Optimize/simplify code for last commit and fix a longstanding indexing bug when collapsing subpaths

(the first command of a path and all of its parameters were never optimized and as many paths consist only of one moveto command with many parameters the functionality might have been broken in many cases)

scour/scour.py

@@ -404,6 +404,8 @@ default_properties = {  # excluded all properties with 'auto' as default
 
 
 def is_same_sign(a, b): return (a <= 0 and b <= 0) or (a >= 0 and b >= 0)
+
+
 def is_same_slope(x1, y1, x2, y2): return y1/x1 - y2/x2 == 0
 
 
@@ -2407,25 +2409,30 @@ def cleanPath(element, options):
     # Reuse the data structure 'path', since we're not adding or removing subcommands.
     # Also reuse the coordinate lists, even if we're deleting items, because these
     # deletions are relatively cheap.
-    for pathIndex in range(1, len(path)):
+    if not has_markers:
+        for pathIndex in range(len(path)):
             cmd, data = path[pathIndex]
-        if cmd in ['h', 'v'] and len(data) > 1 and not has_markers:
+
-            coordIndex = 1
+            # the first (moveto) command in a path is always absolute, so we have to skip it
-            while coordIndex < len(data):
+            startIndex = (pathIndex == 0)
-                if is_same_sign(data[coordIndex - 1], data[coordIndex]):
+
-                    data[coordIndex - 1] += data[coordIndex]
+            if cmd in ['h', 'v'] and len(data) > startIndex+1:   # h,v expect only one parameter
-                    del data[coordIndex]
+                coordIndex = startIndex
+                while coordIndex+1 < len(data):
+                    if is_same_sign(data[coordIndex], data[coordIndex+1]):
+                        data[coordIndex] += data[coordIndex+1]
+                        del data[coordIndex+1]
                         _num_path_segments_removed += 1
                     else:
                         coordIndex += 1
-        if cmd in ['m', 'l'] and len(data) > 3 and not has_markers:
+            elif cmd in ['m', 'l'] and len(data) > (startIndex+1)*2:  # m,l expect two parameters
-            coordIndex = 2
+                coordIndex = startIndex * 2
-            while coordIndex < len(data):
+                while coordIndex+2 < len(data):
-                if is_same_slope(data[coordIndex-2], data[coordIndex-1], data[coordIndex], data[coordIndex+1]):
+                    if is_same_slope(*data[coordIndex:coordIndex+4]):
-                    data[coordIndex - 2] += data[coordIndex]
+                        data[coordIndex] += data[coordIndex+2]
-                    data[coordIndex - 1] += data[coordIndex+1]
+                        data[coordIndex+1] += data[coordIndex+3]
-                    del data[coordIndex]
+                        del data[coordIndex+2]  # delete the next two elements
-                    del data[coordIndex]
+                        del data[coordIndex+2]
                         _num_path_segments_removed += 1
                     else:
                         coordIndex += 2