Although my blog has become relatively stagnant, the rest of my life has been changing — and there are even bigger changes ahead.

My children have been growing into adulthood one by one, and my parenting time has been shrinking as a result. To take up the slack, I bought a bike a few years ago and started riding it on the many local bike trails. Initially cycling was a way to get healthy and enjoy the outdoors, but it has turned into much more. Riding a bike is great exercise, but it’s also a fantastic social activity when you do it with friends, and I have made many new friends in the very large and growing cycling community here in Ohio.

The last few years I’ve also been racing my bike competitively in the many amateur bicycle races held during the spring and summer. I never played organized sports as a kid, so this has given me an avenue to explore an unfamiliar side of myself.

While cycling has changed my life in many ways, even bigger personal changes are on the horizon. I’ve been divorced (or as I often say, “married to my bike”) for many years, but even that will be changing later this year — unless she changes her mind before we seal the deal.

In addition to the many personal changes, I’m also making some professional changes. I’ve accepted a contract offer to join the software development team of Belgium based Bricsys, maker of BricsCAD. I will continue my philanthropic work, including work on the OpenDCL project and my participation in online ObjectARX, AutoLISP, and C++ programming forums. I will continue maintaining and supporting ManuSoft software products. I will even continue blogging here and writing for upFront.eZine, but maybe my focus will shift a bit.

I’m looking forward to all these new challenges, and excited to see where this new road leads. Thank you for travelling with me!

QuirkyPolyline: exposing foolish programmers

In AutoCAD, the AcDbCurve class defines a general parametrized curve. On a parametrized curve, points in space are mapped to real numbers (parameters) by an arbitrary function F(p) for values of p from the curve start parameter to the curve end parameter. Defining a curve this way simplifies working with complex 3D curves because one can work in the curve’s one dimensional “parameter space” instead of the more complex three dimensional cartesian space.

The choice for how to parametrize a curve entity is up to the implementor. Parameters are designed to be opaque, so consumers of parametrized curves must make no assumptions about how a specific curve implements them. The only thing guaranteed about the parameters of a curve is that all points on the curve map to a unique parameter in a continuous range from the starting parameter to the ending parameter.

AutoCAD entities such as lines, circles, arcs, polylines, rays, and others are derived from AcDbCurve. These basic curve entities have very simple and straighforward parameter mappings that can be reverse engineered with very little effort, so lazy programmers sometimes make assumptions that are not guaranteed to always be true. Even smart programmers often get tripped up on parametrized curves because they use parameter space when they should be using distance space (that is, distance along the curve). The AcDbCurve interface provides functions to translate from parameter space back and forth to distance space, as well as back and forth to three dimensional cartesian space.

Wise programmers always let the curve itself perform all translations to or from distance space or cartesian space so that their code never relies on the actual value of a parameter. Foolish programmers take shortcuts by making assumptions about parameter values. For example, it happens that in all past versions of AutoCAD, the parameter of the midpoint of a polyline segment is exactly halfway between the segment starting parameter and the segment ending parameter, and the segment starting and ending parameters are always equal to the index number of the corresponding vertex. A foolish programmer (e.g. here and here) may use this knowledge to calculate the midpoint of the segment by guessing it’s parameter. The foolish programmer’s code will fail when a case arises where that guess is wrong. It is the purpose of QuirkyPolyline to provide such a case.

QuirkyPolyline defines a QPOLY command that prompts for a selection set of lightweight polylines in AutoCAD, then converts the selected polylines to “quirky polylines” that expose a completely different parameter scheme. Quirky polylines look and act perfectly normal in all respects. If you save quirky polylines, they will be stripped of their quirkiness. There are no long term effects of making polylines quirky; it’s just a temporary change that wears off on its own.

Making quirky polylines is useful for testing code that works with parametrized curves. If your code makes assumptions that it shouldn’t, quirky polylines will expose the error of your ways. Over the years, I have had arguments with people who insisted that their assumption had been validated by extensive testing. My counterargument is that someone, somewhere (possibly even Autodesk itself) already has or eventually will generate a derived entity where the assumption is not true. In addition to providing a proving ground, QuirkyPolyline is designed to demonstrate to the naysayers that unusual parametrization implementations can exist in the wild.

