Programming in XPCE/Prolog: Section 10.6

## 10.6 Window layout in a frame

A frame is the gateway between a collection of tiled window s (graphics, dialog) and the Window System. Any displayed window has a frame. The `window`->`create' method (invoked by `window`->`open') will create a default frame for a window if the window does not have a frame.

Windows in a frame are controlled by a hierarchy of tile objects. The leaves of this hierarchy manage an individual window, while the non-leaf tiles either manages a left-to-right list of sub-tiles or a top-to-bottom list. A non-leaf horizontal (left-to-right) tile forces all windows to be as high as the highest wishes to be and distributes the horizontal space over the sub-tiles, while a vertical tile forces all members to the same (widest) member and distributes the vertical space.

A tile hierarchy is built using the methods `window`->`above', etc. described below. Each window is born with a leaf-tile. If two windows are connected using `->`left or `->`right, a horizontal tile is created. Any other window associated to the left or right will be added as a member to this horizontal tile. A analogous story applies to vertically stacked windows.

If a window or collection of windows is placed left of a vertical tiled stack of windows, a horizontal tile is created.

Whenever a window receives one of the `->`above, `->`left, etc. messages, it will forward these messages to the root of the associated tile hierarchy. Assuming both windows are not yet related, the root tiles negotiate the alignment (combine, become member, create a new root).

Suppose we want to realise the window layout shown in figure 16. Now, look for windows that have equal width or height. This is the starting point, W3 and W4 in this example. So, the first statement is:

            send(W3, above, W4)

Figure 16 : Demo window layout

Note that `send(W4, below, W3)' is the same, except that if both W3 and W4 have a frame attached, the frame of the argument of the message will hold both windows, while the frame of the receiver is destroyed.

Now simply continue inwards-out:

            send(W2, left, W3),
            send(W1, above, W2),
            send(W5, below, W2)

Note that `send(W2, left, W4)' is exactly the same as positioning W2 left of W3. The resulting tile hierarchy is shown in figure 17. The numbers indicate the order of creation of the various objects.

Figure 17 : Tile hierarchy of example

### 10.6.1 Windows sizes and automatic adjustment

A tile defines six size parameters, described below.

tile ->ideal_width: int
tile ->ideal_height: int
  These two parameters describe the ideal size of the tile. The initial values for these parameters are read from the window for which the tile is created. A non-leaf horizontal tile sets the ideal width to the sum of its members and the ideal height to the maximum of its members.
tile ->hor_stretch: 0..100
tile ->ver_stretch: 0..100
  These two parameters describe how easy the window stretches (gets bigger). A non-leaf horizontal tile sets hor_stretch to the maximum of its members and ver_stretch to the minimum of its members.
tile ->hor_shrink: 0..100
tile ->ver_shrink: 0..100
  Same, but deals with making the window/tile smaller than its ideal size.

The various built-in window types have the following defaults shown in table 7.

class | width | height | hor_shrink | ver_shrink | hor_stretch | ver_stretch
window | 200 | 100 | 100 | 100 | 100 | 100
picture | 400 | 200 | 100 | 100 | 100 | 100
dialog | 200α | 100α | 0 | 0 | 0 | 0
browser | 25β | 10β | 0 | 100 | 0 | 100
view | 80β | 20β | 100 | 100 | 100 | 100

(1)If the dialog is not empty, the bounding box of the contents with the `<-`gap around it will be used.

(2)Interpreted as character units.

Table 7 : The window types and their default sizes

These rules will often suffice for simple applications. You may adjust the stretch and shrink parameters after creating the window, but before opening the window.

### 10.6.2 Manipulating an open frame

Windows may be added to an open frame using the `->`above, etc. message, specifying any of the member windows as argument. Windows may be deleted from a frame using `frame`->`delete'. If a window is added or deleted from an open window, the message `frame`->`fit' will be called to readjust the contents. This will normally change the size of the frame. If this is not desired, class frame must be sub-classed as below. Note that fixed_size should not be set to @on before the frame is open.

    :- pce_begin_class(my_dynamic_frame, frame,
                       "Add fixed_size").

    variable(fixed_size, bool := @off, both,
             "Do not resize on ->fit").

    fit(F) :->
            "Request to fit the contents"::
            (   get(F, fixed_size, @on)
            ->  send(F, resize)
            ;   send(F, send_super, fit)
            ).