Using Controls
Volume Number: 1
Issue Number: 4
Column Tag: Forth Forum
By Jörg Langowski
In this month’s column I want to introduce to you some concepts of control
handling on the Macintosh under MacForth. Controls, as you might have guessed by
now, are a very basic concept of the Macintosh user interface: a major part of mouse
input to an application is done through controls.
The four main types of controls that show up to you when you work with an
application are buttons, check boxes, radio buttons and dials, and these are the ones
that we will be talking about this time.
All control handling routines are built into the toolbox ROM. Therefore, one can
call them - in principle - from any programming environment as toolbox traps.
MacForth, of course, makes this job a little easier by providing a large number of
predefined routines. Interestingly enough, most of these routines are already present
in Version 1.1, even though the manual says that 1.1 does not support controls. I
suppose this was a typo. They wanted to say that it does not document controls. Well,
the Inside Macintosh manual does that very extensively and as you will see, it is not
hard to transfer those concepts into Forth.
Let’s first look at the definitions of the four control types, as they are given in
IM:
Buttons are the little rounded rectangles that have a text inside. When you click a
button with the mouse, you tell the application to perform some action as shown in the
example below.
“Yes” and “No” are buttons and you may choose either one.
Check boxes show the state of a parameter that can be on or off, and can be clicked
on/off with the mouse:
Radio buttons are sets of buttons, only one of which may be on. They are used to
set and display parameters that can assume discrete values or states, such as integer
numbers:
Dials, the scroll bar being the most familiar example, are used to set and display
a parameter that can change continuously (or quasi-continuously, such as the position
in a text file).
Generating a control in your active window is very simple, it requires only one
toolbox call. Just putting a control into a window like that, however, is useless. You
can click and point at it as long as you wish, it won’t do anything unless you tell it what
to do. Clicking a control only generates an event that your program has to recognize.
For instance, if a radio button is clicked you have to make sure that the corresponding
parameter is set on and all others that belong to the same group of radio buttons are
turned off. If the page region in a scroll bar is clicked you have to tell the system what
to do, change the parameter value and show the scroll bar with its new value.
But then, there is not much more to do. The Control Manager will auto- matically
determine if you clicked a control and which one, and will also ‘track’ the control, that
is, display it changing while you perform some action on it with the mouse. It will
also, if appropriate, inactivate a control, which is then displayed in a different way
and any actions on it are ignored (like the scroll bars in the Finder windows if all the
icons fit into the window).
Let’s assume we want to generate a window that contains the following controls:
• a scroll bar that can be changed through a range from 0 to 300
• a check box that is used to turn the scroll bar on and off.
An example program that does these functions is given below, and most of it
should be self-explanatory. The Toolbox function NewControl that creates a new
control in a window, however, has to be explained in a little more detail.
It expects 10 parameters on the stack, from bottom to top:
- 4 bytes for the function result ControlHandle
- WindowPtr, the pointer to the window that the new control belongs to
- boundsRect, the address of a rectangle that gives the control’s size and location in
the window’s local coordinates
- title, a pointer to the control’s title
- visible, a boolean value (16 bit); if TRUE, the control is actually drawn inside
the window, otherwise, it’s invisible
- value, a 16-bit integer, the control’s initial value
- min, 16-bit integer, the control’s minimum value
- max, 16-bit integer, the control’s maximum value
- procID, 16-bit integer, a number that defines the type of control:
- 0 - simple button, 1 - check box, 2 - radio button, 16 - scroll bar.
- refCon, 32-bit integer, a number that you may use as a unique reference
number; it is not used by the Control Manager at all.
This set of parameters is rather impressive, and you can immediately see that
none of the standard toolbox trap defining words in MacForth can be used to call this
function. First, only function calls with at most one parameter are supported, for the
others you have to include space for the result on the stack and use the MT defining
word. Second, there are five 16-bit parameters between 32-bit ones, and Forth
normally pushes 32-bit items on the stack.
