Attempt at avoiding the false changes seen on Xue. Seems that alpha-blending

produces minute differences where there should be none.

- scripts/ppmdiff/ppmdiff.c (diff): instead of looking for all or noting
  changes, also detect gradual changes
- scripts/ppmdiff/ppmdiff.c (diff, main): don't mark areas with differences
  in the main images if using shadow images
- scripts/schps2ppm: new option to disable alpha blending
- scripts/schhist2web: cache pixmaps with default line thickness and no
  alpha blending in hard_*
- scripts/schhist2web: base marking of areas with differences exclusively
  on the hard_* pixmaps

scripts/ppmdiff/ppmdiff.c

@@ -150,11 +150,12 @@ static void set_pixel(uint8_t *p, const uint8_t *color, const uint8_t *value)
 }
 
 
-static uint8_t *diff(const uint8_t *a, const uint8_t *b, int xres, int yres)
+static uint8_t *diff(const uint8_t *a, const uint8_t *b, int xres, int yres,
+    int mark_areas)
 {
 	uint8_t *res, *p;
 	int x, y;
-	int has_a, has_b;
+	unsigned val_a, val_b;
 
 	res = p = malloc(xres*yres*3);
 	if (!res) {
@@ -163,17 +164,20 @@ static uint8_t *diff(const uint8_t *a, const uint8_t *b, int xres, int yres)
 	}
 	for (y = 0; y != yres; y++)
 		for (x = 0; x != xres; x++) {
-			has_a = (a[0] & a[1] & a[2]) != 255;
+			val_a = a[0]+a[1]+a[2];
-			has_b = (b[0] & b[1] & b[2]) != 255;
+			val_b = b[0]+b[1]+b[2];
-			if (has_a && has_b) {
+			if (val_a == val_b) {
 				set_pixel(p, both, b);
-			} else if (has_a) {
+			} else if (val_a < val_b) {
 				set_pixel(p, a_only, a);
+				if (mark_areas)
 					change(x, y);
-			} else if (has_b) {
+			} else if (val_a > val_b) {
 				set_pixel(p, b_only, b);
+				if (mark_areas)
 					change(x, y);
 			} else {
+				abort();	/* no longer used */
 				memset(p, 255, 3);
 //				memcpy(p, "\0\0\xff", 3);
 			}
@@ -280,7 +284,7 @@ static void usage(const char *name)
 {
 	fprintf(stderr,
 "usage: %s [-f] [-a color] [-b color] [-c color] [-d pixels]\n"
-"%6s %*s [-m color] [-n color] [-w pixels] file_a.ppm file_b.ppm\n\n"
+"%6s %*s [-m color] [-n color] [-w pixels] file_a.ppm file_b.ppm\n"
 "%6s %*s [file_a'.ppm file_b'.ppm] [out.ppm]\n\n"
 "  file_a.ppm and file_b.ppm   are two input images\n"
 "  file_a'.ppm and file_b'.ppm if present, are searched for changes as well\n"
@@ -385,7 +389,7 @@ int main(int argc, char *const *argv)
 	}
 	if (!force && !areas && !memcmp(old, new, x*y*3))
 		return 1;
-	d = diff(old, new, x, y);
+	d = diff(old, new, x, y, !shadow_old);
 	if (frame_dist)
 		mark_areas(d, x, y);
 

