Plain Text

The plain and plain-ext formats produce output using a simple, line-based language. The latter format differs in that, on edges, it provides port names on head and tail nodes when applicable.

Example outputs of a simple graph with two nodes connected with an edge:

$ echo 'digraph { a->b }' | dot -Tplain
graph 1 0.75 1.5
node a 0.375 1.25 0.75 0.5 a solid ellipse black lightgrey
node b 0.375 0.25 0.75 0.5 b solid ellipse black lightgrey
edge a b 4 0.375 0.99579 0.375 0.88865 0.375 0.7599 0.375 0.64045 solid black
stop

$ echo 'digraph { a->b }' | dot -Tplain-ext
graph 1 0.75 1.5
node a 0.375 1.25 0.75 0.5 a solid ellipse black lightgrey
node b 0.375 0.25 0.75 0.5 b solid ellipse black lightgrey
edge a b 4 0.375 0.99579 0.375 0.88865 0.375 0.7599 0.375 0.64045 solid black
stop

There are four types of statements.

 graph scale width height
 node name x y width height label style shape color fillcolor
 edge tail head n x₁ y₁ .. xₙ yₙ [label xl yl] style color
 stop

graph

The width and height values give the width and height of the drawing. The lower left corner of the drawing is at the origin. The scale value indicates how the drawing should be scaled if a size attribute was given and the drawing needs to be scaled to conform to that size. If no scaling is necessary, it will be set to 1.0. Note that all graph, node and edge coordinates and lengths are given unscaled.

node

The name value is the name of the node, and x and y give the node's position. The width and height are the width and height of the node. The label, style, shape, color and fillcolor give the node's label, style, shape, color and fillcolor, respectively, using attribute default values where necessary. If the node does not have a style attribute, "solid" is used.

edge

The tail and head values give the names of the head and tail nodes. In plain-ext format, the head or tail name will be appended with a colon and a portname if the edge connects to the node at a port. n is the number of control points defining the B-spline forming the edge. This is followed by 2*n numbers giving the x and y coordinates of the control points in order from tail to head. If the edge has a label, this comes next followed by the x and y coordinates of the label's position. The edge description is completed by the edge's style and color. As with nodes, if a style is not defined, "solid" is used.

Note: The control points given in an edge statement define the body of the edge. In particular, if the edge has an arrowhead to the head or tail node, there will be a gap between the last or first control points and the boundary of the associated node. There are at least 3 possible ways of handling this gap:

• Arrange that the input graph uses dir=none, arrowhead=none, or arrowtail=none for all edges. In this case, the terminating control points will always touch the node.
• Consider the line segment joining the control point and the center of the node, and determine the point where the segment intersects the node's boundary. Then use the control point and the intersection point as the main axis of an arrowhead. The problem with this approach is that, if the edge has a port, the edge will not be pointing to the center of the node. In this case, rather than use the control point and center point, one can use the control point and its tangent.
• Arrange that the input graph uses headclip=false or tailclip=false. In this case, the edge will terminate at the node's center rather than its boundary. If arrowheads are used, there will still be a gap, but normally this will occur within the node. The application will still need to clip the spline to the node boundary. Also, as with the previous item, if the edge points to a node port, this technique will fail.

The output consists of one graph line, a sequence of node lines, one per node, a sequence of edge lines, one per edge, and a final stop line. All units are in inches, represented by a floating point number.

Note that the plain formats provide minimal information, really giving not much more than node positions and sizes, and edge spline control points. These formats are usually most useful to applications wanting just this geometric information, and willing to fill in all of the graphical details. The only real advantages to these formats is their terseness and their ease of parsing. In general, the dot and xdot are preferable in terms of the quantity of information provided.