NAME
Prima::TextView - rich text browser widget
DESCRIPTION
Prima::TextView accepts blocks of formatted text, and provides basic
functionality - scrolling and user selection. The text strings are
stored as one large text chunk, available by the "::text" and
"::textRef" properties. A block of a formatted text is an array with
fixed-length header and the following instructions.
A special package "tb::" provides the block constants and simple
functions for text block access.
Capabilities
Prima::TextView is mainly the text block functions and helpers. It
provides function for wrapping text block, calculating block
dimensions, drawing and converting coordinates from (X,Y) to a block
position. Prima::TextView is centered around the text functionality,
and although any custom graphic of arbitrary complexity can be embedded
in a text block, the internal coordinate system is used ( TEXT_OFFSET,
BLOCK ), where TEXT_OFFSET is a text offset from the beginning of a
block and BLOCK is an index of a block.
The functionality does not imply any text layout - this is up to the
class descendants, they must provide they own layout policy. The only
policy Prima::TextView requires is that blocks’ BLK_TEXT_OFFSET field
must be strictly increasing, and the block text chunks must not
overlap. The text gaps are allowed though.
A text block basic drawing function includes change of color, backColor
and font, and the painting of text strings. Other types of graphics can
be achieved by supplying custom code.
Block header
A block’s fixed header consists of "tb::BLK_START - 1" integer scalars,
each of those is accessible via the corresponding "tb::BLK_XXX"
constant. The constants are separated into two logical groups:
BLK_FLAGS
BLK_WIDTH
BLK_HEIGHT
BLK_X
BLK_Y
BLK_APERTURE_X
BLK_APERTURE_Y
BLK_TEXT_OFFSET
and
BLK_FONT_ID
BLK_FONT_SIZE
BLK_FONT_STYLE
BLK_COLOR
BLK_BACKCOLOR
The second group is enclosed in "tb::BLK_DATA_START" -
"tb::BLK_DATA_END" range, like the whole header is contained in 0 -
"tb::BLK_START - 1" range. This is done for the backward
compatibility, if the future development changes the length of the
header.
The first group fields define the text block dimension, aperture
position and text offset ( remember, the text is stored as one big
chunk ). The second defines the initial color and font settings.
Prima::TextView needs all fields of every block to be initialized
before displaying. block_wrap method can be used for automated
assigning of these fields.
Block parameters
The scalars, beginning from "tb::BLK_START", represent the commands to
the renderer. These commands have their own parameters, that follow
the command. The length of a command is located in @oplen array, and
must not be changed. The basic command set includes "OP_TEXT",
"OP_COLOR", "OP_FONT", "OP_TRANSPOSE", and "OP_CODE". The additional
codes are "OP_WRAP" and "OP_MARK", not used in drawing but are special
commands to block_wrap.
OP_TEXT - TEXT_OFFSET, TEXT_LENGTH, TEXT_WIDTH
"OP_TEXT" commands to draw a string, from offset
"tb::BLK_TEXT_OFFSET + TEXT_OFFSET", with a length TEXT_LENGTH. The
third parameter TEXT_WIDTH contains the width of the text in
pixels. Such the two-part offset scheme is made for simplification
or an imaginary code, that would alter ( insert to, or delete part
of ) the big text chunk; the updating procedure would not need to
traverse all commands, but just the block headers.
Relative to: "tb::BLK_TEXT_OFFSET".
OP_COLOR - COLOR
"OP_COLOR" sets foreground or background color. To set the
background, COLOR must be or-ed with "tb::BACKCOLOR_FLAG" value. In
addition to the two toolkit supported color values ( RRGGBB and
system color index ), COLOR can also be or-ed with
"tb::COLOR_INDEX" flags, in such case it is an index in
"::colormap" property array.
Relative to: "tb::BLK_COLOR", "tb::BLK_BACKCOLOR".
OP_FONT - KEY, VALUE
As the font is a complex property, that itself includes font name,
size, direction, etc keys, "OP_FONT" KEY represents one of the
three parameters - "tb::F_ID", "tb::F_SIZE", "tb::F_STYLE". All
three have different VALUE meaning.
Relative to: "tb::BLK_FONT_ID", "tb::BLK_FONT_SIZE",
"tb::BLK_FONT_STYLE".
