Provided by: libtickit-perl_0.72-1_amd64 
NAME
"Tickit::RenderBuffer" - efficiently render text and line-drawing
SYNOPSIS
package Tickit::Widget::Something;
...
sub render_to_rb
{
my $self = shift;
my ( $rb, $rect ) = @_;
$rb->eraserect( $rect );
$rb->text_at( 2, 2, "Hello, world!", $self->pen );
}
$win->set_on_expose( sub {
my ( $win, $rb, $rect ) = @_;
$rb->eraserect( $rect );
$rb->text_at( 2, 2, "Hello, world!" );
});
DESCRIPTION
Provides a buffer of pending rendering operations to apply to the terminal. The buffer is
modified by rendering operations performed by widgets or other code, and flushed to the
terminal when complete.
This provides the following advantages:
• Changes can be made in any order, and will be flushed in top-to-bottom, left-to-right
order, minimising cursor movements.
• Buffered content can be overwritten or partly erased once stored, simplifying some
styles of drawing operation. Large areas can be erased, and then redrawn with text or
lines, without causing a double-drawing flicker on the output terminal.
• The buffer supports line-drawing, complete with merging of line segments that meet in a
character cell. Boxes, grids, and other shapes can be easily formed by drawing separate
line segments, and the "RenderBuffer" will handle the corners and other junctions
formed.
• A single buffer can be passed around all of the windows or widgets to properly combine
line segments and layering effects, making it possible to create many kinds of sub-
divided or layered output.
Drawing methods come in two forms; absolute, and cursor-relative:
• Absolute methods, identified by their name having a suffixed "_at", operate on a
position within the buffer specified by their argument.
• Cursor-relative methods, identified by their lack of "_at" suffix, operate at and update
the position of the "virtual cursor". This is a position within the buffer that can be
set using the "goto" method. The position of the virtual cursor is not affected by the
absolute-position methods.
State Stack
The "RenderBuffer" stores a stack of saved state. The state of the buffer can be stored
using the "save" method, so that changes can be made, before finally restoring back to
that state using "restore". The following items of state are saved:
• The virtual cursor position
• The clipping rectangle
• The render pen
• The translation offset
• The set of masked regions
When the state is saved to the stack, the render pen is remembered and merged with any pen
set using the "setpen" method.
The queued content to render is not part of the state stack. It is intended that the state
stack be used to implement recursive delegation of drawing operations down a tree of code,
allowing child contexts to be created by saving state and modifying it, to later restore
it again afterwards.
CONSTRUCTOR
new
$rb = Tickit::RenderBuffer->new( %args )
Returns a new instance of a "Tickit::RenderBuffer".
Takes the following named arguments:
lines => INT
cols => INT
The size of the buffer area.
METHODS
lines
cols
$lines = $rb->lines
$cols = $rb->cols
Returns the size of the buffer area
line
col
$line = $rb->line
$col = $rb->col
Returns the current position of the virtual cursor, or "undef" if it is not set.
save
$rb->save
Pushes a new state-saving context to the stack, which can later be returned to by the
"restore" method.
savepen
$rb->savepen
Pushes a new state-saving context to the stack that only stores the pen. This can later be
returned to by the "restore" method, but will only restore the pen. Other attributes such
as the virtual cursor position will be unaffected.
This may be more efficient for rendering runs of text in a different pen, than multiple
calls to "text" or "erase" using the same pen. For a single call it is better just to pass
a different pen directly.
restore
$rb->restore
Pops and restores a saved state previously created with "save".
clip
$rb->clip( $rect )
Restricts the clipping rectangle of drawing operations to be no further than the limits of
the given rectangle. This will apply to subsequent rendering operations but does not
affect existing content, nor the actual rendering to the terminal.
Clipping rectangles cumulative; each call further restricts the drawing region. To revert
back to a larger drawing area, use the "save" and "restore" stack.
mask
$rb->mask( $rect )
Masks off the given area against any further changes. This will apply to subsequent
rendering operations but does not affect the existing content, nor the actual rendering to
the terminal.
