X-Git-Url: http://git.asbjorn.biz/?p=swftools.git;a=blobdiff_plain;f=lib%2Fgfxpoly%2Fpoly.c;h=d2c52953b1d471289aaee304db3915170a5581e9;hp=9dc42b003d5c895ec2abf5c5996451e907c72aaa;hb=fec1ab31707e68c2396b186e0e4928632402d649;hpb=66a03382aab040571f94b0861719753bda3ff8f1

diff --git a/lib/gfxpoly/poly.c b/lib/gfxpoly/poly.c
index 9dc42b0..d2c5295 100644
--- a/lib/gfxpoly/poly.c
+++ b/lib/gfxpoly/poly.c
@@ -1,26 +1,59 @@
 #include <stdlib.h>
-#include <assert.h>
 #include <memory.h>
 #include <math.h>
+#include "../mem.h"
+#include "../types.h"
 #include "../q.h"
+#include "../MD5.h"
 #include "poly.h"
 #include "active.h"
 #include "xrow.h"
+#include "wind.h"
+#include "convert.h"
 
-#define DEBUG
+static gfxpoly_t*current_polygon = 0;
+void gfxpoly_fail(char*expr, char*file, int line, const char*function)
+{
+    if(!current_polygon) {
+	fprintf(stderr, "assert(%s) failed in %s in line %d: %s\n", expr, file, line, function);
+	exit(1);
+    }
+
+    void*md5 = init_md5();
+   
+    int s,t;
+    gfxpolystroke_t*stroke = current_polygon->strokes;
+    for(;stroke;stroke=stroke->next) {
+	for(t=0;t<stroke->num_points;t++) {
+	    update_md5(md5, (unsigned char*)&stroke->points[t].x, sizeof(stroke->points[t].x));
+	    update_md5(md5, (unsigned char*)&stroke->points[t].y, sizeof(stroke->points[t].y));
+	}
+    }
+    unsigned char h[16];
+    char filename[32+4+1];
+    finish_md5(md5, h);
+    sprintf(filename, "%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x.ps",
+	    h[0],h[1],h[2],h[3],h[4],h[5],h[6],h[7],h[8],h[9],h[10],h[11],h[12],h[13],h[14],h[15]);
+
+    fprintf(stderr, "assert(%s) failed in %s in line %d: %s\n", expr, file, line, function);
+    fprintf(stderr, "I'm saving a debug file \"%s\" to the current directory.\n", filename);
 
-char point_equals(const void*o1, const void*o2) 
+    gfxpoly_save(current_polygon, filename);
+    exit(1);
+}
+
+static char point_equals(const void*o1, const void*o2)
 {
     const point_t*p1 = o1;
     const point_t*p2 = o2;
     return p1->x == p2->x && p1->y == p2->y;
 }
-unsigned int point_hash(const void*o) 
+static unsigned int point_hash(const void*o)
 {
     const point_t*p = o;
     return p->x^p->y;
 }
-void* point_dup(const void*o) 
+static void* point_dup(const void*o)
 {
     const point_t*p = o;
     point_t*n = malloc(sizeof(point_t));
@@ -28,14 +61,14 @@ void* point_dup(const void*o)
     n->y = p->y;
     return n;
 }
-void point_free(void*o) 
+static void point_free(void*o)
 {
     point_t*p = o;
     p->x = 0;
     p->y = 0;
     free(p);
 }
-type_t point_type = {
+static type_t point_type = {
     equals: point_equals,
     hash: point_hash,
     dup: point_dup,
@@ -43,65 +76,147 @@ type_t point_type = {
 };
 
 typedef struct _status {
-    int y;
+    int32_t y;
     actlist_t*actlist;
     heap_t*queue;
-#ifdef DEBUG
+    xrow_t*xrow;
+    windrule_t*windrule;
+    windcontext_t*context;
+    segment_t*ending_segments;
+    polywriter_t writer;
+#ifdef CHECKS
     dict_t*seen_crossings; //list of crossing we saw so far
     dict_t*intersecting_segs; //list of segments intersecting in this scanline
     dict_t*segs_with_point; //lists of segments that received a point in this scanline
 #endif
 } status_t;
 
-int compare_events(const void*_a,const void*_b)
+typedef struct _event {
+    eventtype_t type;
+    point_t p;
+    segment_t*s1;
+    segment_t*s2;
+} event_t;
+
+/* compare_events_simple differs from compare_events in that it schedules
+   events from left to right regardless of type. It's only used in horizontal
+   processing, in order to get an x-wise sorting of the current scanline */
+static int compare_events_simple(const void*_a,const void*_b)
 {
     event_t* a = (event_t*)_a;
-    event_t* b = (event_t*)_b; 
-    if(a->p.y < b->p.y) {
-        return 1;
-    } else if(a->p.y > b->p.y) {
-        return -1;
-    } else if(a->type < b->type) {
-        return 1;
-    } else if(a->type > b->type) {
-        return -1;
-    } else if(a->p.x < b->p.x) {
-        return 1;
-    } else if(a->p.x > b->p.x) {
-        return -1;
-    } else
-        return 0;
-}
-
-gfxpoly_t* gfxpoly_new()
+    event_t* b = (event_t*)_b;
+    int d = b->p.y - a->p.y;
+    if(d) return d;
+    d = b->p.x - a->p.x;
+    if(d) return d;
+    return 0;
+}
+
+static int compare_events(const void*_a,const void*_b)
 {
+    event_t* a = (event_t*)_a;
+    event_t* b = (event_t*)_b;
+    int d = b->p.y - a->p.y;
+    if(d) return d;
+    /* we need to schedule end after intersect (so that a segment about
+       to end has a chance to tear up a few other segs first) and start
+       events after end (in order not to confuse the intersection check, which
+       assumes there's an actual y overlap between active segments, and 
+       because ending segments in the active list make it difficult to insert
+       starting segments at the right position)). 
+       Horizontal lines come last, because the only purpose
+       they have is to create snapping coordinates for the segments (still)
+       existing in this scanline.
+    */
+    d = b->type - a->type;
+    if(d) return d;
     return 0;
+
+    /* I don't see any reason why we would need to order by x- at least as long
+       as we do horizontal lines in a seperate pass */
+    //d = b->p.x - a->p.x;
+    //return d;
 }
-void gfxpoly_destroy(gfxpoly_t*poly)
+
+int gfxpoly_size(gfxpoly_t*poly)
 {
-    segment_t* s = poly;
-    while(s) {
-        segment_t*right = s->right;
-        free(s);
-        s = right;
-        if(s==poly)
-            break;
+    int s,t;
+    int edges = 0;
+    gfxpolystroke_t*stroke = poly->strokes;
+    for(;stroke;stroke=stroke->next) {
+	edges += stroke->num_points-1;
     }
+    return edges;
+}
+
+char gfxpoly_check(gfxpoly_t*poly)
+{
+    dict_t*d = dict_new2(&point_type);
+    int s,t;
+    gfxpolystroke_t*stroke = poly->strokes;
+    for(;stroke;stroke=stroke->next) {
+	for(s=0;s<stroke->num_points;s++) {
+	    point_t p = stroke->points[s];
+	    int num = (s>=1 && s<stroke->num_points-1)?2:1; // mid points are two points (start+end)
+	    if(!dict_contains(d, &p)) {
+		dict_put(d, &p, (void*)(ptroff_t)num);
+	    } else {
+		int count = (ptroff_t)dict_lookup(d, &p);
+		dict_del(d, &p);
+		count+=num;
+		dict_put(d, &p, (void*)(ptroff_t)count);
+	    }
+	}
+    }
+    DICT_ITERATE_ITEMS(d, point_t*, p, void*, c) {
+        int count = (ptroff_t)c;
+        if(count&1) {
+            fprintf(stderr, "Point (%f,%f) occurs %d times\n", p->x*poly->gridsize, p->y*poly->gridsize, count);
+            dict_destroy(d);
+            return 0;
+        }
+    }
+    dict_destroy(d);
+    return 1;
 }
 
