Slug is a professional software library for rendering high-quality, resolution-independent text in 3D applications
on the GPU. It can be used for drawing graphical user interfaces, rendering heads-up displays, showing debugging information,
and placing text inside a 3D world or virtual environment.
Slug renders character glyphs on the GPU directly from outline data composed of quadratic Bézier curves to produce
crisp text at any scale or from any perspective. There are no precomputed texture images or signed distance fields. Slug uses a
breakthrough mathematical algorithm that we invented to achieve perfect robustness
with high performance, and it is the only existing GPU method that renders properly antialiased glyph shapes with no
artifacts under both magnification and minification.
Slug also provides text layout services that calculate the positions of the glyphs that would be drawn for a given
string of Unicode characters. In addition to basic bounding box and advance width calculations, it can perform kerning,
ligature replacement, combining diacritical mark placement, character composition, and alternate substitution.
More high-level information is available on the Slug fact sheet.
The full set of features provided by Slug is described in the Slug User Manual.
Demo
A demo of the Slug library for Windows is available here:
Download Slug Demo
(Updated 13-August-2018)
The demo contains several pages of text that highlight rendering capabilities and typographic features.
On most pages, left-clicking and dragging will scroll the text, right-clicking and dragging will rotate the text,
and moving the mouse wheel will zoom in and out.
The text on the fifth page of the demo can be changed by placing a file named story.txt in the same folder
as the demo application. This text file should be encoded as UTF-8, and up to 64 lines of it will be rendered in the demo.
The font used for this text is story.slug in the Fonts folder. By default, this is just a copy
of the Arial font, but you can change it by using the slugfont tool to import another TTF file. To do so,
copy the TTF file into the Fonts folder, and execute the following command line with the actual font name:
slugfont <fontname>.ttf -o story.slug
Glyph Rendering
Each glyph is rendered by drawing a quad that covers its bounding box. (Because it’s only a box, it can be clipped or subdivided
to match another surface inside a 3D environment.) A specialized shader efficiently determines how much each pixel inside the box
is covered by the glyph using the original Bézier curve data stored in the font. Because no precomputed images or distance fields
are involved, the result is a sharp outline at all resolutions with no faceting or blurring. Slug has the ability to apply a couple
speed optimizations at large font sizes, one of which is rendering a tight bounding polygon instead of a plain box. The image to
the right was rendered by Slug using Times New Roman at a 500-pixel font size.
In addition to boring old letters and numbers, Slug can render full-color emoji and pictographs with the same
resolution independence that gives every contour a clean, crisp appearance at any scale. Slug supports the complete set of color
characters defined by Unicode, and it can handle skin tone modifiers as well as zero-width joiner sequences.
The image to the left was rendered by Slug using the Segoe UI Emoji font at a 40-pixel size. This font ships with Windows and
contains color layer data that elegantly provides the ability to scale multicolor emoji and pictographs with the same versatility
as conventional black-and-white glyphs.
The Product
Slug is distributed as a static library that has a basic C++ interface, and full source is included with every license. Slug currently runs
on Windows, Mac, Linux, and PlayStation 4, and it can be used with OpenGL, DX11, DX12, and Vulkan. The API is fully documented ine the
Slug User Manual.
The primary function of Slug is to take a Unicode string (encoded as UTF-8), lay out the corresponding glyphs, and generate a vertex buffer
containing the data needed to draw them. When text is rendered, your application binds the vertex buffer, one of our glyph shaders, and two texture
maps associated with the font. One texture holds all of the Bézier curve data, and the other texture holds spatial data structures that Slug uses
for efficient rendering.
Slug renders each glyph as a single quad. (There is also an optimization that uses a tighter polygon having up to eight vertices that can
be enabled to increase speed at larger sizes.) This has the advantage that it’s easy to clip to an irregular shape or project onto a
curved surface in a 3D environment. It also means that vertex buffer storage requirements do not depend on the complexity of the glyphs.
Slug comes with a standalone tool that reads a TrueType .ttf file and generates a new file with the .slug
extension containing all of the information necessary to render the font on the GPU. The .slug file includes the original
glyph outline data, optimization data used by the glyph shader, kerning data, join sequence data, mark attachment data, and color layer data.
A .slug file may contain a subset of the original font so that unneeded characters do not take up any space. The data used
for kerning, join sequences, mark attachments, and color layers is all optional.
The technical details about how the patent pending Slug algorithm works and how the data is organized in .slug files are
discussed in a paper by Eric Lengyel in the Journal of Computer Graphics Techniques.
There is also a detailed slide presentation about the Slug algorithm.
Why the name “Slug”?
A slug is what they used to call a full line of text cast as one piece of hot lead by a Linotype machine.
The primary function of our software is to lay out and render lines of text.
