Controls

The use of this tool is exemplified in Vectors and Euclidean Geometry.

The configuration panel of CONTROLS may have as many lines as desired. Each line defines a control and looks like this:

[4,3]'C':control=C:size=4:colour=black

Controls are points that the user can drag with the mouse.

The configuration of a control is a chain of expressions separated by : which determine several properties of the control.

The configuration line of a control starts with the coordinates of its initial location in square brackets, for example [-3.2,2.5]. These coordinates must be constant. Next comes a chain of strings, flanked by single quotes ' , and numbers or numerical expressions separated from each other by a + sign (see the documentation of TEXTS for a detailed description of this feature). Then, after a  :  , the expression control=C comes, where C may be any word. C is the internal name of the control and is all important if the control coordinates are to have any effect on the applet. The coordinates of the control C are C.x and C.y and they may be used in graphps, equations, variables and functions. They may be used also as parameters, as the example Vectors shows. Another feature that may appear in the configuration line of a control is the expression size=3 which defines the radius of the circle signaling the position of the control (in this case the radius would be 3 pixels). An expression colour=black, defining the colour of the border of the control's circle (in this case black) may also be present. By default the radius is 2. All controls are red inside, only the border colour may be chosen by the user. The default border colour is black.

The following example shows a control with internal name P whose coordinates are used as parameters. In this case, when the control is dragged, the coordinates are actualized on the spinners. The control may also be moved by changing the values of the coordinates of P with the spinners.

This example illustrates the use of the external name of the control coordinates. By default these names would be P.x and P.y. The external names were defined in the example by writting name='abscissa' and name='ordinate' in the configuration lines of the PARAMETERS P.x and P.y, respectively .

A control may be restricted to move on a curve. To do this it suffices to add the equation of the curve in the configuration line of the control. For example, if the configuration line of the control P in the previous example is substituted by:

[P.x,P.y]'P':control=P:size=4:colour=black:x*x+y*y=25

then the control will be restricted to move on the circle of radius 5 centered at the origin. The equation defining the curve to which the control will be restricted, is called a constriction. The example on Euclidean Geometry uses a constriction on all the controls.

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	Ministerio de Educación, Cultura y Deporte. Aņo 2000