 void gfxpoly_dump(gfxpoly_t*poly)
 {
-    segment_t* s = (segment_t*)poly;
-    while(s) {
-        printf("[%d] (%d,%d) -> (%d,%d) %s\n",
-                s->nr, s->a.x, s->a.y, s->b.x, s->b.y,
-                s->dir==DIR_UP?"up":"down");
-        s = s->right;
-        if(s==poly)
-            break;
+    int s,t;
+    double g = poly->gridsize;
+    fprintf(stderr, "polyon %08x (gridsize: %f)\n", poly, poly->gridsize);
+    gfxpolystroke_t*stroke = poly->strokes;
+    for(;stroke;stroke=stroke->next) {
+	for(s=0;s<stroke->num_points-1;s++) {
+	    point_t a = stroke->points[s];
+	    point_t b = stroke->points[s+1];
+	    fprintf(stderr, "%s(%f,%f) -> (%f,%f)%s\n", s?" ":"[", a.x*g, a.y*g, b.x*g, b.y*g,
+		                                        s==stroke->num_points-2?"]":"");
+	}
     }
 }
 
+void gfxpoly_save(gfxpoly_t*poly, const char*filename)
+{
+    FILE*fi = fopen(filename, "wb");
+    fprintf(fi, "%% gridsize %f\n", poly->gridsize);
+    fprintf(fi, "%% begin\n");
+    int s,t;
+    gfxpolystroke_t*stroke = poly->strokes;
+    for(;stroke;stroke=stroke->next) {
+	for(s=0;s<stroke->num_points-1;s++) {
+	    point_t a = stroke->points[s];
+	    point_t b = stroke->points[s+1];
+	    fprintf(fi, "%g setgray\n", stroke->dir==DIR_UP ? 0.7 : 0);
+	    fprintf(fi, "%d %d moveto\n", a.x, a.y);
+	    fprintf(fi, "%d %d lineto\n", b.x, b.y);
+	    fprintf(fi, "stroke\n");
+	}
+    }
+    fprintf(fi, "showpage\n");
+    fclose(fi);
+}
+
 inline static event_t event_new()
 {
     event_t e;
@@ -109,29 +224,48 @@ inline static event_t event_new()
     return e;
 }
 
-void event_dump(event_t*e)
+static void event_dump(event_t*e)
 {
-    if(e->type == EVENT_START) {
-        printf("event: segment [%d] starts at (%d,%d)\n", e->s1->nr, e->p.x, e->p.y);
+    if(e->type == EVENT_HORIZONTAL) {
+        fprintf(stderr, "Horizontal [%d] (%d,%d) -> (%d,%d)\n", e->s1->nr, e->s1->a.x, e->s1->a.y, e->s1->b.x, e->s1->b.y);
+    } else if(e->type == EVENT_START) {
+        fprintf(stderr, "event: segment [%d] starts at (%d,%d)\n", e->s1->nr, e->p.x, e->p.y);
     } else if(e->type == EVENT_END) {
-        printf("event: segment [%d] ends at (%d,%d)\n", e->s1->nr, e->p.x, e->p.y);
+        fprintf(stderr, "event: segment [%d] ends at (%d,%d)\n", e->s1->nr, e->p.x, e->p.y);
     } else if(e->type == EVENT_CROSS) {
-        printf("event: segment [%d] and [%d] intersect at (%d,%d)\n", e->s1->nr, e->s2->nr, e->p.x, e->p.y);
-    } else assert(0);
+        fprintf(stderr, "event: segment [%d] and [%d] intersect at (%d,%d)\n", e->s1->nr, e->s2->nr, e->p.x, e->p.y);
+    } else {
+        assert(0);
+    }
 }
 
 static inline max32(int32_t v1, int32_t v2) {return v1>v2?v1:v2;}
 static inline min32(int32_t v1, int32_t v2) {return v1<v2?v1:v2;}
 
-void segment_init(segment_t*s, int x1, int y1, int x2, int y2)
+static void segment_dump(segment_t*s)
 {
-    assert(y1!=y2);
-    if(y1<y2) {
-        s->dir = DIR_DOWN;
+    fprintf(stderr, "[%d] (%d,%d)->(%d,%d) ", s->nr, s->a.x, s->a.y, s->b.x, s->b.y);
+    fprintf(stderr, " dx:%d dy:%d k:%f dx/dy=%f\n", s->delta.x, s->delta.y, s->k,
+            (double)s->delta.x / s->delta.y);
+}
+
+static void segment_init(segment_t*s, int32_t x1, int32_t y1, int32_t x2, int32_t y2, int polygon_nr, segment_dir_t dir)
+{
+    s->dir = dir;
+    if(y1!=y2) {
+	assert(y1<y2);
     } else {
-        int x = x1;x1=x2;x2=x;
-        int y = y1;y1=y2;y2=y;
+        /* up/down for horizontal segments is handled by "rotating"
+           them 90° anticlockwise in screen coordinates (tilt your head to
+           the right) 
+           TODO: is this still needed?
+	 */
         s->dir = DIR_UP;
+        if(x1>x2) {
+            s->dir = DIR_DOWN;
+            int32_t x = x1;x1=x2;x2=x;
+            int32_t y = y1;y1=y2;y2=y;
+        }
     }
     s->a.x = x1;
     s->a.y = y1;
@@ -141,16 +275,18 @@ void segment_init(segment_t*s, int x1, int y1, int x2, int y2)
     s->left = s->right = 0;
     s->delta.x = x2-x1;
     s->delta.y = y2-y1;
+    s->minx = min32(x1,x2);
+    s->maxx = max32(x1,x2);
+
     s->pos = s->a;
-    s->tmp = -1;
-#ifdef DEBUG
-    static int segment_count=0; //for debugging
+    s->polygon_nr = polygon_nr;
+    static int segment_count=0;
     s->nr = segment_count++;
-#endif
 
+#ifdef CHECKS
     assert(LINE_EQ(s->a, s) == 0);
     assert(LINE_EQ(s->b, s) == 0);
-    
+
     /* check that all signs are in order:
        a        a
        |\      /|
@@ -163,86 +299,146 @@ void segment_init(segment_t*s, int x1, int y1, int x2, int y2)
     assert(LINE_EQ(p, s) <= 0);
     p.x = max32(s->a.x, s->b.x);
     assert(LINE_EQ(p, s) >= 0);
+#endif
 
+    /* TODO: make this int_type */
     dict_init2(&s->scheduled_crossings, &ptr_type, 0);
 }
 
