Issue 1-20, April 24, 1996

Be Engineering Insights: Using Loadable Code to Enhance Your Application

By Dominic Giampaolo

One of the most welcome advances in application design over the last few years is the introduction of "plug-in" modules. Plug-ins are external pieces of code that you can load into your application, thereby extending the utility and intelligence of your app. This style of design, made popular by applications such as Photoshop, has many advantages:

On the BeBox, plug-ins are called "add-ons". As an application writer, you define a set of functions that you want add-on modules to provide. Your app can then load any module that provides those functions.

As an example, consider a video application that wants to let the user apply a "wipe" between two video sources. But the application itself doesn't provide any wiping routines—instead, it loads an add-on that provides a wipe function, and then finds and calls that function.

To do this, the application and the add-on have to agree on a protocol for the function. As a graphical routine, wiping is a well-defined problem in which two input frames are processed to produce a third. The protocol of the wipe_frame() function, below, embodies the parameters of the process: It accepts the input frames as (fictitious) VideoFrame object arguments, and returns the processed frame as a third VideoFrame. The function also takes a float argument that specifies where we are in the wipe, given as a percentage of the total process:

VideoFrame *wipe_frame(VideoFrame *input_a,
                       VideoFrame *input_b,
                       float percent);

Any add-on that provides such a frame-wiping function can be loaded into and used by the video application.

What does the code look like on the application side? First, we set a BFile to represent the add-on, and load the file through the Kernel Kit's load_add_on() function:

BFile      add_on_file;
image_id   add_on_image;

/* We'll assume that a_ref is a valid record_ref
 * that refers to the add-on file.

add_on_image = load_add_on(&add_on_file);
if (add_on_image < B_NO_ERROR) {
    /* error */

In the example, add_on_image is an image_id value that identifies the add-on that was loaded. All further references to the add-on are based on this, the add-on's "image ID" number.

Now we need to get a handle on the add-on's wipe_frame() function. To do this, we declare a function pointer variable (add_on_wipe), and point it at wipe_frame() through the Kit's get_image_symbol() function:

/* Declare the variable ...*/
int (*add_on_wipe)(VideoFrame *input_a,
                   VideoFrame *input_b,
                   float percent);

/* and set its value. */
if (get_image_symbol(add_on_image,
                        &add_on_wipe) < B_NO_ERROR)
      /* Error; unload the add-on (at least). */

The get_image_symbol() function is, admittedly, a bit cryptic. In particular, the second argument needs some explanation: The C++ compiler mangles a function's name to encode the function's protocol. When you ask an add-on for a particular function, you identify the function by its compiler-mangled name. See the Kernel Kit chapter of The Be Book for more information on name-mangling and the get_image_symbol() function.

Getting back on track, we now have a variable, add_on_wipe, that points to the add-on's wipe_frame() function. We can now call the dynamically-loaded code with this short snippet: float percent;

VideoFrame *frame_a, *frame_b, *wiped_frame;

/* You would undoubtedly set up a loop to get
 * successive pairs of frames from the VideoFrame
 * sources, to do something with the processed frame,
 * and to bump the percent value.
while (...) {
      wiped_frame = add_on_wipe(frame_a, frame_b, percent);

At each pass through the loop, wiped_frame points to the next stage of the wipe. Our video application doesn't need to know how the wipe_frame() function works, it merely manages the input and output data, and provides a framework for the add-on to operate in.

One can imagine useful modules for other types of applications. For example, a spread sheet could recognize add-ons that calculate a result based on the input from a range of cells. A MIDI app might use add-ons to provide patch editors for various types of synthesizers. A paint program could use add-ons for different "brushes", a sound editor could use them to store different filters. The same add-on-loading technique is used in all these instances.

Now let's consider a more complicated example. Suppose we want to write a library that will load (graphic) images that are stored in various formats—GIF, JPEG, TIFF, and so on. Furthermore, we want our library to be able to load graphics that are stored in formats that aren't defined yet—we don't want the introduction of new formats to make our library (and the applications built from it) obsolete. Not only do we not want to re-write the library's code, we don't even want to recompile.

To implement this ideal, we have to add a couple of rules: Our shared library must present an immutable API that applications can depend on, and the add-on modules (files) must be kept in a place that the library knows about.

As a simple example of this model, let's say our graphic-loading library provides a single function, LoadGraphic(record_ref ref). The interface between the library and the add-on is a function that's also called LoadGraphic(). When the application calls LoadGraphic(), the library decides which add-on to use (it could do this by looking at the file type or filename extension of the argument ref, or by loading add-ons one by one until it finds a winner), and then it passes the ref to the add-on's LoadGraphic() function.

