% This file was created automatically from usercomm.msk.
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\Chapter{User Communication}

{\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.

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

Popups & 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.
\enditems

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


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Menus in Graphic Sheets}

\>`Menu( <sheet>, <title>, <ents>, <fncs> )'{Menu![menu]}@{`Menu'!`[menu]'} O
\>`Menu( <sheet>, <title>, <zipped> )'{Menu![menu]}@{`Menu'!`[menu]'} 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.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{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):

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



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{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.



%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.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{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'{Query!for popup}@{`Query'!for popup}

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> )!{for text selectors}
\>Enable( <sel>,<btindex>,<flag> )!{for text selectors}

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

\>Relabel( <sel>, <list> )!{for text selectors}
\>Relabel( <sel>, <index>, <text> )!{for text selectors}

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> )!{for text selectors}

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> )!{for text selectors}

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

\>Close( <sel> )!{for text selectors}

Closes a text selector. It vanishes from screen.

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

\>`IndexOfSelectedText'{IndexOfSelectedText}@{`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'{IndexOfSelectedButton}@{`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.