Info Catalog elisp: Textual Scrolling elisp: Windows elisp: Horizontal Scrolling

elisp: Vertical Scrolling

 
 27.22 Vertical Fractional Scrolling
 ===================================
 
 “Vertical fractional scrolling” means shifting text in a window up or
 down by a specified multiple or fraction of a line.  Each window has a
 “vertical scroll position”, which is a number, never less than zero.  It
 specifies how far to raise the contents of the window.  Raising the
 window contents generally makes all or part of some lines disappear off
 the top, and all or part of some other lines appear at the bottom.  The
 usual value is zero.
 
    The vertical scroll position is measured in units of the normal line
 height, which is the height of the default font.  Thus, if the value is
 .5, that means the window contents are scrolled up half the normal line
 height.  If it is 3.3, that means the window contents are scrolled up
 somewhat over three times the normal line height.
 
    What fraction of a line the vertical scrolling covers, or how many
 lines, depends on what the lines contain.  A value of .5 could scroll a
 line whose height is very short off the screen, while a value of 3.3
 could scroll just part of the way through a tall line or an image.
 
  -- Function: window-vscroll &optional window pixels-p
      This function returns the current vertical scroll position of
      WINDOW.  The default for WINDOW is the selected window.  If
      PIXELS-P is non-‘nil’, the return value is measured in pixels,
      rather than in units of the normal line height.
 
           (window-vscroll)
                ⇒ 0
 
  -- Function: set-window-vscroll window lines &optional pixels-p
      This function sets WINDOW’s vertical scroll position to LINES.  If
      WINDOW is ‘nil’, the selected window is used.  The argument LINES
      should be zero or positive; if not, it is taken as zero.
 
      The actual vertical scroll position must always correspond to an
      integral number of pixels, so the value you specify is rounded
      accordingly.
 
      The return value is the result of this rounding.
 
           (set-window-vscroll (selected-window) 1.2)
                ⇒ 1.13
 
      If PIXELS-P is non-‘nil’, LINES specifies a number of pixels.  In
      this case, the return value is LINES.
 
  -- Variable: auto-window-vscroll
      If this variable is non-‘nil’, the ‘line-move’, ‘scroll-up’, and
      ‘scroll-down’ functions will automatically modify the vertical
      scroll position to scroll through display rows that are taller than
      the height of the window, for example in the presence of large
      images.
 

Info Catalog elisp: Textual Scrolling elisp: Windows elisp: Horizontal Scrolling