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 those graphical objects have corresponding GAP objects, which are created by constructors and can be used later on by operations.
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.
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.
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
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
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
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:
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:
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
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.ctrl are used.
This function is used in
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
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);
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.
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
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.
actually puts a popup on screen.
Query returns the string of the
selected entry or
false if the user clicks outside the popup.
Query for dialogs in Query.
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
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
operation and the string of a text can be changed via
Enables or disables the button bt (string value) or btindex (integer index) of the text selector sel, according to flag.
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.
Every string in a text selector has a name. The names are stored in
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.
Resets all strings of a text selector, such that they are no longer selected.
Closes a text selector. It vanishes from screen.
Note that you have access to the indices and names of strings and buttons:
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.
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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