The TTauri Icon File Format is used for storing a single multicolor icon in a simple binary format.

All values are in little endian byte order.

Paths in a icon are drawn in-order following the painter's algorithm.

type	Name	description
char[4]	magic_number	"TTIC" Magic Number
uint16_t	nr_paths	Number of paths
path[nr_paths]	paths	Paths

Path

If both fill and stroke are non-transparent, then the path will be filled first followed by stroke.

type	Name	description
color	fill_color	Fill color index.
color	stroke_color	Stroke color index.
fixed1_13_t	stroke_width	Width of the stroke + line join style flag
uint16_t	nr_contours	Number of contours
contour[nr_contours]	contours	Contour

Line Join Style flag:

true = Bevel
false = Miter

Contour

A closed contour is drawn counter clockwise.

type	Name	description
uint16_t	nr_points	Size of the contour data.
point[nr_points]	points	Points

Point

Very much like how glyphs inside a font file are encoded, the points describe coordinates in em space. The origin is at the bottom left of the em box; on the base-line, on the leading edge. Positive values go up and to the right.

type	Name	description
fixed1_13_t	x	x, flag A
fixed1_13_t	y	y, flag B

The flags identify the type of point.

flag A	flag B	description
0	0	Anchor Point.
1	0	Cubic Bezier control point 1.
0	1	Cubic Bezier control point 2.
1	1	Quadratic Bezier control point.

As optimizations some points may be omitted:

An anchor point is automatically inserted at the midpoint between two quadratic control points.
A cubic control point 1 is automatically inserted between an anchor point and a cubic control point 2 by reflecting the previous control point 2 through the anchor point.
Two anchor points are interpreted as a line.

fixed1_14_t

This is a signed fixed point number, encoding a number between -2.0 and almost 2.0. The following formula is used to convert a number to this fixed point format: floor(x * 16384) this integer is then encoded as a int16_t.

fixed1_13_t

This is the same format as fixed1_14_t, but the least-significant-bit is used as a boolean flag.

Color

Colors are encoded as wide-gamut linear scRGB colors.

Linear floating point color component values are converted by floor(x * 8192) + 4096. The full range is of color component values is -0.5 - 7.5; the range between 0.0 - 1.0 are within the sRGB gamut.

The alpha value is encoded with: alpha * 65535. The color component are not pre-multiplied with the alpha value.

type	description
uint16_t	Red component
uint16_t	Green component
uint16_t	Blue component
uint16_t	Alpha component