Apr 96 Factory Floor
|Column Tag:||From The Factory Floor
From the Factory Floor
By Dave Mark
In this months Factory Floor, well meet Greg Dow. Greg designed and wrote PowerPlant, the next generation framework from Metrowerks. Before we get to the interview, I wanted to take a sec and thank Jim Trudeau for all his help in putting this interview together. Cognac and cigars on me at WWDC, Jim!
Dave: Greg, since not all of our readers have a background in object programming, lets start things off by defining a few terms. What is the difference between a class library and a framework?
Greg: People often use the terms interchangeably. However, I think of a class library as a collection of utilities and a framework as a structure for building programs.
With a class library, you are in control. You design the program structure and use library classes where convenient. For example, you can use the ANSI C++ streams class library to handle file I/O.
With a framework, the framework is in control. You usually start with a do nothing program provided by the framework and add your own code. The framework calls your code at the appropriate time.
PowerPlant is a framework, but it also has families of utility classes that you can use independently.
Dave: Why would a C programmer want to move to C++ and PowerPlant? What are the advantages?
Greg: Using PowerPlant lets you build upon code written by other programmers. Its code that you dont have to write yourself. PowerPlant classes handle mundane tasks such as menu and window management, as well as more advanced features such as Apple events and threads. By not having to start from scratch, you have more time to concentrate on the unique features of your program.
Another big advantage is Constructor, which lets you graphically lay out the visual elements of your PowerPlant programs. PowerPlant can create a window and its contents from information edited in Constructor, so its possible to create a program that displays items such as scrolling pictures, text, and buttons without ever writing a line of code.
Dave: Once someone has learned the basics of C++ and object programming, how do they pick up on PowerPlant?
Greg: The first thing everyone should do is read The PowerPlant Book, which is part of the Inside PowerPlant for CW8 manual that comes with CW8. This book, written by Jim Trudeau, is an excellent guide to understanding and using PowerPlant.
After that, they should start using PowerPlant. Look over the sample programs. Run the samples and use the source debugger to single-step through some of the code to follow the flow of control. For example, set a breakpoint in the main event loop, then hit a key and follow the resulting sequence of calls to see how PowerPlant handles it.
Finally, talk with other people who use PowerPlant by getting a modem and an Internet account. Read the Usenet newsgroup comp.sys.mac.programmer.codewarrior. (A new group, comp.sys.oop.powerplant, will probably form soon.) Metrowerks also has an active forum on America Online. And join the PowerPlant Dream Team.
Dave: What exactly is the PowerPlant Dream Team? What do they do? How do you go about joining?
Greg: The PowerPlant Dream Team is an organization of developers interested in learning PowerPlant in a team-based environment. It started as a study group formed by Stephen Jovanovic, but has grown to over 200 people. A small subset of the PP Dream Team wrote an LNewTextEdit class that supports styled text and drag-and-drop editing. Very cool. To find out more about the PP Dream Team, visit their Web page at: http://petrified.cic.net/powerplant-dt/
Dave: Tell me about the PowerPlant architecture.
Greg: One of my favorite toys is Lego blocks. You can build complex structures by combining simple parts. PowerPlant follows this approach by using a mixin architecture, where the base classes are relatively simple, and subclasses use multiple inheritance to combine features.
For example, the EditField class multiply inherits from Pane (so it can draw and handle mouse clicks), Commander (so it can handle keystrokes and menu commands), and Periodical (so it gets time during the event loop to flash the insertion point).
I also tried to eliminate dependencies between classes so that you can use them separately. In particular, PowerPlant is not just an application framework. You can use PowerPlant to build code resources such as HyperCard XCMDs and control panels, or even integrate PowerPlant classes into existing procedural programs.
Dave: What is your favorite part of PowerPlant?
Greg: Other than the overall design, my favorite feature of PowerPlant is the Drag Manager support. Drag and drop is cool, and its one of the better implemented features in the Mac OS. The API is clean and simple. It took me only two days (and three classes) to implement all the basic support.
Dave: Tell me about your life before Metrowerks.
Greg: I have a Bachelors degree from MIT in chemical engineering, and I spent a few years at UC Berkeley working on a Ph.D., also in chemical engineering, that I never completed. My thesis research was computer modeling of coal gasification reactors, and I did a lot of scientific programming in FORTRAN.
During that time, I became more interested in programming than in chemical engineering, so I started taking computer science classes. In July 1987, I bought my first personal computer, a Mac SE. A few months later, I dropped out of school to devote my time to learning Mac programming.
One of my first projects was writing a generic application shell. I kept tinkering with this shell, and it eventually turned into version 1.0 of the THINK Class Library (TCL), which Symantec shipped with THINK C in July 1989.
Dave: How did you get hooked up with Metrowerks? Did Greg Galanos recruit you? Was the company already building CodeWarrior when you started work on PowerPlant?
Greg: My first contact with Metrowerks was actually with Jean Belanger, sometime before the MacWorld Expo in January 1992. I lead the Programmers Group at BMUG (Berkeley Macintosh Users Group), and Jean called up looking for some volunteers to staff his booth at the show. At the time, Metrowerks was selling Pascal and Modula 2 compilers for the education market.
I never actually met anyone from Metrowerks then, but a year later John McEnerney asked me if I was interested in writing a new C++ framework for some little Canadian company. John is the PowerPC Compiler Architect for Metrowerks, and he worked at Symantec when I wrote TCL 1.0.
I met with Greg Galanos and started working on PowerPlant in March 1993. Codewarrior as we know it did not exist. There was a prototype C compiler and environment. It fit on a floppy disk.
Dave: A lot of people ask about cross-platform development using PowerPlant. I know that the Microsoft Foundation Classes (MFC) are the de facto standard on the Windows side. Whats the best way to get a PowerPlant-based application ported to run under Windows?
Greg: I know that a lot of people are interested in developing programs that run on both the Mac and Windows. However, PowerPlant is a Mac-only framework. Metrowerks has no intention of developing a Windows version of PowerPlant.
To port code to Windows, I recommend that people investigate Mac2Win from Altura Software. The Mac2Win libraries emulate the Mac Toolbox on Windows. Metrowerks is using these libraries to port portions of the CodeWarrior environment to Windows.
Dave: What are your future plans for PowerPlant?
Greg: My future work with PowerPlant will concentrate on three major areas: (1) Visual programming; (2) OpenDoc; and (3) Copland.
Right now, you can specify the static layout of interface elements using PowerPlant Constructor. Future versions of Constructor will let you specify runtime relationships between objects. For example, adding Attachments to Panes and linking Broadcasters to Listeners.
If you know what youre doing, you can use PowerPlant today to develop both OpenDoc parts and OpenDoc container applications. In fact, a few programmers (besides me) have already done so. However, its not easy. Future versions of PowerPlant will make it as easy to create an OpenDoc part as it is to create a stand-alone application.
Copland, the next major version of the Mac OS, will provide many new capabilities and interface elements. I intend to keep PowerPlant on the leading edge of Mac development by supporting these new features as soon as possible.