Frequently asked questions about the XView-PC user interface:
(With some extra questions about interesting topics added)

General topics:

Q: How can I generate events using the timer?
A: Very simple:
   - Redirect the timer tick interrupt to a new routine that does
     only this (Pascal):
     IF ie_code=-1 THEN ie_code:=5000;
     This will create an event with code 5000 when an interrupt
     occurs while the interface is waiting for events.
   - Make your event handlers do what you want when receiving
     ie_code with the value 5000. Use the interposer if you want
     the events used independently of the mouse position.
   This does not work with the djgpp version under Go32 with the mouse
   emulator active (see below).

Q: I need a text editor window.
A: I need too. Some day I will write one. It is possible to use the
   handlers of a canvas to implement a complete mouse-driven editor.
   Simpler solutions are an event handler in a tty object that allows
   adding (trivial) or deleting (not so) text at the end of the text
   buffer, or several lines of textfield objects (good for forms).

Q: How to make the program know when a window is being opened or
   resized?
A: The notify handler of any canvas object in the window will be called
   in these occasions. It is possible to create a canvas with zero
   dimensions, or out of the frame area, and use its notify handler
   only to detect these events.

Q: How to create a "password" field, where what is typed is not visible?
A: Put a textfield in a separate window with exclusive access, and set
   the textfield edit colors to the window background color before
   opening the window. Make the notify handler of the textfield close
   the window and restore the normal colors.    

Q: How to generate an event by software? For example, how to make the
   notify handler of a textfield start the edition of another textfield
   when the user finishes the edition?
A: Not very elegant, but works:
   - Create an integer variable "newevent", and initialize it with 0.
   - Redirect the timer tick interrupt to a new routine that does this:
     IF (newevent<>0) and (ie_code=-1) THEN BEGIN
       ie_code:=newevent;
       newevent:=0
     END;
   - To generate an event, just set "newevent" to the desired event code.
     The next time when the interface enters the internal polling loop the
     event will be generated. Use "mouse_move" to locate the mouse pointer
     over the object that will receive the event. The code in the notify
     handler of a textfield to cause the edition of another textfield below
     it would be:
     mouse_move(mousex,mousey+15);
     newevent:=MS_LEFT;
   Again, this may not work with djgpp (see below).

Q: How to implement window minimization and maximization?
A: This is not very practical. It is better to simply close unnecessary
   windows. But a possible implementation is:
   To "minimize" a window: Close the window, and open another small
   window containing a "message" with the icon representing the minimized
   window. Do this in the notify handler of a button or a menu.
   To restore a "minimized" window: Make the notify handler of the
   message with the icon close the small window and open the original
   window.
   Some details: Set xv_end to FALSE, or 0 in C, after the closing of
   the windows, because "xv_main_loop" will exit if all the windows are
   closed. Set "adjust_exit" in the minimized windows to TRUE, or 1,
   to avoid the closing of these windows with the central mouse button.
   Set the minimum dimensions of the minimized frames so that they
   always have space for the bitmaps (as always must be done with
   frames containing bitmaps).

DJGPP V1 (The version in the xv_pc17.zip file) version:

Q: The program compiles correctly, but crashes when executed, before
   drawing anything.
A: The DOS environment variable "TCBGI" must be set to where is the
   "LITT.CHR" file, or the program will crash.

Q: The program is plotting text in black over black background.
A: Recompile part of the bcc2grx library, as explained in the xview.h
   file. The source code for the library is correct, but the library
   does not correspond to the code.

Q: The initial screen appears black with some strange colored dots
   marking where the windows should be. When I redraw the windows
   by resizing them, they appear correctly.
A: Caused by some bug in a 16 colors driver. Set the "GO32" environment
   variable to nc 256.

Q: I am using timer interrupts. The program crashes when using the mouse
   emulator.
A: A bug in the go32 interrupt handling. Redirected timer interrupts inside
   some DOS interrupts may cause crashes. Run the program under DPMI, as in
   a Windows DOS session, use djgpp V2 (not tested), or use the Borland C
   version.

DJGPP V2 (in the file xv_pc18.zip) version:

Q: Where is the background hatch?
A: The required function was not implemented in GRX20, but is present in
   GRX22. Update your versions of GRX and BCC2GRX.

Q: All the windows operations are very slow.
A: Change the number of colors to 256. The 16 colors modes in GRX20/22 are
   unusably slow, at this time. Set the DOS environment variable GRX20DRV:
   set grx20drv=nc 256
   
Q: There is no text in the interface elements.
A: Set the DOS environment variable GRXFONT to where the GRX fonts are:
   set grxfont=c:\djgpp\contrib\grx22\fonts

Last update: 21/7/1998 
Antonio Carlos M. de Queiroz
http://www.coe.ufrj.br/~acmq