hterm: switch cursor positioning to use CSS vars

Calculating the position of the cursor in pixels is done entirely in JS.
The actual display of rows and their cumulative height is done in CSS.
This leads to a situation where, on some zoom settings, the precision of
floating point math in the two systems are slightly different leading to
skew in positioning.

Since we're already exporting the character size to CSS variables, we can
export the position (in cols/rows) to CSS too, and then let the CSS side
do the final calculation.  This simplifies the JS code, makes the CSS code
more readable, and improves the cursor positioning over zoom levels.

Change-Id: Ibcb98c8f37cede5f2538892a4eb4d260602498d0
Reviewed-by: Brandon Gilmore <>
Tested-by: Mike Frysinger <>
1 file changed
tree: 921c89a8fb4b85d6dc8e0bc5cf05cd399fb76cc2
  1. .gitignore
  5. hterm/
  6. libdot/
  7. nassh/
  8. package.json
  9. saltpig/
  10. ssh_client/
  11. wam/
  12. wash/


This repository contains the libdot JavaScript library and some web applications that make use of it.

The official copy of this repository is hosted at

There is also a mirror on github at Keep in mind that this mirror may occasionally be behind the official repository.

All changes must go through the Gerrit code review server on Github pull requests cannot be accepted. Please see the document in this directory for the details.

Top level directories

  • libdot/ is a small set of JS libraries initially developed as part of hterm, now available as shared code. It provides a base layer for web applications. The code is intended to work in any modern browser, in either a plain web page or a “privileged” environment such as a Chrome platform application or Firefox extension. In practice, it's only been put to use in Chrome platform applications so far.

  • hterm/ is a JS library that provides a terminal emulator. It is reasonably fast, reasonably correct, and reasonably portable across browsers.

  • nassh/ is the Secure Shell Chrome App (currently a “v1.5” app, soon to become a “v2” or platform app) that combines hterm with a NaCl build of OpenSSH to provide a PuTTY-like app for Chrome users.

  • ssh_client/ is the NaCl port of OpenSSH. It is used by nassh to create the Secure Shell App.

  • wash/ is a library for cross-origin virtual filesystems, similar to the Plan 9 filesystem. This directory also contains a simple bash-like shell environment for exploring these filesystems. The code in this directory is a work-in-progress.