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7 User Communication


  1. Menus in Graphic Sheets
  2. Mouse Events
  3. Dialogs
  4. Popups

XGAP has two main means to communicate with the user. The first is the normal command processing: The user types commands, they are transmitted to GAP, are executed, and produce output, which is displayed in the command window. The second is the mouse and the other parts of the graphical user interface. This latter part can be divided into menus, mouse events, dialogs, and popups.

Most of the windows of XGAP have menus. The user can select entries in them and this information is transformed to a function call in GAP. Menu entries can be checked or not, so menus can also display information.

Mouse Events
A mouse event is the pressing or releasing of a mouse button, together with the position where the mouse pointer is in the exact moment this happens and the state of certain keyboard keys (mainly shift and control). Such events also trigger GAP function calls and the corresponding functions can react on these events and for example wait for others.

Dialogs are windows which display information and into which the user can enter information for example in form of text fields.

Popups are special dialogs where the user can not type text but can only click on certain buttons. XGAP has so called ``text selectors'' which are a convenient construct to display textual information and let the user select parts of it.

Most of those graphical objects have corresponding GAP objects, which are created by constructors and can be used later on by operations.

7.1 Menus in Graphic Sheets

  • Menu( sheet, title, ents, fncs ) O
  • Menu( sheet, title, zipped ) O

    Menu returns a pulldown menu. It is attached to the sheet sheet under the title title. In the first form ents is a list of strings consisting of the names of the menu entries. fncs is a list of functions. They are called when the corresponding menu entry is selected by the user. The parameters they get are the graphic sheet as first parameter, the menu object as second, and the name of the selected entry as third parameter. In the second form the entry names and functions are all in one list zipped in alternating order, meaning first a menu entry, then the corresponding function and so on. Note that you can delete menus but it is not possible to modify them, once they are attached to the sheet. If a name of a menu entry begins with a minus sign or the list entry in ents is not bound, a dummy menu entry is generated, which can sort the menu entries within a menu in blocks. The corresponding function does not matter.

  • Check( menu, entry, flag ) O

    Modifies the ``checked'' state of a menu entry. This is visualized by a small check mark behind the menu entry. menu must be a menu object, entry the string exactly as in the definition of the menu, and flag a boolean value.

  • Enable( menu, entry, flag ) O
  • Enable( menu, boollist ) O

    Modifies the ``enabled'' state of a menu entries. Only enabled menu entries can be selected by the user. Disabled menu entries are visualized by grey or shaded letters in the menu. menu must be a menu object, entry the string exactly as in the definition of the menu, and flag a boolean value. entry can also be a natural number meaning the index of the corresponding menu entry. In the second form boollist must be a list where each entry has either a boolean value or the value fail The list must be as long as the number of menu entries in the menu menu. All menu entries where a boolean value is provided are enabled or disabled according to this value.

    See the explanation of GraphicSheet (Close!Callback) for the ``Close'' event, which occurs when the user selects the menu entry close graphic sheet in the Sheet menu.

    7.2 Mouse Events

    When a mouse event occurs, this is communicated to GAP via a function call which in turn triggers a callback. As described in GraphicSheet to CtrlRightPBDown the following callback keys are predefined as reactions on mouse events: LeftPBDown, RightPBDown, ShiftLeftPBDown, ShiftRightPBDown, CtrlLeftPBDown, CtrlRightPBDown.

    Note that when your function gets called, the mouse button will still be pressed. So it can react and for example wait for the release. There is an easy way to find out about the state of the mouse buttons after the event:

  • WcQueryPointer( id ) F

    id must be a WindowId of an XGAP sheet. This function returns a vector of four integers. The first two are the coordinates of the mouse pointer relative to the XGAP sheet. Values outside the window are represented by −1. The third element is a number where the pressed buttons are coded. If no mouse button is pressed, the value is zero. BUTTONS.left is added to the value, if the left mouse button is pressed and BUTTONS.right is added, if the right mouse button is pressed. The fourth value codes the state of the shift and control. Here the values BUTTONS.shift and BUTTONS.ctrl are used.

    This function is used in

  • Drag( sheet, x, y, bt, func ) O

    Call this function when a button event has occurred, so the button bt is still pressed. It waits until the user releases the mouse button and calls func for every change of the mouse position with the new x and y position as two integer parameters. You can implement a dragging procedure in this way as in the following example: (we assume that a LeftPBDown event just occurred and x and y contain the current mouse pointer position):

      storex := x;
      storey := y;
      box := Rectangle(sheet,x,y,0,0);
      if Drag(sheet,x,y,BUTTONS.left,
                local bx,by,bw,bh;
                if x < storex then
                  bx := x;
                  bw := storex - x;
                  bx := storex;
                  bw := x - storex;
                if y < storey then
                  by := y;
                  bh := storey - y;
                  by := storey;
                  bh := y - storey;
                if bx <> box!.x or by <> box!.y then
                if bw <> box!.w or bh <> box!.h then
              end) then
        the box had at one time at least a certain size
        ... work with box ...
        the box was never big enough, we do nothing

    7.3 Dialogs

  • Dialog( type, text ) O

    creates a dialog box and returns a GAP object describing it. There are currently two types of dialogs: A file selector dialog (called Filename) and a dialog type called OKcancel. text is a text that appears as a title in the dialog box.

  • Query( obj ) O
  • Query( obj, default ) O

    Puts a dialog on screen. Returns false if the user clicks ``Cancel'' and a string value or filename, if the user clicks ``OK'', depending on the type of dialog. default is an optional initialization value for the string.

    7.4 Popups

  • PopupMenu( name, labels ) O

    creates a new popup menu and returns a GAP object describing it. name is the title of the menu and labels is a list of strings for the entries. Use Query to actually put the popup on the screen.

  • Query

    actually puts a popup on screen. Query returns the string of the selected entry or false if the user clicks outside the popup. See also Query for dialogs in Query.

  • TextSelector( name, list, buttons ) O

    creates a new text selector and returns a GAP object describing it. name is a title. list is an alternating list of strings and functions. The strings are displayed and can be selected by the user. If this happens the corresponding function is called with two parameters. The first is the text selector object itself, the second the string that is selected. A selected string is highlighted and all other strings are reset at the same time. Use Reset to reset all entries.

    buttons is an analogous list for the buttons that are displayed at the bottom of the text selector. The text selector is displayed immediately and stays on screen until it is closed (use the Close operation). Buttons can be enabled and disabled by the Enable operation and the string of a text can be changed via Relabel.

  • Enable( sel,bt,flag )
  • Enable( sel,btindex,flag )

    Enables or disables the button bt (string value) or btindex (integer index) of the text selector sel, according to flag.

  • Relabel( sel, list )
  • Relabel( sel, index, text )

    Changes the strings that are displayed in the text selector. In the first form list must be a list of strings. The second form only changes the text at index index.

  • SetName( sel, index, string )

    Every string in a text selector has a name. The names are stored in the list names component of the text selector. So sel!.names ist a list containing the names. The names are initialized with the strings from the creation of the text selector.

  • Reset( sel )

    Resets all strings of a text selector, such that they are no longer selected.

  • Close( sel )

    Closes a text selector. It vanishes from screen.

    Note that you have access to the indices and names of strings and buttons:

  • IndexOfSelectedText

    Whenever the user clicks on a text in a text selector, the global variable is set to the index of the text in the text selector.

  • IndexOfSelectedButton

    Whenever the user clicks on a button in a text selector, the global variable is set to the index of the button in the text selector.

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    XGAP manual
    February 2024