hints.c

远程桌面连接工具

/*
:h2 id=subpath.Navigation Through Edge Lists
 
For continuity checking purposes, we need to navigate through edge
lists by the "subpath" chains and answer questions about edges.  The
subpath chain links together edges that were part of the same subpath
(no intervening move segments) when the interior of the path was
calculated.  Here we use the term "edge" to mean every edge list
that was created in between changes of direction.
 
The subpath chains are singly-linked circular chains.  For the convenience
of building them, they direction of the list (from edge to edge) is the
reverse of the order in which they were built.  Within any single edge,
the subpath chain goes from top-to-bottom.  (There might be a violation
of this because of the way the user started the first chain; see
:hdref refid=fixsubp..).
 
:h3.ISTOP() and ISBOTTOM() - Flag Bits for Edge Lists at the Top and
Bottom of Their SubPaths
*/
 
#define   ISTOP(flag)     ((flag)&0x20)
#define   ISBOTTOM(flag)  ((flag)&0x10)
/*
:h3.ISLEFT() - Flag Bit for Left Edges
*/
 
#define   ISLEFT(flag)    ((flag)&0x08)
 
/*
:h3.XofY() - Macro to Find X Value at Given Y
 
This macro can only be used if it is known that the Y is within the
given edgelist's ymin and ymax.
*/
 
#define   XofY(edge, y)   edge->xvalues[y - edge->ymin]
 
/*
:h3.findXofY() - Like XofY(), Except not Restricted
 
If the Y is out of bounds of the given edgelist, this macro will
call SearchXofY to search the edge's subpath chain for the correct
Y range.  If the Y value is off the edge, MINPEL is returned.
*/
#define   findXofY(edge, y)  ((y < edge->ymin || y >= edge->ymax) ? SearchXofY(edge, y) : XofY(edge, y))
 
/*
:h4.SearchXofY() - Routine Called by FindXofY() for Difficult Cases
 
The concept of this routine is to follow the subpath chain to find the
edge just below (i.e., next in chain) or just above (i.e., immediately
before in chain.  It is assumed that the Y value is no more than one
off of the edge's range; XofY() could be replace by FindXofY() to
call ourselves recursively if this were not true.
*/
 
static pel SearchXofY(edge, y)
       register struct edgelist *edge;  /* represents edge                   */
       register pel y;       /* 'y' value to find edge for                   */
{
       register struct edgelist *e;  /* loop variable                        */
 
       if (y < edge->ymin) {
               if (ISTOP(edge->flag))
                       return(MINPEL);
               for (e = edge->subpath; e->subpath != edge; e = e->subpath) { ; }
               if (e->ymax == edge->ymin)
                        return(XofY(e, y));
       }
       else if (y >= edge->ymax) {
               if (ISBOTTOM(edge->flag))
                       return(MINPEL);
               e = edge->subpath;
               if (e->ymin == edge->ymax)
                         return(XofY(e, y));
       }
       else
               return(XofY(edge, y));
 
       abort("bad subpath chain");
       /*NOTREACHED*/
}
/*
:h3.ISBREAK() Macro - Tests if an Edge List is at a "Break"
 
The subpath chains are organized top to bottom.  When the bottom of
a given edge is reached, the subpath chain points to the top of the
next edge.  We call this a "break" in the chain.  The following macro
is the simple test for the break condition:
*/
 
#define  ISBREAK(top,bot) (top->ymax != bot->ymin)
 
 
/*
:h3.ImpliedHorizontalLine() - Tests for Horizontal Connectivity
 
This function returns true if two edges are connected horizontally.
They are connected horizontally if they are consecutive in the subpath,
and either we are at the bottom and the first edge is going down or we
are at the top and the first edge is going up.
*/
 
#define  BLACKABOVE  -1
#define  BLACKBELOW  +1
#define  NONE         0
 
static int ImpliedHorizontalLine(e1, e2, y)
       register struct edgelist *e1,*e2;  /* two edges to check              */
       register int y;       /* y where they might be connected              */
{
       register struct edgelist *e3,*e4;
 
       if (ISDOWN(e1->flag) == ISDOWN(e2->flag))
               return(NONE);  /* can't be consecutive unless different directions */
/*
Now we check for consecutiveness:  Can we get from 'e1' to 'e2' with
only one intervening break?  Can we get from 'e2' to 'e1' with only one
intervening break?  'e3' will be as far as we can get after 'e1'; 'e4'
will be has far as we can get after 'e2':
*/
       for (e3 = e1; !ISBREAK(e3, e3->subpath); e3 = e3->subpath) { ; }
       for (e3 = e3->subpath; e3 != e2; e3 = e3->subpath)
               if (ISBREAK(e3, e3->subpath))
                       break;
 
       for (e4 = e2; !ISBREAK(e4, e4->subpath); e4 = e4->subpath) { ; }
       for (e4 = e4->subpath; e4 != e1; e4 = e4->subpath)
               if (ISBREAK(e4, e4->subpath))
                       break;
/*
If the edges are mutually consecutive, we must have horizontal lines
both top and bottom:
*/
       if (e3 == e2 && e4 == e1)
               return(TRUE);
/*
If the edges are not consecutive either way, no horizontal lines are
possible:
*/
       if (e3 != e2 && e4 != e1)
               return(NONE);
/*
Now let's swap 'e1' and 'e2' if necessary to enforce the rule that 'e2'
follows 'e1'.  Remember that subpath chains go in the opposite direction
from the way the subpaths were built; this led to the simplest way
do build them.
*/
       if (e4 != e1) {
               e2 = e1;
               e1 = e3;  /* remember e3 == e2, this just swaps 'e1' and 'e2' */
       }
/*
Now we have everything to return the answer:
*/
       if (ISTOP(e1->flag) && y == e1->ymin)
               return(ISDOWN(e2->flag));
       else if (ISBOTTOM(e1->flag) && y == e1->ymax)
               return(!ISDOWN(e2->flag));
       else
               abort("ImpliedHorizontalLine:  why ask?");
       /*NOTREACHED*/
}
 
/*
:h3 id=fixsubp.FixSubPaths() - Must be Called to Organize Subpath Chains
 
The region-building code in Interior(), in particular splitedge(),
maintains the rule that sub-paths are linked top-to-bottom except
at breaks.  However, it is possible that there may be a "false break"
because the user started the subpath in the middle of an edge (and
went in the "wrong" direction from there, up instead of down).  This
routine finds and fixes false breaks.
 
