X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=Documentation%2Fcontributor%2Fregressions.itexi;fp=Documentation%2Fcontributor%2Fregressions.itexi;h=365582e87f7a8beef00a6e437f67d7b005fba98a;hb=0ac07f31e0f95fc18e5916ce756b9c746af7cc58;hp=7bca714f2c412b1aa56a77962c98e5fa7731216b;hpb=2f1263e2ccdddcac2eb9f7d8ce2ed92867d3d160;p=lilypond.git

diff --git a/Documentation/contributor/regressions.itexi b/Documentation/contributor/regressions.itexi
index 7bca714f2c..365582e87f 100644
--- a/Documentation/contributor/regressions.itexi
+++ b/Documentation/contributor/regressions.itexi
@@ -7,6 +7,7 @@
 * Precompiled regression tests::
 * Compiling regression tests::
 * Regtest comparison::
+* Pixel-based regtest comparison::
 * Finding the cause of a regression::
 * Memory and coverage tests::
 * MusicXML tests::
@@ -135,6 +136,11 @@ something is suspicious!
 @item
 Profile files: give information about
 TODO?  I don't know what they're for.
+Apparently they give some information about CPU usage.  If you got
+tons of changes in cell counts, this probably means that you compiled
+@code{make test-baseline} with a different amount of CPU threads than
+@code{make check}. Try redoing tests from scratch with the same
+number of threads each time -- see @ref{Saving time with the -j option}.
 
 @end itemize
 
@@ -209,7 +215,7 @@ Run @code{make} with current git master without any of your changes.
 
 @item
 Before making changes to the code, establish a baseline for the comparison by
-going to the @file{lilypond-git/build/} directory and running:
+going to the @file{$LILYPOND_GIT/build/} directory and running:
 
 @example
 make test-baseline
@@ -293,6 +299,58 @@ and want to do regtests comparison for all of them, you can
 @code{make test-clean}, @code{make} and @code{make check} it without doing
 @code{make test-baseline} again.}
 
+@node Pixel-based regtest comparison
+@section Pixel-based regtest comparison
+
+As an alternative to the @code{make test} method for regtest checking (which
+relies upon @code{.signature} files created by a LilyPond run and which describe
+the placing of grobs) there is a script which compares the output of two
+LilyPond versions pixel-by-pixel.  To use this, start by checking out the
+version of LilyPond you want to use as a baseline, and run @code{make}.  Then,
+do the following:
+
+@example
+cd $LILYPOND_GIT/scripts/auxiliar/
+./make-regtest-pngs.sh -j9 -o
+@end example
+
+The @code{-j9} option tells the script to use 9 CPUs to create the
+images - change this to your own CPU count+1.  @code{-o} means this is the "old"
+version.  This will create images of all the regtests in
+
+@example
+$LILYPOND_BUILD_DIR/out-png-check/old-regtest-results/
+@end example
+
+Now checkout the version you want to compare with the baseline.  Run
+@code{make} again to recreate the LilyPond binary.  Then, do the following:
+
+@example
+cd $LILYPOND_GIT/scripts/auxiliar/
+./make-regtest-pngs.sh -j9 -n
+@end example
+
+The @code{-n} option tells the script to make a "new" version of the
+images.  They are created in
+
+@example
+$LILYPOND_BUILD_DIR/out-png-check/new-regtest-results/
+@end example
+
+Once the new images have been created, the script compares the old images with
+the new ones pixel-by-pixel and prints a list of the different images to the
+terminal, together with a count of how many differences were found.  The
+results of the checks are in
+
+@example
+$LILYPOND_BUILD_DIR/out-png-check/regtest-diffs/
+@end example
+
+To check for differences, browse that directory with an image
+viewer.  Differences are shown in red.  Be aware that some images with complex
+fonts or spacing annotations always display a few minor differences.  These can
+safely be ignored.
+
 
 @node Finding the cause of a regression
 @section Finding the cause of a regression