This method of operation completely decouples the shared library from any specific knowledge about the various graphic formats. A user can "educate" his or her system simply by installing a new or improved add-on: All applications using the shared library will immediately benefit from the new code. This enriches the user's environment, and creates a new market for third parties.

In summary, add-ons provide a way to make an application extensible, for the good of developers and users:

Without a doubt, add-ons are cool.

The App Modeler Application

By Marc Verstaen

The prospect of developing applications on a new platform is always delightful. Everything is allowed, everything CAN be created again, from scratch, and you're THE creator: The empty page is in front of you.

Then comes the first step...and the first problem: Everything HAS TO be created again, from scratch. Once again you have to spend time and energy designing buttons, positioning text and pictures, loading menus, intercepting and interpreting mouse-clicks. All this dirty work, when your target is to create THE ultimate pea-sorting algorithm (I'm not allowed here to deal with apples), or THE view object that will create drawings that rival Picasso's—whatever part of software you like.

When my company, Lorienne [Now BeatWare], began to use the BeBox, we found many features we were waiting for: a good multitasking, multithreaded OS, a fast window system, an innovative approach to the file system—all these features on the same computer. But still, there was that old black hole into which time disappears when you don't have a good application modeling tool. Rather than throw up our hands and mutter "tant pis" with a dismissively Gallic sniff, we decided to inch up to the abyss and peek in.

First of all, we tried to determine the requirements of a "sufficient" app modeling solution. We agreed on these specifications:

Voila, voila, as we say in France. With such a tool, our problems disappear. But...who's going to write it?

Many times, I thought the solution was on my desk: the new Super++Tool™ . But there was something missing: either it was impossible to add my own objects into the framework, or I had to use a different language than the one I was developing with. Super++Tool gets better with each release, but we needed to go in a slightly different direction.

So we decided to write it ourselves.

The toughest part of a C++ application modeling tool is the language itself. Unlike other object-oriented languages, such as Objective C or Pascal Object, C++ doesn't know how to instantiate objects from classes that are added dynamically. To create custom objects, the tool has to generate, compile, and link a piece of source code. Generating source code is dangerous—programmers will want modify that code, and so our fifth requirement is threatened. But we found no way to escape this, so we did our best: We designed the program to generate as little code as possible.

The Application Modeler (as it's currently called) is running on selected BeBoxes around the world. Soon it will be shipped with every machine. The app isn't thoroughly polished—we plan to modify some features, especially for the user interface—but, still, you can create an interface, add and manipulate your own objects, and many other things.

We at Lorienne [Now BeatWare] are, of course, the first users of this tool. We're using it now to develop other applications: a word processor, drawing and paint programs, a spread sheet—but we'll leave these for another article.

For more information, send an e-mail message to

Be Developer Profile: Verified Logic

UNIX just isn't my idea of a lot of fun,” says Willy Langeveld, a Ph.D. physicist at the Stanford Linear Accelerator Center (a government-funded scientific research institution) in Palo Alto, California.

I work mostly on UNIX systems by day,” Willy says. “So I decided that in my free time, I wanted to enjoy myself.” That's why he's developing for the BeBox. “When I heard about the BeBox, it felt just like 10 years ago with the Amiga—it sounded like it would be fun!

Willy is no software rookie. While he formally established his company, Verified Logic, just this year, he's been developing for the Amiga for many years. His products include the terminal emulator VLT, the REXX support libraries rexxarplib and rexxmathlib, and the XPR (external file transfer protocol) standard. He also worked with Tom Rokicki of Radical Eye Software on a port of Maplesoft's Maple V release 3 to the Amiga.

Aside from fun, what Willy likes best about the BeBox is its fast, powerful multi-processor design. “It's faster than any Amiga.” And as for the BeOS? “I think it could easily eclipse AmigaDOS within a year.

Currently, Willy is working on "rfs", a client/server protocol that mounts the BeBox file system on an Amiga. “One might ask what use this will be once the BeBox acquires an NFS server—the answer is that rfs isn't a BeBox-only program. The file server isn't platform specific, it will run on just about anything. And anyone could write a client part to use with something other than an Amiga.” He expects rfs to be available this summer.

Langeveld's BeBox plans include the possibility of a port of Maple V. Also, many people have asked him to port VLT to the BeBox.

My hopes are that the BeBox will become the next Amiga. After that, it will take over the world,” says Langeveld. Of course, being a scientist, he admits, “I'm too much of a realist to believe that both of these hopes will be realized. But I really think the first one might happen!

In the meantime, we're happy to report that Langeveld is accomplishing his goals: “It's fun! Really fun! That's all I want right now.

