path: root/man/2/prefab-element

.TH PREFAB-ELEMENT 2
.SH NAME
prefab: Element \- menu and display elements for ITV toolkit
.SH SYNOPSIS
.EX
include "draw.m";
include "prefab.m";
prefab := load Prefab Prefab->PATH;

# types of Elements
EIcon:      con 0;
EText:      con 1;
ETitle:     con 2;
EHorizontal:con 3;
EVertical:  con 4;
ESeparator: con 5;

# first arg to Element.adjust: size of elements
Adjpack:    con 10; # leave alone, pack tightly
Adjequal:   con 11; # make equal
Adjfill:    con 12; # make equal, filling available space

# second arg: position of element within space
Adjleft:    con 20;
Adjup:      con 20;
Adjcenter:  con 21;
Adjright:   con 22;
Adjdown:    con 22;

Layout: adt
{
  font:    ref Draw->Font;
  color:   ref Draw->Image;
  text:    string;
  icon:    ref Draw->Image;
  mask:    ref Draw->Image;
  tag:     string;
};

Element: adt
{
  kind:   int;
  r:      Draw->Rect;
  environ:ref Environ;  
  tag:    string;       
  
  # different fields defined for different kinds of Elements
  kids:   cyclic list of ref Element; # children of elists
  str:    string;           # text in an EText element
  mask:   ref Draw->Image;  # part of Eicon, ESeparator
  image:  ref Draw->Image;  # part of Eicon, ESeparator, EText, Etitle
  font:   ref Draw->Font;   # part of EText, Etitle
  
  icon:      fn(env: ref Environ, r: Draw->Rect,
               icon, mask: ref Draw->Image):
               ref Element;
  text:      fn(env: ref Environ, text: string,
               r: Draw->Rect, kind: int): ref Element;
  layout:    fn(env: ref Environ, lay: list of Layout,
               r: Draw->Rect, kind: int): ref Element;
  elist:     fn(env: ref Environ, elem: ref Element, kind: int):
               ref Element;
  separator: fn(env:ref Environ, r: Draw->Rect,
               icon, mask: ref Draw->Image): ref Element;

