Older blog entries for raph (starting at number 381)


haruspex, nomis: it's great having this discussion with people who care about curves and the UI's for editing them.

haruspex wrote:

The fact is, any geometrical figure - ellipse, circle, parabola - is irrelevant to the problem of fitting a natural, drawn curve. Pure geometric shapes (with the exception of straight lines) rarely occur in a letter outline, so I disregard them as modelling test cases. Instead, I ask, how well can this primitive deal with a pre-mathematical, natural curve, as might have come from the designer's hand? How awkward is the translation? (Your curve continuity arguments are relevant theoretical ammunition here I think, although my assessments are usually subjective, not objective.)

Absolutely. I wasn't trying to say that an ellipse had any special status as a smooth curve, or that its simple mathematical representation has any relevance to the question of smoothness. However, I do believe it is an example of a smooth curve.

That said, I could probably have come up with a better example, for example, an "S" curve. Whatever curve primitive you use has to interpolate between a fairly tight negative curvature on one side and a roughly equal positive curvature on the other, with an inflection point somewhere near the middle. Obviously, some fonts have smooth S curves, and others don't. Cubic Beziers are actually pretty good at making an S curve, in my opinion. Certainly, it's not uncommon in professional fonts to see a single Bezier traverse from a vertical tangent in the upper left corner to another vertical tangent in the lower right.

And here, I believe, circular segments don't necessarily do a good job. If you try to do it in two or three arcs, you'll be able to see the knots pretty clearly. The S in Computer Modern has three, and suffers badly from it in my opinion.

The UI makes a pretty big difference when designing with circular arcs, too. Most of the masters I've seen from Bitstream have the centers of the circular arcs explicitly drawn. If you draw the main slope of the S with, say, eight arcs, then the centers should describe a fairly continuous path in and of themselves. In the hands of a master designer, I'm sure that using one circular arc for every 15 to 30 degrees of the original curve can lead to some of the cleanest, smoothest curves you can imagine. But if you don't do a good job visualizing the radii of curvature, and put the tool in novice hands, my guess is that you'll see bad curves.

To sum, cubic Beziers do a good job fitting smooth curves, such as the main body of an S, but it's also very easy to draw unsmooth curves. Circular arcs take more primitives to fit the same curves, but, at least with good discipline and a good UI for visualizing curvature, result in much more reliably smooth curves.

I think the Cornu spiral has a good chance of combining the best of both primitives. A single Cornu spiral segment can make a pretty darn good S all by itself. Conversely, I'm hoping that any unsmoothness that results from drawing a curve from curvature-continuous Cornu spiral segments was placed there deliberately, or at the very least, should be obvious to a moderately trained eye just from looking at the control points. [this last property is related to the property I mentioned last time of maintaining smoothness when the control points are perturbed, but is expressed more in terms of user experience than math.] I don't believe any other geometric primitive can come close to claiming all these properties.

nomis asked what a UI for Cornu spiral curves might look like. While there are no doubt many ways to do it, my first cut is going to look something like this. Basically, you just put down a series of on-curve points. Math fills in the rest. I like to keep things simple.

nomis also wrote:

The point I am trying to make: I don't think that the fundamental primitive is that important. It is the way we present it to the user that makes the difference.

I very much agree that the UI is important, more important even than the choice of primitive, but I still feel there's a strong case to be made for a primitive which yields very good results with a small number of control points.

That having said: Cornu splines obviously will be approximated with e.g. beziers at some point, so we are actually talking about user interface here... :-)

Not surprisingly, one of the first things I've implemented is a converter from Cornu segments to quadratic Beziers, but that transformation is not as inevitable as you might think. The killer advantages of Beziers are ease of affine transformation and subdivision (using De Casteljau), the latter of which is especially nice for rendering. That said, the Cornu spiral is remarkably well behaved for being a "special function", and it's probably not anywhere nearly as painful as you might think to work directly in the space of the Cornu parameters. The key property is that the motion along arclength goes at a constant rate with respect to the parameter; with Beziers, it's not hard to set up curves for which this motion goes through or near zero, which results in numerically fairly tricky curves. Also, two cubic Beziers can intersect at up to nine points, while I think it may be true that two Cornu spiral segments each traversing no more than 180 degrees of arc intersect at no more than two points.

Also, thanks for the kind feedback on FontFocus! Your eyes are sharp - it does indeed work in the X direction (on vertical stems) but not in the Y direction (on horizontals). In general, having an uneven baseline or x-height line is a pretty serious artifact, while subtly distorting widths and spacing isn't. It might still be worth playing around with, though, especially for non-latin scripts.

haruspex wrote:

I think it's long been clear that Beziers are not a good user abstraction for curve editing - but what's wrong with circle segments between on-curve knots, as chosen by IKARUS, METAFONT, et al? I am not sure anything could be more natural. I suppose the Cornu could be seen as a French-curve style extension of circles. I think I need to write that experimental path editor I always planned, to play with these alternatives :)

What's wrong with circle segments? I'll tell you what's wrong...