F_STYLE
Contains a combination of "fs::XXX" constants, such as
"fs::Bold", "fs::Italic" etc.
Default value: 0
F_SIZE
Contains the relative font size. The size is relative to the
current widget’s font size. As such, 0 is a default value, and
-2 is the widget’s default font decreased by 2 points.
Prima::TextView provides no range checking ( but the toolkit
does ), so while it is o.k. to set the negative "F_SIZE" values
larger than the default font size, one must be vary when
relying on the combined font size value .
If "F_SIZE" value is added to a "F_HEIGHT" constant, then it is
treated as a font height in pixels rather than font size in
points. The macros for these opcodes are named respectively
"tb::fontSize" and "tb::fontHeight", while the opcode is the
same.
F_ID
All other font properties are collected under an ’ID’. ID is a
index in the "::fontPalette" property array, which contains
font hashes with the other font keys initialized - name,
encoding, and pitch. These three are minimal required set, and
the other font keys can be also selected.
OP_TRANSPOSE X, Y, FLAGS
Contains a mark for an empty space. The space is extended to the
relative coordinates (X,Y), so the block extension algorithms take
this opcode in the account. If FLAGS does not contain
"tb::X_EXTEND", then in addition to the block expansion, current
coordinate is also moved to (X,Y). In this regard,
"(OP_TRANSPOSE,0,0,0)" and "(OP_TRANSPOSE,0,0,X_EXTEND)" are
identical and are empty operators.
There are formatting-only flags,in effect with block_wrap function.
"X_DIMENSION_FONT_HEIGHT" indicates that (X,Y) values must be
multiplied to the current font height. Another flag
"X_DIMENSION_POINT" does the same but multiplies by current value
of resolution property divided by 72 ( basically, treats X and Y
not as pixel but point values).
"OP_TRANSPOSE" can be used for customized graphics, in conjunction
with "OP_CODE" to assign a space, so the rendering algorithms do
not need to be re-written every time the new graphic is invented.
As an example, see how Prima::PodView deals with the images.
OP_CODE - SUB, PARAMETER
Contains a custom code pointer SUB with a parameter PARAMETER,
passed when a block is about to be drawn. SUB is called with the
following format:
( $widget, $canvas, $text_block, $font_and_color_state, $x, $y, $parameter);
$font_and_color_state ( or $state, through the code ) contains the
state of font and color commands in effect, and is changed as the
rendering algorithm advances through a block. The format of the
state is the same as of text block, so one may notice that for
readability F_ID, F_SIZE, F_STYLE constants are paired to
BLK_FONT_ID, BLK_FONT_SIZE and BLK_FONT_STYLE.
The SUB code is executed only when the block is about to draw.
OP_WRAP ON_OFF
"OP_WRAP" is only in effect in block_wrap method. ON_OFF is a
boolean flag, selecting if the wrapping is turned on or off.
block_wrap does not support stacking for the wrap commands, so the
"(OP_WRAP,1,OP_WRAP,1,OP_WRAP,0)" has same effect as "(OP_WRAP,0)".
If ON_OFF is 1, wrapping is disabled - all following commands
treated an non-wrapable until "(OP_WRAP,0)" is met.
OP_MARK PARAMETER, X, Y
"OP_MARK" is only in effect in block_wrap method and is a user
command. block_wrap only sets (!) X and Y to the current
coordinates when the command is met. Thus, "OP_MARK" can be used
for arbitrary reasons, easy marking the geometrical positions that
undergo the block wrapping.
As can be noticed, these opcodes are far not enough for the full-weight
rich text viewer. However, the new opcodes can be created using
"tb::opcode", that accepts the opcode length and returns the new opcode
value.
Rendering methods
block_wrap
"block_wrap" is the function, that is used to wrap a block into a
given width. It returns one or more text blocks with fully
assigned headers. The returned blocks are located one below
another, providing an illusion that the text itself is wrapped. It
does not only traverses the opcodes and sees if the command fit or
not in the given width; it also splits the text strings if these do
not fit.
By default the wrapping can occur either on a command boundary or
by the spaces or tab characters in the text strings. The
unsolicited wrapping can be prevented by using "OP_WRAP" command
brackets. The commands inside these brackets are not wrapped;
"OP_WRAP" commands are removed from the output blocks.
