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Dmitry Karasik

NAME

Prima::Drawable::TextBlock - rich text representation

API

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 of 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 when not preceded by OP_BIDIMAP.

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 mode

OP_WRAP is only in effect in block_wrap method. mode is a flag, selecting the wrapping command.

   WRAP_MODE_ON   - default, block commands can be wrapped
   WRAP_MODE_OFF  - cancels WRAP_MODE_ON, commands cannot be wrapped
   WRAP_IMMEDIATE - proceed with immediate wrapping, unless ignoreImmediateWrap options is set

block_wrap does not support stacking for the wrap commands, so the (OP_WRAP,WRAP_MODE_ON,OP_WRAP,WRAP_MODE_ON,OP_WRAP,WRAP_MODE_OFF) has same effect as (OP_WRAP,WRAP_MODE_OFF). If mode is WRAP_MODE_ON, wrapping is disabled - all following commands treated an non-wrapable until (OP_WRAP,WRAP_MODE_OFF) 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.

OP_BIDIMAP VISUAL, BIDIMAP

OP_BIDIMAP is used when the text to be displayed is RTL (right-to-left) and requires special handling. This opcode is automatically created by block_wrap. It must be present before any OP_TEXT opcode, because when in effect, the OP_TEXT offset calculation is different - instead of reading characters from $self->{text}, it reads them from VISUAL, and BLK_TEXT_OFFSET in the block header is not used.

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.

- OP_BIDIMAP added to the output, if the text to be displayed in the block contains right-to-left characters.

walk BLOCK, %OPTIONS

Cycles through block opcodes, calls supplied callbacks on each.

AUTHOR

Dmitry Karasik, <dmitry@karasik.eu.org>.

SEE ALSO

Prima::TextView, Prima::Drawable::Markup, examples/mouse_tale.pl.