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the ctx protocol

The ctx text format is a direct serialization of the canvas API. This protocol permits sending rendering commands over serial, ptys and other forms of network - enabling remote and/or sandboxed rendering.

When used in the ctx terminal, the ctx rendering mode is entered by issuing the escape sequence \e[?200h this makes the terminal interpret commands for a ctx context created for the line the cursor currently is in. To end ctx mode transmit  X  or  DONE .

The bash example ctx-clock.sh, renders an analog clock that scales with the terminal window.

#!/bin/bash
echo -ne "\e[?1049h" # alt-screen on
echo -ne "\e[?25l"   # text-cursor off
function cleanup {
  echo -ne " X "        # leave ctx mode; in case we're there
  echo -ne "\e[?1049l"  # alt-screen off
  echo -ne "\e[?25h"    # text-cursor on
}
trap cleanup EXIT # restore terminal state on ctrl+c and regular exit

for a in b{1..1000}; do
hour_radians=`bc <<<"scale=3;(($(date +%H|sed 's/^0//')+($(date +%M|sed s'/^6//')/60.0))/12.0+0.75)*3.14152*2"`
minute_radians=`bc <<<"scale=3;($(date +%M|sed 's/^0//')/60.0+0.75)*3.14152*2"`
second_radians=`bc <<<"scale=3;($(date +%S|sed 's/^0//')/60.0+0.75)*3.14152*2"`
radius=45
echo -ne "\e[2J\e[H" # clear screen and go to top left corner
echo -e "\e[?200h"   # enter ctx mode
rgba 1 1 1 0.5
arc 50% 50% $radius% 0.0 6.4 0
lineWidth $((radius/10))%
stroke
lineCap round
moveTo 50% 50%
arc 50% 50% $(($radius * 70 / 100))% $minute_radians $minute_radians 0
moveTo 50% 50%
arc 50% 50% $(($radius * 50 / 100))% $hour_radians $hour_radians 0
stroke
lineWidth $((radius/40))%
moveTo 50% 50%
arc 50% 50% $((radius * 90 / 100))%  $second_radians $second_radians 0
rgba 1 0.1 0.1 1
stroke
done "; sleep 0.1; done

This format maps to the C API if you turn camelCase into snake_case, and prefix each command with ctx_.

When a keyword is parsed the parser expects a series of commands of the same type, following arguments will be consumed in chunks as the number of arguments fill up, until a command change. Each command also has a short one-byte long name, where applicable these match the SVG path data format.

gray	gray	sets gray source, and color model
graya	gray alpha	sets gray alpha source, and color model
rgb	r g b	sets rgb source
rgba	r g b a	rgb alpha color source
cmyk	c m y k	cmyk color source
cmyka	c m y k a	cmyk alpha color source
drgb	r g b	sets rgb source, in device space
drgba	r g b a	rgb alpha color source, in device space
dcmyk	c m y k	cmyk color source, in device space
dcmyka	c m y k a	cmyk alpha color source, in device space
a relArcTo	5
b clip
c relCurveTo	6
d lineDash	1-N	specify stroke dashing pattern, empty to reset
e translate	x y
f linearGradient	x0 y0 x1 y1
g save
h relHorLine	x
ka globalAlpha	alpha
kb textBaseline	alphabetic | top | bottom | middle | hanging | ideographic
kB blendMode	normal | multiply | screen | overlay | darken | lighten | colorDodge | colorBurn | hardLight | softLight | difference | exclusion | hue | saturation | color | luminosity | divide | addition | subtract
kc lineCap cap	none | round | square
kf fontSize	font_size
kj lineJoin join	bevel | round | miter	0 1 or 2 are also valid values
kl miterLimit	miter_limit
km compositingMode	sourceOver | copy | clear | sourceIn | sourceOut | sourceAtop | destinationOver | destination | destinationIn | destination_out | destinationAtop | xor
kt textAlign	start | end | center | left | right
kw lineWidth	line_width
l relLineTo	x y
m relMoveTo	x y
n font	"font name"
o radialGradient	6
p gradientAddStop addStop	pos R G B A	arguments depend on current color model, you can change the color model without setting a color by specifying a color without arguments.
q relQuadTo	cx cy x y
r rectangle rect	x y width height
s relSmoothTo	cx cy x y
t relSmoothQuadTo	x y
u strokeText	"utf8-string"
v relVerLine	y
w glyph	unichar	draws a single unicode character, the character no is currently passed in as decimal. (might be made internal), since a text string duplicates the API.
x text	"utf8-string" | kerning	Interspersed with utf8 sequences of text numbers can appear that shift the horizontal position.
y identity
z closePath
A arcTo	x1 y1 x2 y2 radius
B arc	x y radius angle1 angle2 direction
C curveTo	cx1 cy1 cx2 cy2 x y
E stroke
F fill
G restore
H horLineTo	x
J rotate	radians
L lineTo	x y
M moveTo	x y
N beginPath
O scale	scale_x scale_y
Q quadTo	cx cy x y
S smoothTo	cx cy x y
T smoothQuadTo	x y
U reset
V verLineTo	y
W transform	a b c d e f	applies the transformation matrix
X exit
X done
Y roundRectangle	x y width nheight radius
Z closePath
] colorSpace	icc_slot ~a85encoded icc profile~	sets the color space of a given space in rasterizer.
{ startGroup		starts a compositing group
} endGroup		ends a compositing group, and blends and composites it with the content before the group using the now current compositing mode, blending mode and global alpha.

Detailed syntax description

The language consists of a stream of words, numbers and strings, optionally separated by white space. The characters ,=(); are also treated as white-space. Words are substrings consisting of one or more characters in the ranges a-z and A-Z. Numbers are sequences of 0-9. Numbers can be followed by the suffixes % or @, indicating that units of percent canvas width/height should be used or a global em / cell-size. ^ is equivalent to CSS vh, and ~ vw, this can be used to override the automatic choice done by %, which favors height for dimensions that are independent of x/y like lineWidth and shadowBlur. Strings are raw binary UTF8 contained in ' or " pairs. "\n\r" etc from C are available for escaping newlines, though they can also be directly included in the string. # introduces a comment and the rest of the line is ignored.

Blobs can also be represented as a85