2-d geometry

Use the Geo->New figure->geo2d menu to make a new 2-d geometry session. This will open a new level with a ``subsession'' (group of commandlines) at the left, a 2-d screen in the middle, and the controls at the right. If there are parameters, they will be below the controls at the right. The subsession is a list of commandline levels. Evaluation of a commandline level will automatically reevaluate all levels below (i.e. with a higher level number), therefore if you use one level to define an object and modify the definition of this object later, all objects depending on this object will be modified. Modification of a level defining a point or a 1-d parameter can be done interactively with the mouse either in the geometric screen or in the parameter area (below the controls).

The geometry level has a mode, which affects how the mouse behave.

• In all modes, right-clicking (or double-clicking) on an object displays a dialog box so that you can easily modify the object attributes (or delete the object).
• In 2-d frame mode, draging the mouse will move the visualization windows and scrolling will zoom in/out.
• In pointer mode, you can move an existing point, push the mouse near the point (when the mouse is near enough, it will show a different cursor) and move the mouse, release it at the new postion.
• In point mode, the mouse can be used to define new points or segments. To define a new point, just click somewhere not near another point or segment. To define a segment, push the mouse button at the beginning, move the mouse, release the mouse at the end of the segment (if you release the mouse out of the screen, the segment will be cancelled).
• You can draw a few more complex object with the mouse using the other modes, like triangles, circles, bisectors, ....
• You may also type Xcas commands (from the Geo menu) in a commandline at the left of the graphic. Each command may evaluate to a graphic object and be displayed or to a non graphical object which may be used later in the construction.

To erase a geometrical object, right-click on it, select Delete or select it's level in the subsession at the left, and use the Edit->Suppress levels menu or Backspace key.

For example, you can click three points with the mouse (in point mode), this will create 3 levels with definitions for points A,B,C. Then you can make the circle containing A, B, C either by selecting the Circles->circumcircle mode and click on A,B,C or by entering in a commandline the circumcircle command (menu Geo->Circles)
c:=circumcircle(A,B,C)

Remark: how to work with several figures in a tab
When you create objets in a figure with a mouse, the name of the created object is automatically choosen. This name is shared between figures of the same tab so that they don't interfer if you have several figures in the same tab. If you want to copy a part of a figure in another figure, enter in a level of the target figure the instruction eval([ ],1) where you put inside the brackets the names of the objects to be copied (e.g. eval([A,B,AB],1) will copy A, B and AB from a previous figure to the new figure). If you change the initial figure (where A, etc. were defined), you must reeval the instruction in the target figure to reflect the changes (press Enter in the first level of the target figure).