gggroup: 'GGroup' is the base class for ggroup and all box containers/

In jverzani/gWidgetsWWW2: Toolkit implementation of the gWidgets API for use with web pages

Description

Box containers pack in child objects in a left to right manner (horizontal) or top to bottom (horizonta=FALSE). In the gWidgets API the space allocated to a child dependsd on the arguments expand, fill and anchor. These have a different interpretation in gWidgetsWWW2, as there are no analogs in Ext's Box layouts.

Details

Let's discuss vertical box containers, turn this on the side to think about horizontal ones. A vertical box container places its children from top to bottom. When packing each child has its requested height. If the sum of these is less than the height of the box (and no flex values is given) then there is excess space in the bottom of the box. If the sum is greater, the argument use.scrollwindow should make it so that parent box containers has scrollbars allowing the user to scroll to see the bottom widgets. This has been an issue getting to work though.

Now, when there is more availabe verticle space than requested space, we can also have the widgets request more availabel space. The expand argument can be a logical indicating if the available space to a widget should expand to fill the possible space. In Ext, this maps to a value of flex, which is a weight so child items with bigger flex values get a weighted amount of space. As such, you can specify a positive number to the expand argument. A logical is simply converted to 0 or 1;

As for horizontal space, the FILL argument should be used to indicate if a child item should expand in the horizontal space allotted. However, Ext doesn't allow per item sizing of children, rather the 'align' property is a property of the parent container (the box). We set it to 'stretch'. This gives similar behaviour as RGtk2, where child components always stretch to fill the direction orthogonal to the packing direction. (This can lead to undesirable layouts. To override, pass in something like ext.args=list(layout=list(type="hbox",align="top")), say.)

This can lead to large box containers, when a box container is also a child of a parent box container. The size of the child box can be controlled through the width and height arguments. These map to maxWidth and maxHeight, not the usual width and height which are really requests, but additional space can be allocated.

The anchor argument is meant to locate the actual widget within the space allocated to the widget. In the gWidgets spec if expand=TRUE, fill=FALSE, then the widget may have additional space to fill than it needs. The anchor specifies in x and y coordinates where it should go values are in -1,0,1 x -1, 0, 1.

jverzani/gWidgetsWWW2 documentation built on Feb. 9, 2020, 5:18 p.m.