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Each window contains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.
This function returns the display-start position of window window. If
window is nil, the selected window is used. For example,
(window-start)
⇒ 7058
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When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or 1 if the buffer doesn't have any.
Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)—for example, to make sure point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay.
For a realistic example of using window-start, see the description of
count-lines. Voir Definition of count-lines.
This function returns the position of the end of the display in window
window. If window is nil, the selected window is used.
Simply changing the buffer text or moving point does not update the value
that window-end returns. The value is updated only when Emacs
redisplays and redisplay completes without being preempted.
If the last redisplay of window was preempted, and did not finish,
Emacs does not know the position of the end of display in that window. In
that case, this function returns nil.
If update is non-nil, window-end always returns an
up-to-date value for where the window ends, based on the current
window-start value. If the saved value is valid, window-end
returns that; otherwise it computes the correct value by scanning the buffer
text.
Even if update is non-nil, window-end does not attempt
to scroll the display if point has moved off the screen, the way real
redisplay would do. It does not alter the window-start value. In
effect, it reports where the displayed text will end if scrolling is not
required.
This function sets the display-start position of window to position in window's buffer. It returns position.
The display routines insist that the position of point be visible when a
buffer is displayed. Normally, they change the display-start position (that
is, scroll the window) whenever necessary to make point visible. However,
if you specify the start position with this function using nil for
noforce, it means you want display to start at position even if
that would put the location of point off the screen. If this does place
point off screen, the display routines move point to the left margin on the
middle line in the window.
For example, if point is 1 and you set the start of the window to 2, then point would be “above” the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example:
;; Here is what ‘foo’ looks like before executing ;; the |
If noforce is non-nil, and position would place point off
screen at the next redisplay, then redisplay computes a new window-start
position that works well with point, and thus position is not used.
This function returns non-nil if position is within the range
of text currently visible on the screen in window. It returns
nil if position is scrolled vertically out of view. Locations
that are partially obscured are not considered visible unless
partially is non-nil. The argument position defaults to
the current position of point in window; window, to the selected
window.
If position is t, that means to check the last visible position
in window.
The pos-visible-in-window-p function considers only vertical
scrolling. If position is out of view only because window has
been scrolled horizontally, pos-visible-in-window-p returns
non-nil anyway. Voir la section Horizontal Scrolling.
If position is visible, pos-visible-in-window-p returns
t if partially is nil; if partially is
non-nil, and the character after position is fully visible, it
returns a list of the form (x y), where x and
y are the pixel coordinates relative to the top left corner of the
window; otherwise it returns an extended list of the form (x
y rtop rbot rowh vpos), where the rtop
and rbot specify the number of off-window pixels at the top and bottom
of the row at position, rowh specifies the visible height of
that row, and vpos specifies the vertical position (zero-based row
number) of that row.
Here is an example:
;; If point is off the screen now, recenter it now.
(or (pos-visible-in-window-p
(point) (selected-window))
(recenter 0))
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This function returns information about text line line in
window. If line is one of header-line or
mode-line, window-line-height returns information about the
corresponding line of the window. Otherwise, line is a text line
number starting from 0. A negative number counts from the end of the
window. The argument line defaults to the current line in
window; window, to the selected window.
If the display is not up to date, window-line-height returns
nil. In that case, pos-visible-in-window-p may be used to
obtain related information.
If there is no line corresponding to the specified line,
window-line-height returns nil. Otherwise, it returns a list
(height vpos ypos offbot), where height
is the height in pixels of the visible part of the line, vpos and
ypos are the vertical position in lines and pixels of the line
relative to the top of the first text line, and offbot is the number
of off-window pixels at the bottom of the text line. If there are
off-window pixels at the top of the (first) text line, ypos is
negative.
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Ce document a été généré par Eric Reinbold le 13 Octobre 2007 en utilisant texi2html 1.78.