Decoding Bracket Layers: A Deep Dive Into Glyphs And Google Fonts

Hey everyone, let's dive into a quirky issue I've been wrestling with in the world of font design, specifically concerning bracket layers and their behavior in the context of Google Fonts and the tools we use to build them, like glyphsLib. I've run into some head-scratching compilation differences when dealing with glyphs that have these bracket layers, especially when the conditions defining them are… well, empty or missing. It's like the code is doing something unexpected, and I'm starting to wonder if it's a bug or a feature we've just got to live with. This situation has led me down a rabbit hole of font variations, GSUB feature entries, and the nuances of the design space. So, buckle up, because we're about to explore the ins and outs of bracket layers in font design!

The Mystery of Empty Bracket Layers

So, what exactly are we talking about when we say "bracket layers with empty conditions"? In font design, particularly within tools like Glyphs, you can create alternate versions of a glyph using bracket layers. Think of these as different variations of a single character, say, the letter "a", that appear based on specific conditions. These conditions are usually tied to the design axes of your font, such as weight, width, or slant. For example, you might create a heavier version of "a" to appear when the font's weight is set to bold. Easy peasy, right?

However, the plot thickens when these bracket layers don't have any specific conditions attached to them. Imagine a bracket layer for "a" with no rules. It's like saying, "Here's an alternate 'a', but it should appear… everywhere?" This leads to some peculiar behavior during font compilation. What ends up happening is that the font creation tools, like glyphsLib, will often create an alternate version of that glyph and then insert a GSUB (Glyph Substitution) feature variation entry. This entry is designed to swap in that alternate glyph for the original, but the substitution happens across almost the entire design space. "Almost," because there's a small catch: it seems the substitution doesn't apply at the absolute minimum of the design space. The logic appears to be using a "greater than" (>) comparison instead of "greater than or equal to" (>=).

This behavior is what's causing these compilation differences I'm encountering. It's a bit like a hidden puzzle, and the more I dig, the more I start to question whether this is the intended functionality or a bug that needs squashing. It's a tricky situation because, on one hand, we want our fonts to behave predictably. On the other hand, we have to make sure it doesn't break compatibility with the current tools. We'll be looking into the details later in this article. But first, let's look at why this might happen.

Why Does This Happen? (Possible Reasons)

Alright, why might we end up with bracket layers that lack specific conditions? One possible reason is human error. Maybe a designer accidentally left a bracket layer without defining its axis rules. Another possibility is a quirk in the design workflow or the way the font files are being exported. Perhaps, in some design tools or workflows, empty conditions are the default behavior or the result of a specific setting.

Another cause could be an issue with how the font design software, such as Glyphs, handles bracket layers or how the data is interpreted by the compiler, like glyphsLib. If the software isn't explicitly instructed to handle the absence of conditions, it might default to the behavior we've observed: creating an alternate version and applying it broadly across the design space. The lack of clear guidance or an explicit error message when a bracket layer has no conditions could also be the problem. It leaves the designer unaware of the potential issues until they see unexpected results during compilation or font usage.

Finally, it's possible that this behavior stems from legacy code or design decisions in the tools used. The developers might have opted for this approach to handle undefined bracket layers, perhaps to ensure compatibility with older font formats or to simplify the implementation. The current behavior could have been accepted as a workaround or a compromise, even though it might not be the most elegant or intuitive solution.

Understanding the reasons behind this behavior is crucial for addressing the issue, whether through bug fixes, documentation updates, or workflow adjustments. It helps us determine the best course of action.

The Impact of Empty Conditions

Now, let's explore the impact of these empty conditions. The primary effect is the creation of alternate glyphs and the implementation of GSUB feature variations. This can lead to a few issues:

• Unexpected Glyph Swapping: The widespread substitution of glyphs might create a font that doesn't behave as intended. Designers often create bracket layers for specific variations within their design space. When these variations are applied across the entire space, the design intent is lost.
• Increased File Size: Creating duplicate glyphs can increase the size of the font file, which affects loading times and performance, especially on the web. Extra glyphs means more data to store and process.
• Complex Feature Definitions: The added GSUB entries make the feature definitions more complex, increasing the chance of errors or unexpected behavior during rendering. The more code, the more problems.
• Compatibility Issues: These variations may not be compatible with all font rendering engines or applications, potentially causing display issues. Compatibility is always a concern for font creators.

Sample Project: Epunda Slab

To make things concrete, I've included a sample project based on Epunda Slab, a font I've been working with. You can find the specific file here.

This sample project highlights the issue, focusing on the Italic style and the behavior of bracket anchors. The problem specifically arises when bracket layers don't have defined conditions. This helps illustrate how these issues pop up in a real-world project, and it can assist in pinpointing the issues.

Possible Solutions

So, what can we do to address this issue? Here are a few potential solutions:

• Ignoring Empty Bracket Layers: The simplest approach might be to have glyphsLib ignore bracket layers with empty conditions entirely. This would prevent the creation of alternate glyphs and GSUB feature variations, avoiding the problems we've discussed. However, this might also lead to unexpected results if the designer intended to use the bracket layer but made a mistake in the conditions. Maybe a warning is appropriate.
• Adding a Warning: Alternatively, the tool could provide a warning or error message during the compilation process whenever it encounters a bracket layer with no conditions. This gives the designer a heads-up and a chance to correct their mistake before generating the font. This is useful for catching mistakes.
• Automatic Condition Assignment: The tool could automatically assign a default condition to empty bracket layers. This could be a condition that applies across the entire design space, or it could be a warning to make the designer aware of the issue. Automatic solutions, however, are tricky and could lead to more problems than they solve.
• Improving Documentation: Clear documentation is essential. Documenting this behavior and providing examples of how to handle empty bracket layers could help designers avoid the issue altogether. Documentation is always important.

Conclusion: The Path Forward

So, where does this leave us? The handling of bracket layers with empty conditions in font design is a complex issue. It requires careful consideration of the tools, the design process, and the intended behavior of the fonts. While it might seem like a small detail, the impact on font file size, rendering, and overall design integrity can be significant.

Ultimately, the best solution will likely involve a combination of approaches. The tools should provide clear feedback to the designer, either through warnings or errors, to prevent these issues from arising in the first place. The tools could also provide clear documentation to show the nuances. The community of font designers can help by creating best practices and working collaboratively to avoid any problems. By being aware of the issue, we can make informed decisions and build robust and reliable fonts.

In the meantime, I'm leaning toward the idea that we might just want to ignore bracket layers with empty conditions. But, the more I think about it, the more I wonder if that's the right choice. Maybe we need a warning. Or maybe, something else entirely. What do you guys think? Let me know your thoughts!