-segment_t*segment_new(int x1, int y1, int x2, int y2)
+static segment_t* segment_new(point_t a, point_t b, int polygon_nr, segment_dir_t dir)
 {
-    segment_t*s = malloc(sizeof(segment_t));
-    segment_init(s, x1, y1, x2, y2);
+    segment_t*s = (segment_t*)rfx_calloc(sizeof(segment_t));
+    segment_init(s, a.x, a.y, b.x, b.y, polygon_nr, dir);
     return s;
 }
 
-void segment_insert_before(segment_t**list, segment_t*add)
+static void segment_clear(segment_t*s)
 {
-    if(!*list) {
-        *list = add;
-        add->left = add->right = add;
-    } else {
-        add->left = (*list)->left;
-        add->right = (*list);
-        add->right->left = add;
-        add->left->right = add;
+    dict_clear(&s->scheduled_crossings);
+}
+static void segment_destroy(segment_t*s)
+{
+    segment_clear(s);
+    free(s);
+}
+
+static void advance_stroke(heap_t*queue, gfxpolystroke_t*stroke, int polygon_nr, int pos)
+{
+    while(pos < stroke->num_points-1) {
+	assert(stroke->points[pos].y <= stroke->points[pos+1].y);
+	segment_t*s = segment_new(stroke->points[pos], stroke->points[pos+1], polygon_nr, stroke->dir);
+	s->stroke = stroke;
+	s->stroke_pos = ++pos;
+#ifdef DEBUG
+	/*if(l->tmp)
+	    s->nr = l->tmp;*/
+	fprintf(stderr, "[%d] (%d,%d) -> (%d,%d) %s (%d more to come)\n",
+		s->nr, s->a.x, s->a.y, s->b.x, s->b.y,
+		s->dir==DIR_UP?"up":"down", stroke->num_points - 1 - pos);
+#endif
+	event_t e = event_new();
+	e.type = s->delta.y ? EVENT_START : EVENT_HORIZONTAL;
+	e.p = s->a;
+	e.s1 = s;
+	e.s2 = 0;
+	heap_put(queue, &e);
+	if(e.type != EVENT_HORIZONTAL) {
+	    break;
+	}
     }
 }
 
-void segments_enqueue(segment_t*list, heap_t*queue)
+static void gfxpoly_enqueue(gfxpoly_t*p, heap_t*queue, int polygon_nr)
 {
-    segment_t*l = list;
-    while(l) {
-        segment_t*right = l->right;
-        l->left = l->right = 0;
-        event_t e = event_new();
-        e.type = EVENT_START;
-        e.p = l->a;e.s1 = l;e.s2 = 0;
-        heap_put(queue, &e);
-        e.type = EVENT_END;
-        e.p = l->b;e.s1 = l;e.s2 = 0;
-        heap_put(queue, &e);
-        l = right;
-        if(l==list) break;
+    int t;
+    gfxpolystroke_t*stroke = p->strokes;
+    for(;stroke;stroke=stroke->next) {
+	assert(stroke->num_points > 1);
+
+#ifdef CHECKS
+	int s;
+	for(s=0;s<stroke->num_points-1;s++) {
+	    assert(stroke->points[s].y <= stroke->points[s+1].y);
+	}
+#endif
+	advance_stroke(queue, stroke, polygon_nr, 0);
     }
 }
 
-void schedule_crossing(status_t*status, segment_t*s1, segment_t*s2, int miny)
+static void schedule_endpoint(status_t*status, segment_t*s)
+{
+    // schedule end point of segment
+    assert(s->b.y > status->y);
+    event_t e;
+    e.type = EVENT_END;
+    e.p = s->b;
+    e.s1 = s;
+    e.s2 = 0;
+    heap_put(status->queue, &e);
+}
+
+static void schedule_crossing(status_t*status, segment_t*s1, segment_t*s2)
 {
     /* the code that's required (and the checks you can perform) before
        it can be said with 100% certainty that we indeed have a valid crossing
        amazes me every time. -mk */
+#ifdef CHECKS
     assert(s1!=s2);
-
-    if(dict_contains(&s1->scheduled_crossings, s2)) {
-        // we already know about this one
-        return;
-    }
-
-    /* we probably could precompute these */
-    int32_t minx1 = min32(s1->a.x,s1->b.x);
+    assert(s1->right == s2);
+    assert(s2->left == s1);
     int32_t miny1 = min32(s1->a.y,s1->b.y);
-    int32_t maxx1 = max32(s1->a.x,s1->b.x);
     int32_t maxy1 = max32(s1->a.y,s1->b.y);
-    int32_t minx2 = min32(s2->a.x,s2->b.x);
     int32_t miny2 = min32(s2->a.y,s2->b.y);
-    int32_t maxx2 = max32(s2->a.x,s2->b.x);
     int32_t maxy2 = max32(s2->a.y,s2->b.y);
-    
-    if(maxx1 <= minx2 || maxx2 <= minx1 ||
-       maxy1 <= miny2 || maxy2 <= miny1) {
+    int32_t minx1 = min32(s1->a.x,s1->b.x);
+    int32_t minx2 = min32(s2->a.x,s2->b.x);
+    int32_t maxx1 = max32(s1->a.x,s1->b.x);
+    int32_t maxx2 = max32(s2->a.x,s2->b.x);
+    /* check that precomputation is sane */
+    assert(minx1 == s1->minx && minx2 == s2->minx);
+    assert(maxx1 == s1->maxx && maxx2 == s2->maxx);
+    /* both segments are active, so this can't happen */
+    assert(!(maxy1 <= miny2 || maxy2 <= miny1));
+    /* we know that right now, s2 is to the right of s1, so there's
+       no way the complete bounding box of s1 is to the right of s1 */
+    assert(!(s1->minx > s2->maxx));
+    assert(s1->minx != s2->maxx || (!s1->delta.x && !s2->delta.x));
+#endif
+
+    if(s1->maxx <= s2->minx) {
+#ifdef DEBUG
+            fprintf(stderr, "[%d] doesn't intersect with [%d] because: bounding boxes don't intersect\n", s1->nr, s2->nr);
+#endif
         /* bounding boxes don't intersect */
         return;
     }
-    double adx = s1->delta.x;
-    double ady = s1->delta.y;
-    double bdx = s2->delta.x;
-    double bdy = s2->delta.y;
-    double det = adx*bdy - ady*bdx;
+
+#define REMEMBER_CROSSINGS
+#ifdef REMEMBER_CROSSINGS
+    if(dict_contains(&s1->scheduled_crossings, (void*)(ptroff_t)s2->nr)) {
+        /* FIXME: this whole segment hashing thing is really slow */
+#ifdef DEBUG
+        fprintf(stderr, "[%d] doesn't intersect with [%d] because: we already scheduled this intersection\n", s1->nr, s2->nr);
+//	DICT_ITERATE_KEY(&s1->scheduled_crossings, void*, x) {
+//	    fprintf(stderr, "[%d]<->[%d]\n", s1->nr, (int)(ptroff_t)x);
+//	}
+#endif
+        return; // we already know about this one
+    }
+#endif
+
+    double det = (double)s1->delta.x*s2->delta.y - (double)s1->delta.y*s2->delta.x;
     if(!det) {
         if(s1->k == s2->k) {
             // lines are exactly on top of each other (ignored)
+#ifdef DEBUG
             fprintf(stderr, "Notice: segments [%d] and [%d] are exactly on top of each other\n", s1->nr, s2->nr);
+#endif
             return;
         } else {
+#ifdef DEBUG
+            fprintf(stderr, "[%d] doesn't intersect with [%d] because: they are parallel to each other\n", s1->nr, s2->nr);
+#endif
             /* lines are parallel */
             return;
         }
@@ -251,9 +447,16 @@ void schedule_crossing(status_t*status, segment_t*s1, segment_t*s2, int miny)
     double bsign2 = LINE_EQ(s1->b, s2);
     if(asign2<0 && bsign2<0) {
         // segment1 is completely to the left of segment2
+#ifdef DEBUG
+            fprintf(stderr, "[%d] doesn't intersect with [%d] because: [%d] is completely to the left of [%d]\n", s1->nr, s2->nr, s1->nr, s2->nr);
+#endif
         return;
     }
     if(asign2>0 && bsign2>0)  {
+	// TODO: can this ever happen?
+#ifdef DEBUG
+            fprintf(stderr, "[%d] doesn't intersect with [%d] because: [%d] is completely to the left of [%d]\n", s1->nr, s2->nr, s2->nr, s1->nr);
+#endif
         // segment2 is completely to the left of segment1
         return;
     }
@@ -275,10 +478,16 @@ void schedule_crossing(status_t*status, segment_t*s1, segment_t*s2, int miny)
     double bsign1 = LINE_EQ(s2->b, s1);
     if(asign1<0 && bsign1<0) {
         // segment1 is completely to the left of segment2
+#ifdef DEBUG
+            fprintf(stderr, "[%d] doesn't intersect with [%d] because: [%d] is completely to the left of [%d]\n", s1->nr, s2->nr, s1->nr, s2->nr);
+#endif
         return;
     }
     if(asign1>0 && bsign1>0)  {
         // segment2 is completely to the left of segment1
+#ifdef DEBUG
+            fprintf(stderr, "[%d] doesn't intersect with [%d] because: [%d] is completely to the left of [%d]\n", s1->nr, s2->nr, s2->nr, s1->nr);
+#endif
         return;
     }
     if(asign1==0) {
@@ -296,158 +505,79 @@ void schedule_crossing(status_t*status, segment_t*s1, segment_t*s2, int miny)
         return;
     }
 
