4.1 Venndir Borders

The underlying geometry of each polygon is represented as a JamPolygon object (Ward 2025), a new S4 object designed for geometries used in Venndir.

An important distinction from typical polygons in R is that the objects are capable of describing three borders:

1. 'border': Line along the exact edge of the polygon.
2. 'innerborder': Line drawn on the inside edge.
3. 'outerborder': Line drawn on the outsideedge.

JamPolygon objects allow adjacent borders to co-exist without rendering two borders on top of each other.

Figure 4.1 illustrates four examples of borders, showing the problem being addressed with innerborder. The left object has two halves labeled A and B, with borders gold and purple, respectively. When using 'border' the gold border is covered by the purple border down the center line between A and B.

Instead, the next object with C and D shows the effect of using 'innerborder', with the respective gold and purple borders both visible. Also notice the object is not enlarged by adding the border, the line width extends inside the polygon.

The next panel shows E and F, with 'outerborder' wrapping around them both. The outerborder extends outside the object, and in fact the outerborder does not extend inside the object at all.

The right panel shows G and H, and includes each type of border, drawn in order: innerborder, outerborder, border. The 'border' was configured as a thin line, otherwise it could potentially cover both the innerborder and outerborder.

Figure 4.1: Four standard objects are displayed on the top row. The bottom row shows the effect of adding distinct borders: border, innerborder, outerborder, and all borders.

4.1.1 Venndir Rendering Steps

Venndir draws borders in a specific order to provide a layering effect, followed by other graphics elements such as labels and connecting line segments.

1. Venn Sets

   • The outerborder is drawn using set_colors darkened slightly.
   • Other borders are not drawn: fill color, border, and innerborder.

2. Venn Overlaps

   • Colors from the overlapping sets, from set_colors, are blended.
   • The fill color is drawn after applying poly_alpha.
   • The filled region does not include the innerborder.lwd if the innerborder is defined.
   • The innerborder is drawn using the fill color, darkened slightly, and with no alpha transparency.
   • Other borders are not drawn: border and outerborder.

3. Count Labels

   • The font colors are adjusted for contrast, relative to the background colors behind each label.

4. Item Labels (if enabled)

5. Line Segments (if enabled)

6. Venndir Legend (if enabled)

7. Main Title (if enabled)

The order that Venndir polygons are rendered, as described in (1) and (2) above, is determined by the order of polygons present in the Venndir 'jps' S4 slot. For example, if v is a Venndir object, the JamPolygon entries are accessed using v@jps.

The order in 'jps' can be modified, but all entries are required for the Venndir object to be valid. For example, Highlight Venn Overlaps re-orders 'jps' to place the highlighted overlap region last, thereby preventing border and outerborder from being overdrawn by other entries in 'jps'.

Additional JamPolygon entries may be added to v@jps, however the new names must not conflict with existing names(v@jps).

Additional notes:

• When plotting a Venndir object, the ellipses '...' can be used to provide custom border settings, and are described in Customize Venndir borders.
• By default, Venndir objects do not use border, they use outerborder for sets, and innerborder for overlap regions.
• The overlap regions use colors that are blended based upon set_colors defined for the Venndir object.
• Default borders are quite subtle, but the effect is more distinctive when using larger values for innerborder.lwd and outerborder.lwd.
• It is usually best to use the same numeric value for both innerborder.lwd and outerborder.lwd, due to the way the borders are layered.

4.1.2 Customize Venndir borders

The border options can be customized directly when plotting the Venndir object, adding named arguments to any function that produces a Venndir plot: * venndir(...) * render_venndir(Venndir, ...) * plot(Venndir, ...)

A few common alternatives are shown in Figure 4.2.

v1 <- venndir(make_venn_test(),
   innerborder=NA, outerborder=NA)
v2 <- venndir(make_venn_test(),
   border="black", border.lwd=1,
   innerborder=NA, outerborder=NA)
v3 <- venndir(make_venn_test(),
   innerborder="white", outerborder="white")
v4 <- venndir(make_venn_test(),
   label_style="lite box", innerborder.lwd=1,
   outerborder="white", outerborder.lwd=1)

Figure 4.2: Venndir diagrams demonstrating common border styles.

These options are useful for global changes to borders, but are not ideal to modify a specific region. For those customizations, see Modify Venn Overlaps.