But first, while circular arcs were the basis of some font formats (most notably Bitstream), they were definitely not the primitive of Metafont, and I'm not sure about Ikarus either. Metafont's primitive is the cubic Bezier, just like PostScript, but, unlike Type1 fonts, Metafont lets you do stroking with elliptical pens and constructive area geometry.

From what I've been able to learn about Ikarus, the IK file format itself just specified corner points, tangent points, and on-curve points. It was basically up to the application to figure out how to fit an actual curve to those points. Certainly, circular arcs would be one approach, but I suspect that Hermite splines may have been used as well.

Now, in order to argue which geometric primitive is best, I have to define the goals. One such goal is that it be expressive, meaning that, given an arbitrary smooth curve, I can fit it with a relatively small number of primitives (each with a relatively small number of paramters). Love or hate them, cubic Beziers are awesomely expressive.

And circular arcs do not have this property. You need quite a few of them to closely fit an ellipse, say. Take a look at some Bitstream designs -- you'll see a great many more control points than in a typical Type1 font.

I believe that curve smoothness is best defined as variation in curvature. By this metric, circular arcs are not that great; as you follow a curve, you'll have constant curvature along arcs, but a discontinuities at the joins between arcs. Of course, the more arcs you use, the less the discontinuity, but that's true of just about any primitive. Heck, you can make a decent enough outline from straight lines if you're willing to use enough.

Beziers can in fact be made to be curvature-continuous, at joins as well as the interior of the primitive. In fact, one of the central themes of John Hobby's work on Metafont was a global optimizer to choose tangents at knots to minimize curvature discontinuities (technically, for reasons of numerical stability, his algorithm zeros out the discontinuity in "mock curvature", a linear approximation to curvature, but the difference is subtle).

But Beziers are not naturally curvature continuous. In fact, my experience is that it's very difficult to design smooth Bezier curves by eyeball, especially as more control points are added. This is a subjective criterion, but I think it's possible to quantify it, as well: how well does curve smoothness hold up when you perturb the control points (or other parameters)? In general, if you start with a smooth Bezier curve, perturbation will make it worse.

This criterion is especially important when you're dealing with meta-fonts (of whatever flavor). In fact, Adobe's use of linear interpolation of cubic Bezier control points in their Multiple Master technology doesn't even guarantee tangent continuity, much less smoothness. It can be made to work well, but requires care and skill.

By these criteria, segments of the Cornu spiral are an excellent primitive. They are expressive in a way that circular arcs are not (in particular, you can cut from the central segment to make a very pretty "S" curve), while at the same time a Hobby-style global optimizer to determine the tangents can guarantee continuity of curvature across the whole curve. Variation of curvature is linear along the interior of the primitive, so you can't get wide swings there either, as you can in Beziers.

It also helps that the Cornu spiral representation is so concise - the primitive is fully determined by the endpoints and tangents at the endpoints (six degrees of freedom, as opposed to four for straight lines and eight for cubic Beziers). I believe this will help make the user interface both simple to learn and productive to use.

And I am hacking on a pattern plate editor, so if you're patient you will be able to play with it before too long.


I haven't said much here except for hints, but it now looks like Heather and I are getting divorced. We hadn't talked about it with the kids, but yesterday Alan asked some direct questions, so now he knows. I didn't want him learning about it by someone saying, "hey, I read on your dad's blog that your parents are getting divorced, sorry to hear about it." Stranger things have happened, though, I suppose.

Other than that, things are reasonably good. I was at a post-birthday party for my longtime friend Dan Rice on Saturday, and had a great time.

The spam in my mailbox is rather out of control. I'm experimenting now with a gmail account. If you want to contact me there, use the firstname.lastname@gmail.com convention.


Fonts have been my friend through all the turmoil. I've been active on the typophile discussion board. Also, I was pleased to see some of my previous postings on fonts picked up by typographica and Luc Devroye.

My Century Catalogue is coming along well; I have all alphanumerics and a bunch of punctuation, but have to draw a bunch more fiddly shapes to fill out an AdobeStandard encoding vector. I'm also playing around with Centaur, an astonishingly beautiful font, and have a rough draft of the capitals.

I've also been playing with the Cornu spline (PDF of the curve) as a primitive for curve design, and am now absolutely convinced that it's better than Bezier curves.


And now for something of a dramatic announcement. The secret font rendering project I've been working on can now be discussed publicly. Ladies and Gentlemen, I introduce FontFocus.

We're primarily looking for commercial licenses of this technology, but also plan to sort out some kind of free software release soon. I personally would love to see this rendering technology integrated into a good web browser.

Scans of font books

The British Library is doing it right: they are making their high quality scans of Shakespeare editions and other rare books available for all. Most other rare book collections are much more proprietary about their holdings.