+    /* TODO: should we precompute these? */
     double la = (double)s1->a.x*(double)s1->b.y - (double)s1->a.y*(double)s1->b.x;
     double lb = (double)s2->a.x*(double)s2->b.y - (double)s2->a.y*(double)s2->b.x;
 
     point_t p;
-    p.x = (int32_t)ceil((-la*bdx +lb*adx) / det);
-    p.y = (int32_t)ceil((+lb*ady -la*bdy) / det);
-    /* we only schedule crossings if they are *after* the current y. That way, we don't
-       schedule the same crossing twice */
-    if(p.y >= miny) {
-#ifdef DEBUG
-        point_t pair;
-        pair.x = s1->nr;
-        pair.y = s2->nr;
-        assert(!dict_contains(status->seen_crossings, &pair));
-        dict_put(status->seen_crossings, &pair, 0);
-#endif
-        event_t e = event_new();
-        e.type = EVENT_CROSS;
-        e.p = p;
-        e.s1 = s1;
-        e.s2 = s2;
-#ifdef DEBUG
-        printf("schedule crossing between [%d] and [%d] at (%d,%d)\n", s1->nr, s2->nr, e.p.x, e.p.y);
+    p.x = (int32_t)ceil((-la*s2->delta.x + lb*s1->delta.x) / det);
+    p.y = (int32_t)ceil((+lb*s1->delta.y - la*s2->delta.y) / det);
+
+#ifndef REMEMBER_CROSSINGS
+    if(p.y < status->y) return;
 #endif
-        /* we insert into each other's intersection history because these segments might switch
-           places */
-        dict_put(&s1->scheduled_crossings, s2, 0);
-        dict_put(&s2->scheduled_crossings, s1, 0);
 
-        heap_put(status->queue, &e);
-    }
-    return;
-}
+    assert(p.y >= status->y);
+#ifdef CHECKS
+    assert(p.x >= s1->minx && p.x <= s1->maxx);
+    assert(p.x >= s2->minx && p.x <= s2->maxx);
 
-/* routine dealing with the special case of a number of line segments intersecting in exactly one
-   point */
-void exchange_many(status_t*status, event_t*e)
-{
-    int size = 16;
-    int n = 0;
-    segment_t**segs = (segment_t**)malloc(sizeof(segment_t*)*size);
-    segs[n] = e->s1;e->s1->tmp = n;n++;
-    segs[n] = e->s2;e->s2->tmp = n;n++;
-#ifdef DEBUG
-    dict_put(status->intersecting_segs, e->s1, 0);
-    dict_put(status->intersecting_segs, e->s2, 0);
-#endif
-    while(1) {
-        event_t*ee = heap_peek(status->queue);
-        if(ee->p.x != e->p.x ||
-           ee->p.y != e->p.y ||
-           ee->type != e->type) {
-            break;
-        }
-        if(n>=size-1) {
-            size *= 2;
-            segs = realloc(segs, sizeof(segment_t*)*size);
-        }
-        ee = heap_chopmax(status->queue);
-        if(ee->s1->tmp<0) {
-            segs[n] = ee->s1;ee->s1->tmp = n;n++;
-        }
-        if(ee->s2->tmp<0) {
-            segs[n] = ee->s2;ee->s2->tmp = n;n++;
-        }
-#ifdef DEBUG
-        dict_put(status->intersecting_segs, ee->s1, 0);
-        dict_put(status->intersecting_segs, ee->s2, 0);
+    point_t pair;
+    pair.x = s1->nr;
+    pair.y = s2->nr;
+#ifdef REMEMBER_CROSSINGS
+    assert(!dict_contains(status->seen_crossings, &pair));
+    dict_put(status->seen_crossings, &pair, 0);
+#endif
 #endif
-    }
-    int t;
 #ifdef DEBUG
-    printf("event: multi-intersect: ");
-    for(t=0;t<n;t++) {
-        printf("[%d] ", segs[t]->nr);
-    }
-    printf("\n");
-#endif
-    segment_t*left = 0;
-    segment_t*right = 0;
-    char warn = 0;
-    for(t=0;t<n;t++) {
-        if(!segs[t]->left || segs[t]->left->tmp<0) {
-            assert(!left);
-            left = segs[t];
-        }
-        if(!segs[t]->right || segs[t]->right->tmp<0) {
-            assert(!right);
-            right = segs[t];
-        }
-        if(segs[t]->tmp<0)
-            warn = 1;
-    }
-    if(warn)
-        fprintf(stderr, "Warning: multi-cross section contains rogue segments\n");
+    fprintf(stderr, "schedule crossing between [%d] and [%d] at (%d,%d)\n", s1->nr, s2->nr, p.x, p.y);
+#endif
 
