eeshow/README: document modes of usage

eeshow/README

@@ -27,6 +27,141 @@ libgit2-dev
 libgtk-3-dev
 
 
+Development status
+------------------
+
+Eeshow is still incomplete. It should generally be usable, but still has
+many limitations, especially in the following areas:
+
+- not all details are rendered, e.g., pin attributes such as "clock input"
+
+- rendering isn't always exactly the same as in KiCad, e.g., text size may
+  differ significantly
+
+- interactive use is not streamlined yet, e.g., revision selection
+
+- there may be bugs
+
+More details on pending items can be found in the file TODO.
+
+
+
+Non-interactive rendering
+=========================
+
+Eeshow can be invoked from the command line to render KiCad schematics
+to FIG, PDF, and PNG.
+
+
+Invocation
+----------
+
+The general form of invocation for rendering is as follows:
+
+eeshow [-r] file.lib ... file.sch -- format [options]
+
+Common if using PDF, the option -r can be used (after "eeshow") to
+recursively process sub-sheets. For PDF and PNG, the options -s scale
+and -o output-file can be used to control the size of the output and
+the output file. By default, eeshow writes to standard output.
+
+Examples:
+
+eeshow test.lib test.sch -- png -s 2 -o test.png
+
+eeshow -r neo900.lib kicad-libs/components/powered.lib neo900.sch \
+  -- pdf -o neo900.pdf
+
+More details on the above example can be found in the file DEMO.
+
+
+Revision access
+---------------
+
+If the files are stored in a git repository, a revisions can be selected
+by prefixing file names with the commit ID, e.g.,
+
+eeshow neo900.lib kicad-libs/components/powered.lib 6a9f71:neo900_SS_5.sch \
+  -- png -s 2 -o old.png
+
+Revision selection propagates to dependent files, unless explicitly
+overridden. E.g., the above example selects also revision 6a9f71 of
+neo900.lib.
+
+
+Non-interactive differences
+===========================
+
+Eeshow can render two versions of a sheet to a bitmap and then compare them
+pixel by pixel, highlighting areas where differences are found. The output
+is written to a PNG file.
+
+
+Invocation
+----------
+
+The general form of invocation for rendering is as follows:
+
+eeshow file.lib ... file.sch -- diff [options] file.lib ... file.sch
+
+The usual options and revision selection can be used here as well.
+
+Example:
+
+LIBS="neo900.lib kicad-libs/components/powered.lib"
+eeshow $LIBS  6a9f71:neo900_SS_5.sch \
+  -- diff -s 2 -o diff.png $LIBS neo900_SS_5.sch
+
+
+GUI mode
+========
+
+GUI mode allows exploration of schematics and the comparison of different
+git revisions. Compared to eeschema, eeshow currently offers the following
+additional features:
+
+- access to the git revision history with visual differences between
+  versions.
+
+- on hover, global labels show on which other sheets the label is used.
+  Clicking on a name jumps to that sheet.
+
+- fast sheet change with PgUp/PgDn
+
+
+Invocation
+----------
+
+The basic invocation of GUI mode is as follows:
+
+eeshow file.lib ... file.sch
+
+Add the option -r to recursively load sub-sheets of file.sch
+
+If file.sch is in a git repository, eeshow automatically loads the
+revision history. The depth of the history can be limited with the
+option -N number-of-commits
+
+Examples:
+
+eeshow -N 30 -r neo900.lib kicad-libs/components/powered.lib neo900.sch
+
+eeshow `sed -n '/pcbnew/q;/^LibName[0-9]*=/{s///;s/$/.lib/p;};d' anelok.pro` \
+  anelok.sch
+
+
+Mouse function in GUI mode
+--------------------------
+
+Hover			show additional details on revisions, sheets, global
+			labels
+Left-click		jump to sheet (on sub-sheet, sheet stack, global
+			label hover box), open history, select revision
+Left-click and drag	scroll history
+Middle-click and drag	pan sheet
+Scroll wheel		zoom in or out
+
+
 Key functions in GUI mode
 -------------------------
 
@@ -34,7 +169,7 @@ Key functions in GUI mode
 -			zoom out
 *			zoom to extents
 Home			go to the top sheet
-Delete or Backspace	go to the previous sheet
+Delete or Backspace	go to the next higher sheet in hierarchy
 PgUp			go to the previous sheet in sequence
 PgDn			go to the next sheet in sequence
 Up or Down		invoke the revision history (WIP)