help on ManhattanLength function added

1 files changed, 34 insertions, 0 deletions

diff --git a/docs/xml/corelib/fpg_base.xml b/docs/xml/corelib/fpg_base.xml
index 84e96c8b..0d9f56c2 100644
--- a/docs/xml/corelib/fpg_base.xml
+++ b/docs/xml/corelib/fpg_base.xml
@@ -5541,6 +5541,40 @@ Right. And the Top is always smaller than the Bottom.
         <short>A record structure holding the RGBA values of a color.</short>

         <descr>This is the same declaration as the one found in FPImage (include with Free Pascal Compiler). In future when FPImage is integrated with fpGUI, I will remove this declaration.</descr>

       </element>

+

+<element name="TfpgPoint.ManhattanLength">

+<short>Quick calculation of the length between points</short>

+<descr><p>Returns the sum of the absolute values of X and Y,

+traditionally known as the "Manhattan length" of the vector from

+the origin to the point. For example:</p>

+<code>

+var

+  oldPosition: TfpgPoint;

+  newPosition: TfpgPoint;

+begin

+  newPosition := MousePosition - oldPosition;

+  if (newPosition.ManhattanLength > 5) then

+  begin

+    // the mouse has moved more than 5 pixels since the oldPosition

+  end;

+end;

+</code>

+<p>

+Accuracy is traded for speed. This is a useful, and quick to calculate, approximation to the

+true length:</p>

+<code>

+    TrueLength := sqrt(power(X, 2) + power(Y, 2));

+</code>

+<p>

+The tradition of "Manhattan length" arises because such distances

+apply to travelers who can only travel on a rectangular grid, like

+the streets of Manhattan.</p>

+<p>For a further explanation of "Manhattan length" see the WikiPedia article at

+<link>http://en.wikipedia.org/wiki/Taxicab_geometry</link></p>

+</descr>

+</element>

+

+

     </module>

     <!-- fpg_base -->

   </package>