-    assert(left);
-    assert(right);
-    assert(left!=right);
-    actlist_invert_fromto(status->actlist, left, right);
-    for(t=0;t<n;t++) {
-        segs[t]->tmp = -1;
-    }
-    free(segs);
-    if(right->left)
-        schedule_crossing(status, right->left, right, status->y);
-    if(left->right)
-        schedule_crossing(status, left, left->right, status->y);
+#ifdef REMEMBER_CROSSINGS
+    /* we insert into each other's intersection history because these segments might switch
+       places and we still want to look them up quickly after they did */
+    dict_put(&s1->scheduled_crossings, (void*)(ptroff_t)(s2->nr), 0);
+    dict_put(&s2->scheduled_crossings, (void*)(ptroff_t)(s1->nr), 0);
+#endif
+
+    event_t e = event_new();
+    e.type = EVENT_CROSS;
+    e.p = p;
+    e.s1 = s1;
+    e.s2 = s2;
+    heap_put(status->queue, &e);
+    return;
 }
 
-void exchange_two(status_t*status, event_t*e)
+static void exchange_two(status_t*status, event_t*e)
 {
     //exchange two segments in list
     segment_t*s1 = e->s1;
     segment_t*s2 = e->s2;
-#ifdef DEBUG
-    dict_put(status->intersecting_segs, s1, 0);
-    dict_put(status->intersecting_segs, s2, 0);
+#ifdef CHECKS
+    if(!dict_contains(status->intersecting_segs, s1))
+        dict_put(status->intersecting_segs, s1, 0);
+    if(!dict_contains(status->intersecting_segs, s2))
+        dict_put(status->intersecting_segs, s2, 0);
 #endif
-    segment_t*left = actlist_left(status->actlist, s2);
-    segment_t*right = actlist_right(status->actlist, s1);
-    assert(left == s1);
-    assert(right == s2);
+    assert(s2->left == s1);
+    assert(s1->right == s2);
     actlist_swap(status->actlist, s1, s2);
-    assert(actlist_right(status->actlist, s2) == s1);
-    assert(actlist_left(status->actlist, s1) == s2);
-    left = actlist_left(status->actlist, s2);
-    right = actlist_right(status->actlist, s1);
+    assert(s2->right  == s1);
+    assert(s1->left == s2);
+    segment_t*left = s2->left;
+    segment_t*right = s1->right;
     if(left)
-        schedule_crossing(status, left, s2, status->y);
+        schedule_crossing(status, left, s2);
     if(right)
-        schedule_crossing(status, s1, right, status->y);
-}
-
-void insert_point_into_segment(segment_t*s, point_t p)
-{
-    if(s->pos.x == p.x && s->pos.y == p.y) {
-#ifdef DEBUG
-        fprintf(stderr, "Notice: tried to add (%d,%d) to segment [%d] twice\n", p.x, p.y, s->nr);
-#endif
-        return;
-    }
-#ifdef DEBUG
-    printf("[%d] gets extra point (%d,%d)\n", s->nr, p.x, p.y);
-#endif
-    s->pos = p;
+        schedule_crossing(status, s1, right);
 }
 
