utsikt

utsikt is a browser engine I am writing from scratch in c0, for moonshot, my operating system. It reads an HTML file off the filesystem, builds a DOM, applies a subset of CSS, lays the document out as blocks, lines and tables, and paints it into a window. Links are followed with the mouse and Backspace goes back.

"utsikt" is Swedish for view, or outlook.

There is no networking, on purpose. moonshot's network stack is the last subsystem it will get, so for a long while a page is a file. Everything that fetches bytes goes through one function, load_document() in utsikt.c0, so the day there is a network stack, one function changes.

utsikt ships inside every moonshot release, so you do not need this repository to use it. This is where it is developed.

What works

• HTML: a tokenizer and tree builder in one pass. Character references, comments, doctype, void elements, <style> blocks, whitespace collapsing, the common implied end tags (<p>, <li>, <td>, <tr>, <dt>, <dd>), stray end tags dropped, end tags matched by name, unknown tags treated as inline. <pre> keeps its whitespace and a <script>'s contents are raw text. Default styles for the headings h1 to h6, the sectioning elements, blockquote, pre, ol, dl, figure, and inline ones such as u, s, del, mark, small, kbd and abbr. Kept attributes are class, href, src, id, type and onclick.
• CSS: type, class, tag.class and descendant (div p) selectors in comma-separated lists, with real specificity. color, background, background-color, font-size, font-weight, display, margin, padding, text-align, text-decoration (underline, line-through), white-space (pre) and list-style-type (disc, decimal, none). Colours as #rgb, #rrggbb and fifteen names. The default stylesheet is written in CSS and goes through the same parser as a page's own.
• Layout: block boxes, inline content broken into lines at spaces, collapsing vertical margins between siblings, lists with drawn markers or numbers, <hr>, and tables as a grid of equal-width columns.
• Scripting: glimt (glimt.c0), a small part of c0 compiled to x86-64 machine code, runs <script type="text/x-glimt"> and the onclick attributes of a page whose scripts are glimt. A script reaches the page through ten builtins, and elements and strings are checked handles, never pointers. glimt sits behind an interface (script.c0) that any engine can plug into, by registering the <script type> it runs. Scripts no engine claims, JavaScript among them, do not run. A test engine (engine_test.c0) with a single command, set ID TEXT, exercises the interface on its own.
• Interaction: scrolling by arrow keys, PageUp, PageDown, Home and End; links by mouse click; Backspace for back; r to reload; an address line saying which file is open; re-wrapping when the window is resized.

The font is the kernel's, fetched glyph by glyph with a syscall, so a page and the shell beside it are set in the same face.

Getting it running

utsikt only runs inside moonshot, and moonshot is built by coff, so you need all three side by side.

git clone [email protected]:cofflang/coff.git c0-coff
git clone [email protected]:cofflang/moonshot.git moonshot
git clone [email protected]:cofflang/utsikt.git utsikt

cd utsikt
./dev.sh run

The first build bootstraps coff and takes a few minutes; moonshot's README lists the packages it needs. When the QEMU window comes up, log in as root with an empty password and type start utsikt.elf, or start utsikt.elf about.html to open another page.

./dev.sh builds the utsikt in this checkout into the kernel, so an edit here is what you see after the next ./dev.sh run. ./dev.sh test runs the browser's tests. See CONTRIBUTING.md for the rest.

What is in the repository

File	What it is
utsikt.c0	The program: window setup, loading a document, the load, parse, style and lay out pipeline, the key and mouse loop, navigation. It includes the files below, in this order, with moonshot's moon.c0 after paint.c0.
paint.c0	The frame buffer, rectangles, the font cache and text drawing, and the string helpers.
dom.c0	HTML bytes in, a tree of nodes out.
style.c0	The stylesheet parser and the cascade that gives every node a computed style.
flow.c0	Normal flow. The tree becomes boxes and lines, measured in one pass and painted in a second, so a background is painted before the text on it.
script.c0	The scripting interface. Engines register here, and get a page's scripts and clicks through it.
engine_test.c0	A one-command test engine for the interface.
glimt.c0	glimt, the scripting language, compiled to machine code.
dev.sh	Builds this checkout into a moonshot checkout next to it, and boots it or tests it.

c0's include is textual, so the files are one translation unit and the include order is the order the compiler reads them in.

How it gets into moonshot

moonshot carries a copy of this repository in programs/utsikt/, added with git subtree, so a moonshot clone builds on its own and every byte of the browser the kernel bakes in has its source right there. Each copy records the utsikt commit it came from. On the moonshot side, ./sync_utsikt.sh pulls a newer utsikt in, and ./sync_utsikt.sh --check says whether its copy matches this repository.

Changes go to this repository first. A fix made inside moonshot's programs/utsikt/ is sent back here before anything else.

License

GPL-3.0-or-later. See LICENSE.

Copyright (C) 2026 tavro