The download contains ARX modules for AutoCAD 2000 through AutoCAD 2015. To use QuirkyPolyline, just load the module that matches your version and architecture of AutoCAD. Create a lightweight polyline with the PLINE command, then use the QPOLY command to convert the normal polyline to a quirky polyline. You can use the LIST command to verify that it did become quirky, but you should notice no other detectable changes.

[Note: the download has since been updated and moved to the ARX freebies page]

Here is a useful little lisp function that defines a PP command for displaying the parameter value of a picked point on a selected curve entity. You can use this to explore other curve entities, and to see how the polyline’s parametrization changes after it becomes quirky.

(defun C:PP (/ sel pointoncurve param)
(if (setq sel (entsel))
(setq pointoncurve (apply 'vlax-curve-getclosestpointto sel))
(setq param (vlax-curve-getparamatpoint (car sel) pointoncurve))
(princ (strcat "nParam = " (rtos param)))

I hope this helps you avoid the pitfalls of parametric curve code. Remember, don’t be a foolish programmer!

All your base are belong to us

Excited news stories this morning about how your computer is vulnerable to attack from a phone plugged into your USB port made me chuckle. This “novel hack” involves making an Android phone mimic a USB keyboard in order to send keystrokes to the computer. Cool, but why wouldn’t a hacker just use a USB keyboard in the first place?

This is a good example of the over-hyped threats that often generate headlines. Sure, it’s true that allowing potentially compromised USB devices to be plugged into your computer could be harmful, but opening your web browser is much more likely to result in damage. The only thing remotely novel about this “attack” is the notion that your own phone could be the source. That’s interesting, but hardly worthy of the breathless coverage it’s getting.

The bottom line is that most malicious attacks are the result of you doing something you know you shouldn’t do, such as opening an email attachment or blithely running downloaded programs without regard to their trustworthiness. Very few malicious attacks occur without your explicit permission.

This post reminds me of the one time my computer was infected with a virus. It arrived on a floppy disk that I received from, of all places, my local health department. I guess smart phones are the new floppy disk.

Infinite Computing: Bah, Humbug!

At Autodesk University, Autodesk CEO Carl Bass introduced the term “Infinite Computing” in an attempt to define Autodesk’s perspective on “the cloud” from a unique angle. I think the term is a brilliant and effective use of terminology because it focuses an otherwise nebulous concept and it radiates a sense of real and immediate purpose.

Infinite computing is not really infinite, of course, and it’s certainly not infinitely accessible. However the metaphor is apt, because like the physical universe, as long as the virtual universe keeps expanding it is essentially infinite. [I can’t resist having some fun and taking the analogy a little bit further: at some point, Moore’s law will encounter relativistic effects, and we’ll realize that every transistor warps the virtual space-time continuum in proportion to the square of its clock speed.]

So why am I bearish on the prospect of infinite computing?

Let’s say you buy a computer with multiple processors for, say, AutoCAD. Two processors can produce a nice performance boost, because AutoCAD can utilize 100% of one processor while the operating system uses the other. But what happens if you quadruple your capacity to eight processors? Unless you’re running independent programs that can use the extra processors, they offer very little benefit and are essentially wasted.

The moral of the story is this: an infinite computer is ineffective and inefficient unless it has an infinite number of simultaneous tasks to perform. It costs computing power to manage parallel tasks, so the practical limitations of “infinite” computing make it obviously unrealistic for all but highly specialized tasks. Even if we give it a more accurate name like “massively parallel computing“, such a system is hardly “sustainable” (to use another modern term of art) due to the inherent inefficiencies.

A compromise is necessary. There are new ways to look at old problems that enable a more parallel approach to finding solutions, and I have no doubt that many engineering problems can be restated in a way that makes them amenable to parallel processing solutions — but that’s hardly a revolutionary concept, and it certainly does not require an infinite computer for its implementation.

In the final analysis, “the cloud” is going to be about individuals connecting to each other and to their data seamlessly and in a location-agnostic way, and the “infinite computer” will be what they use to do it. Nothing more, nothing less.