NAME
art, art2pic – edit line–art

SYNOPSIS
art [ –f font ] [ –b picture ]

art2pic file

DESCRIPTION
Art is an interactive program to create precise line–art in the style of pic(1). It is mostly mouse–operated, with a few commands entered from the keyboard. It divides its window into four areas: a menu bar at the top, a one–line rectangle immediately below for echoing typed–in characters, another one–line rectangle below that for printing messages, and a large area at the bottom for displaying the drawing. The –b option displays the specified picture (in the format of picfile(9.6)) as a background for the drawing.

A small caret, whose apex is the current point, appears on the screen. The lines, arcs, and other elements of a drawing are constructed by placing the caret at each of a sequence of points that define the item. When the caret moves, two other markers (a square and a cross) trail it, showing its previous positions. Items on the screen near the caret attract it. Important points on items, like endpoints or intersections, pull harder than more mundane points, making precise alignment easy.

On request, art will automatically construct alignment lines and circles, which it displays more faintly than items in the drawing. Certain lines and points in a drawing are hot. Art constructs circles of given radii and lines of given slopes at hot points, and parallels at given distances from hot lines and lines at given angles to their endpoints. Menus pulled down from the menu bar control what alignment items are constructed. Items are automatically heated when added to the drawing and will be heated or cooled on command.

The `important points' on a line segment to which the caret preferentially gravitates are its endpoints and midpoint. On a circle, the center is important. On an arc, the endpoints are important. On a box, the corners, the midpoints of the sides and the center are important. Likewise, on a piece of text, the corners, midpoints and center of its bounding box are important. On a spline, the control points are important, and in a group, the important points of the group members are important.

Whenever button 1 is pressed, the caret follows the mouse cursor. On release, the item the caret is touching, if any, is selected and highlighted. If more than one item touches the caret, clicking button 1 repeatedly will cycle through them.

Pressing button 2 pops up a menu of commands that add new items to the drawing. Every item is described by several control points: a line by its endpoints, a circular arc by its endpoints and a third point on the arc, and so forth. A new item is specified by moving the caret in turn to each control point but the last, selecting a menu entry with button two, then using button 1 to place the caret on the last control point. (Buttons 2 and 3 will cancel the command.) While the caret is being dragged to the last control point, art displays and updates the item on the screen (``rubber–banding''). In all cases, after making an addition to the drawing, the new item becomes the current selection. The button 2 menu operations are
line        Add a line segment to the drawing. The two control points are the segment's endpoints.
circle      Add a circle to the drawing. The first control point is the center. The second is a point on the circumference.
arc         Add a circular arc to the drawing. The endpoints are the first and third control points. The second control point is an interior point of the arc.
box         Add a rectangle to the drawing. The box's sides are vertical and horizontal. The two control points are two diagonally opposite corners.
spline      Add a spline curve to the drawing, or extend an existing spline. Splines are a little more complicated than other items because they may have any number of control points. If the current selection is not a spline, there are two control points -- the ends of a new spline. When a spline is selected, the
spline button adds a new control point to the end of the spline closest to the selected point.
group       Add a group to the drawing. The two control points are the diagonally opposite corners of a rectangle. Any item partially or completely contained in the rectangle is made part of the group. Henceforth the group acts as a monolithic item and may be moved, deleted or copied as a unit. The open,
close and flatten commands (on button 3) allow manipulation of the items within a group. Groups may be nested within other groups.

Button 3's menu has commands to manipulate the current selection.
delete      Remove the selection from the drawing. If the whole drawing is selected, art asks for confirmation by pressing mouse button 3. Buttons 1 and 2 cancel the command.
heat        Heat the selected item.
copy        Create a duplicate of the selected item. The duplicate must be dragged to its intended position using button 1. Buttons 2 and 3 cancel the command.
edit        Change the indicated point of the selected item. Button 1 adjusts the point. Buttons 2 and 3 cancel the command. This command's behavior depends on the kind of item and the point at which it is selected.
If a line is selected near an endpoint, that endpoint moves and the other remains fixed. Both endpoints of a line selected near its midpoint move--its length and slope do not change.
If a circle selected at its center, it translates without changing its radius. If selected on its circumference, its radius changes but its center remains fixed.
The control point of an arc or spline nearest the selection point is modified.
If a box is selected near a corner, that corner moves and the other remains fixed. If selected near the middle of an edge, the edge moves, but the opposite edge remains fixed. If selected near its center, the whole box moves without changing its size or shape.
A group or a piece of text translates, regardless of the selection point.
open        The selection must be a group. All commands now operate on the members of the group.
close       The most–recently opened group is closed. Any changes made while it was open are propagated to other copies.
flatten     The selection must be a group. The items in the group are inserted in its place in the drawing. This undoes the effect of the group command. Other copies of the group are unaffected.

Keyboard commands:
t text      Add text to the drawing. The text is in the current font and is drawn centered on the caret.
f name      Set the current typeface. Name is the name of a font file. Subdirectories of /lib/font/bit contain many appropriate fonts.
D          Redraw the display.
q          Quit. Art exits, without asking for confirmation.
w [file]      Write the drawing into a file in art format. File defaults to the last file mentioned in a read or write command. Art files may be converted to pic(1) format by the art2pic command.
r [file]      Read a drawing from a file. File defaults to the last file mentioned in a read or write command.
c          Cool everything. Every hot item is cooled.
a          Select all items. The entire drawing is selected.
d          Drop anchor. The anchor is the fixed point for the not–yet–implemented rotate and scale commands.

Menus pulled down from the menu bar contain commands that alter how art responds to user interaction.
slopes      Most of the entries in this menu are numbers, representing angles in degrees. Those that are marked with a star are the inclination from horizontal of alignment lines constructed at each hot point of the drawing. Selecting a number toggles the star on and off. The measure button measures the slope
of the line connecting the most recent two points selected with the caret. The measurement is printed, and a corresponding new entry is made in the menu.
angles      This menu behaves much like the slopes menu. Items marked with a star are angles at which alignment lines are drawn through the endpoints of hot lines. The measure button measures the angle indicated by the most recent three points selected with the caret.
parallels   Items marked with a star are distances at which alignment lines are drawn parallel to hot lines. The measure button measures the distance between the most recent two points selected with the caret. Distances are nominally in inches, but the program believes the display pitch to be 100 pixels per
inch.
circles     Items marked with a star are radii of alignment circles drawn with centers at hot points. The measure button measures the distance between the most recent two points selected with the caret.
grid        Items in this menu activate a rectangular grid of gravitating points. They have labels like 0,0+.1,.1. The first pair of numbers is the coordinate of a point on the grid; the other pair is the x and y displacements of other points. The off item disables the grid (the default situation). Measure creates
a custom–measured grid using the last two positions of the caret as diagonally adjacent grid–points.
gravity     The starred entry on this menu is the maximum distance that the caret will move from the mouse cursor to snap to an item on the screen.
heating     The heat new button toggles whether objects are automatically heated when created or modified. The item is marked with a star if set, as it is initially.

SOURCE
/sys/src/cmd/art

SEE ALSO
tweak(1)

BUGS
Needs two or more bits per pixel. Doesn't compute intersections of splines with circles or arcs. No filled regions, line styles or arrowheads. Doesn't save construction lines in files. Because it draws in xor mode when rubber–banding, lines can momentarily disappear. Tracks slowly in large drawings.
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