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Using Controls
Volume Number:1
Issue Number:4
Column Tag:Forth Forum

Using Controls

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 + 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 # )
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 .” Value:” . .”    “  ;

( set.control, given a control handle and an integer, sets the control 
  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 )
:  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 
     get.window show.controls ;

( control actions )
: do.controls swap  case my.control of endof
                         my.button  of  do.button endof
                    endcase ;

( event loop for test window )
: my.action show.value if begin
                          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


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