Module Hugin_kit.Symbol

Symbols.

A symbol is a marker shape: the circle, square or star a dot mark draws at each point.

Symbols are sized by their ink: a symbol of size a lays as much ink as the circle of area a painted the same way. Filled, the region it encloses has area a; stroked, its outline is as long as that circle's circumference, 2 √(π a), so that at one stroke width it lays as much ink as the circle. plus, times and asterisk enclose nothing and are sized by length however they are painted. A symbol keeps its shape at every size: the symbol of size a is the symbol of size 1. scaled by √a, so a figure can draw one outline and stamp it at many sizes.

Every symbol is symmetric under a rotation about the origin, so the centroids of the region it encloses and of its outline both lie at the origin: a triangle sits on its data point rather than above it. The plane is the one of hugin.gg, y pointing down, so a symbol that points up points towards negative y.

Some symbols are designed to be filled (filled), the others to be stroked (stroked).

Reference: Mike Bostock. d3-shape symbols, from which the shapes, the two sets and the sizing by ink are taken.

Symbols

#type t

The type for symbols.

#val circle : t

circle is a circle.

#val square : t

square is a square with sides parallel to the axes.

#val diamond : t

diamond is two equilateral triangles joined by a side parallel to the x axis: a rhombus standing on a corner, taller than wide.

#val triangle : t

triangle is an equilateral triangle pointing up.

#val cross : t

cross is a Greek cross: five equal squares, one at the centre and one on each of its sides.

#val star : t

star is a regular five-pointed star pointing up, its inner corners on the lines that join its points.

#val wye : t

wye is a Y: an equilateral triangle with a square on each of its sides, one of them below it.

#val plus : t

plus is two strokes of equal length crossing at their middles, one parallel to each axis.

#val times : t

times is plus turned by an eighth of a turn.

#val asterisk : t

asterisk is three strokes of equal length crossing at their middles, a sixth of a turn apart, one parallel to the y axis.

Sets

Ordered sets of symbols for categories, one for marks that fill their symbols and one for marks that stroke them.

#val filled : t list

filled is the symbols designed to be filled: circle, cross, diamond, square, star, triangle and wye.

#val stroked : t list

stroked is the symbols designed to be stroked: circle, plus, times, triangle, asterisk, square and diamond.

Drawing

#type paint = [

#| `Fill
#| `Stroke

]

The type for the ways a symbol is painted, which decide how it is sized: `Fill by the area it encloses, `Stroke by the length of its outline.

#val path : paint -> float -> t -> Hugin_gg.Path.t

path paint a s is the outline of s at size a painted with paint, its centre at the origin. It is path paint 1. s scaled by √a, up to rounding. Closed outlines are closed subpaths that turn clockwise on screen, as Hugin_gg.Path.rect and Hugin_gg.Path.circle do, and the circle is the one Hugin_gg.Path.circle draws, whose area and length are those of a true circle up to the error of its arcs. plus, times and asterisk are open subpaths of one segment per stroke, so filled they paint nothing. path paint 0. s has every point at the origin.

Raises Invalid_argument if a is negative or not finite.

Comparing and formatting

#val equal : t -> t -> bool

equal s s' is true iff s and s' are the same symbol.

#val pp : Stdlib.Format.formatter -> t -> unit

pp ppf s formats the name of s, such as triangle.