Tutoriel:Introduction GeoGebraScript

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Révision datée du 8 mai 2012 à 09:54 par Noel Lambert (discussion | contributions) (à suivre ...)
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Parfois les possibilités pour vos apprenants d'interagir avec vos feuilles de travail à l'aide des fonctionnalités offertes par GeoGebra ne sont pas assez performantes ou trop difficiles à être utilisées par vos apprenants, surtout les plus jeunes. GeoGebraScript est là pour vous aider à créer des constructions simples à utiliser avec une interactivité plus sophistiquée. C'est une manière simple d'écrire des scripts (petits programmes) dans GeoGebra.

Les utilisations courantes de scripts sont :
  • Contrôler des réponses de vos apprenants en leur faisant les inscrire dans des ChampTextes et en utilisant un script pour vérifier si elles sont correctes.
  • Créer des nouvelles questions / tâches quand l'apprenant a pressé un bouton, déterminées au hasard ou en utilisant un ensemble prédéfini par vous.
  • Démarrer des animations ou faire apparaître des nouveaux éléments de la construction après que l'apprenant ait pressé un bouton ou fini une tâche.
  • (etc..)

Il y a deux langages de programmation dans GeoGebra, GeoGebraScript et JavaScript, mais cette introduction se concentre sur GeoGebraScript parce qu'il utilise la syntaxe des commandes GeoGebra et qu'ainsi il est plus aisé à comprendre et à apprendre pour les utilisateurs de GeoGebra. Il y a certaines différences entre les spécificités des langages de programmation, mais GeoGebraScript est suffisamment puissant dans beaucoup de situations.

Fondements : Commandes

Il n'y a pas que les outils pour créer un objet dans GeoGebra. Vous pouvez en créer avec les commandes dans le champ de saisie.

Exemple: Avec la commande Cercle[(1,2),3] vous créer un cercle de centre le point de coordonnées (1,2) et de rayon 3.

Même si vous utilisez un outil pour créer un objet, GeoGebra utilise une commande en arrière-plan pour créer l'objet. Pour voir la commande utilisée pour créer un objet, on peut la trouver dans le champ Définition de l'onglet Basique de la fenêtre Dialogue Propriétés . Ainsi les outils ne sont plus ou moins qu'une aide pour utiliser ces commandes à l'aide de la souris. Une liste de toutes les commandes pour crée un objet peut être trouvée ici.

Nous avons seulement évoqué les commandes qui créent des objets. La majorité des commandes créent des objets, mais il existe quelques commandes dédiées à être utilisées dans les scripts, nous en parlerons en détail plus tard (pour les curieux, voir Commandes Scripts).

Basics of Scripting

Scripts are, at heart, just a sequence of GeoGebra commands executed in the following two situations:

  • Click: A script is executed after the user clicked on the object.
  • Update: A script is executed when the value or properties of the object changed. This may happen if the user moves elements of the construction around, changes sliders, etc.

Scripting in GeoGebra is object-centered, which means that you can define scripts for each object –one script for clicks, one for updates–, but no script can exist without an object (there is one exception for scripting using JavaScript).

To add scripts to an object just right-click the object in either the Algebra or Graphics View, click the Object Properties… item and select the Scripting tab. Three more tabs will appear, On Click, On Update and Global JavaScript. The third one won't be of interest in this tutorial, but the two others can be used to add Click and Update scripts to the object you selected.

Click to see larger version

Now it's time to actually create a script, we will create a silly example using an Update script first:

Exemple: (Update script, you can also find the whole construction in GeoGebra)
  1. First of all, open a blank GeoGebra 4 window
  2. Now create a point "A" and a line "a". Try out the Line[..] command if you're not familiar with creating objects from the Input Bar.
  3. Open the On Update tab of the scripting panel as described in the paragraph above.
  4. Now enter
SetLineThickness[a, Distance[A, a]*2]
SetPointSize[A, Distance[A,xAxis]]

as a script, click the OK button (very easy to miss!) and close the dialog.

  1. Try to figure out what the script does, then check your assumption by moving the point A around!

As you may have noticed we assigned the update script to the point, not e.g. the line. This means that the script is executed every time you move the point. It doesn't mean, however, that the script must modify any attribute of the point itself.

We've been using the SetLineThickness[] and SetPointSize[] commands, two of those commands intended for scripting we've talked about earlier. At some point you should at least skim the scripting command list to get an idea what's possible with these commands. You're not restricted to this kind of command though, you can e.g. use f(x) = x^2 or c = Circle[(0,0), 5] in your scripts as well.

