Attributes
Most of the drawing functions that you can call have a parameter that let you specify attributes to configure details about what you want them to do. In the end, the attributes boil down to a Clojure map whose keys are keywords that identify the attribute being configured, and whose values are what you want to use for that attribute.
The specific attributes accepted by each function are described in the function documentation. Some attributes are used by the function itself, and some are passed along to the SVG to become SVG attributes of the element you are drawing.
Attribute Expressions
Because you often want to reuse and combine the same sets of
attributes when drawing your diagrams, bytefield-svg offers a
shorthand way to express many useful operations concisely, without
requiring you to build up the map explicitly. Drawing functions which
accept attributes will process this notation for you.
If you are interested in the intricate details, attribute expressions are interpreted by the function
eval-attribute-specnear the top of the source.
Raw Maps
In the simplest case, you can pass a map of attributes that you build
yourself, such as when you want to tell draw-box to consume the
space normally taken by two boxes:
(draw-box 42 {:span 2})The second argument to draw-box is an attribute expression. In this
case we have told it that the :span attribute should have the value
2.
Named Attributes
If you want to use one of the predefined
sets of attributes, instead of a map you can pass the keyword that
names them. For example, if you want to render some text in the same
style normally used for drawing hexadecimal numbers, you can reference
the attribute set named :hex as the second (attribute) argument to
the text function:
(text "NUL" :hex)When a keyword is found as an attribute expression, that keyword is
looked up in the named-attributes table, and the corresponding value
is used as the attributes to control the drawing.
In addition to the predefined values that start out in that table, you
can add your own named attribute definitions by calling the
defattrs function, perhaps in a shared include
file.
Combining Attributes
Sometimes you want to combine multiple attribute specifications, perhaps starting with a named set of attributes and then augmenting or modifying it somehow. To express that you can pass a vector of attribute expressions, and each expression in turn will be evaluated into a map as described by this section, and the later maps will be merged into the earlier ones. The merge process allows later keys to replace earlier values, which is how you can override as well as adding on to the predefined attribute sets.
For example, here is an attribute expression that starts with the
predefined :plain text attributes but establishes a lighter font
weight:
[:plain {:font-weight "light"}]And here is how to draw a box using the predefined :related (dotted)
border styles, in addition to a purple background (assuming your
diagram has called defattrs to set up the :bg-purple style), that
takes up the space of four normal boxes:
(draw-box "Unknown" [:box-related :bg-purple {:span 4}])No Attributes
If you don’t want to pass any attributes at all, you can either pass
an empty map, {}, or nil which is interpreted in the same way.
This tells the function to use its default values and behaviors. But
most functions which accept an attribute parameter also allow you to
call them with fewer parameters, and treat that as if you had passed
nil for the attributes. You only need to pass the nil if you want
to pass a value for parameter that comes later, but don’t care to send
attributes.
Predefined Attributes
The following named attributes are set up for your diagram to use
(although you are free to call defattrs to modify or replace any of
these, as well as to add your own new sets).
| Key | Purpose |
|---|---|
|
The default text style in which hexadecimal values are drawn,
with a |
|
The default text style in which string values are drawn, with
a |
|
A text style you can use for writing math-expression-like
text, with a |
|
A text style for creating subscripted nested |
|
A text style for creating superscripted nested |
|
Adds bolding ( |
|
A line style for drawing dotted lines. Commonly used with
borders, but you can use it when calling the
|
|
The line styles for drawing the borders of boxes whose content is separate from the boxes around them (this uses the default line drawing style). |
|
The line styles styles for drawing the borders of
boxes that are related to those around them (this uses a
|
|
A set of border styles for the first box in a row of related boxes. It uses the unrelated style for its left, top, and bottom borders, and the related style for its right border. |
|
A set of border styles for a middle box in a row of related boxes. It uses the unrelated style for its top, and bottom borders, and the related style for its left and right borders. |
|
A set of border styles for the last box in a row of related boxes. It uses the unrelated style for its right, top, and bottom borders, and the related style for its left border. |
|
A set of border styles for a box that is open to the row below. It draws only its left, right, and top borders. |
|
A set of border styles for a box that is open to
the row below and related to the previous box. It draws only its
left, right, and top borders, and the left border is drawn in the
|
|
A set of border styles for a box that is open to the row above. It draws only its left, right, and bottom borders. |
For examples of how to combine the box styles, the source for the diagrams in the DJ Link Ecosystem Analysis is full of variations. You can see it by clicking the Edit this Page link at the top right of a page that looks interesting.