Element: graphic_window.layers[ ]

Type

layer[]

Description

Every graphic window has a number of graphic layers associated with it. Some are system layers, others are application-created vector layers displaying graphic primitives delineated by group.

The window.layers[] array gives access to these layers, enabling rendering order and other characteristics to be modified. When a graphic window is repainted the layers are rendered in the order of this array.

There are various types of layer available:

Type	Creation	Contents	Access
background	Automatic on window creation	The background color or fillstyle.	window.background_layer
cloth	Automatic, resulting from a wcloth command	A set of image files defined as a backcloth.	window.cloth_layers
vector	By direct correspondence with window.group_order	Graphic primitives which are members of an entity group.	window.vector_layers window.vector_layer(group)
pre_vector	Automatic, resulting from the presence of a window.redraw callback	Any manually drawn graphics invoked during execution of the callback.	window.pre_vector_layer
post_vector	Automatic, resulting from the presence of a window.post_redraw callback	Any manually drawn graphics invoked during execution of the callback.	window.post_vector_layer
annotation	Automatic on window creation	Autotext annotation.	window.annotation_layer
grid	Automatic, resulting from a grid -on command	A grid of polylines.	window.grid_layer
scalebar	Automatic, resulting from a scalebar -on command	An annotated measured scalebar symbol	window.scalebar_layer
vane	Automatic, resulting from a vane -on command	A direction vane symbol.	window.vane_layer

A new graphic window initially has 3 layers, a background layer, a default vector layer associated with the all group of entities, and an annotation layer. This is no change from earlier Fire versions, but merely provides a default layering system. The background layer is merely for the convenience of accessing and controlling the background color and possibly a background image.

Layers other than vector layers (known as system layers) are added to (or removed from) a window's layer list automatically when other graphic features are enabled (or disabled) for the window, e.g. cloth, autogrid, autovane, pre-vector and post-vector, as listed under Creation in the above table.

Different layer types can be referenced by type as well as by index into the window.layers array, as listed under Access in the above table. Consult these topics for more details.

Vector layers can be created by one of 2 methods:

by adding the group of entities which constitute the layer to the window.group_order array, e.g.

group buildings
gwin.group_order = <all, buildings>

or by extending the window.layers array and then assigning a group to the new array element, e.g.

group buildings
gwin.layers[3] := null;# Add an undefined layer
gwin.layers[3].group = buildings;# Make the layer a vector layer

The layer draw order can be changed merely by re-ordering the window.layers array, although some layers (e.g. the background layer) have a fixed position in the redraw hierarchy and cannot be repositioned elsewhere order. The swap operator is particularly useful for layer re-ordering, e.g.

gwin.layers[3] <=> gwin.layers[4]

See Also