Circos > Documentation > Tutorials > 2d Tracks > Text 3
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6 — 2D Data Tracks

8. Text—Rules

This tutorial shows you how to use rules with the text track. All tracks allow for rules and using rules works the same way for each track. The previous tutorial used rules to color text.

We'll draw some sequence on the image and color the base pairs. We'll use a monospaced font using

label_font = mono

There are two data files used in this example, data/6/sequence.txt (20,000 entries)

# sequence.txt
hs1 2 2 C
hs1 3 3 A
hs1 4 4 A

and data/6/sequence.long.txt (100,000 entries).

# sequence.long.txt
hs1 1 1 A
hs1 1 1 C
hs1 1 1 A
hs1 1 1 G
hs1 2 2 T
hs1 2 2 A
hs1 2 2 C
hs1 2 2 T

The ideogram in the image is hs1:0-20kb, but it's a good idea to start with a smaller interval to see how things work, e.g. hs1:0-1. A track with 100,000 bases can take a very long time to draw—the code that determines the character layout has not been optimized.

applying text rules

A good way to include rules is using the <<include ... >> directive to read them from another file. This keeps the configuration file tidy and allows you to reuse the same rules for other tracks.


# default values for all <plot> blocks
type       = text
color      = black
label_font = mono
label_size = 32
# radial padding
rpadding   = 0.2r


file       = data/6/sequence.txt
r1         = 0.9r
r0         = 0.3r
label_size = 16
# angular padding
padding    = -0.25r 

<<include rule.textcolor.conf>>



The rule.textcolor.conf file is

condition = var(value) eq "A"
color     = red

condition = var(value) eq "T"
color     = blue

condition = var(value) eq "C"
color     = green

The text label is referenced using var(value) and the conditions check whether the text is A, T or C. The default track coloring assumes the label is G, so we don't have to check for this condition.

adjusting text size

With rules, you can adjust any attribute of the text characters. For example, you can adjust the size of the letters in the label by setting label_size. This is done in the tracks immediately inside and outside the circle.

# If the text is not A, then hide it. When this rule triggers,
# other rules are not evaluated.
condition  = var(value) ne "A"
show       = no

# This rule is applied to any text that didn't pass the previous
# rule (i.e. only A). The label is set to a random value between
# 12 and 48. The rand() function returns a uniformly sampled
# random value in the interval [0,1).

condition  = 1
label_size = eval(12+32*rand())