The Million Books project has scans available of two landmark font books: the ATF 1923 specimen book and the Manual of Linotype Typography. I've had trouble with the DjVu viewer (it seems to hang Safari on my Mac), but these look like good resources. Of course, I have many of my own scans of the ATF 1923 on my own site. I've done the original scans at 2400 dpi, but don't have the big scans up on the server (it's about 5G worth of data right now). Maybe I should contact the archive.org folks to see if they're receptive to hosting my scans.

13 Aug 2004 (updated 13 Aug 2004 at 22:36 UTC) »
Musings on fonts

I've been kinda immersed in fonts for the past week or so, and have some things to share with you font nuts out there.

First, I've picked a font revival to work on: ATF Century Catalogue. I think this may be one of the most underappreciated fonts out there. It's definitely a representative of Beatrice Warde's Crystal Goblet theory of font design, as opposed to all the ego-driven stuff work churned out now.

In particular, I believe an adaptation of Century Catalogue is an excellent candidate for a font to supplant Computer Modern as a font for setting math. In addition to aesthetic beauty, an important consideration is continuity with existing traditions of math typography. A great many math texts in the last century have been set in Monotype Roman No. 8, of which Knuth's Computer Modern fonts are a reasonably accurate digital revival. But this is far from the only font well represented in the literature, nor, arguably, the best.

The model that Knuth acknowledges as the most aesthetically pleasing is Volumes 23 and 24 of the Transactions of the AMS (see p. 20 of his book, Digital Typography). The sample he shows appears to be set in a variant of Monotype Old Style (not exactly No. 2, as the tail of the 'c' in the latter are curved up more). Even so, he doesn't like some aspects, for example the angularity of the italic 'x'.

I agree that the shape of the italic 'x' is important - indeed, to me, it strongly connotes variableness, in much the same way that a copperplate gothic connotes the style of a banker or lawyer, or Old English Gothic connotes an old-style newspaper banner.

So, after looking at dozens of fonts, I've concluded that Century Catalogue is the one. The roman resembles the Monotype Old Style fairly strongly, but is in my opinion better drawn (by master typographer Morris Benton Fuller). In addition, its italic (which is more closely based on ATF's Baskerville Italic than a member of the Century family, but is nonetheless stylistically quite coherent with the Roman) is much closer to what people now expect from math fonts.


Perhaps the biggest complaint about Computer Modern is that it's too light. Both the weight of vertical stems, and the relative weight of serifs and hairlines compared to the vertical stems are lighter than mainstream text fonts.

When I got my copy of Knuth's Digital Typography, I was struck by how much better it looked than most of the TeX output I'm used to seeing, especially from laser printers. I now believe I know the secret: press gain, probably in this case introduced deliberately to make the body text look good. You can see the effect pretty clearly in my 2400dpi scans.

What is the best primitive for curve design?

Most 2D curve design (including fonts) done today uses cubic Bezier splines. Almost all of the remainder is quadratic Beziers. There are other choices, and I wonder if some might be better.

In particular, I find it tricky to make smooth curves when there are a lot of control points. I'm sure it gets easier with practice, but I'm not sure people should have to adapt to the underlying polynomial nature of the spline, when perhaps smoother, more natural primitives exist.

For example, Ikarus used Hermite splines, in which all the control points lie on the curve. In Beziers, you have to position the off-curve control points so that they "magically" adjust the curve how you want it.

From what I can see, the main reason inexpertly drawn Beziers look unsmooth is large variations in curvature, both discontinuities at the knots and in greater deviation in curves than needed to smoothly connect the endpoints. I'm thinking of building a tool that graphs curvature along the path of an outline. I have little doubt that this tool's output would reveal much less variation and discontinuity in splines drawn by experts than by newbies.

So, to me, the most promising approach is to use a primitive that has smoothness of curvature built-in, so that by default it's easier to draw smooth curves than unsmooth. Of course, it should still be possible to do the latter, but I have no problem with making it require more control points than an equivalent unsmooth Bezier curve.

The most promising primitive I've seen so far is the "circle spline" of Carlo Sequin and students [SIGGRAPH PowerPoint presentation]. Near the end of that presentation, he raises the possibility of using a Cornu Spiral, which is mathematically constructed so that curvature is continuous at endpoints, and linearly interpolated in between.

For those more interested in this issue, John Hobby's paper "Smooth, Easy to Compute Interpolating Splines" is a must-read. My gut feeling is that his work is good, but that replacing his choice of cubic Bezier as a primitive with a circle spline or Cornu Spiral may give better results. He found that making curvature continuous can yield instable results, so he uses a linear approximation which guarantees stability. I wouldn't be surprised if this instability would go away with a better primitive.


The Wikipedia is fun (and I've been contributing a bit to it), but one of the things that really irritates me is how ripoff sites usually manage to get higher Google rankings than the real thing. Most people don't know better, and often link to the ripoff pages, further strengthening their rank.

