ctx is a media-rich terminal and a vector graphics stack, built around a textual serialization protocol. The textual serialization has a corresponding binary representation that is used by the core rasterizer as well as sharing data among threads. The ctx protocol is available as an extension to ANSI escape sequences in the ctx terminal - the terminal launched when running the ctx binary with no arguments. This extension allows scripts in any language to output vector graphics in addition to or instead of monospace text in each tab/window, and also provides network transparent rendering.

The clock in the above screenshot is a shellscript.

Library

Ctx is usable as a single header library, to be dropped into a source tree, ctx header/library, it can also be installed system-wide.

Applications written using the C library can run either inside the ctx terminal, or stand-alone using SDL2, fbdev/DRM or in-terminal braille as output.

Mouse and touch events are registered for the currently active path, with propagation control to earlier registered interactions.

Running directly with the SDL2 or framebuffer backends has higher performance than going through the terminal abstraction, reducing this gap through tuning and refactoring is a work in progress, for applications the difference between 12fps and 120fps is smaller and small rather than global updates are done.

multiplexing

The self-contained static builds are sufficient to run minimalistic desktop+shells only sessions with low RAM requirements. The rasterizer which for multi-core use is used in parallell for multiple threads, started off written to fit on microntrollers, with the right defines a RGBA 8bit rasterizer can be made to fit in 32kb of code also for 64bit x86.

VT4xx, ECMA-48
Almost full vt100 and vt220 escape sequence handling, scrollback, like xterm, dterm window manipulation (among tabs/clients), bracketed paste, 256 and 24bit colors are supported - and a growing subset of vt420 and other relevant terminal escape sequences.
Low-latency
The ctx terminal tries to re-render as little as possible, as fast as posisble using multiple threads, and SIMD when possible (AVX2 ands 64-bit-pseudo-SIMD implemented). Results of running typometer measuring latency under a composited GNOME3, numers are average milliseconds per update, lower is better:
terminologymltermctxkittygnome-terminal
38.239.839.442.672.0
  Ametameric                    
The terminals 16 color palette called ametameric is optimized for legibility for both main varieties dichromats as well as trichromats.
HTML5 canvas 2D context
Easily bindable C API and protocol builds directly on this standard. Compositing and blending is according to compositing and blending level 2; ctx goes further than the standard and permits all blending modes to be combined with all compositing modes.
backends: ctx, DRM, fbdev, SDL2, braille
ctx comes with 5 interactive backends, the ctx backend renders the ctx protocol to stdout, and reads input, this provides the client interface for interactive vector clients running in the ctx terminal.
DRM and fbdev backend takes take keyboard input from stdin and tries to read mouse events are from /dev/input/mice. The SDL2 backend permits using ctx clients under wayland/X11 and probably other platforms.
RGB and CMYK, 8pc and 32bit floating point
Supporting RGB332, RGB565 and grayscale + 1bit mode render targets. ICC based color management of RGB user/device spaces through babl as an optional dependency. CMYK colors can be generated on the fly from RGB or set and retained in CMYK mode - when set in CMYK mode the colors correspond directly to the device colors in CMYK mode.

deferred rendering
These drawlist representations are used for scanline/chunk-based rendering on microcontrollers where framebuffer is to large to fit in RAM and tiles and threaded rendering on multi-core systems with SDL2 and /dev/fb0 backends and network transparent rendering inside ctx terminal. Another way to drive larger than RAM is to re-render the frame for each segment instead of buffering it, buffering is however useful when doing networked rendering, ctx can be configured and adapted to deal with a wide range of scenarios. .
text rendering
Three font loading backends, stb_truetype, native-ctx and ctx-fs. The ctx.h header ships with a built-in native-ctx font. In following screenshot a text-file with the commands for the @ glyph is being edited in vim, with instant update across all clients. This massively slows down the UI but not enough to be unusuable. With a simple visual vector editor working directly with the ctx-protocol this provides for an almost complete live font-editor.
The text-shaping is currently limited to horizontal advances + horizontal kerning, no ligatures, RTL or vertical glyph advances - interacting directly with harfbuzz could give us wider support.
sixels
DEC terminal family standard for raster graphics transfer
kitty graphics
kitty style raster graphics transfer
iterm2 inline images
iterm2 style raster grarphics transfer
atty
audio recording and playback (only raw pcm for now, opus codec NYI)
stb_truetype.h
If the declarations for stb_truetype are included before ctx.h - functions to load fonts from TTF/OTF files become available.
SDL2
Optional backend and support code that that gets build when SDL.h is included before ctx.h
cairo
support code to render to cairo contexts if cairo.h is included before ctx.h, useful for conformance verfication and SVG and PDF output.

downloads / sources

The single header and static binaries for download are autogenerated together with this website each time the git repository is synched.

ctx.h760KThe singleheader library ctx.
git repo
$ git clone https://ctx.graphics/.git
                                      
The repository contains the sources for examples and tests, and the implementation of 2D vector rasterization and protocl parser and serializer.
ctx-font-regular.h128KExample font to use with ctx, to be a true single header solution - the ascii subset of this is already defined in ctx.h
ctx-x86_64-static64bit static linux binary - should work in many distros on framebuffer /dev/fb0 and braille backends
ctx-i486-static32bit static linux binary - should work in many distros on framebuffer, /dev/fb0 and braille backends.

license and funding

The terminal is available under GPLv3+, and ctx.h is available under LGPLv3+ you can encourage continued development of ctx and dissimilar technologies by financially supporting me, Øyvind Kolås who is doing independent pro-bono R&D through patreon and similar. If my income through such sources is above 4000USD per month for a year, or a similar amount in shorter time I want to relicense the rasterizer and protocol parts of ctx under the ISC license.

future work

pressing issues

The current status of ctx is beyond proof of concept - but still does not fully realize a minimal system demonstrating it's capabilities - some features are also broken and need repair - and for third party use probably more urgently than the following wishlist. When this list is nearing 0 it is time for a tarball/versioned release of ctx. The single header ctx.h linked from this page is a rolling release.

desirable improvements