LENS(9.1)                                               LENS(9.1)

          lens - bitmap magnifier


          Lens is an interactive screen bitmap magnifier.  When it
          starts, it displays an enlarged image of a magnifying glass
          in its layer, which becomes a setting sun when lens wants to
          confirm a command to exit.

          The first item in the button 2 menu, which rotates among go,
          peek and stop, determines the activity of the magnifier.
          Clicking button 1 serves as an abbreviation for selecting go
          or peek. When the magnifier is going, a crawling-bordered
          rectangle is drawn around the source, and the lens window
          contains the magnified image.  The mouse controls the posi-
          tion of the source rectangle.

          During peeking, the rectangle last selected while going is
          re-examined periodically, and the contents are magnified,
          whether or not the lens window is currently selected.

          When stopped, the lens window is inactive.

          The button 2 menu also allows changing the magnification
          factor.  The magnification factors are chosen from the
          Fibonacci numbers, and menu items for the next size smaller
          and larger are presented as, e.g., 3x or 8x. The current
          magnification factor is not displayed in the menu, only the
          next factors larger and smaller.  The initial magnification
          factor is two.

          Button 2 may also be used to select the intervals at which
          peeking updates occur.  These intervals are selected, in
          ticks, from among the powers of two, where a tick is one-
          sixtieth of a second.  These choices are presented as, e.g.,
          32 ticks or 128 ticks. The initial interval between peeks is
          64 ticks, approximately one second.

          The image window may be controlled by the button 2 menu item
          which toggles between inset and full size. In inset mode,
          the image is displayed inside the image window of the magni-
          fied lens icon.  In full size mode, the image is displayed
          in the entire lens window.

          The final buton 2 menu entry is exit. A setting sun is dis-
          played, and button 3 must be clicked to confirm.

     LENS(9.1)                                               LENS(9.1)

          While going, the display is only refreshed when the mouse is
          moved.  Inconsistent results may be obtained when lens is
          used to examine its own image window.

          While peeking, it is assumed that the lens window contains
          an accurate magnification of what was on the screen at the
          time of the last magnification.  If lens is used to examine
          its own image, strange things may occur.

          Due to the bitmap reshaping techniques employed by the mag-
          nification algorithms, high magnification factors will not
          work with large image windows.  Precisely, if the product of
          the vertical magnification factor and the width of the des-
          tination rectangle overflows a signed short integer, pre-
          dictable but undesirable results will occur.