ERuler - screen rule and measurement tools.

ERuler is a software that allows on-screen virtual rule and
measurement of areas.

USAGE
=====

The traditional use is to press your mouse's left-button to start
measuring, then move your mouse to the end point and release. This
will give you a box with both points, the origin coordinates as well
as the region size -- all in pixels.

One can also use the keyboard to do the above flow by using "Space"
key to mark start and end points, using the mouse or keyboard arrows
to move the cursor. While using the arrows one can press "Shift" key
modifier to use 10 pixels instead of a single one in that direction,
useful for large regions.

Alternatively one can type the coordinates during runtime by using "@"
shortcut, or using the "Type coordinates" button. This will give you a
text entry so you can type "x y width height" values (all separated by
spaces).

Last but not least you can use the command line argument "--ruler" (-r
for short) to pre-populate the screen. In the case of using multiple
screens you must specify the origin as absolute position in a global
scene (if you have two 800x600 screens side by side and want to
address the horizontal position 10 in right one, use 810 (800 + 10).

It is possible to change the type/style of the measurement box (ruler)
by using "t" shortcut or the Style selector in the toolbox.

One can create multiple measurements by using "c" shortcut or the
"Create Ruler" button in the toolbox. The operations will then all be
on the newly created ruler. The distance between all rulers are
displayed in semi-transparent colors and once mouse-over they become
bolder. If those distance hints are distracting you, use "d" ("Show
distances") to toggle its visibility.


NOTE ABOUT ZOOM
---------------

There is no way in X11 to zoom into a screen region, particularly if
we're not the compositor. To provide the zoom capability we take a
screenshot at the beginning and use this copy. However once the screen
is updated, the copy becomes out of sync and one must toggle zoom to
refresh it. You'll see that ERuler will hide itself for a moment then
restore automatically, this is an implementation annoyance we can't
get rid anytime soon :-(


KEYBOARD SHORTCUTS
------------------

 * Escape: quit;
 * F2: toggle ERuler visibility;
 * p: print size to stdout;
 * c: create new ruler;
 * Control-c: clear current zone rulers;
 * g: toggle display of guide lines;
 * d: toggle display of distances between boxes;
 * t: toggle ruler type (dark, light, filled...);
 * z: toggle zoom;
 * x: toggle display of colors in hexadecimal;
 * @: open command box to type ruler placement;
 * Space: start or stop measure using keyboard;
 * Left: move ruler start point to the left (Shift to use 10px step);
 * Control-Left: move ruler end point to the left (Shift to use 10px
   step);
 * Right: move ruler start point to the right (Shift to use 10px
   step);
 * Control-Right: move ruler end point to the right (Shift to use 10px
   step);
 * Up: move ruler start point up (Shift to use 10px step);
 * Control-Up: move ruler end point up (Shift to use 10px step);
 * Down: move ruler start point down (Shift to use 10px step);
 * Control-Down: move ruler end point down (Shift to use 10px step).