Areas within the clipping region may be arbitrarily masked. Masks are scoped to the depth
of the stack they are applied at; once the "restore" method is invoked, any masks applied
since its corresponding "save" will be removed.
translate
$rb->translate( $downward, $rightward )
Applies a translation to the coordinate system used by "goto" and the absolute-position
methods *_at. After this call, all positions used will be offset by the given amount.
reset
$rb->reset
Removes any pending changes and reverts the "RenderBuffer" to its default empty state.
Undefines the virtual cursor position, resets the clipping rectangle, and clears the stack
of saved state.
clear
$rb->clear( $pen )
Resets every cell in the buffer to an erased state. A shortcut to calling "erase_at" for
every line.
goto
$rb->goto( $line, $col )
Sets the position of the virtual cursor.
setpen
$rb->setpen( $pen )
Sets the rendering pen to use for drawing operations. If a pen is set then a $pen argument
is optional to any of the drawing methods. If a pen argument is supplied as well as having
a stored pen, then the attributes are merged, with the directly-applied pen taking
precedence.
Successive calls to this method will replace the active pen used, but if there is a saved
state on the stack it will be merged with the rendering pen of the most recent saved
state.
This method may be preferable to passing pens into multiple "text" or "erase" calls as it
may be more efficient than merging the same pen on every call. If the original pen is
still required afterwards, the "savepen" / "restore" pair may be useful.
skip_at
$rb->skip_at( $line, $col, $len )
Sets the range of cells given to a skipped state. No content will be drawn here, nor will
any content existing on the terminal be erased.
Initially, or after calling "reset", all cells are set to this state.
skip
$rb->skip( $len )
Sets the range of cells at the virtual cursor position to a skipped state, and updates the
position.
skip_to
$rb->skip_to( $col )
Sets the range of cells from the virtual cursor position until before the given column to
a skipped state, and updates the position to the column.
If the position is already past this column then the cursor is moved backwards and no
buffer changes are made.
skiprect
$rb->skiprect( $rect )
Sets the range of cells given by the rectangle to skipped state.
text_at
$cols = $rb->text_at( $line, $col, $text, $pen )
Sets the range of cells starting at the given position, to render the given text in the
given pen.
Returns the number of columns wide the actual $text is (which may be more than was
actually printed).
text
$cols = $rb->text( $text, $pen )
Sets the range of cells at the virtual cursor position to render the given text in the
given pen, and updates the position.
Returns the number of columns wide the actual $text is (which may be more than was
actually printed).
erase_at
$rb->erase_at( $line, $col, $len, $pen )
Sets the range of cells given to erase with the given pen.
erase
$rb->erase( $len, $pen )
Sets the range of cells at the virtual cursor position to erase with the given pen, and
updates the position.
erase_to
$rb->erase_to( $col, $pen )
Sets the range of cells from the virtual cursor position until before the given column to
erase with the given pen, and updates the position to the column.
If the position is already past this column then the cursor is moved backwards and no
buffer changes are made.
eraserect
$rb->eraserect( $rect, $pen )
Sets the range of cells given by the rectangle to erase with the given pen.
LINE DRAWING
The "RenderBuffer" supports storing line-drawing characters in cells, and can merge line
segments where they meet, attempting to draw the correct character for the segments that
meet in each cell.
There are three exported constants giving supported styles of line drawing:
• LINE_SINGLE
A single, thin line
• LINE_DOUBLE
A pair of double, thin lines
• LINE_THICK
A single, thick line
Note that linedrawing is performed by Unicode characters, and not every possible
combination of line segments of differing styles meeting in a cell is supported by
Unicode. The following sets of styles may be relied upon:
• Any possible combination of only "SINGLE" segments, "THICK" segments, or both.
• Any combination of only "DOUBLE" segments, except cells that only have one of the four
borders occupied.