It's not just the wikipedia, of course, even though that's a notable and recent case. If you go searching for free fonts, you don't come across many sites of people who've put time and effort into creating, collecting, and critiquing the fonts, but you sure do find the ones that aggregate thousands of fonts (most of which are ripoffs of proprietary versions themselves), then presumably make some money off ads and whatnot.

I'll be releasing the math fonts under some form of free license so that they can be included in Ghilbert, of course, but it would be nice if there were some way to discourage them from being ripped off. If I continue to make fonts, I'm tempted not to release them freely, partly because of the ripoffs, and partly because free fonts are seen as junky.

31 Jul 2004 (updated 31 Jul 2004 at 23:56 UTC) »
Great Hackers

The inestimable Paul Graham has another essay out: Great Hackers. Worth reading. Go ahead, I'll wait.

Back already? Ok, good. I find a lot of what Paul writes to be resonant. I especially liked his section on "nasty little problems" - I think the elimination of nasty little problems, as opposed to genuinely difficult and challenging ones, should be a top priority, especially for free software developers. Longtime readers will not be surprised to hear me categorize the auto* suite as a particularly rich source of such nasty little problems, for all that it does a pretty good job solving a set of real problems, and is a huge improvement over what came before.

Paul seems to be addressing the issues at the scale of individuals or small (startup) companies. I would like to see more attention given to issues at a much broader scale: the interaction between hackers and society as a whole.

One way for society to view its great hackers is as a resource, comparable to a natural resource such as mines for valuable metals, or fertile fields for agriculture. Most healthy societies try to convert the potential of those resources into wealth. They plant good seed and tend the land, rather than salting the fields. Of course, societies vary in the extent to which they do a good job of this; famine is much more common in Africa than in the West.

Societies vary even more widely in their ability to get good work out of hackers. Paul explains fairly well what's needed: mostly, let us do our thing and get the hell out of the way. I think his section "More than Money" tells part of the story. I don't think hackers hate money, but I do think we hate spending time hustling for money. There are plenty of people who do, and they tend to become investment bankers and the like. I don't think those people understand us very well.


There's a fair amount of emotional turmoil in my marriage right now, and I've been taking refuge by spending time with a subject very dear to my heart: font design.

In particular, I've been scanning ATF type specimen books and carefully studying the designs therein. I now have a great scanner (Epson 4870), and the scans at 2400 dpi really pick up the detail, and let you see the quality of the printing.

I was especially surprised to compare the quality across the decades. I have four books, one each from 1912, 1921, 1934, and 1941 (all collected by my father). The printing quality from 1912 is head and shoulders above the rest. As a seat-of-the-pants estimate, I'd say it's roughly equivalent to a 2000dpi digital printer.

I've especially grown to appreciate the work of Morris Benton, the chief type designer at ATF for many years. I get the feeling that he was positively obsessed with printing quality. His father was a very gifted inventor, and worked on many machines used in type design and typefounding. In particular, his pantographic "delineating machine" and matrix engraver not only scaled a single design to many sizes, but could also apply general affine transformations, just like PostScript today.

One of the secrets revealed by close study of these specimen books is how type scaled to different sizes. Most fonts today are designed at one size, then enlarged or reduced using strictly mathematical scaling. Master printers over the centuries, however, have long understood that smaller fonts should have more robust features, while larger ones can be more elegant and refined. Periodically, type designers working with new technologies try to rediscover this fact, but it always seems like an uphill battle, probably because of how much extra work it takes to optically scale a font. Adobe is producing many fine optically scaled fonts now, but one gets the impression they're still a small minority of their entire font catalog. Another important example, from the world of free software no less, is the Computer Modern fonts of TeX, which, while technically way ahead of their time, are not considered especially appealing by serious typographers.

So it's especially interesting to learn that ATF used almost purely automated techniques to produce different sizes of font from a single "pattern plate". I came across an excellent article by Patricia Cost which explains the process in considerable detail.

I'll try to strip out the mechanical and historical stuff and just describe the underlying "algorithm". The scaling happens when a matrix (or mold from which the actual metal type with raised letter is cast) is engraved from a pattern plate.

The pattern plate is a piece of metal about 4 inches high, which contains a raised outline of the letter. Placed in the matrix engraving machine, a "follower," or stylus, traces the inside of this outline. The motion of this follower describes a path.

At the same time, a high-speed drill traces a scaled version of this path, cutting into the matrix. Through the mechanical ingenuity of Linn Boyd Benton, the scale factors can be different for horizontal and vertical movement. Typically, the pattern plate was designed for a 36pt font size. To cut a matrix for a 6pt letter, the x scaling would be a factor of 1.19 of the y scaling.

The path traced by the follower, though, isn't exactly the same as the inner outline on the pattern plate, nor is the outline of the letter engraved in the matrix exactly the same as the path of the drill. The follower has a nonzero diameter, so the path it traces is "shrunk" by half that diameter, so that the width of strokes is reduced by one diameter. Similarly, the cutting tool has a nonzero diameter, so the outline engraved into the matrix is "grown" by half that diameter, so that stroke width is increased by one diameter. When the ratio between these two diameters is the same as the scaling factor, the outlines correspond closely (especially if the letter on the pattern plate has slightly rounded, rather than perfectly square, corners), and stroke weight should be identical (after scaling, of course).