scripts/schhist2web

@@ -193,10 +193,11 @@ for n in $first `cd "$dir" && git rev-list --reverse $first..HEAD`; do
 	schname="$new"
     fi
     tmp=`pwd`/_schhist2web
-    trap "rm -rf \"$cache/ppm_$n\" \"$cache/fat_$n\" \"$tmp\"" 0
+    trap "rm -rf \"$cache/ppm_$n\" \"$cache/fat_$n\" \"$cache/ps_$n\" \
+      \"$cache/hard_$n\" \"$tmp\"" 0
     if [ ! -d "$cache/ppm_$n" ]; then
-	rm -rf "$cache/ppm_$n" "$cache/fat_$n" "$cache/ps_$n"
+	rm -rf "$cache/ppm_$n" "$cache/fat_$n" "$cache/ps_$n" "$cache/hard_$n"
-	mkdir "$cache/ppm_$n" "$cache/fat_$n" "$cache/ps_$n"
+	mkdir "$cache/ppm_$n" "$cache/fat_$n" "$cache/ps_$n" "$cache/hard_$n"
 	#
 	# potential optimization here: remember Postscript files from previous
 	# run (or their md5sum) and check if they have changed. If not, skip
@@ -205,12 +206,21 @@ for n in $first `cd "$dir" && git rev-list --reverse $first..HEAD`; do
 	#
 	gitsch2ps $sanitize  "$dir" "$schname" $n "$tmp" || exit
 	for m in "$tmp"/*.ps; do
-	    ppm="$cache/ppm_$n/`basename "$m" .ps`.ppm"
+	    # Postscript, for making PDFs later
-	    normalizeschps -w 120 "$m" | schps2ppm - "$ppm" || exit
-	    ppm="$cache/fat_$n/`basename "$m" .ps`.ppm"
-	    normalizeschps -w 500 "$m" | schps2ppm - "$ppm" || exit
 	    ps="$cache/ps_$n/`basename "$m"`"
 	    normalizeschps "$m" "$ps" || exit
+
+	    # Unadorned pixmap, for comparison
+	    ppm="$cache/hard_$n/`basename "$m" .ps`.ppm"
+	    schps2ppm -n "$ps" "$ppm" || exit
+
+	    # Pixmap with thin lines, for the detail views
+	    ppm="$cache/ppm_$n/`basename "$m" .ps`.ppm"
+	    normalizeschps -w 120 "$m" | schps2ppm - "$ppm" || exit
+
+	    # Pixmap with thick lines, for the thumbnails
+	    ppm="$cache/fat_$n/`basename "$m" .ps`.ppm"
+	    normalizeschps -w 500 "$m" | schps2ppm - "$ppm" || exit
 	done
 	rm -rf "$tmp"
     fi
@@ -295,19 +305,21 @@ for n in `cd "$dir" && git rev-list $first..HEAD~1` $first; do
     while read m; do
 	a="$cache/ppm_$n/$m.ppm"
 	fat_a="$cache/fat_$n/$m.ppm"
+	hard_a="$cache/hard_$n/$m.ppm"
 	b="$cache/ppm_$next/$m.ppm"
 	fat_b="$cache/fat_$next/$m.ppm"
+	hard_b="$cache/hard_$next/$m.ppm"
 	diff="$out/diff_$next/$m.png"
 	thumb="$out/thumb_$next/$m.png"
 
 	if [ -f "$a" -a -f "$b" ]; then
 	    s="$s<TD align=\"center\" valign=\"middle\">"
-	    if ! pngdiff cat "$diff" "$a" "$b"; then
+	    if ! pngdiff cat "$diff" "$a" "$b" "$hard_a" "$hard_b"; then
 		s="$s<IMG src=\"unchanged.png\""
 		continue
 	    fi
 	    pngdiff shrink "$thumb" -f $THUMB_OPTS "$fat_a" "$fat_b" \
-	      "$a" "$b" || exit
+	      "$hard_a" "$hard_b" || exit
 	    mkdir -p "$out/pdf_$next"
 	    schps2pdf -T BEFORE -T AFTER -o "$out/pdf_$next/$m.pdf" \
 	      "$cache/ps_$n/$m.ps" "$cache/ps_$next/$m.ps" || exit

scripts/schps2ppm

@@ -20,14 +20,18 @@ usage()
     cat <<EOF 1>&2
 usage: $0 [options] [file.ps [file.ppm]]
 
+  -n      disable alpha blending
   -r XxY  image resolution (default: $RES)
 EOF
     exit 1
 }
 
 
+alpha=true
 while true; do
     case "$1" in
+    -n)	alpha=false
+	shift;;
     -r)	[ -z "$2" ] && usage
 	RES="$2"
 	shift 2;;
@@ -48,5 +52,6 @@ res=`expr 72 \* $X / 800`
 
 cat "$in" |
   gs -sDEVICE=ppmraw -sOutputFile=- -g$IRES -r$res \
-  -dTextAlphaBits=4 -dGraphicsAlphaBits=4 -q - |
+   `$alpha && echo '' -dTextAlphaBits=4 -dGraphicsAlphaBits=4` \
+   -q - |
   pnmflip -r270 >"$out"