• Any combination of "SINGLE" and "DOUBLE" segments except where the style changes
between "SINGLE" to "DOUBLE" on a vertical or horizontal run.
Other combinations are not directly supported (i.e. any combination of "DOUBLE" and
"THICK" in the same cell, or any attempt to change from "SINGLE" to "DOUBLE" in either the
vertical or horizontal direction). To handle these cases, a cell may be rendered with a
substitution character which replaces a "DOUBLE" or "THICK" segment with a "SINGLE" one
within that cell. The effect will be the overall shape of the line is retained, but close
to the edge or corner it will have the wrong segment type.
Conceptually, every cell involved in line drawing has a potential line segment type at
each of its four borders to its neighbours. Horizontal lines are drawn though the vertical
centre of each cell, and vertical lines are drawn through the horizontal centre.
There is a choice of how to handle the ends of line segments, as to whether the segment
should go to the centre of each cell, or should continue through the entire body of the
cell and stop at the boundary. By default line segments will start and end at the centre
of the cells, so that horizontal and vertical lines meeting in a cell will form a neat
corner. When drawing isolated lines such as horizontal or vertical rules, it is preferable
that the line go right through the cells at the start and end. To control this behaviour,
the $caps bitmask is used. "CAP_START" and "CAP_END" state that the line should consume
the whole of the start or end cell, respectively; "CAP_BOTH" is a convenient shortcut
specifying both behaviours.
A rectangle may be formed by combining two "hline_at" and two "vline_at" calls, without
end caps:
$rb->hline_at( $top, $left, $right, $style, $pen );
$rb->hline_at( $bottom, $left, $right, $style, $pen );
$rb->vline_at( $top, $bottom, $left, $style, $pen );
$rb->vline_at( $top, $bottom, $right, $style, $pen );
hline_at
$rb->hline_at( $line, $startcol, $endcol, $style, $pen, $caps )
Draws a horizontal line between the given columns (both are inclusive), in the given line
style, with the given pen.
vline_at
$rb->vline_at( $startline, $endline, $col, $style, $pen, $caps )
Draws a vertical line between the centres of the given lines (both are inclusive), in the
given line style, with the given pen.
linebox_at
$rb->linebox_at( $startline, $endline, $startcol, $endcol, $style, $pen )
A convenient shortcut to calling two "hline_at" and two "vline_at" in order to draw a
rectangular box.
char_at
$rb->char_at( $line, $col, $codepoint, $pen )
Sets the given cell to render the given Unicode character (as given by codepoint number,
not character string) in the given pen.
char
$rb->char( $codepoint, $pen )
Sets the cell at the virtual cursor position to render the given Unicode character (as
given by codepoint number, not character string) in the given pen, and updates the
position.
While this is also achieveable by the "text" and "text_at" methods, these methods are
implemented without storing a text segment, so can be more efficient than many single-
column wide "text_at" calls.
copyrect
moverect
$rb->copyrect( $dest, $src )
$rb->moverect( $dest, $src )
Copies (or moves) buffered content from one rectangular region to another. The two
regions may overlap.
The move operation is identical to the copy operation followed by setting the vacated
areas of the source rectangle not covered by the destination to skipping state.
get_cell
$cell = $rb->get_cell( $line, $col )
Returns a structure containing the content stored in the given cell. The $cell structure
responds to the following methods:
$cell->char
On a skipped cell, returns "undef". On a text or char cell, returns the unicode
codepoint number. On a line or erased cell, returns 0.
$cell->linemask
On a line cell, returns a representation of the line segments in the cell. This is a
sub-structure with four fields; "north", "south", "east", "west" to represent the four
cell borders; the value of each is either zero, or one of the "LINE_" constants.
On any other kind of cell, returns "undef".
$cell->pen
Returns the "Tickit::Pen" for non-skipped cells, or "undef" for skipped cells.
flush_to_term
$rb->flush_to_term( $term )
Renders the stored content to the given Tickit::Term. After this, the buffer will be
cleared and reset back to initial state.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>