Difference between revisions of "Construction of a constrained point"

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A point can depend on another geometric object. This dependence can be given by using JavaScript syntax or by using
 
GEONExT syntax.
 
=== GEONExT syntax ===
 
Here is an example using GEONExT syntax.
 
The point A is draggable. The point B depends on point A: Its y-coordinate is set to 1 and its x-coordinate is set
 
to the x-coordinate of A.
 
<source lang="javascript">
 
var b = JXG.JSXGraph.initBoard('jxgbox1', {originX: 40, originY: 100, unitX: 40, unitY: 40});
 
var free = b.createElement('point',[0,0], {name:'A', style:5});
 
var dep = b.createElement('point',["X(A)",1], {name:'B', style:8});
 
</source>
 
<html>
 
<link rel="stylesheet" type="text/css" href="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraph.css" />
 
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/prototype.js"></script>
 
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraphcore.js"></script>
 
<div id="jxgbox1" class="jxgbox" style="width:600px; height:200px;"></div>
 
<script type="text/javascript">
 
var b = JXG.JSXGraph.initBoard('jxgbox1', {originX: 40, originY: 100, unitX: 40, unitY: 40});
 
var free = b.createElement('point',[0,0], {name:'A', style:5});
 
var dep = b.createElement('point',["X(A)",1], {name:'B', style:8});
 
</script>
 
</html>
 
=== JavaScript syntax ===
 
Now we do exactly the same with JavaScript syntax.
 
<source lang="javascript">
 
var b2 = JXG.JSXGraph.initBoard('jxgbox2', {originX: 40, originY: 100, unitX: 40, unitY: 40});
 
var free = b2.createElement('point',[0,0], {name:'A', style:5});
 
var dep = b2.createElement('point',[function(){ return free.X();}, 1], {name:'B', style:8});
 
</source>
 
<html>
 
<div id="jxgbox2" class="jxgbox" style="width:600px; height:200px;"></div>
 
<script type="text/javascript">
 
var b2 = JXG.JSXGraph.initBoard('jxgbox2', {originX: 40, originY: 100, unitX: 40, unitY: 40});
 
var free = b2.createElement('point',[0,0], {name:'A', style:5});
 
var dep = b2.createElement('point',[function(){ return free.X();}, 1], {name:'B', style:8});
 
</script>
 
</html>
 
The JavaScript syntax is much more robust against changes of the construction, but of course it looks more complicated.
 
Lets look at it again in detail:
 
First we construct a free, draggable point called "free".
 
<source lang="javascript">
 
var free = b2.createElement('point',[0,0], {name:'A', style:5});
 
</source>
 
Then we construct the dependend point "dep".
 
<source lang="javascript">
 
var dep = b2.createElement('point',[function(){ return free.X();}, 1], {name:'B', style:8});
 
</source>
 
The first coordinate of "dep" is given as an anonymous function:
 
<source lang="javascript">
 
function(){ return free.X();}
 
</source>
 
This function returns the x-coordinate of the point "free".
 
  
 
[[Category:Examples]]
 

Latest revision as of 12:09, 17 September 2008