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TUTORIAL
UserPort because this is the message
port at which Intuition IDCMP event messages
will arrive. This address obviously
needs to be available to the event handler
and is obtained from the window
Structure set up by Intuition by using the
window pointer in conjunction with a
wd _UserPort displacement like this
movect windom_p,e1
movecl md_UserPortfolt,o2
address
Within the event handler proper two
events. namelY the user hitting the window's
'close' gadget or selecting a 'Quit to
Workbench' menu option, result in an exit
flag being set that eventually causes the
program to terminate. You'll see from the
source that a check is also made for menu
events whose code field is set to
MENUNULL This is important since these
events are generated whenever a
user activates the menu, but then fails to
make a selection (such events need to be
recognised in order lo be safely ignored).
The other menu option, incidentally, is just
tags
workbench_p
gad too LI i It
IcA
dt.t
dc.1
dc.1
dt.l
dc.l
dc.l
dc.i
dc.1
dc.1
did
dc,t
dc.t
dc.1
dc.1
dc.l
dc.l
dc.l
user pert
VA_Pub S r e
1
WO_Lef 1,300
WA_Top.,0
VO_Ii1dth,340
WSJ i gh I o
il) WO_Oraggar,ttlti
OhJeo th Godge I, RUE
1101_0 loseadge t Ritt
itA_SI refiadget,IllfiE
1111_61dge to
Mat
Listing 2 :
tag-based
window
description
littjoom,1 om_do es
WA _II WI IRWIN
WAJI , 10
Ojai& 4th,640
VAJlaell I gh ,256
PA_IPCNP,ICICAPJEMPP1(K I IEMP_CLOSEVIIIDOW
t e,o indoo_name
TAG _DOME,MUL
Listing Cl
The e ve nt
handling
code from
this month's
•sompto
program
Amiga Computing
OCTOBER 1995_
Even Oland er
Eventliand le a
fietliessage
Menuttessage
title bar (olap5ed window5
With the preliminary program layout discussions now
safely out of the way we can deal with the real topic
of the month — namely, how to produce windows that
initially reside in, or can be made to collapse into, a
window's title bar. Perhaps surprisingly. it is very
easy to do because all it takes is a few well chosen
tag list entnes in the window definition_
Firstly, provide a zero WA_Top value and set
WA_Left to a value which places the 'window' at a
suitable position within the title bar. Then set the
Window initial width and height tags. WA_Width and
WA_Height, to define a window which has only a 10
pixel height (i.e. the height of a window title bar). For
instance:
dc.t MI_Top,(1
did Majeft,300
dc .1 lia_llidth,340
dc 11A_Keigh , 10
Having clone that you then just arrange for the real
co-ordinates of your window to be stored as the
'alternate' zoom gadget set, This involves using a
nevem, t d0-11a0-a1,-te1)
e tr. t
Fovea, I 12,10
tatCSYS goitPortp.AbsisecOott
Ji
cmpi.l , OTIOE,d2
brics Eventliandltri
G
Noyes. 1 to7t4,d1)-111 Jog-12
e
rts
t
l
i
soota.l 12,10 g e t port 14
e MASTS ietgag,_AblEettliole
s tit.l d 0
sbtu.
s Sttesnageit
o 0411
g@ave.(
e _ t loss lot ),d3
e
w o_tode tot 1,0X
CALLSti Itepleltsg,_fibtElectis se
110CMP_CLOSEWINfiall,d3
linea Menullessage
Mfg 111100,d2
bras centime
cool I E K , d 3
Unt.i e t M e s s a ge
cow .11
boo.' fietMessage
15,6
andil •SIF,di
btu.' DoRenulten0
move; et1eUE,d2
bro • s f,tttniage
tollenultes0 ! s r Wiothirg
bra s 6 . ttle ssage
ie e ss a peE s t r t s d i holds slit flog
lied to a dummy routine so nothing actually
happens when the menu item is selected.
This act of tying a menu option to a 'do
nothing routine in this way is actually a
very useful trick dunng development of fully
fledged applications. You may have
dozens of menu options that relate to code
sections that are as yet unwritten, and tying
such options to dummy routines allows
the event handler and overall structure of
WA Zoom tag in the window definition to identify a
pointer to a set of alternate window dimensions that
will be used when the window's zoom gadget is
selected_ These dimensions have to be provided as
an array of word (16-bit) entries, so in the example
program you'll find this lag entry:
de. t WO_Loom soon_dato
along with this cicw directive which identities the corresponding
set of alternate window co-ordinates:
toom_dota dt.o ISO
4
50,140,200
The result? The window opens initially inside the fille
bar and can be expanded to normal use Size by
selecting the zoom gadget, You will, of course, be
able to see the effect of these statements when you
run this month's example program. To get the
reverse effect, namely initially having the window
open normally, but collapsing into the tale bar when
the zoom gadget is activated, you just reverse the
original and alternate sets of window co-ordinatesl
preserve registers
tteer etit 'Rog
port address
exit Slag set!
restore registers
Logical end of routine
drext in if
pet tbe messoge
did it /tilt?
opy pointer to it
cops ',mot cleft
copy mug. coot
then seld lessege back
net kW signa l. to e xit routine
check mesoage class
ignore other 'estop types
ignore il MENUPOLL
Wren menu tel number
Nitt be either 0 or
net GOIT tignal to exit routine
Chia foe Ore Se M ge s
,
the code to be developed, even thoug
many associated routines may not yet
written.
As the corresponding real routine
become available, you just replace the
appropriate call to the dummy routine w
a call to the real version. Another benefit
this type of approach is that it automatic
provides an 'incremental testing' pathway
It for example, your program works
until you swap, say a... jsr DoNothing c
with a call to a real routine, then you'll k
straightaway that any faults that appear a
almost certainly connected with the co
present in the newly added routine!
Most of the event handling code shou
be easy enough to follow, but it may help
examine the diagram shown in figure I
This provides a fairly high-level, gener
description of the code's operation in I
chart form
•11.160, 1 1 6 1 11.1 .
NI M PW4 4
7197
- • buss
St I L J 1
1 t S 5
Figure I ; ba sic progra m structure
in flowcha rt form
• I
s
t i
M
is