Difference between revisions of "Lesson 20"

Revision as of 04:07, 17 December 2005

Windows

Let's now return to the listing for grDemo. After we set the bounds and justifications for the dPane and the three Indicators, we declare dView, which is to be the contView of our window. This can be a plain View, since it doesn't need to have any other special properties.

Five values are created next. The first pair are the coordinate point on the Mac screen of the top left corner of the window that the program will occupy: coordinates 40,60. The next two are the coordinates for the right bottom corner of the program window. These values will be suitable for the small Mac screen (on e.g. a Classic), but should look all right on any Mac screen. These figures will be recalled later when it comes time to create the window for the program.

To avoid possible later confusion, you should note that the first window actually has ID = 8, because it has a zoom box, the small square in the top right hand corner. Mops' Window+ class adds the zoom box because of the line:

true setZoom: self \ zoomable

When the window is created, Window+ adds 8 to the procID if zoom is set true. Hence a docWind (0) becomes a ZoomdocWind (8), and non-growable doc window (ID=4) would become a ZoomNoGrow (12). Not all windows can have zoom boxes, though' so don't set Zoom TRUE if you are using, for example, a rndWind.

Whenever you define a new window, choose one of the window types by number. Mops has established three constants”docWind, dlgWind, and rndWind”that you can substitute in place of the number, in case it's easier for you to remember names than numbers. The Mops constant names are shown in Figure I-18. This Mops demo graphics program uses docWind, since Apple's Human Interface Guidelines recommend we use this for a standard growable window.

Even plain windows are relatively complex objects inside the Macintosh Toolbox. To give you an idea of their complexity, look at the long list of instance variables in the predefined class, Window (in the file WindowMod.txt in the folder ˜Module source').
Among the items you can control”and sometimes must control”in a window are:

• the kind of window (see above)
• the rectangular area on the screen to enclose the window
• whether a window is growable
• the area on the screen within which a window can grow
• whether a window is draggable
• the area on the screen within which a window can be dragged
• how it is to respond to key-down and mouse-down events

[#Window The GrDemo Window]

class grWind, a subclass of Window+ (itself a subclass of Window) lays the framework for the window of this graphics demonstration. As we have seen in the last lesson, all Window+ objects contain a view, the contView, which simply covers the whole area of the window. The window knows which view is its contView, since this is specified when the NEW: message is sent to the window object to fire it up. In our example, the contView of our grWind window is called dView.

Giving the window enough parameters to present itself on the screen is simplified in this program in the NEW: method, which is an extension of the NEW: method of class Window+. The only parameters needed are the address and length of the title of the window, and the address of the contView. The other pieces, the address of the window's rectangular bounds, the type of window (rndWind), and flags for being visible on the screen and having no close box are supplied within the method or as constants already defined. Once all the items are on the stack in the proper order, the method calls the superclass' NEW: method.

One of the actions performed by the NEW: method in class Window+ is to send NEW: to the contView. This will cause NEW: to also be sent to every view in the window, since one of the actions of NEW: in class View is to send NEW: to all its child views.

Once the window and all its views have been fired up, the views will draw themselves. As we have seen, views draw themselves when they get a DRAW: message. And what do we have to do to start this process off? You may remember we mentioned this in the last lesson, but by now you might be able to guess it anyway. The answer: we have to send DRAW: to the contView!

On the Mac, drawing in a window normally takes place when a window is updated. Drag the grDemo window to the bottom of the screen so part of it runs off the screen. Release the mouse button. Now drag it back near the center of the screen. For everything in the window to be visible again requires updating. When the Mac system recognizes that a window has to be updated, it sends an ˜update event' to the application which owns the window. You don't need to worry about the details at this stage, but Mops catches this update event and sends a DRAW: message to the window.

And this is how the contView gets the DRAW: message that will cause all the views to be drawn. The DRAW: method in the Window+ class basically just sends DRAW: to the contView. Easy!

dWind

Continuing with the grDemo listing, straight after our definition of the grWind class, we define our window, dWind, which is an object of the class grWind we just defined.

A new definition, @DPARMS, gets things ready for the drawing of the graphics in the view dPane. This definition is a shortcut that allows us to use one word to do work which is needed for each of the four following definitions.

The first thing we have to do is erase whatever was in the view area before, and then we have to draw a rectangle as a border around the view, Now remember that the graphic drawing will be done as a result of a DRAW: message being sent to dPane, and that at this time the rectangle tempRect will have been set to the border of the view. This makes our job easy”we simply write clear: tempRect draw: tempRect.

The other task for @DPARMS is to fetch the current readings of each control.

The words of the four following definitions should look familiar. The definitions are extensions of the spiral, spin, lj, and dragon curves defined in Turtle. Here, however, they have been modified to fetch three control parameters, place those numbers as ivars of the drawing device (the pen or poly, as the case may be), and draw the graphics accordingly.

You will notice that instead of using : and ; in these definitions, we have used :a and ;a. We did this because these words are action handlers”their addresses will later be stored in a Menu object, to define the actions that are to take place when the user makes a menu selection. We will see in a later section when discussing modules that action handlers in modules need to be declared with :a and ;a. This is not strictly necessary in the main dictionary, where we are now, but it does no harm either. It is therefore a good idea to always use :a and ;a for action handlers, as it will make your programs clearer and also make it easier for you if you later move code into modules.

