11.5 Tabular layout

XPCE provides various mechanisms for two-dimensional layout.

11.5.1 Using format

Class format can be seen as a poor-mens version of table. On the other hand, there are two cases that still make it a valuable solution. One is to deal with simple compound graphicals, such as a bitmap with a label displayed below it. The other is for browsing collections of graphical objects such as images.

The class icon below displays a label-text below an image.

:- pce_begin_class(icon, device).

:- pce_global(@icon_format, make_icon_format).

make_icon_format(F) :-
        new(F, format(horizontal, 1, @on)),
        send(F, adjustment, vector(center)),
        send(F, row_sep, 2).

initialise(Icon, Img:image, Label:name) :->
        send_super(Icon, initialise),
        send(Icon, format, @icon_format),
        send(Icon, display, bitmap(Img)),
        send(Icon, display, text(Label, center)). 

:- pce_end_class.

An example using format for distribution graphicals over a window is the library library(pce_image_browser).

11.5.2 Using table using the ``tabular'' library

The class table acts much the same way as class format in the sense that it is attached to a device and modifies the layout management of this device. For this purpose it uses an interface defined in XPCE version 5.0 and realised using the methods `device<->layout_manager' and `graphical<->layout_interface'. Figure 22 gives an overview of the classes realising tabular layout.

Figure 22 : Layout manager interface for tables

The advantage of the approach using layout manager objects is that they can easily be associated with any subclass of device, such as a window. The disadvantage is that the communication gets more difficult due to the different objects involved. This complication is hidden in the XPCE/Prolog class tabular, a subclass of device with an associated table and methods for guiding the messages for common usage.

tabular ->initialise:
Create a device with associated table.
tabular ->append:
Append a new cell. Cells are places left-to-right. The arguments are:

tabular ->append_label_button: Field:name
This method appends a button that is nicely aligned with the cell. If the button is depressed it activates ->sort_rows, providing the column index and the row below the row holding the button.
tabular ->sort_rows: Col:int, Row:int
A virtual method with a body that prints an informative message. It is called from a button installed using ->append_label_button and receives the column to sort-on as well as the first row to sort.
tabular <-table:
Table Returns the table serving as <-layout_manager.
tabular ->table_width: Width:int
Force the table to perform the layout in the indicated width. Initially the width of a tabular is defined by the content. Setting the width forces the table to negotiate with its columns and then force the width of the columns.
tabular ->event: Event:event
This refinement of `device->event' determines the cell in which the event occurs. If this cell has a `cell<->note_mark' attached and the graphical defines the method ->on_mark_clicked, the event is checked against the mark-image. Otherwise the event is forwarded to the graphical inside the cell, even it it doesn't occur in the area of the graphical, making small (text-)objects sensitive to all events in the cell. Finally, this method checks for attempts to drag the column-borders, changing the layout of the table.

As tabular delegates all messages not understood to the <-table, the messages of this class are also available. Below are the most important ones.

table ->next_row: EndGroup:[bool]
Start the next row in the table. If EndGroup is @on, the just-finished row is marked to end a row-group. See also ->rules.
table ->border: Border:0..
Defines the thickness of border and rule-lines. Default is 0, not drawing any lines.
table ->frame: {void,above,below,hsides,vsides,box}
Defines which parts of the box around the table are painted (if <-border > 0). The terminology is from HTML-3.
table ->rules: {none,groups,rows,cols,all}
Defines which lines between rows/columns are painted (if <-border > 0). The terminology is from HTML-3.
table ->cell_padding: Padding:int|size
Defines the space around the content of a cell. If this is an integer this space is the same in horizontal and vertical directions. If it is a size these can be specified independently.
table ->cell_spacing: Spacing:int|size
Defines the distance between the cells. Same rules as for ->cell_padding applies. In some cases pretty effects can be achieved setting this value to minus the <-border.

Below we build a small example.

:- use_module(library(tabular)).
:- use_module(library(autowin)).

make_table :-
        new(P, auto_sized_picture('Table with merged cells')), 
        send(P, display, new(T, tabular)),
        send(T, border, 1),
        send(T, cell_spacing, -1),
        send(T, rules, all),
                  [ append(new(graphical), rowspan := 2),
                    append('Length/mm', bold, center, colspan := 3),
                    append('body', bold, center),
                    append('tail', bold, center),
                    append('ears', bold, center),
                    append('males', bold),
                    append('females', bold),
        send(P, open).

Figure 23 : Small table with row/column spanning