Apart from some special features, described in more detail below, executing a GeoGebraScript has the same effect as entering the single lines of the script into the input bar. You now basically know how to write scripts in GeoGebra, the rest of this tutorial will be about some special objects for scripting like textfields or buttons. Apart from the scripting commands the most useful one is probably If[...], you should look at the other logic and list commands as well if you did not already.

Note : Many scripting commands just perform an action once and do not form a permanent connection as you may know them from dependent objects, so e.g. SetLineThickness[a, Distance[A, a]*2] will just copy the current value of Distance[A,a]*2 at the time of the execution, afterwards that value will not change unless you execute the command again or change the thickness manually. Our example may make the impression that there is some kind of connection, but that's just because the script is executed every time the point is moved. You can see that by moving the line instead. The line thickness will not change unless you move the point again.
Note : If you're familiar with other programming languages you may have noticed that there is no need for a semicolon at the end of a line in GeoGebraScript.

Buttons

Buttons are great because all your students know that they can click them and will try to do that. Apart from that buttons don't have any special behavior, so a click script of a button is as good as a click script of any other object. You can create a button using the Tool Insert Button.gif Insert Button Tool.

Input Boxes

Input boxes (also called textfields), see the Tool Insert Textfield.gif Insert Input Box Tool, are maybe the most powerful objects in GeoGebra. They allow your students to enter text, numbers, functions and every other input you can (manually) convert from text to some GeoGebra objects.

There are multiple ways how you can use input boxes in your construction, you can either link them with objects, associate a click script to them or process them later using another object (e.g. a button). Don't worry, everything will be explained in detail right now.

Linked Input Boxes

Linked input boxes are input boxes which are linked to an existing GeoGebra object: That means that the input box shows the current value of the object and if you change the value in the input box the original object will change its value as well. You can use that to let your students change function definitions or numbers without using sliders. Basically they are input boxes which can just change a single object and thus much easier to use and without any danger of students damaging their worksheets.

The following example illustrates how you can create linked input boxes in GeoGebra.

Exemple: (Linked input boxes, the construction can be found at GeoGebra again)
  1. Open a blank GeoGebra window
  2. Enter a function, e.g. f(x) = x^2, into the input bar
  3. Select the Tool Insert Textfield.gif Insert Input Box Tool in the toolbar (in the second tool group from the right).
  4. Now click on some spot in your worksheet, a dialog will pop out. For the caption enter "f(x) =" and as linked object select your function f.
  5. You're done. Move the graph of f to see how the textfield will automatically display the new definition of your function. You can also change the textfield and press enter to see how you can change the function's definition using the textfield.
Note : As mentioned above you can not only link functions, but also numbers and basically ever other object, just try it out.

Input Boxes with Click Scripts

On contrast to the first example we will now not link the input box to a specific object but use its Click script to apply its value to other objects (the reason why this is called click script is unknown to the author ;-)). The script will be very similar to the one in the first example, the new issue now is how to access the value of the input box in the script. The answer is %0. Seriously.

Exemple: (Input box with click script, see GeoGebra)
  1. Open a blank GeoGebra window
  2. Create a point A and a line a.
  3. Select the input box tool and click onto the canvas (as above), but this time use the label "Size:" and leave the "Linked Object" field empty.
  4. Go to the Click script tab of the new input box (instructions how to do that way above).
  5. Now add the following script (note the %0):
SetPointSize[A, %0/2]
SetLineThickness[a, %0]
  1. Click "Ok" again and close the dialog.
  2. Now enter a new value into the input box and press enter.

As you can see the placeholder %0 indeed carries the value of the input box.

ToDo

If you know something (a little) about scripting: You're help and participation is very welcome! You could add something for the following topics or think of something else:

  • More step-by-step instructions for beginners
  • More concrete examples (also links to GeoGebra files using scripting)

Example Scripts

Buttons: Increment/Decrement Buttons

Instead of using a showing a slider to go through a step-by-step explanation, you can use a button.

Exemple:
  • Create an integer slider, called Steps.
  • Create a Button using Button Tool
  • Enter for caption the visible label on the button
  • Enter the script SetValue[Steps,Steps+1] or simply Steps=Steps + 1

To decrement change "+" to "-". To change the size of the steps change 1 to your value.

Note : The command Steps=Steps + 1 is only available in scripting. If you enter a command like that in the input bar, you'll get an error circular definition

es:Introducción a Guiones GeoGebraScript fr:Tutoriael:Introducion GeoGebraScript it:Tutorial:Introduzione a GeoGebraScript

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