Because each of the drawing types has a different range of parameters, the !ranges definition lets us set the maximum number for each control, depending on which graphics type we select from the menu. The minimum values are always one. (We will discuss controls in more detail shortly).

In the next three lines of code, the text of the message that appears on the screen in response to the ˜About Curves' menu items is assigned to two string constants, AB1 and AB2. Following that come three program lines that define what is to happen when that selection is made. It selects the font Times in 14-point (Times has font number 20), positions the cursor at point 28,40, and ˜types' the two strings on the screen. It then calls the word WaitClick, which will just wait for the user to click the mouse or type a key. Then it sends an UPDATE: message to dWind to cause it to redraw itself, erasing the text we ˜typed'.

Next, both the pen Bic and the polygon Anna are told where the center point of the graphics rectangle is located. Importantly, the coordinates given are relative to the top left corner of the view dPane, since that is where the origin will be whenever dPane receives a DRAW: message.

Controls

In the Macintosh environment, a control is a screen object that responds to interaction from the mouse in such a way that the mouse causes either instant action or a change in function for a later operation. A good example of the ˜instant action' kind of control is the elevator knob on the volume control in the Sound Control Panel. By adjusting the knob with the mouse, you immediately adjust the volume of the sound played by the Mac through its speaker.
Likewise, when you click an ˜OK' button in a dialog box, you are working with a control for immediate action. A ˜delayed action˜ control would be something like the check box inside a Get Info dialog window that locks or unlocks documents for dragging to the trash. When you click the mouse pointer in an empty box, an ˜X' fills in the box, and the document is locked, but no particular action occurs in response. Click the pointer again, and the X disappears, so you can go ahead and trash the document.

In Mops, controls are View subclasses. Thus, they are sized and positioned via the justification and bounds quantities we talked about in the last lesson, and they are drawn when they get a DRAW: message. But, as well as this, they have a number of interactions with the Mac system.

A scroll bar is one of the most common kind of control. It consists of five parts, each of which responds differently in the course of a program.
The five parts are:

1. Up arrow
2. Page Up region
3. Thumb
4. Page Down region
5. Down arrow

Each region is programmed to respond as needed.

GrDemo Controls

The special scroll bar controls in grDemo inherit their instance variables from the superclasses View and Control. The list of available ivars includes an integer for the definition ID, an X-array for the addresses of a scroll bar's five possible actions, and an Ordered-col for the actions' corresponding part numbers.

Whenever a VScroll object is created, its CLASSINIT: method automatically makes it a scroll bar by putting the control ID number 16 into its ID ivar. The method also places null values in each of the object's actions. When it receives a NEW: message, which all views do when they are to display themselves, it makes the appropriate call to the system to cause itself to appear. It also makes this call whenever it gets a DRAW: message. The definition for the VScroll class is in the file Ctl in the Toolbox Classes folder.

Scroll Bar Actions

Continuing down the demo program, the list of 5 definitions are the actions that occur when you click each part of each scroll bar. The formats for each action handler definition is much like the other except for the amount of increment. A key element of these definitions, however, is that they call upon a special Mops construction using the value ThisCTL.

ThisCTL essentially tracks the address of the most recently activated control. Therefore, if you click the PageUp part of the second of our three scroll bars, thisCTL remembers that it was the second scroll bar you activated. In the action handler definition, then, get: [ thisCTL ] fetches the previous value of the second scroll bar. The object of the get: method is determined dynamically at runtime, a technique explained in Part II as late-binding. After the value of the second scroll bar is decremented by 10, a put: [ thisCTL ] stores the value in the second scroll bar's ivar before sending the update message to the window. The importance of this late-binding mechanism is that it eliminates the need for us to define five action handlers for each scroll bar or to concoct some algorithm to keep all that code to a minimum. ThisCtl allows us full control flexibility with a minimum of code.

The doThumb definition is a special one that automatically calculates a value based on the relative position of the thumb along the range of the scroll bar. The doPgUp and doPgDn increment and decrement (respectively) the value of the scroll bar by 10. And the doLnUp and doLnDn adjust the figure by one in their respective directions.

In the line after the action handler definitions, the address of the lj definition (the one that draws Lissajous figures) is plugged into dwind as the type of graphic that gets drawn when grDemo first fires up. The notation ' (tick) returns an execution token, or xt, a quantity which can be saved and used later to execute the word. In this case, the xt of lj, which was defined a bit earlier in this program, is passed as a parameter in the setdraw: dwind message. Checking at dwind's class definition, we find that the setdraw: method stores the xt of a graphics routine (lj, spin, etc.) in the draw ivar of dwind. This will all come together at the end of the program.

A small digression: in Mops, as in many Forths, this execution token is actually the address of the compiled, executable code for the word. However this isn't true of all Forths, and so the new ANSI standard now uses the more general term ˜execution token'.

Next, the xts of the five control actions are stored in each scroll bar's actions ivars. The syntax here, xts{ ... } is a shortcut for entering the xt of each action handler word. Addresses for each definition are passed as parameters to the scroll bars' actions ivars.