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The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines.
In some cases, text lines are truncated on the screen rather than continued
onto additional screen lines. In these cases, vertical-motion moves
point much like forward-line. Voir la section Truncation.
Because the width of a given string depends on the flags that control the
appearance of certain characters, vertical-motion behaves
differently, for a given piece of text, depending on the buffer it is in,
and even on the selected window (because the width, the truncation flag, and
display table may vary between windows). Voir la section Usual Display Conventions.
These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned. If you intend to use them heavily, Emacs provides caches which may improve the performance of your code. Voir la section cache-long-line-scans.
This function moves point to the start of the screen line count screen lines down from the screen line containing point. If count is negative, it moves up instead.
vertical-motion returns the number of screen lines over which it
moved point. The value may be less in absolute value than count if
the beginning or end of the buffer was reached.
The window window is used for obtaining parameters such as the width,
the horizontal scrolling, and the display table. But vertical-motion
always operates on the current buffer, even if window currently
displays some other buffer.
This function returns the number of screen lines in the text from beg
to end. The number of screen lines may be different from the number
of actual lines, due to line continuation, the display table, etc. If
beg and end are nil or omitted, they default to the
beginning and end of the accessible portion of the buffer.
If the region ends with a newline, that is ignored unless the optional third
argument count-final-newline is non-nil.
The optional fourth argument window specifies the window for obtaining parameters such as width, horizontal scrolling, and so on. The default is to use the selected window's parameters.
Like vertical-motion, count-screen-lines always uses the
current buffer, regardless of which buffer is displayed in window.
This makes possible to use count-screen-lines in any buffer, whether
or not it is currently displayed in some window.
This function moves point with respect to the text currently displayed in the selected window. It moves point to the beginning of the screen line count screen lines from the top of the window. If count is negative, that specifies a position -count lines from the bottom (or the last line of the buffer, if the buffer ends above the specified screen position).
If count is nil, then point moves to the beginning of the line
in the middle of the window. If the absolute value of count is
greater than the size of the window, then point moves to the place that
would appear on that screen line if the window were tall enough. This will
probably cause the next redisplay to scroll to bring that location onto the
screen.
In an interactive call, count is the numeric prefix argument.
The value returned is the window line number point has moved to, with the top line in the window numbered 0.
This function scans the current buffer, calculating screen positions. It scans the buffer forward from position from, assuming that is at screen coordinates frompos, to position to or coordinates topos, whichever comes first. It returns the ending buffer position and screen coordinates.
The coordinate arguments frompos and topos are cons cells of the
form (hpos . vpos).
The argument width is the number of columns available to display text;
this affects handling of continuation lines. nil means the actual
number of usable text columns in the window, which is equivalent to the
value returned by (window-width window).
The argument offsets is either nil or a cons cell of the form
(hscroll . tab-offset). Here hscroll is the number
of columns not being displayed at the left margin; most callers get this by
calling window-hscroll. Meanwhile, tab-offset is the offset
between column numbers on the screen and column numbers in the buffer. This
can be nonzero in a continuation line, when the previous screen lines'
widths do not add up to a multiple of tab-width. It is always zero
in a non-continuation line.
The window window serves only to specify which display table to use.
compute-motion always operates on the current buffer, regardless of
what buffer is displayed in window.
The return value is a list of five elements:
(pos hpos vpos prevhpos contin) |
Here pos is the buffer position where the scan stopped, vpos is the vertical screen position, and hpos is the horizontal screen position.
The result prevhpos is the horizontal position one character back from
pos. The result contin is t if the last line was
continued after (or within) the previous character.
For example, to find the buffer position of column col of screen line
line of a certain window, pass the window's display start location as
from and the window's upper-left coordinates as frompos. Pass
the buffer's (point-max) as to, to limit the scan to the end of
the accessible portion of the buffer, and pass line and col as
topos. Here's a function that does this:
(defun coordinates-of-position (col line)
(car (compute-motion (window-start)
'(0 . 0)
(point-max)
(cons col line)
(window-width)
(cons (window-hscroll) 0)
(selected-window))))
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When you use compute-motion for the minibuffer, you need to use
minibuffer-prompt-width to get the horizontal position of the
beginning of the first screen line. Voir la section Minibuffer Contents.
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Ce document a été généré par Eric Reinbold le 13 Octobre 2007 en utilisant texi2html 1.78.