  append:    fn(elist: self ref Element, elem: ref Element): int;
  adjust:    fn(elem: self ref Element, equal: int, dir: int);
  clip:      fn(elem: self ref Element, r: Draw->Rect);
  scroll:    fn(elem:self ref Element, d: Draw->Point);
  translate: fn(elem:self ref Element, d: Draw->Point);
  show:      fn(elist: self ref Element, elem: ref Element): int;
};
.EE
.SH DESCRIPTION
.B Prefab
.B Elements
are the building blocks of the ITV toolkit.
They represent and display text and pictures that can be grouped in
arbitrary two-dimensional menus to be walked by the infrared remote control.
.B Elements
are packaged within
.B Compounds
(see
.IR prefab-compound (2))
for display.
.TF environ
.PD
.TP
.B environ
This specifies the element's environment.
.TP
.B image
If the element needs an
.B Image
object (see
.B kind
below), this member specifies it.
.TP
.B kind
The
.B Prefab
module defines six
.B Element
varieties, each labelled by a defined constant in the
.B kind
member.
.RS
.TP
.B EIcon
An image.
.TP
.B EHorizontal
A horizontal list of elements.
.TP
.B ESeparator
An
.B Image
object, like an
.BR EIcon ,
but intended to fill space in a list, rather than to serve
as an element of the list.
Separators are ignored when selecting or highlighting list elements.
.TP
.B EText
A single line of text.
Text for this element will be drawn with
.B Style.textfont
and
.BR Style.textcolor .
.TP
.B ETitle
A single line of text, usually giving the title of a
.B Compound
object.
Text for this element will be drawn with
.B Style.titlefont
and
.BR Style.titlecolor .
.TP
.B EVertical
A vertical list of elements.
.RE
.TP
.B mask
When an element contains an
.B Image
object, the
.B Image.draw
function will be used to display it on the screen.
The
.B mask
image is used as an argument to
.BR Image.draw ;
see
.IR draw-intro (2)
for more information.
.TP
.B r
All
.B Elements
are rectangular, occupying the
position on the display specified by
.BR r.min .
The size of the element also depends on
.BR r .
During creation,
if the rectangle is degenerate (has
zero size), the element takes its size from the
sizes of its components:
the image size for icons, text width for strings, etc.
Otherwise, the element's size matches the rectangle.
.TP
tag
The
.B tag
of an element serves two purposes: it allows an element to be labelled
with arbitrary invisible text, and provides a mechanism to control which
elements of a list may be selected: see the description of
.B Compound.tagselect
in
.IR prefab-compound (2).
The
.B tag
field of an element may be modified freely after the element is created.
.TP
.BI icon( env\fP,\fP\ r\fP,\fP\ icon\fP,\fP\ mask )
Build one
.B EIcon
element to be drawn with the
.I icon
and
.IR mask .
The rectangle,
.IR r ,
gives the element's position and size.
.TP
.BI text( env\fP,\fP\ text\fP,\fP\ r\fP,\fP\ kind )
Build a textual element or a list of textual elements.
.I Kind
may be
.B EText
or
.BR ETitle ,
determining the style of the drawn
.IR text .
The resulting
.B Element
object may be a single element or a
.B EVertical
list of the appropriate kind, if the text occupies
more than one line.
The text is folded as necessary to
accommodate the available horizontal space; newlines in
the text cause line breaks.
The width of the
text is determined by
.IR r ,
but if
.I r
has no width, it will be
set by the text itself.
The height of the Element is also
determined by
.IR r ;
again, if the height of
.I r
is zero, the Element will be made as tall as necessary (if
.I r
is not tall enough, the rest of the text may be made visible
by calls to
.BR Element.scroll ).
Thus one may choose
a specific size or let the
.I text
determine the size by setting
.I r
suitably.
.TP
.BI layout( env\fP,\fP\ lay\fP,\fP\ r\fP,\fP\ kind )
Like
.BR Element.text ,
but builds a structure using the contents of the list
.I lay
of
.B Layout
structures.  The
.B Layout
type
allows construction of a more general form of textual display
by providing fine control over the font and colour in which to
display text and the inclusion of images as textual elements.
It also allows setting of the
.B tag
for each component of the resulting element or list of elements.
If the
.B Layout
has a
.RB non- nil
.B image
field, it is taken as a description of a
picture to be incorporated in the text as an
.B EIcon
element (and the
.B text
field is ignored);
otherwise the
.B text
field specifies the text to be drawn in the indicated
.B font
and
.BR color .
As with
.BR Element.text ,
.B Element.layout
does all the geometry management, text line breaking and folding, etc.
.TP
.BI elist( env\fP,\fP\ elem\fP,\fP\ kind )
Start a list of
.B Element
objects.
The
.I kind
may be
.B Prefab\->EHorizontal
or
.BR Prefab\->EVertical ,
specifying the orientation of the list.
.I Elem
will be the first element of the list.
It may be
.BR nil ,
which creates an empty list of the
requested orientation.
Subsequent
.B Element.append
calls build the list.
.TP
.BI separator( env\fP,\fP\ r\fP,\fP\ icon\fP,\fP\ mask )
Build one
.B ESeparator
element to be drawn with the
.I icon
and
.IR mask .
The rectangle,
.IR r ,
gives the element's position and size.
.TP
.IB elist .append( elem )
Append one
.BR Element ,
.IR elem ,
to an existing list,
.IR elist .
The new element will appear after those already
there, either to the right for
.B EHorizontal
or below for
.B EVertical
lists.
.TP
.IB elem .adjust( spacing\fP,\fP\ dir )
Format the list so its elements abut.
The list-building functions such as
.B append
attempt to build a sensible geometry.
Alternatively, one can build a list using
degenerate geometry and then let
.B adjust
compute the geometry for the whole list.
For example, one could place all the elements
at (0,\ 0) and then call
.B adjust
to decide where the elements belong.
.IP ""
.I Spacing
specifies how the elements fit together:
.RS
.TP
.B Adjequal
Makes them all equal sized in the dimension of the list,
but only as big as the largest element.
For example, if the element is a horizontal list,
all elements will be as wide as the widest item.
If the list is too big for the allocated space,
only some will be visible. 
.TP
.B Adjfill
Makes them all equal sized in the dimension of the list,
expanding the elements to fit the space of the list's
.BR Element.r .
If the list is too big for the allocated space,
only some will be visible. 
.TP
.B Adjpack
Packs elements as tightly as possible,
using the ``natural'' size of each element
and setting their rectangles against one another.
.RE
.IP ""
.I Dir
controls how each element is placed in its allotted space:
.RS
.TP
.B Adjcenter
Place each element in the middle of its space.
.TP
.B Adjdown
In a vertical list, move each element to the bottom.
.TP
.B Adjleft
In a horizontal list, move each element to the left.
.TP
.B Adjright
In a horizontal list, move each element to the right.
.TP
.B Adjup
In a vertical list, move each element to the top.
.RE
.TP
.IB elem .clip( r )
The drawing model for
.B Element
objects is that they occupy some space in 
the plane, which may be larger or smaller than the space occupied
by its constituent text, icons, sub-elements, etc.
The
.I clip
function sets the rectangle of
.I elem
to
.IR r ,
without changing its internal geometry.
Any space made newly visible by this
will be filled in by the list's
.BR Style.elemcolor .
For example, if
.B e
is an icon element just large enough to display its image,
.B e.clip(e.r.inset(-2))
will make a two-pixel-wide border around the icon when
it is drawn.
As another example, lists are scrolled by leaving their clip
rectangle intact while translating the list elements' coordinates.
.TP
.IB elem .scroll( d )
.I D
is a
.BR Point ,
representing a vector;
.I elem
is an
.B Element
object to be scrolled.
The
.B scroll
function leaves the element's
.B r
alone and translates all the constituent pieces of the list by
.IR d ,
causing a different portion of
.I elem
to be visible in its rectangle.
.TP
.IB elem .translate( d )
Like
.IB elem .scroll( d ),
but moves
.B r
too, thus translating the entire
.B Element
rather than just the visible part within a fixed rectangle.
.TP
.IB elist .show( elem )
.B Show
does nothing if
.I elem
is not a list.
If it is a list, the list is scrolled
so
.IR elem ,
which must be a member of the list, is visible through
.IR elist.r .
.PP
The geometry of elements and the membership of lists
may be modified only through
the provided functions; the Limbo-visible structure is
(intended to be) read-only.
Tags, text, and images may be modified freely
by the application, but at the moment there is no way to recalculate
the geometry if the components of an
textual or image icon change size.
.PP
.B Element
objects are never drawn explicitly, nor are they drawn after any
.B Element
operation.
They are made visible only by calls to
.BR Compound.draw ,
described by
.IR prefab-compound (2).
.SH SOURCE
.B /libinterp/prefab.c
.B /libprefab/*.c
.SH SEE ALSO
.IR prefab-compound (2)
.IR prefab-environ (2)
.IR prefab-style (2)