Lesson 21

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A Mops program uses menus which are stored as separate resources. This is the normal Mac method for defining menus, since it makes it easy for users to customize the menu text with a resource editor such as Rezilla.

Menus work in a way analogous to controls in that the program contains definitions of menu handler words, which the menu selections invoke. Menu selections are usually more powerful in a Mac program than controls, because menus typically divert the program into a relatively drastic change in program mode. In a typical File menu, for example, selecting the Load... option halts the main program, while the user's attention is shifted to the dialog box for the selection of a file to open. In grDemo, the primary menu, Graphics, changes the type of graphics the program will draw, sending you from Lissajous mode to Dragon Curves mode, for example.

Menus take a bit more setting up than controls, since there are two separate steps. First, you have to create a resource file to contain the menu resources. This can be done with a resource editor. For the demo program, we have provided a resource file called 'Demo.rsrc'. This is in the Mops ƒ (68k Mops) or Demo folder (PowerMops). Then the second step is to set up your Mops menu objects to correspond with the resources — we'll talk about this now.

Menus have an ID number associated with them. It's important to note that this menu ID is different from the resource ID that menu resources have. The existence of two separate ID numbers for a menu frequently causes confusion, but this can be minimized if you normally make these numbers the same.

Menus have an ID number associated with them. It's important to note that this menu ID is different to the resource ID that menu resources have. The existence of two separate ID numbers for a menu frequently causes confusion, but this can be minimized if you normally make these numbers the same.

By convention, the Apple menu is ID=1. We've assigned ID=2 to Graphics. These ID numbers are stored in the menu resources, and are used by the Mac system to identify which menu has been selected. You will see now that in Mops there is a simple way of associating a set of actions with a particular menu, using the menu ID number to identify the menu.

Returning to the grDemo program listing, we now define a menu object called Grafmen, specifying that it has six members. Applemen does not need to be created here, because Mops created it.

Next come the menu handler word definitions for Grafmen. Each one places the cfa of the drawing word in the draw ivar of dwind. Yet another syntax for obtaining the cfa of a word is demonstrated here: ['] lj. ['] is the equivalent of ' within a definition. Each definition also places the maximum control values for each type of drawing. Then it sends an update message for the entire window, which draws the revised scroll bar values and the drawing for the current settings.

SetReps is a word that establishes the maximum number of repetitions for drawings created using the pen bic and the polygon anna. You may wish to increase the value for bic if you find your numeric selections on the scroll bars Don't draw complete figures. Conversely, some drawings may repeat on themselves after only 100 or fewer repetitions, in which case it seems that the program is unresponsive for several seconds.

Next we set up the menus. We do this by sending an INIT: message to each menu object. As you can see, this method takes an xt list on the stack, which we specify using the xt{ ... } syntax. It also takes another number, which is the menu ID number we've already talked about. The xts in each list refer to the words which will be executed when a selection is made from the menu, starting from the top item. Thus if the first item of GrafMen is selected, the word that will be executed is doLiss. This corresponds to the item 'Lissajous' which is in the menu resource. It is your responsibility to make sure that the words that you put in your xt lists correspond, item for item, with the text that you have put in the items in your menu resource. The Mac has no way of knowing that doLiss corresponds to the text 'Lissajous'. If you get the xts in the wrong order, you will get some interesting things happening when you make menu selections, but it won't be what you want!

In the GrafMen resource, we have included a gray line between 'Dragon curves' and 'Quit', which (as is customary) is the last item. Even this gray line must have a corresponding xt in the list. You can use any word at all here, since it will never be executed; however to make our intention clearer we have used the word 'Null', which is a word that does nothing anyway.

You will notice that for the Apple menu, AppleMen, we have put only two items in the xt list.
All right, what about all the dozens of items that may be sitting under your Apple menu? We are actually taking care of them, with the use of another feature of Mops — if there are more items in a menu than were present in the xt list, and one of the 'excess' items is selected, the last xt in your list is called. The word DoDsk handles the firing up of a DA or whatever is under the Apple menu. In our program here it will handle everything except the first item, which (as is normal Mac practice) is 'About...', in this case 'About Curves'.

Running the Program

The last definition of this program is that of a word that gets the whole program running. This is where everything done so far comes together when you type the word, GO.

In the first line we do a couple of things if the value Instld? is False. Now this value will be True if this is a standalone (double-clickable) application, and False otherwise, that is if we have just loaded this program into the Mops dictionary. We will see in the next lesson how to install our demo program as a doubleclickable application.

These two actions then, are things we need to do when testing our program in Mops. The first action is to open the resource file, demo.rsrc, which contains the menu resources we need. In a standalone application we don't want to carry around a separate resource file, so our normal practice will be for any extra needed resources to be added to the application itself with a resource editor. In this case the resources will be available without any other file having to be opened. On the other hand, Mach-O executable should not have its resource fork, so we should keep separate resource files in a Mach-O standalone application. During testing, however, it is more convenient for extra resources to be in a separate file even in case of PEF/CFM PowerMops.

Next we fire up the Menu objects. The GETNEW: messages sent to each Menu object gets the needed Menu resources and initializes the menu. We then set up the menu bar (at the top of the screen) by sending an INIT: message to our Menubar object. This message takes the menu object addresses on the stack, followed by a count of the number of menus.

Bic and Anna have their respective maximum repetitions set (SETREPS), the max values for the three scroll bars are put in place, and the cursor is turned off.

In the next line, we bring our window, dWind, to life with a NEW: message. We pass in the address and length of the text that will appear as the title of the window. The syntax " Curves" (with a space after the first ") compiles the text 'Curves' into the dictionary, and at run time pushes the address and length of the text on to the stack, which is what we need to pass with the NEW: message.

At the end, the word EventLoop enters an endless loop which continually 'listens' to mouse events as they affect controls and menus.

Last of all we define the error word. This is needed for an installed application, since the full Mops system won't be there, so you have to provide a word to be executed if some error arises which normally gives a Mops error message. We customarily call this word CRASH, which is a good description! Here it just beeps twice and quits to the Finder.
A 'real' application would need to do something more helpful, probably with an alert box, but this is, after all, a demo.

If you want the program to start up right away after loading, all you have to do is enter the startup word, go, as the last word of the grDemo source file. When the file is loaded, Mops will act on that startup word as if you had typed it at the Mops prompt.

In Summary

Now that you have seen the entire grDemo program, you should notice some key points about Mops programs.

First come the definition of the classes of objects that appear on the screen. The balance of the program concerns itself with defining handler words that work their wonders when controls and menus are activated by the mouse. It is wise to think of your program action in terms of handler words.

And lastly comes the definition of the word that starts your program. It calls the words you've defined in the dictionary to create objects and let the program respond to your input.

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