Loon layers

Loon supports layering of visuals and groups of visuals. The l_layer function is a generic method.

l_layer(widget, x, ...)

Arguments

widget	widget path as a string or as an object handle
x	for UseMethod: an object whose class will determine the method to be dispatched.
...	additional arguments, often state definition for the basic layering function

Value

layer object handle, layer id

Details

loon's displays that use the main graphics model (i.e. histogram, scatterplot and graph displays) support layering of visual information. The following table lists the layer types and functions for layering on a display.

Type	Description	Creator Function
group	a group can be a parent of other layers	l_layer_group
polygon	one polygon	l_layer_polygon
text	one text string	l_layer_text
line	one line (i.e. connected line segments)	l_layer_line
rectangle	one rectangle	l_layer_rectangle
oval	one oval	l_layer_oval
points	n points (filled) circle	l_layer_points
texts	n text strings	l_layer_text
polygons	n polygons	l_layer_polygons
rectangles	n rectangles	l_layer_rectangles
lines	n sets of connected line segments	l_layer_lines
smooth	fitted smooth line	l_layer_smooth
rasterImage	one raster image	l_layer_rasterImage
heatImage	one heat image	l_layer_heatImage
contourLines	contour lines	l_layer_contourLines

Every layer within a display has a unique id. The visuals of the data in a display present the default layer of that display and has the layer id 'model'. For example, the 'model' layer of a scatterplot display visualizes the scatterplot glyphs. Functions useful to query layers are

Function	Description
l_layer_ids	List layer ids
l_layer_getType	Get layer type

Layers are arranged in a tree structure with the tree root having the layer id 'root'. The rendering order of the layers is according to a depth-first traversal of the layer tree. This tree also maintains a label and a visibility flag for each layer. The layer tree, layer ids, layer labels and the visibility of each layer are visualized in the layers inspector. If a layer is set to be invisible then it is not rendered on the display. If a group layer is set to be invisible then all its children are not rendered; however, the visibility flag of the children layers remain unchanged. Relevant functions are:

Function	Description
l_layer_getParent	Get parent layer id of a layer
l_layer_getChildren	Get children of a group layer
l_layer_index	Get the order index of a layer among its siblings
l_layer_printTree	Print out the layer tree
l_layer_move	Move a layer
l_layer_lower	Switch the layer place with its sibling to the right
l_layer_raise	Switch the layer place with its sibling to the left
l_layer_demote	Moves the layer up to be a left sibling of its parent
l_layer_promote	Moves the layer to be a child of its right group layer sibling
l_layer_hide	Set the layers visibility flag to FALSE
l_layer_show	Set the layers visibility flag to TRUE
l_layer_isVisible	Return visibility flag of layer
l_layer_layerVisibility	Returns logical value for whether layer is actually seen
l_layer_groupVisibility	Returns all, part or none for expressing which part of the layers children are visible.
l_layer_delete	Delete a layer. If the layer is a group move all its children layers to the layers parent.
l_layer_expunge	Delete layer and all its children layer.
l_layer_getLabel	Get layer label.
l_layer_relabel	Change layer label.
l_layer_bbox	Get the bounding box of a layer.

All layers have states that can be queried and modified using the same functions as the ones used for displays (i.e. l_cget, l_configure, `[` and `[<-`). The last group of layer types in the above table have n-dimensional states, where the actual value of n can be different for every layer in a display.

The difference between the model layer and the other layers is that the model layer has a selected state, responds to selection gestures and supports linking.

For more information run: l_help("learn_R_layer")

See also

l_info_states, l_scaleto_layer, l_scaleto_world;

some l_layer S3 methods: l_layer.density, l_layer.map, l_layer.SpatialPolygonsDataFrame, l_layer.SpatialPolygons, l_layer.Polygons, l_layer.Polygon, l_layer.SpatialLinesDataFrame, l_layer.SpatialLines, l_layer.Lines, l_layer.Line, l_layer.SpatialPointsDataFrame, l_layer.SpatialPoints

Examples

if(interactive()){

# l_layer is a generic method
newFoo <- function(x, y, ...) {
  r <- list(x=x, y=y, ...)
  class(r) <- 'foo'
  return(r)
}

l_layer.foo <- function(widget, x) {
    x$widget <- widget
    id <- do.call('l_layer_polygon', x)
    return(id)
}

p <- l_plot()

obj <- newFoo(x=c(1:6,6:2), y=c(3,1,0,0,1,3,3,5,6,6,5), color='yellow')

id <- l_layer(p, obj)

l_scaleto_world(p)
}