 typedef struct _box {
     point_t left1, left2, right1, right2;
 } box_t;
-static inline box_t box_new(int x, int y)
+static inline box_t box_new(int32_t x, int32_t y)
 {
     box_t box;
     box.right1.x = box.right2.x = x;
@@ -456,52 +586,129 @@ static inline box_t box_new(int x, int y)
     box.left2.y = box.right2.y = y;
     return box;
 }
-        
-/* possible optimizations:
-   1.) keep two different active lists around, one for negative and one for
-       positive slopes
-   2.) delay starting events until after this function (tricky, because we *do*
-       need the start coordinates)
-*/
+
+static void insert_point_into_segment(status_t*status, segment_t*s, point_t p)
+{
+    assert(s->pos.x != p.x || s->pos.y != p.y);
+
+#ifdef CHECKS
+    if(!dict_contains(status->segs_with_point, s))
+        dict_put(status->segs_with_point, s, 0);
+    assert(s->fs_out_ok);
+#endif
+
+    if(s->fs_out) {
+#ifdef DEBUG
+        fprintf(stderr, "[%d] receives next point (%d,%d)->(%d,%d) (drawing)\n", s->nr,
+                s->pos.x, s->pos.y, p.x, p.y);
+#endif
+        // omit horizontal lines
+        if(s->pos.y != p.y) {
+            point_t a = s->pos;
+            point_t b = p;
+            assert(a.y != b.y);
+	    status->writer.moveto(&status->writer, a.x, a.y);
+	    status->writer.lineto(&status->writer, b.x, b.y);
+        }
+    } else {
+#ifdef DEBUG
+        fprintf(stderr, "[%d] receives next point (%d,%d) (omitting)\n", s->nr, p.x, p.y);
+#endif
+    }
+    s->pos = p;
+}
+
+typedef struct _segrange {
+    double xmin;
+    segment_t*segmin;
+    double xmax;
+    segment_t*segmax;
+} segrange_t;
+
+static void segrange_adjust_endpoints(segrange_t*range, int32_t y)
+{
+#define XPOS_EQ(s1,s2,ypos) (XPOS((s1),(ypos))==XPOS((s2),(ypos)))
+    segment_t*min = range->segmin;
+    segment_t*max = range->segmax;
+
+    /* we need this because if two segments intersect exactly on
+       the scanline, segrange_test_segment_{min,max} can't tell which
+       one is smaller/larger */
+    if(min) while(min->left && XPOS_EQ(min, min->left, y)) {
+        min = min->left;
+    }
+    if(max) while(max->right && XPOS_EQ(max, max->right, y)) {
+        max = max->right;
+    }
+    range->segmin = min;
+    range->segmax = max;
+}
+static void segrange_test_segment_min(segrange_t*range, segment_t*seg, int32_t y)
+{
+    if(!seg) return;
+    /* we need to calculate the xpos anew (and can't use start coordinate or
+       intersection coordinate), because we need the xpos exactly at the end of
+       this scanline.
+     */
+    double x = XPOS(seg, y);
+    if(!range->segmin || x<range->xmin) {
+        range->segmin = seg;
+        range->xmin = x;
+    }
+}
+static void segrange_test_segment_max(segrange_t*range, segment_t*seg, int32_t y)
+{
+    if(!seg) return;
+    double x = XPOS(seg, y);
+    if(!range->segmax || x>range->xmax) {
+        range->segmax = seg;
+        range->xmax = x;
+    }
+}
+
 /*
    SLOPE_POSITIVE:
-       +     \ +        
------- I      \I       
-      -I\----  I      
+      \+     \ +
+------ I      \I
+      -I\----  I
        I \   --I\---
        I  \    I \  -------
        +   \   +  \
 */
-void add_points_to_positively_sloped_segments(status_t*status, xrow_t*xrow, int32_t y)
+static void add_points_to_positively_sloped_segments(status_t*status, int32_t y, segrange_t*range)
 {
+    segment_t*first=0, *last = 0;
     int t;
-    for(t=0;t<xrow->num;t++) {
-        box_t box = box_new(xrow->x[t], y);
+    for(t=0;t<status->xrow->num;t++) {
+        box_t box = box_new(status->xrow->x[t], y);
         segment_t*seg = actlist_find(status->actlist, box.left2, box.left2);
-        if(seg) 
-            seg = seg->right;
-        else    
-            seg = actlist_leftmost(status->actlist);
+
+        seg = actlist_right(status->actlist, seg);
         while(seg) {
             if(seg->a.y == y) {
-                // this segment just started, ignore it
-            } else if(seg->delta.x < 0) {
+                // this segment started in this scanline, ignore it
+                seg->changed = 1;last = seg;if(!first) {first=seg;}
+            } else if(seg->delta.x <= 0) {
                 // ignore segment w/ negative slope
             } else {
+                last = seg;if(!first) {first=seg;}
                 double d1 = LINE_EQ(box.right1, seg);
                 double d2 = LINE_EQ(box.right2, seg);
-                if(d1>=0 || d2>=0) {
-#ifdef DEBUG
-                    dict_put(status->segs_with_point, seg, 0);
-#endif
-                    insert_point_into_segment(seg, box.right2);
+                if(d1>0 || d2>=0) {
+                    seg->changed = 1;
+                    insert_point_into_segment(status, seg, box.right2);
                 } else {
-                    break;
+                    /* we unfortunately can't break here- the active list is sorted according
+                       to the *bottom* of the scanline. hence pretty much everything that's still
+                       coming might reach into our box */
+                    //break;
                 }
             }
             seg = seg->right;
         }
     }
+    segrange_test_segment_min(range, first, y);
+    segrange_test_segment_max(range, last, y);
 }
 /* SLOPE_NEGATIVE:
    |   +   /|  +  /    /
@@ -511,85 +718,303 @@ void add_points_to_positively_sloped_segments(status_t*status, xrow_t*xrow, int3
    |   I    | /I   /
    |  /+    |/ +  /
 */
-void add_points_to_negatively_sloped_segments(status_t*status, xrow_t*xrow, int32_t y)
+static void add_points_to_negatively_sloped_segments(status_t*status, int32_t y, segrange_t*range)
 {
+    segment_t*first=0, *last = 0;
     int t;
-    for(t=xrow->num-1;t>=0;t--) {
-        box_t box = box_new(xrow->x[t], y);
+    for(t=status->xrow->num-1;t>=0;t--) {
+        box_t box = box_new(status->xrow->x[t], y);
         segment_t*seg = actlist_find(status->actlist, box.right2, box.right2);
+
         while(seg) {
             if(seg->a.y == y) {
-                // this segment just started, ignore it
-            } else if(seg->delta.x >= 0) {
+                // this segment started in this scanline, ignore it
+                seg->changed = 1;last = seg;if(!first) {first=seg;}
+            } else if(seg->delta.x > 0) {
                 // ignore segment w/ positive slope
             } else {
+                last = seg;if(!first) {first=seg;}
                 double d1 = LINE_EQ(box.left1, seg);
                 double d2 = LINE_EQ(box.left2, seg);
                 if(d1<0 || d2<0) {
-#ifdef DEBUG
-                    dict_put(status->segs_with_point, seg, 0);
-#endif
-                    insert_point_into_segment(seg, box.right2);
+                    seg->changed = 1;
+                    insert_point_into_segment(status, seg, box.right2);
                 } else {
-                    break;
+                    //break;
                 }
             }
             seg = seg->left;
         }
     }
+    segrange_test_segment_min(range, last, y);
+    segrange_test_segment_max(range, first, y);
+}
+
+/* segments ending in the current scanline need xrow treatment like everything else.
+   (consider an intersection taking place just above a nearly horizontal segment
+   ending on the current scanline- the intersection would snap down *below* the
+   ending segment if we don't add the intersection point to the latter right away)
+   we need to treat ending segments seperately, however. we have to delete them from
+   the active list right away to make room for intersect operations (which might
+   still be in the current scanline- consider two 45° polygons and a vertical polygon
+   intersecting on an integer coordinate). but once they're no longer in the active list,
+   we can't use the add_points_to_*_sloped_segments() functions anymore, and re-adding
+   them to the active list just for point snapping would be overkill.
+   (One other option to consider, however, would be to create a new active list only
+    for ending segments)
+*/
+static void add_points_to_ending_segments(status_t*status, int32_t y)
+{
+    segment_t*seg = status->ending_segments;
+    while(seg) {
+        segment_t*next = seg->right;seg->right=0;
+
+        assert(seg->b.y == status->y);
+
+        if(status->xrow->num == 1) {
+            // shortcut
+	    assert(seg->b.x == status->xrow->x[0]);
+            point_t p = {status->xrow->x[0], y};
+            insert_point_into_segment(status, seg, p);
+        } else {
+            int t;
+            int start=0,end=status->xrow->num,dir=1;
+            if(seg->delta.x < 0) {
+                start = status->xrow->num-1;
+                end = dir = -1;
+            }
+            for(t=start;t!=end;t+=dir) {
+                box_t box = box_new(status->xrow->x[t], y);
+                double d0 = LINE_EQ(box.left1, seg);
+                double d1 = LINE_EQ(box.left2, seg);
+                double d2 = LINE_EQ(box.right1, seg);
+                double d3 = LINE_EQ(box.right2, seg);
+                if(!(d0>=0 && d1>=0 && d2>=0 && d3>0 ||
+                     d0<=0 && d1<=0 && d2<=0 && d3<0)) {
+                    insert_point_into_segment(status, seg, box.right2);
+                    break;
+                }
+            }
+
+#ifdef CHECKS
+            /* we *need* to find a point to insert. the segment's own end point
+               is in that list, for Pete's sake. */
+            assert(t!=end);
+#endif
+        }
+        // now that this is done, too, we can also finally free this segment
+        segment_destroy(seg);
+        seg = next;
+    }
+    status->ending_segments = 0;
+}
+
+static void recalculate_windings(status_t*status, segrange_t*range)
+{
+#ifdef DEBUG
+    fprintf(stderr, "range: [%d]..[%d]\n", SEGNR(range->segmin), SEGNR(range->segmax));
+#endif
+    segrange_adjust_endpoints(range, status->y);
+
+    segment_t*s = range->segmin;
+    segment_t*end = range->segmax;
+    segment_t*last = 0;
+
+#ifdef DEBUG
+    s = actlist_leftmost(status->actlist);
+    while(s) {
+        fprintf(stderr, "[%d]%d%s ", s->nr, s->changed,
+            s == range->segmin?"S":(
+            s == range->segmax?"E":""));
+        s = s->right;
+    }
+    fprintf(stderr, "\n");
+    s = range->segmin;
+#endif
+#ifdef CHECKS
+    /* test sanity: check that we don't have changed segments
+       outside of the given range */
+    s = actlist_leftmost(status->actlist);
+    while(s && s!=range->segmin) {
+        assert(!s->changed);
+        s = s->right;
+    }
+    s = actlist_rightmost(status->actlist);
+    while(s && s!=range->segmax) {
+        assert(!s->changed);
+        s = s->left;
+    }
+    /* in check mode, go through the whole interval so we can test
+       that all polygons where the fillstyle changed also have seg->changed=1 */
+    s = actlist_leftmost(status->actlist);
+    end = 0;
+#endif
+
+    if(end)
+        end = end->right;
+    while(s!=end) {
+#ifndef CHECKS
+        if(s->changed)
+#endif
+        {
+            segment_t* left = actlist_left(status->actlist, s);
+            windstate_t wind = left?left->wind:status->windrule->start(status->context);
+            s->wind = status->windrule->add(status->context, wind, s->fs, s->dir, s->polygon_nr);
+            fillstyle_t*fs_old = s->fs_out;
+            s->fs_out = status->windrule->diff(&wind, &s->wind);
+
+#ifdef DEBUG
+            fprintf(stderr, "[%d] %s/%d/%s/%s %s\n", s->nr, s->dir==DIR_UP?"up":"down", s->wind.wind_nr, s->wind.is_filled?"fill":"nofill", s->fs_out?"draw":"omit",
+		    fs_old!=s->fs_out?"CHANGED":"");
+#endif
+            assert(!(!s->changed && fs_old!=s->fs_out));
+            s->changed = 0;
+
+#ifdef CHECKS
+            s->fs_out_ok = 1;
+#endif
+        }
+        s = s->right;
+    }
+}
+
+/* we need to handle horizontal lines in order to add points to segments
+   we otherwise would miss during the windrule re-evaluation */
+static void intersect_with_horizontal(status_t*status, segment_t*h)
+{
+    segment_t* left = actlist_find(status->actlist, h->a, h->a);
+    segment_t* right = actlist_find(status->actlist, h->b, h->b);
+
+    /* not strictly necessary, also done by the event */
+    xrow_add(status->xrow, h->a.x);
+    point_t o = h->a;
+
+    if(!right) {
+        assert(!left);
+        return;
+    }
+
+    left = actlist_right(status->actlist, left); //first seg to the right of h->a
+    right = right->right; //first seg to the right of h->b
+    segment_t* s = left;
+
+    while(s!=right) {
+        assert(s);
+        int32_t x = XPOS_INT(s, status->y);
+#ifdef DEBUG
+        fprintf(stderr, "...into [%d] (%d,%d) -> (%d,%d) at (%d,%d)\n", s->nr,
+                s->a.x, s->a.y,
+                s->b.x, s->b.y,
+                x, status->y
+                );
+#endif
+        assert(x >= h->a.x);
+        assert(x <= h->b.x);
+        assert(s->delta.x > 0 && x >= s->a.x || s->delta.x <= 0 && x <= s->a.x);
+        assert(s->delta.x > 0 && x <= s->b.x || s->delta.x <= 0 && x >= s->b.x);
+        xrow_add(status->xrow, x);
+
+        s = s->right;
+    }
 }
 