However, by using a smaller or larger diameter follower, it's possible to increase or decrease the stroke weight, respectively. And, after studying the font books, I see that the typefounders at ATF did consistently apply this technique for scaling fonts. A typical recipe would be to use a grow radius of 100/ptsize - 3 units (on a 1000 unit/em grid), while applying a horizontal scaling of 1.18/ptsize + .967 (both additive factors chosen to normalize for 36pt design). It's worth noting that the Computer Modern fonts use a width scaling of about 1.3/ptsize, so the stretch of smaller sizes is even more exaggerated compared to the ATF example.

I want to write this stuff up, but to do it justice will require quite a bit of time, especially to produce the illustrations. In the meantime, this image of two lowercase a's from Lightline should whet the appetite of you type fiends out there. The two images are superimposed with a "difference" blend mode, so you can see two outlines. The sharper image is an 18pt "a", scanned at 2400 dpi, and scaled in the horizontal direction by a factor of 1.15. The fuzzer image is a 6pt version of the same character, scanned at 2400 dpi, then enlarged by a factor of 3x. Thus, 0.001" at that size corresponds to 7.2 pixels. You should be able to see, then, that the 6pt version is grown by a little less than a mil with respect to the 18pt version.

The good news is that it wouldn't be that hard to adapt this process to the present-day practice of digital typography, and that it can be almost entirely automated, so generating a good family of optically scaled fonts wouldn't be that much more labor-intensive than drawing a single good font (which is difficult enough as it is!)


I still haven't re-caught the blogging bug, for whatever reason. So I'll just weigh in with a few bits of personal trivia.

My mom just went back home to Virginia after visiting here for a couple weeks. It was a good visit - she and the kids get along famously.

Both the server hosting Advogato (casper2) and the original casper.ghostscript.com have had various problems as of late - the latter a failing hard drive. rillian has been doing the heavy lifting on recovering these systems, but I helped out some, including a laying-on-of hands to the physical servers (located at transbay.net in Oakland).

Experiencing such server failures, I can't help but think that the future will hold self-configuring high-availability features, especially for content repositories such as CVS and blogs. There's no reason why the data can't be replicated across several servers, and if one fails, for whatever reason, it should be possible to just throw it away and have the others take up the slack.

I think a large part of what makes P2P apps so compelling is the fact that, at heart, they are self-configuring high-availability servers, albeit with limited functionality. I'm most struck by BitTorrent's ability to resume a download (or upload, for that matter) even on a laptop which hops from one WiFi network to another.

I've also been spending some quality time with my collection of type specimen books. I'm enjoying rediscovering the beauty and engineering mastery that Morris Fuller Benton put into his classic ATF fonts from the first quarter of the last century. I'll happily write a blog post about what I've been finding if there is interest.

There are a couple of other things in my blogging queue, including progress on my Ghilbert proof language and applications of formal logic to programming. I may subject my reading audience to further thoughts on the economics of free software, as well. Feedback on which of these topics, if any, you're interested in hearing (or, for that matter, dread), is always appreciated.


Whew, it's been a long time since I've blogged. That's largely because of the site outage here, but also just inclination - after all, if I really wanted to, I could blog at my personal site.

I'm mostly doing well. Among other things, I'm really trying to put some time aside to finish my thesis. I had a great dinner last night (at the Blue Agave in Pleasanton) with Roger Dingledine and Rachel Greenstadt, during which we mostly talked about trust networks, stamp trading in particular, and how to make at least some of that work in the real world.

In any case, welcome back, everyone!

More Letter Quality

You don't see too much sign of it on his weblog, but Robb Beal is going absolutely wild researching issues around letter quality displays, and what it'll take to get free software to adequately support them. If you care about these things (which, from the response I typically get from my LQ blog entries, is rather improbable), he'd be a great person to get in touch with.

The near-letter quality and letter-quality devices continue to roll out. In the former camp is the Sony EBR-1000 book reader, which has an exotic monochrome 170 dpi e-ink display. The software is a mixed bag - apparently it has really crippling DRM, but on the other hand it's Linux based, so presumably people will be able to run good software on it. Hey, send me one and I'll see that Ghostscript gets ported.

One of the newest letter quality devices is the Archos AV500, sporting an approximately 200dpi 706x480 screen. The main app for this thing is playing movies stored on its internal hard drive. As far as I know, it's the first such device play at near-DVD resolution (and, in the 4" form factor, DVD resolution and letter quality are pretty much synonymous). The main competition in this field would appear to be the Portable Media Center platform from Microsoft, which as far as I can tell specs a 320x240 LCD.

LQ: What is to be done?

