channelGrob: Create a Grob That Spans Multiple Viewports

In ggalign: A 'ggplot2' Extension for Consistent Axis Alignment

Create a Grob That Spans Multiple Viewports

Description

This function initializes a communication channel to share location signals across different viewports. It returns a channelSenderGrob object, which can transmit multiple signals using its ⁠$signal⁠ method (see the "Signal" section below for details). When drawn, all collected signals are passed to the make_content function to generate the final grob.

Usage

channelGrob(make_content, ..., name = NULL, vp = NULL)

Arguments

make_content	A function that accepts the list of signal locations and returns a grob.
...	Additional arguments passed to make_content.
name	a character identifier for the grob. Used to find the grob on the display list and/or as a child of another grob.
vp	a viewport object (or NULL).

Value

A channelSenderGrob object.

Signal

A channelSenderGrob can emit multiple location signals using the ⁠$signal⁠ method. This method accepts the following arguments:

• x: X-coordinate.

• y: Y-coordinate.

• default.units: The default units for x and y.

• tag: A character string used to identify the location.

• name: A name for the returned grob.

• vp: A viewport for the returned grob.

The ⁠$signal⁠ method returns a channelSignalGrob.

Examples

# we create a new channel, we will emit two singals
# here: we just add a line between the two signals
channel <- channelGrob(function(locations) {
    # you can also use `tag` to identify the locations
    loc1 <- .subset2(locations, 1L)
    loc2 <- .subset2(locations, 2L)
    grid::segmentsGrob(loc1$x, loc1$y, loc2$x, loc2$y)
})

gt <- gtable::gtable(unit(1:2, c("cm")), unit(5, "cm"))
gt <- gtable::gtable_add_grob(
    gt,
    list(
        grid::rectGrob(gp = gpar(color = "black", fill = NA)),
        channel$signal(0.5, 0.5, "npc")
    ),
    t = 1, l = 1, name = c("rect1", "signal1")
)
gt <- gtable::gtable_add_grob(
    gt,
    list(
        grid::rectGrob(gp = gpar(color = "red", fill = NA)),
        channel$signal(0.5, 0.5, "npc")
    ),
    t = 1, l = 2, name = c("rect2", "signal2")
)
grid::grid.newpage()
grid::grid.draw(gt)

ggalign documentation built on June 8, 2025, 11:25 a.m.