MacForth 2.0 has the word ADD.CONTROL built in, which is called with the stack
set up like above, only the integers are all 32-bit. ADD.CONTROL then converts
visible, value, min, max, and procID to 16 bits and calls NewControl, which creates
the control. However, if you have MacForth 1.1, you can define your own ADD.CONTROL
by using the 16-bit push PUSHW that was defined in the last MacTech. The example
below contains the definitions of PUSHW and ADD.CONTROL.
The scroll bar that we define is horizontal. The up button and page-up regions of
a horizontal bar are on the left side, but the bar is incremented to the right (an
inconsistency in the Control Manager). Therefore the program decrements the
control’s value when the up button is clicked and increments it on the down button.
The only other control in the example is a check box that turns the scroll bar on
and off. I have not included simple buttons or radio buttons; you may want to try them
out on your own by setting procID to different values. Remember, if you define a set of
radio buttons, your program has to keep track of which one is on and turn the others
off. There is no way how the Control Manager could know which buttons belong to the
same group.
( Demo program for using the Control Manager from Mac Forth )
( © 1985 MacTutor by J. Langowski )
( pushw, new.control ) hex
: pushw s0 @ >R sp@ 2- s0 ! sp! r> s0 ! drop ;
A954 mt (new.control)
: add.control
>r ( refCon ) >r ( procID ) >r ( max ) >r ( min ) >r ( value
)
pushw ( visible ) r> pushw ( value )
r> pushw ( min ) r> pushw ( max ) r> pushw ( procID ) r> (
refCon )
(new.control) ;
( test window for new.control ) ( JL Jan 1985 )
decimal new.window my.window 50 100 200 450 my.window w.bounds
close.box size.box + my.window w.attributes my.window add. window
50 50 75 300 rect my.scroll
( set up scroll bar )
0 my.window my.scroll
“ “ ( no title )
-1 ( visible=true )
100 ( value )
0 ( min )
300 ( max )
16 ( procID for scroll bar )
here ( to get a unique ref # )
add.control
constant my.control in.heap ( so that handle is released when
FORGETting )
( on/off box for test window )
25 50 40 200 rect button.a.rect ( check box )
0 my.window button.a.rect “ Scroll Bar Off” -1 0 0 1 1 ( check box )
here add.control
constant my.button in.heap my.window show.controls
80 50 95 150 rect text.rect ( for output )
( control tracking )
( track control, given a control handle and mouse position, tracks a
control )
: my.track this.control @ @mouse track.control ;
( get.control, given a control handle, gets the value of that control
)
: show.value my.control get.control text.rect erase.rect
0 textfont 50 90 move.to .” Value:” . .” “ ;
( set.control, given a control handle and an integer, sets the
control to
that integer value )
( scroll bar )
: do.thumb my.track drop get.window show.controls show.value ;
: inc.scroll this.control @ dup get.control 1+ set.control show.value
;
: dec.scroll this.control @ dup get.control 1- set.control show.value
;
: inc10.scroll this.control @ dup get.control 10 + set.control
show.value ;
: dec10.scroll this.control @ dup get.control 10 - set.control
show.value ;
( scroll bar )
: do.scroll.bar case in.thumb of do.thumb endof
up.button of dec.scroll endof down.button of inc.scroll
endof
page.up of dec10.scroll endof page.down of inc10.scroll
endof
endcase ;
( check box )
( hilite.control, given control handle and integer value, sets the
control
active if value=0 and inactive if value=255 )
: do.button drop my.track if this.control @ dup get.control 1 swap -
my.control over 255 * hilite.control
set.control then
get.window show.controls ;
( control actions )
: do.controls swap case my.control of do.scroll.bar endof
my.button of do.button endof
endcase ;
( event loop for test window )
: my.action show.value if begin do. events
case mouse.down of @mouse.dn get. window
find.control ?dup if do.controls then
endof
endcase again
else .” My Window Deactivated” then ;
my.window on.activate my.action
Referenced by (2):