The issue of how to best support LQ displays is among the many things tor and I discussed. He disagrees with my proposal to have a global "pixels per px" (pppx) ratio for the entire display, and do pixel-doubling at a low level for applications which are not LQ-aware.

I see his point. Presumably, new LQ-aware apps are going to do the right thing, so having extra machinery for automatic pixel-doubling is just more cruft. Pixel-doubling is only relevant for older, legacy apps. I tend to use xv as something of a canonical example, given it's very old-school handcoded X interface (clearly, toolkits are for weenies), a website more than three years stale, a questionable license, and, last but not least, the fact that it's still my image viewer of choice.

Obviously, if you run xv on a letter quality screen, the 5 point fonts won't be very appealing. There are several ways to fix, or at least partially fix, the problem. Probably the way most consistent with the free software philosophy is to build an old-school, yet 2 pppx UI for xv, and patch it in. Of all the approaches, this one probably gives the best overall results.

Alternatively, you could do automatic pixel doubling, somehow recognizing that xv is not LQ-aware. You could do pixel doubling manually (this would, of course, be the most Unix-like way of doing things - provide an incredibly powerful array of tools for solving problems, but don't go 1/200th of an inch towards making them do the right thing by default). In the latter case, you'd have any number of different choices for implementing the pixel-doubling, including an Xnest-like application, running everything through VNC, and I'm sure others will think of more.

Other possibilities include ditching xv and upgrading to an image viewer which is LQ aware, or treating the entire dot matrix resolution X desktop as a retrocomputing target (it's worth noting that many emulators already do pixel-doubling, to adequately display really low res UI's on modern dot-matrix displays).

I still think that automatic pixel-doubling is the most user-friendly thing to do, but perhaps not implementing it is exactly the sort of mosquito bite necessary to motivate the army of Linux developers to fix their favorite apps to be properly LQ aware.

The pppx ratio should be a global configuration parameter

So, while I'm not going to make a strong argument about a pixel-doubling policy, I would like to make a strong argument in favor of explicitly promoting pppx to the status of global configuration parameter. After all, pixel-doubling is merely a stopgap along the road of true LQ support, while fucking up the pppx ratio will continue to make life difficult until my grandkids get sick of the situation and decide to do something about it. (and hopefully, while they're at it, will they please fix the last vestige of the backspace problem? That's generally ok in a Linux-only world, but still bites people when mixing with Mac OS X)

Unless people actually start listening to me, we most likely won't see a global pppx parameter, and so here are my predictions of the bad things that will happen.

Without an explicit pppx ratio, application writers will invariably attempt to guess it on their own, based on information such as monitor resolution information reported through the EDID channel. Inevitably, different apps will come to different conclusions, depending on the exact parameters, so the relative visual size of interface units will be even more inconsistent than today (however, inconsistent UI appearance is very much the X/Unix way, so maybe that doesn't bother people - perhaps I've simply been spoiled by the time I've spent using Mac OS X).

What are the different ways to derive a pppx ratio? I'm sure the most common will be to try to dictate the physical size of a px. If you read the literature on scalable user interfaces, you'll see many people advocating the "point" as the unit of user interfaces, which would effectively nail the pppx ratio to the monitor dpi divided by seventy-two. Other reasonable approaches would be to set pppx to 1 for dot-matrix displays, 2 for letter-quality, and flip a coin for intermediate values of resolution.

Worse, when people are unsatisfied with the pppx ratio guessed on their behalf, they will resort to even uglier hacks to work around it. If the pppx is derived from the monitor dpi, then people will figure out ways to lie about that, which will of course break other apps that actually depend on a correct value.

What's wrong with nailing a px to a definite physical size unit (for example, equating px with point)? In short, because not everybody has the same visual acuity. Software developers, who tend to be uniformly young and virile, easily lose sight of that fact. Currently, on almost all systems, the pppx ratio is fixed at 1, so users have a very handy way to configure the physical size of a px - simply choose a monitor resolution. On CRT's, this is easily done with modelines, but for LCD's, you pretty much have to choose that when you buy the panel. Even so, for most people the choice of an LCD is a fairly intimate, personal decision, and I imagine people consider the size of the px carefully, whether they're consciously aware of it or not. For me, low-res panels display blocky-looking text, and images are not crisp enough. For many others, on higher-res panels, text is too small. I wrote about this over three years ago; Apple was actually touting the low resolution of their expensive displays as a feature, which of course it is if your preference is a fairly large px value, and the only way to achieve that preference is through hardware choice.

Of course, the whole point of high resolution displays is to not have to make the tradeoff between desired px value and display sharpness (the third prong of the tradeoff, of course, is the added cost of generating all those extra pixels in the CPU and turning them into light, but Moore's Law should take care of that, in time).

If, as a software developer, you are tempted to fix the px to a definite physical size, then I suggest you go to your local bookstore, library, or church, and suggest banning all large print books and small print bibles. After all, readability studies have proven that 10-12 point text has optimum readability (for the average reader, anyway).

