24.  AES-LIBRARY



APPL_INIT


If you use APPL_INIT() in a GFA-Basic program the function returns 0, 
although my Dutch GFA-manual states otherwise.



EVNT_MESAG


With EVNT_MESAG you can use '0' for the address of the message-buffer so 
the default buffer at address MENU(-2) is automatically used:

     ~EVNT_MESAG(0)



GRAF_GROWBOX and GRAF_SHRINKBOX


The box-parameters for calling GRAF_SHRINKBOX should be the same as those 
for calling GRAF_GROWBOX:

     ~GRAF_GROWBOX((x2-x1)/2,(y2-y1)/2,0,0,x1,y1,x2-x1,y2-y1)
     COLOR 1                  ! any colour, except 0
     BOX x1,y1,x2,y2          ! and draw the box
     (...)
     COLOR 0                  ! background-colour
     BOX x1,y1,x2,y2          ! erase the box
     ~GRAF_SHRINKBOX((x2-x1)/2,(y2-y1)/2,0,0,x1,y1,x2-x1,y2-y1)     

In my Dutch GFA-manual someone switched start and finish in the 
description of GRAF_SHRINKBOX.



ALERT and FORM_ALERT


An Alert-box with one button (usually 'OK') is a little frustrating for 
the user. Try to offer a choice:

     ALERT 3,"This job will take |about 25 minutes",1,"OK|Cancel",k


If you need an empty line in an Alert-box, use a space between two 
vertical rules:

     ALERT,3,"...| |...",1,"...",k
GFA-Basic allows 4 lines of 30 characters (High/Medium rez) if you use 
ALERT, but with FORM_ALERT you can use 5 lines. In both cases you can use 
not more than 3 buttons, each at most 8 characters (High/Medium rez) wide:

     m$=" line 1 | line 2 | line 3 | line 4 "
     ALERT 3,m$,1," OK ",k
     '
     m$="[3][ line 1 | line 2 | line 3 | line 4 | line 5 ][ OK ]"
     k=FORM_ALERT(1,m$)


You can show a GFA-error in an ALERT-box as follows:

     gfa$=ERR$(ERR)
     m$=MID$(gfa$,4,LEN(gfa$)-11)
     m$="  *** GFA-Error *** |"+m$
     ALERT 3,m$,1,"Sorry",k


If some characters are not visible in a button (or a button is completely 
invisible), try broadening the Alert-box by adding spaces to the widest 
text-line. If the widest text-line is as long as the button-string, the 
Alert-box should look allright.


If you have pressed the left mouse-button on the very spot where an Alert-
button is about to appear, something goes wrong. GEM appears to remember 
your last mouse-click, and erroneously assumes you pressed the button 
after the Alert-box appeared. GEM only selects the button if the mouse-
click occurred in the exact area of the Alert-button. To avoid this 
problem you should make sure the user has released the mouse-button before 
you call the Alert-box:

     REPEAT
     UNTIL MOUSEK=0      ! wait until mouse-buttons released


By the way, the AES uses an 8K buffer (one quarter of the screen) to save 
the part of the screen where the Alert-box appears. Ditto for a menu.



SHEL_GET and SHEL_PUT


GFA-Basic is run from a 'Shell-Program', usually the desktop. In that case 
the file DESKTOP.INF can be found in the Environment-Buffer. You can 
examine this file by transferring it to a string:

     d$=STRING$(1024,0)
     r%=SHEL_GET(1024,d$)

PRINTing this string is much easier than using a disk-editor to examine 
DESKTOP.INF. 
After changing the string, you could put it back in the buffer with:

     r%=SHEL_PUT(1024,d$)

This way you could change the lay-out of the desktop. If you change the 
string, you should know that the desktop recognizes the end of DESKTOP.INF 
by the byte &H1A. So don't forget to put CHR$(26) at the end. If you want 
to save the new buffer, try:

     OPEN "O",#1,"\DESKTOP.INF"
     PRINT #1,LEFT$(d$,INSTR(d$,CHR$(26)))
     CLOSE #1
























Is that all there is to tell about the AES-library? Certainly not, so at 
this point you will probably be disappointed, unless you have read the 
paragraph 'The Author' in the chapter 'INTRODUCTION' (page 11). If you 
have any useful addition for this chapter, please send it to me!




                         Procedures (CHAPTER.24)


Alert (page 24-1)                                                    ALERT
Alert-box with 5 text-lines (instead of 4):
     m$="Line 1|Line 2|Line 3|Line 4|Line 5"
     @alert(1,m$,1," OK ",k)            ! same parameters as ALERT


Box_grow and Box_shrink (page 24-1)                               BOX_GROW
Show growing/shrinking box before drawing/erasing a rectangle:
     @box_grow(50,50,200,200)
     (...)
     @box_shrink(50,50,200,200)