-void event_apply(status_t*status, event_t*e)
+static void event_apply(status_t*status, event_t*e)
 {
     switch(e->type) {
+        case EVENT_HORIZONTAL: {
+            segment_t*s = e->s1;
+#ifdef DEBUG
+            event_dump(e);
+#endif
+            intersect_with_horizontal(status, s);
+	    advance_stroke(status->queue, s->stroke, s->polygon_nr, s->stroke_pos);
+            segment_destroy(s);e->s1=0;
+            break;
+        }
         case EVENT_END: {
             //delete segment from list
-            event_dump(e);
             segment_t*s = e->s1;
-            insert_point_into_segment(s, s->b);
-            segment_t*left = actlist_left(status->actlist, s);
-            segment_t*right = actlist_right(status->actlist, s);
+#ifdef DEBUG
+            event_dump(e);
+#endif
+#ifdef CHECKS
+            dict_del(status->intersecting_segs, s);
+            dict_del(status->segs_with_point, s);
+            assert(!dict_contains(status->intersecting_segs, s));
+            assert(!dict_contains(status->segs_with_point, s));
+#endif
+            segment_t*left = s->left;
+            segment_t*right = s->right;
             actlist_delete(status->actlist, s);
-            dict_clear(&s->scheduled_crossings);
             if(left && right)
-                schedule_crossing(status, left, right, status->y+1);
+                schedule_crossing(status, left, right);
+
+	    /* schedule segment for xrow handling */
+            s->left = 0; s->right = status->ending_segments;
+            status->ending_segments = s;
+	    advance_stroke(status->queue, s->stroke, s->polygon_nr, s->stroke_pos);
             break;
         }
         case EVENT_START: {
             //insert segment into list
+#ifdef DEBUG
             event_dump(e);
+#endif
             segment_t*s = e->s1;
-            actlist_insert(status->actlist, e->p, s);
-            segment_t*left = actlist_left(status->actlist, s);
-            segment_t*right = actlist_right(status->actlist, s);
+	    assert(e->p.x == s->a.x && e->p.y == s->a.y);
+            actlist_insert(status->actlist, s->a, s->b, s);
+            segment_t*left = s->left;
+            segment_t*right = s->right;
             if(left)
-                schedule_crossing(status, left, s, status->y+1);
+                schedule_crossing(status, left, s);
             if(right)
-                schedule_crossing(status, s, right, status->y+1);
+                schedule_crossing(status, s, right);
+            schedule_endpoint(status, s);
             break;
         }
         case EVENT_CROSS: {
-            // exchange two (or more) segments
-            event_t*ee = heap_peek(status->queue);
-            if(ee->p.x != e->p.x ||
-               ee->p.y != e->p.y ||
-               ee->type != e->type) {
-                event_dump(e);
+            // exchange two segments
+#ifdef DEBUG
+            event_dump(e);
+#endif
+            if(e->s1->right == e->s2) {
+		assert(e->s2->left == e->s1);
                 exchange_two(status, e);
             } else {
-                exchange_many(status, e);
+		assert(e->s2->left != e->s1);
+#ifdef DEBUG
+		fprintf(stderr, "Ignore this crossing ([%d] not next to [%d])\n", e->s1->nr, e->s2->nr);
+#endif
+#ifdef REMEMBER_CROSSINGS
+                /* ignore this crossing for now (there are some line segments in between).
+                   it'll get rescheduled as soon as the "obstacles" are gone */
+                char del1 = dict_del(&e->s1->scheduled_crossings, (void*)(ptroff_t)e->s2->nr);
+                char del2 = dict_del(&e->s2->scheduled_crossings, (void*)(ptroff_t)e->s1->nr);
+                assert(del1 && del2);
+#endif
+#ifdef CHECKS
+                point_t pair;
+                pair.x = e->s1->nr;
+                pair.y = e->s2->nr;
+#ifdef REMEMBER_CROSSINGS
+                assert(dict_contains(status->seen_crossings, &pair));
+                dict_del(status->seen_crossings, &pair);
+#endif
+#endif
             }
         }
     }
 }
 
-#ifdef DEBUG
-void check_status(status_t*status)
+#ifdef CHECKS
+static void check_status(status_t*status)
 {
     DICT_ITERATE_KEY(status->intersecting_segs, segment_t*, s) {
-        if(!dict_contains(status->segs_with_point, s)) {
-            fprintf(stderr, "Error: segment [%d] (%sslope) intersects in scanline %d, but it didn't receive a point\n", 
-                    s->nr, 
+        if((s->pos.x != s->b.x ||
+            s->pos.y != s->b.y) &&
+           !dict_contains(status->segs_with_point, s)) {
+            fprintf(stderr, "Error: segment [%d] (%sslope) intersects in scanline %d, but it didn't receive a point\n",
+                    s->nr,
                     s->delta.x<0?"-":"+",
                     status->y);
             assert(0);
@@ -598,50 +1023,193 @@ void check_status(status_t*status)
 }
 #endif
 