A bit of bitterness

Based on my experience in the world of free software, I feel reasonably confident predicting that we won't get the pppx configuration parameter right. If I were dictator of the universe, there wouldn't be any such problem, but of course that's not the way free software works, and for the most part that's a good thing. (the primary exception, of course, being the chain of keycode mappings applied to the backspace key - if it were up to me, I'd say that everybody should use the mappings that happened to correspond to the keyboard config I'm typing on now, and then of course the problem would be solved for everybody)

The world of proprietary software has been very good to me lately. I don't get to make the big architectural decisions (those are up to space aliens holed up near Redmond), but I do tend to get a lot of appreciation for my ability to solve problems. Money too, which is nice, but here I'm talking about appreciation.

Lately, I've been making gorgeous prints on inkjet devices (most of my work is on an Epson 2200). I love experiencing people's reactions when they see those prints, and the obvious impact that they have on people's decision to license our technology. It's a rush, a high, and I haven't felt anything like that from the free software world in some time.

I do, however, get emails like this one:

To whom it may concern, I have installed the ghost..garbage, and the gsvu garbage software, and it's a bunch of crap. It doesn't work nor does it convert ps to text. Go-on publishing your version after version-it's useless. Moreover, nearly everything you guys have published about it is a bunch of gobledee-gook that says nothing, and is repititious and loops back to nothingness. Why can't you do or say something useful that normal people can understand and use.

Leon Stambler

Another one that stung, perhaps more than it should have, was a recent description of Libart as having been written by a "monkey with a PHD in low level programming." When I started Libart, I had very warm, fuzzy feelings about solving problems of 2D graphics rendering for the benefit of the free software world. Now, while I'm pleased that some of the ideas of Libart seem to have made an impact, every time I see an app develop their own new graphics library, it bugs me a bit (xpdf's splash, sodipodi/inkscape's libnr, mozilla's gfx, qt's "arthur"), not to mention the fact that fontforge still doesn't do aa rendering, roughly five years after my gfonted prototype.

I'm not just trying to whine at the world here. I know I'm not great at coordinating distributed projects, especially with volunteers. What I am saying is that the free software community has a pretty serious process bug in that it's not very good at making use of my knowledge and skill at 2D graphics, nor at giving me back much in the way of "goodies" in return for my contributions.

So, looking forward at the professional work I contemplate, I find myself getting excited about the prospect of building a top-notch printer controller, to be sold as a part of real products. I do not find myself getting excited at all about solving, say, the printing problems of Linux.

That said, my feelings toward free software and the free sofware community are decidedly bittersweet rather than purely bitter. While I don't especially enjoy having my work NIH'd, I do appreciate and respect the culture of learning that so often leads people to code up their own solution to a problem rather than taking an existing solution off the shelf. Hell, I've been guilty of that enough times myself. Further, in the above I'm talking about my professional work. For other things, such as pure speculative research (including, most definitely, Ghilbert), it's impossible to imagine doing things in any other way than free software. Finally, as long as my professional work is Ghostscript, all of my code gets released under the GPL after a year in any case, so I could get as bitter and negative as I wanted, and everybody would still get the benefit of my work.

Apologies for whining. But I did want to get some of these thoughts off my chest, and I do think that writing about these issues is preferable to not writing at all, which is mostly what I've been doing.

ZF inconsistent?

fxn: I haven't gotten the chance to look at Brian Ford's paper, but it sure is intriguing.

If indeed ZF comes crashing down, that would really validate my decision to make proofs in Ghilbert truly portable with respect to axioms, rather than trying to pick a single axiom system that is both powerful enough for the work at hand, but not so powerful as to raise questions about soundness, or raise problems porting the proofs over to other systems.

That said, the timing could have been a little better for me; as a demonstration of Ghilbert's portability, I picked a construction of HOL logic in ZF[C] set theory, and it's only a few proofs away from being done (of the core HOL axioms, I have only the law of the excluded middle (BOOL_CASES) and a theorem to introduce the iota operator). Oh well.

Busy, busy

It has been a busy month since the last time I blogged. Among other things, we had an Artifex staff meeting, and also tor stayed for a couple of weeks. We had a great time talking serious 2D graphics, color, and so on, plus hanging out with the family.


I'm proud of a couple photos I took on Alan's 8th birthday; the portrait of him, and another of the brothers posing with a penguin prop. Both were taken with my archaic Rapid Omega 100 on slow B/W film (6x7cm), then scanned on my brand new Epson 4870 scanner (highly recommended, btw).

Alan's photo page has unbelievably high Google-juice - looking at the referer logs, the most popular images are the ones that currently show up as #1 and #2 for a Google image search on happy. Even more exciting, a photo from last year of him playing his guitar is now on the cover of a book recently published by Wesleyan University Press.