In general, "block_wrap" copies all commands and their parameters
as is, ( as it is supposed to do ), but some commands are treated
especially:
- "OP_TEXT"’s third parameter, "TEXT_WIDTH", is disregarded, and is
recalculated for every "OP_TEXT" met.
- If "OP_TRANSPOSE"’s third parameter, "X_FLAGS" contains
"X_DIMENSION_FONT_HEIGHT" flag, the command coordinates X and Y are
multiplied to the current font height and the flag is cleared in
the output block.
- "OP_MARK"’s second and third parameters assigned to the current
(X,Y) coordinates.
- "OP_WRAP" removed from the output.
block_draw CANVAS, BLOCK, X, Y
The "block_draw" draws BLOCK onto CANVAS in screen coordinates
(X,Y). It can not only be used for drawing inside
begin_paint/end_paint brackets; CANVAS can be an arbitrary
"Prima::Drawable" descendant.
Coordinate system methods
Prima::TextView employs two its own coordinate systems: (X,Y)-document
and (TEXT_OFFSET,BLOCK)-block.
The document coordinate system is isometric and measured in pixels. Its
origin is located into the imaginary point of the beginning of the
document ( not of the first block! ), in the upper-left point. X
increases to the right, Y increases downwards. The block header values
BLK_X and BLK_Y are in document coordinates, and the widget’s pane
extents ( regulated by "::paneSize", "::paneWidth" and "::paneHeight"
properties ) are also in document coordinates.
The block coordinate system in an-isometric - its second axis, BLOCK,
is an index of a text block in the widget’s blocks storage,
"$self->{blocks}", and its first axis, TEXT_OFFSET is a text offset
from the beginning of the block.
Below described different coordinate system converters
screen2point X, Y
Accepts (X,Y) in the screen coordinates ( O is a lower left widget
corner ), returns (X,Y) in document coordinates ( O is upper left
corner of a document ).
xy2info X, Y
Accepts (X,Y) is document coordinates, returns (TEXT_OFFSET,BLOCK)
coordinates, where TEXT_OFFSET is text offset from the beginning of
a block ( not related to the big text chunk ) , and BLOCK is an
index of a block.
info2xy TEXT_OFFSET, BLOCK
Accepts (TEXT_OFFSET,BLOCK) coordinates, and returns (X,Y) in
document coordinates of a block.
text2xoffset TEXT_OFFSET, BLOCK
Returns X coordinate where TEXT_OFFSET begins in a BLOCK index.
info2text_offset
Accepts (TEXT_OFFSET,BLOCK) coordinates and returns the text offset
with regard to the big text chunk.
text_offset2info TEXT_OFFSET
Accepts big text offset and returns (TEXT_OFFSET,BLOCK) coordinates
text_offset2block TEXT_OFFSET
Accepts big text offset and returns BLOCK coordinate.
Text selection
The text selection is performed automatically when the user selects the
region with a mouse. The selection is stored in (TEXT_OFFSET,BLOCK)
coordinate pair, and is accessible via the "::selection" property. If
its value is assigned to (-1,-1,-1,-1) this indicates that there is no
selection. For convenience the "has_selection" method is introduced.
Also, "get_selected_text" returns the text within the selection (or
undef with no selection ), and "copy" copies automatically the selected
text into the clipboard. The latter action is bound to "Ctrl+Insert"
key combination.
Event rectangles
Partly as an option for future development, partly as a hack a concept
of ’event rectangles’ was introduced. Currently, "{contents}" private
variable points to an array of objects, equipped with "on_mousedown",
"on_mousemove", and "on_mouseup" methods. These are called within the
widget’s mouse events, so the overloaded classes can define the
interactive content without overloading the actual mouse events ( which
is although easy but is dependent on Prima::TextView own mouse
reactions ).
As an example Prima::PodView uses the event rectangles to catch the
mouse events over the document links. Theoretically, every ’content’ is
to be bound with a separate logical layer; when the concept was
designed, a html-browser was in mind, so such layers can be thought as
( in the html world ) links, image maps, layers, external widgets.
Currently, "Prima::TextView::EventRectangles" class is provided for
such usage. Its property "::rectangles" contains an array of
rectangles, and the "contains" method returns an integer value, whether
the passed coordinates are inside one of its rectangles or not; in the
first case it is the rectangle index.