For more information, send an e-mail message to

What Business Are We In, Really?

By Jean-Louis Gassée

As always, there is food for thought in, the Internet newsgroup dedicated to the BeBox and the Be OS. Usenet newsgroups are not known for meekness and ours is no exception.

Recent threads suggest that we have made confusing gestures and statements about the company's goals and the vehicles that we think will get us there. They're good questions: Are we in the hardware business or the licensing business? In the PC or the workstation market? (The short answers: Yes, yes, yes, and no).

The confusion is understandable, and we acknowledge our part in prompting it. After all, we seem to want to do everything: we sell hardware but we'll also license the Be OS; the OS is new, but it also supports Posix. This raises more questions, some of which have been posed on the newsgroup: Why not just go Unix all the way (or NeXTStep, or OpenStep)? Why not port the Be OS to Mac hardware (and sell CD-ROMs to Mac users while they wait for Copland)?

To complicate matters, our slogans

Amiga 96” “The Samuel Adams of the PC business” “The muscles of a workstation, and the price of a PC

are a bit, shall we say, "omnidirectional." How could we be surprised by the confusion?

Let's deal with the Unix/Posix/workstation question first. A premise of our work is that we address the structural limitations of aging PC operating systems: The gods have to support an installed base, and that has made them brittle and rigid. We, on the other hand, can afford to be flexible—but we have no applications. So we shift the focus to the positive: We have higher throughput, a simpler programming model, an easier integration of new technology. These are tools for cutting-edge Web and digital media applications built by power-hungry, tinkering users (a.k.a. geeks). A Posix layer—purchased at an affordable amount of effort on our part—seemed a natural fit. It would help our customers by bringing in hundreds of public domain programs and utilities...But that doesn't make the BeBox a workstation.

Furthermore, my own observation of computer hardware and software is that they don't scale down very well. Once you've set out a design, it's much easier to add to it than to make a "lite" version. There is no Windows-lite or Unix Junior, and entry-level workstation hardware doesn't sell. Mindful of the scaling problem, we didn't want to start as a workstation with nowhere to go but bigger and unthinkably expensive. Instead, we set out to produce the least expensive multi-processor hardware we could, settling for the unloved 603.

(Why unloved? Because Motorola kept telling us the 603 “couldn't do” multi-processing. And because the small cache causes poor performance with the 68K emulator/crutch that the PowerMac needs to prop up old applications. Frankly, people who see the BeBox in action can't believe the performance we get out of a "low-end" chip. But it's not just hardware that does it--it's fresh, baggage-free software. And soon, we will scale up and the Be OS will really shine. Joe Palmer has us drooling over his 604-based designs.)

With regard to licensing and hardware: We offer the Be OS for licensing while we also sell it bundled with our quasi-PPCP hardware. I dealt in a prior newsletter with the PPCP opportunity: We can't make PPCP happen all by ourselves. If it becomes the PC/AT of the PowerPC business, our hardware will be PPCP compatible and we'll sell CD-ROMs with the BeOS to run on PPCP machines made by Apple and others.

In any event, there is a strong historic reason to offer OS licenses right from the start: If you don't do it from the very beginning, it's next to impossible to do it later. Let's try a thought experiment -- purely fictitious, of course:

The scene is Apple's boardroom, 1986. Apple is making $1,000 gross margin on every Macintosh they sell. Everyone in the room agrees that the Mac OS should be offered for licensing. But an OS license goes for $100 or less. Shifting the business to licensing means disturbing the smooth graph of ever-increasing earnings that was promised as a sacred trust to Wall Street. So how smart would it be for the CEO and the CFO to face share holders and say:

Sure, we'll take a steep earnings dive for about three years. But after that, we'll re-emerge with a new business model and even greater shareholder value. Trust us.

(Of course, once the earnings were lowered by other factors, Apple's transition became easier--but a couple of CEOs and CFOs had come and gone in the meantime.)

By offering licenses from the very beginning, and sticking with a lean business model, we intend to make the hardware vs. software question a moot one. The most important thing we do is system software. We make hardware because of a chicken-and-egg situation in the PC business: There were no multi-processor personal computers because there was no MP OS, and there was no MP OS because no one made PC-priced MP hardware.

So, we apologize for the confusion. But with time—and success -- confusion transmutes into the more approachable "complexity"; more success and complexity becomes "richness". Look at Microsoft—no one seems to be confused by their being in the OS and the application businesses...and hardware...and servers..and browsers...

Of course, I can't wait to find out where we'll be five years from today. In the meantime we need to continue evangelizing, supporting developers, marketing, and selling the BeBox and the Be OS. We might even get into the T-shirt business.

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