Max, who just turned four last week, is developing quite a subtle sense of humor. A few weeks ago, when I was reading him Eating the alphabet, he asked if I would get him a Xigua melon. I answered that I didn't remember ever seeing one in a store, but that if I did see one, I'd get it for him, then we'd be able to tell if it's as good as a watermelon, or better (watermelon is one of Max's absolute favorites right now). Max replied that he knew that Xiguas are way better than watermelon. I asked him how he knew that, and he said: I can see inside people's minds. Even fruit. And that Xigua melon is thinking, "I'm way better than a watermelon".

More later

"More later" is one of Josh Marshall's favorite catchphrases, and people rib him for it. I've been doing quite a bit of deep thinking lately about the place of free software in the world, among other things, and I do want to write about it, but it will have to wait until I have a bit more time.

Birthday boy

I turned '"' today. I can't think of any particular meaning to that number. Perhaps it is interesting precisely because it is the first uninteresting number.

Letter quality displays

Robb Beal asked me a couple of weeks ago how to get support for letter quality displays in Linux. It's a good question, and it deserves an in-depth answer.

I want to go over the highlights here, though. There are really three parts to the question. First, what can users do to push things along? Second, what are the "configuration science" problems that need to be solved? Third, what are the imaging problems that need to be solved to get high resolution bitmaps to the display hardware?

As a user, probably the most important thing is to let your friendly local developers know that you're interested in having letter quality displays supported. There are a bunch of ways to do so. If I expand this into a full post, I'll have two sample letters. One says, briefly, "you suck, free software developers are commies, by the way why doesn't your software support LQ?" The other says, "I love your software and would love it even more if it had LQ support. By the way, do you have a paypal address or maybe an Amazon wishlist so I can give you a small token of my appreciation?"

Indeed, funding is a large part of the problem, not least because the prototype displays are still rather expensive. Of course, after Microsoft rolls out their LQ stuff, then the hardware will be available at commodity prices, and then as the gear filters into the hands of free software developers, there will naturally be more motivation to support it. It's a shame that we, as a community, suck so hard at organized fund-raising, or else we'd have already put a few of these displays in the hands of the most important developers, as of course Microsoft did years ago.

Yes, that's a whine. On to the configuration science part of the question. The primary configuration parameter that must be discovered by applications and negotiated between application and display subsystem is the "pixels per px" ratio (which I'll abbreviate here as pppx). The px is the fundamental unit of constructing user interfaces, and has no preset size. On current display hardware, the pppx ratio is locked in at 1. If you like, "LQ support" could well be defined as the support of pppx ratios other than 1.

Many people believe (misguidedly, in my humble opinion), that the "correct" configuration parameter is the display dpi. Indeed, it's fairly easy to come by values for this - the EDID standard provides a way for the display to tell it to the video card, and most OS's now provide at least some support to access the info (in X, DisplayWidth and DisplayWidthMM; in Windows, similar information can be obtained from GetDeviceCaps; in Mac OS X, CGDisplayScreenSize).

UI's are built in units of px units, which, because of currently available display technologies, are identified with pixels. They could have been built out of some physical unit, for example points, so that getting a larger DPI value out of the EDID would cause applications to automatically draw their UI's with more pixels. (indeed, for quite some time a display resolution of 72dpi was so common that many people identified pixel and point, as well). If the technology had evolved that way, then LQ support wouldn't have been espcially difficult. However, technology didn't evolve that way. I don't see this as entirely a bad thing - there are good things about a px-based coordinate system, which I think I'll detail if this becomes a full-length article.

So, the negotiation has to happen something like this. The OS knows that a pppx value of, say, 2, is available. If the app is not LQ-aware, then as it asks for a display surface, the OS knows to give it one with 100 dpi "pixels", so that each pixel that the app draws shows up on the hardware as a 2x2 square of pixels (one can imagine other choices here, for example, drawing text at the full device resolution, but it will be a compromise in any case, and the Real Solution is always to make the app LQ-aware. The chunky pixels might not look that good, but at least they won't break anything or introduce bizarre new artifacts).

But if the app asks for the range of available pppx values, the OS will tell it that 2 is available, and then the app can ask for a drawing surface that matches the physical display resolution.

Once we get to that point, then the app has to actually come up with the higher resolution pixels. But this is a relatively straightforward technical problem, and different applications can solve it each in their own best way. Certainly, having a good 2D graphics library under the hood would be nice, but there are a few around (even if one of the more well-known was written by a "monkey with a PhD in low level coding" :), and if none are satisfactory, you can write your own.

By contrast, configuration science problems have a way of not being readily solved. My favorite running example is what happens when you press the backspace key. After many years, Linux systems have pretty much settled down, but if I login from my MacOS X laptop to my Linux box and open a forwarded X11 terminal, I still find that pressing backspace sometimes prints '^H' rather than deleting the character to the left of the cursor. Let us pray that we can do a better job with LQ configuration.

Update at other blog

Not free software related.

372 older entries...

New Advogato Features

New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.

Keep up with the latest Advogato features by reading the Advogato status blog.

If you're a C programmer with some spare time, take a look at the mod_virgule project page and help us with one of the tasks on the ToDo list!