Also, this routine sets the ISTOP and ISBOTTOM flags in the edge lists.
*/
 
static void FixSubPaths(R)
       register struct region *R;       /* anchor of region                */
{
       register struct edgelist *e;     /* fast loop variable                */
       register struct edgelist *edge;  /* current edge in region            */
       register struct edgelist *next;  /* next in subpath after 'edge'      */
       register struct edgelist *break1;  /* first break after 'next'        */
       register struct edgelist *break2;  /* last break before 'edge'        */
       register struct edgelist *prev;    /* previous edge for fixing links  */
       int left = TRUE;
 
       for (edge = R->anchor; edge != NULL; edge = edge->link) {
 
               if (left)
                       edge->flag |= ISLEFT(ON);
               left = !left;
 
               next = edge->subpath;
 
               if (!ISBREAK(edge, next))
                       continue;
               if (edge->ymax < next->ymin)
                       abort("disjoint subpath?");
/*
'edge' now contains an edgelist at the bottom of an edge, and 'next'
contains the next subsequent edgelist in the subpath, which must be at
the top.  We refer to this a "break" in the subpath.
*/
               next->flag |= ISTOP(ON);
               edge->flag |= ISBOTTOM(ON);
 
               if (ISDOWN(edge->flag) != ISDOWN(next->flag))
                       continue;
/*
We are now in the unusual case; both edges are going in the same
direction so this must be a "false break" due to the way that the user
created the path.  We'll have to fix it.
*/
               for (break1 = next; !ISBREAK(break1, break1->subpath); break1 = break1->subpath) { ; }
 
               for (e = break1->subpath; e != edge; e = e->subpath)
                       if (ISBREAK(e, e->subpath))
                               break2 = e;
/*
Now we've set up 'break1' and 'break2'.  I've found the following
diagram invaluable.  'break1' is the first break after 'next'.  'break2'
is the LAST break before 'edge'.
&drawing.
         next
        +------+     +---->+------+
   +--->|    >-----+ |     |    >-----+
   |    |      |   | |     |      |   |
   | +-------------+ |  +-------------+
   | |  |break1|     |  |  |      |
   | +->|    >-------+  +->|    >-----+
   |    |      |           |      |   |
   |    |      |        +-------------+
   |    +------+        |  |      |
   | +----------------+ |  |      |
   | |  +------+      | +->|    >-----+
   | +->|    >-----+  |    |      |   |
   |    |      |   |  | +-------------+
   | +-------------+  | |  |      |
   | |  |edge  |      | |  |break2|
   | +->|    >-----+  | +->|    >-----+
   |    |      |   |  |    |      |   |
   |    |      |   |  |    |      |   |
   |    |      |   |  |    |      |   |
   |    +------+   |  |    +------+   |
   |               |  |               |
   +---------------+  +---------------+
 
&edrawing.
We want to fix this situation by having 'edge' point to where 'break1'
now points, and having 'break1' point to where 'break2' now points.
Finally, 'break2' should point to 'next'.  Also, we observe that
'break1' can't be a bottom, and is also not a top unless it is the same
as 'next':
*/
               edge->subpath = break1->subpath;
 
               break1->subpath = break2->subpath;
               if (ISBREAK(break1, break1->subpath))
                       abort("unable to fix subpath break?");
 
               break2->subpath = next;
 
               break1->flag &= ~ISBOTTOM(ON);
               if (break1 != next)
                       break1->flag &= ~ISTOP(ON);
       }
/*
This region might contain "ambiguous" edges; edges exactly equal to
edge->link.  Due to the random dynamics of where they get sorted into
the list, they can yield false crossings, where the edges appear
to cross.  This confuses our continuity logic no end.  Since we can
swap them without changing the region, we do.
*/
       for (edge = R->anchor, prev = NULL; VALIDEDGE(edge); prev = edge, edge = prev->link) {
 
               if (! ISAMBIGUOUS(edge->flag))
                       continue;
 
               next = edge->subpath;
 
               while (ISAMBIGUOUS(next->flag) && next != edge)
                       next = next->subpath;
/*
We've finally found a non-ambiguous edge; we make sure it is left/right
compatible with 'edge':
*/
               if ( (ISLEFT(edge->flag) == ISLEFT(next->flag) && ISDOWN(edge->flag) == ISDOWN(next->flag) )
                    || (ISLEFT(edge->flag) != ISLEFT(next->flag) && ISDOWN(edge->flag) != ISDOWN(next->flag) ) )
                       continue;
 
/*
Incompatible, we will swap 'edge' and the following edge in the list.
You may think that there must be a next edge in this swath.  So did I.
No!  If there is a totally ambiguous inner loop, for example, we could
get all the way to the outside without resolving ambiguity.
*/
               next = edge->link;  /* note new meaning of 'next' */
               if (next == NULL || edge->ymin != next->ymin)
                       continue;
               if (prev == NULL)
                       R->anchor = next;
               else
                       prev->link = next;
               edge->link = next->link;