on how to do this
  78   please see the section on horizontal bar graphs, ( <A href="3030barplot.html">
  79  Working with bar plots</A> )</P>
  80  <P> The table below shows some examples on different kinds of rotation
  81   to give you an idea of how changing the angle and rotation center may
  82   be used to generate different effects. The top left graph is the
  83   original image. The point of rotation has been marked with a red-cross
  84   in each of the images.</P>
  85  <P><DIV class="example">
  86  <BR> <A href="exframes/frame_rotex0.html" target="blank"><IMG border="0" HEIGHT="170"
  87        src="img/img/img/img/img/img/rotex0.png" WIDTH="270"></A>
  88  <BR><B>Figure 176:</B> Original image <A href="exframes/frame_rotex0.html"
  89  target="blank">[src]</A>&nbsp;
  90  <P></P>
  91  </DIV></P>
  92  <P><DIV class="example">
  93  <BR> <A href="exframes/frame_rotex1.html" target="blank"><IMG border="0" HEIGHT="170"
  94        src="img/img/img/img/img/img/rotex1.png" WIDTH="270"></A>
  95  <BR><B>Figure 177:</B> Rotated 45 degrees around center of plot area <A href="exframes/frame_rotex1.html"
  96  target="blank">[src]</A>&nbsp;
  97  <P></P>
  98  </DIV></P>
  99  <P><DIV class="example">
 100  <BR> <A href="exframes/frame_rotex2.html" target="blank"><IMG border="0" HEIGHT="170"
 101        src="img/img/img/img/img/img/rotex2.png" WIDTH="270"></A>
 102  <BR><B>Figure 178:</B> Rotated 90 degrees around center of plot area <A href="exframes/frame_rotex2.html"
 103  target="blank">[src]</A>&nbsp;
 104  <P></P>
 105  </DIV></P>
 106  <P><DIV class="example">
 107  <BR> <A href="exframes/frame_rotex3.html" target="blank"><IMG border="0" HEIGHT="170"
 108        src="img/img/img/img/img/img/rotex3.png" WIDTH="270"></A>
 109  <BR><B>Figure 179:</B> Rotated 45 degrees around center of the image <A href="exframes/frame_rotex3.html"
 110  target="blank">[src]</A>&nbsp;
 111  <P></P>
 112  </DIV></P>
 113  <P><DIV class="example">
 114  <BR> <A href="exframes/frame_rotex4.html" target="blank"><IMG border="0" HEIGHT="170"
 115        src="img/img/img/img/img/img/rotex4.png" WIDTH="270"></A>
 116  <BR><B>Figure 180:</B> Rotated 90 degrees around center of the image <A href="exframes/frame_rotex4.html"
 117  target="blank">[src]</A>&nbsp;
 118  <P></P>
 119  </DIV></P>
 120  <P><DIV class="example">
 121  <BR> <A href="exframes/frame_rotex5.html" target="blank"><IMG border="0" HEIGHT="170"
 122        src="img/img/img/img/img/img/rotex5.png" WIDTH="270"></A>
 123  <BR><B>Figure 181:</B> Rotated -30 degrees around the lower left point
 124   of the plot area <A href="exframes/frame_rotex5.html" target="blank">
 125  [src]</A>&nbsp;
 126  <P></P>
 127  </DIV></P>
 128  <P></P>
 129  <P> As you can see from the images above if you rotate about any other
 130   point than the center of the plot area the plot can be placed outside
 131   the image after rotation.</P>
 132  <P> Since the rotation, by design, only affects the plot area it is
 133   often most effective to use when the color of the margin is the same as
 134   the background color.</P>
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