-void gfxpoly_process(segment_t*poly)
+static void add_horizontals(gfxpoly_t*poly, windrule_t*windrule, windcontext_t*context)
+{
+    /*
+          |..|        |...........|                 |           |
+          |..|        |...........|                 |           |
+          |..+        +        +..|                 +--+     +--+
+          |...........|        |..|                    |     |
+          |...........|        |..|                    |     |
+     */
+
+#ifdef DEBUG
+    fprintf(stderr, "========================================================================\n");
+#endif
+    heap_t* queue = heap_new(sizeof(event_t), compare_events_simple);
+    gfxpoly_enqueue(poly, queue, 0);
+
+    actlist_t* actlist = actlist_new();
+
+    event_t*e = heap_chopmax(queue);
+    while(e) {
+        int32_t y = e->p.y;
+        int32_t x = 0;
+        char fill = 0;
+#ifdef DEBUG
+        fprintf(stderr, "----------------------------------- %d\n", y);
+        actlist_dump(actlist, y-1);
+#endif
+#ifdef CHECKS
+        actlist_verify(actlist, y-1);
+#endif
+        do {
+            if(fill && x != e->p.x) {
+#ifdef DEBUG
+                fprintf(stderr, "%d) draw horizontal line from %d to %d\n", y, x, e->p.x);
+#endif
+		assert(x<e->p.x);
+
+                gfxpolystroke_t*stroke = rfx_calloc(sizeof(gfxpolystroke_t));
+		stroke->next = poly->strokes;
+		poly->strokes = stroke;
+
+		stroke->num_points = 2;
+		stroke->points = malloc(sizeof(point_t)*2);
+		stroke->dir = DIR_UP; // FIXME
+		stroke->fs = 0;
+		point_t a,b;
+                a.y = b.y = y;
+		/* we draw from low x to high x so that left/right fillstyles add up
+                   (because the horizontal line's fill style controls the area *below* the line)
+		 */
+                a.x = e->p.x;
+                b.x = x;
+		stroke->points[0] = a;
+		stroke->points[1] = b;
+#ifdef CHECKS
+		/* the output should always be intersection free polygons, so check this horizontal
+		   line isn't hacking through any segments in the active list */
+		segment_t* start = actlist_find(actlist, b, b);
+		segment_t* s = actlist_find(actlist, a, a);
+		while(s!=start) {
+		    assert(s->a.y == y || s->b.y == y);
+		    s = s->left;
+		}
+#endif
+            }
+            segment_t*left = 0;
+            segment_t*s = e->s1;
+
+            switch(e->type) {
+                case EVENT_START: {
+		    assert(e->p.x == s->a.x && e->p.y == s->a.y);
+                    actlist_insert(actlist, s->a, s->b, s);
+                    event_t e;
+                    e.type = EVENT_END;
+                    e.p = s->b;
+                    e.s1 = s;
+                    e.s2 = 0;
+                    heap_put(queue, &e);
+                    left = actlist_left(actlist, s);
+                    break;
+                }
+                case EVENT_END: {
+                    left = actlist_left(actlist, s);
+                    actlist_delete(actlist, s);
+		    advance_stroke(queue, s->stroke, s->polygon_nr, s->stroke_pos);
+                    break;
+                }
+                default: assert(0);
+            }
+
+            x = e->p.x;
+            fill ^= 1;//(before.is_filled != after.is_filled);
+#ifdef DEBUG
+            fprintf(stderr, "%d) event=%s[%d] left:[%d] x:%d\n",
+                    y, e->type==EVENT_START?"start":"end",
+                    s->nr,
+                    left?left->nr:-1,
+                    x);
+#endif
+
+            if(e->type == EVENT_END)
+                segment_destroy(s);
+
+            free(e);
+            e = heap_chopmax(queue);
+        } while(e && y == e->p.y);
+
+        assert(!fill); // check that polygon is not bleeding
+    }
+
+    actlist_destroy(actlist);
+    heap_destroy(queue);
+}
+
+gfxpoly_t* gfxpoly_process(gfxpoly_t*poly, windrule_t*windrule, windcontext_t*context)
 {
+    current_polygon = poly;
     heap_t* queue = heap_new(sizeof(event_t), compare_events);
-    segments_enqueue(poly, queue);
+
+    gfxpoly_enqueue(poly, queue, /*polygon nr*/0);
+
     status_t status;
     memset(&status, 0, sizeof(status_t));
     status.queue = queue;
+    status.windrule = windrule;
+    status.context = context;
     status.actlist = actlist_new();
-#ifdef DEBUG
+    gfxpolywriter_init(&status.writer);
+    status.writer.setgridsize(&status.writer, poly->gridsize);
+
+#ifdef CHECKS
     status.seen_crossings = dict_new2(&point_type);
+    int lasty=heap_peek(queue)?((event_t*)heap_peek(queue))->p.y-1:0;
 #endif
-    
-    xrow_t*xrow = xrow_new();
+
+    status.xrow = xrow_new();
 
     event_t*e = heap_chopmax(queue);
     while(e) {
         status.y = e->p.y;
-#ifdef DEBUG
+	assert(status.y>=lasty);
+#ifdef CHECKS
         status.intersecting_segs = dict_new2(&ptr_type);
         status.segs_with_point = dict_new2(&ptr_type);
-        printf("----------------------------------- %d\n", status.y);
-        actlist_verify_and_dump(status.actlist, status.y-1);
 #endif
-        xrow_reset(xrow);
+
+#ifdef DEBUG
+        fprintf(stderr, "----------------------------------- %d\n", status.y);
+        actlist_dump(status.actlist, status.y-1);
+#endif
+#ifdef CHECKS
+        actlist_verify(status.actlist, status.y-1);
+#endif
+        xrow_reset(status.xrow);
         do {
-            xrow_add(xrow, e->p.x);
+            xrow_add(status.xrow, e->p.x);
             event_apply(&status, e);
             free(e);
             e = heap_chopmax(queue);
         } while(e && status.y == e->p.y);
 
-        xrow_sort(xrow);
-        add_points_to_positively_sloped_segments(&status, xrow, status.y);
-        add_points_to_negatively_sloped_segments(&status, xrow, status.y);
+        xrow_sort(status.xrow);
+        segrange_t range;
+        memset(&range, 0, sizeof(range));
 #ifdef DEBUG
+        actlist_dump(status.actlist, status.y);
+#endif
+        add_points_to_positively_sloped_segments(&status, status.y, &range);
+        add_points_to_negatively_sloped_segments(&status, status.y, &range);
+        add_points_to_ending_segments(&status, status.y);
+
+        recalculate_windings(&status, &range);
+#ifdef CHECKS
         check_status(&status);
         dict_destroy(status.intersecting_segs);
         dict_destroy(status.segs_with_point);
 #endif
     }
-#ifdef DEBUG
+#ifdef CHECKS
     dict_destroy(status.seen_crossings);
 #endif
+    actlist_destroy(status.actlist);
     heap_destroy(queue);
-    gfxpoly_destroy(poly);
-    xrow_destroy(xrow);
+    xrow_destroy(status.xrow);
+
+    gfxpoly_t*p = (gfxpoly_t*)status.writer.finish(&status.writer);
+
+    add_horizontals(p, &windrule_evenodd, context); // output is always even/odd
+    return p;
 }