add cairo

1 files changed, 1709 insertions, 0 deletions

diff --git a/libs/cairo-1.16.0/src/cairo-tor22-scan-converter.c b/libs/cairo-1.16.0/src/cairo-tor22-scan-converter.c
new file mode 100644
index 0000000..bf44742
--- /dev/null
+++ b/libs/cairo-1.16.0/src/cairo-tor22-scan-converter.c
@@ -0,0 +1,1709 @@
+/* -*- Mode: c; tab-width: 8; c-basic-offset: 4; indent-tabs-mode: t; -*- */
+/* glitter-paths - polygon scan converter
+ *
+ * Copyright (c) 2008  M Joonas Pihlaja
+ * Copyright (c) 2007  David Turner
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following
+ * conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+/* This is the Glitter paths scan converter incorporated into cairo.
+ * The source is from commit 734c53237a867a773640bd5b64816249fa1730f8
+ * of
+ *
+ *   https://gitweb.freedesktop.org/?p=users/joonas/glitter-paths
+ */
+/* Glitter-paths is a stand alone polygon rasteriser derived from
+ * David Turner's reimplementation of Tor Anderssons's 15x17
+ * supersampling rasteriser from the Apparition graphics library.  The
+ * main new feature here is cheaply choosing per-scan line between
+ * doing fully analytical coverage computation for an entire row at a
+ * time vs. using a supersampling approach.
+ *
+ * David Turner's code can be found at
+ *
+ *   http://david.freetype.org/rasterizer-shootout/raster-comparison-20070813.tar.bz2
+ *
+ * In particular this file incorporates large parts of ftgrays_tor10.h
+ * from raster-comparison-20070813.tar.bz2
+ */
+/* Overview
+ *
+ * A scan converter's basic purpose to take polygon edges and convert
+ * them into an RLE compressed A8 mask.  This one works in two phases:
+ * gathering edges and generating spans.
+ *
+ * 1) As the user feeds the scan converter edges they are vertically
+ * clipped and bucketted into a _polygon_ data structure.  The edges
+ * are also snapped from the user's coordinates to the subpixel grid
+ * coordinates used during scan conversion.
+ *
+ *     user
+ *      |
+ *      | edges
+ *      V
+ *    polygon buckets
+ *
+ * 2) Generating spans works by performing a vertical sweep of pixel
+ * rows from top to bottom and maintaining an _active_list_ of edges
+ * that intersect the row.  From the active list the fill rule
+ * determines which edges are the left and right edges of the start of
+ * each span, and their contribution is then accumulated into a pixel
+ * coverage list (_cell_list_) as coverage deltas.  Once the coverage
+ * deltas of all edges are known we can form spans of constant pixel
+ * coverage by summing the deltas during a traversal of the cell list.
+ * At the end of a pixel row the cell list is sent to a coverage
+ * blitter for rendering to some target surface.
+ *
+ * The pixel coverages are computed by either supersampling the row
+ * and box filtering a mono rasterisation, or by computing the exact
+ * coverages of edges in the active list.  The supersampling method is
+ * used whenever some edge starts or stops within the row or there are
+ * edge intersections in the row.
+ *
+ *   polygon bucket for       \
+ *   current pixel row        |
+ *      |                     |
+ *      | activate new edges  |  Repeat GRID_Y times if we
+ *      V                     \  are supersampling this row,
+ *   active list              /  or just once if we're computing
+ *      |                     |  analytical coverage.
+ *      | coverage deltas     |
+ *      V                     |
+ *   pixel coverage list     /
+ *      |
+ *      V
+ *   coverage blitter
+ */
+#include "cairoint.h"
+#include "cairo-spans-private.h"
+#include "cairo-error-private.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include <setjmp.h>
+
+/*-------------------------------------------------------------------------
+ * cairo specific config
+ */
+#define I static
+
+/* Prefer cairo's status type. */
+#define GLITTER_HAVE_STATUS_T 1
+#define GLITTER_STATUS_SUCCESS CAIRO_STATUS_SUCCESS
+#define GLITTER_STATUS_NO_MEMORY CAIRO_STATUS_NO_MEMORY
+typedef cairo_status_t glitter_status_t;
+
+/* The input coordinate scale and the rasterisation grid scales. */
+#define GLITTER_INPUT_BITS CAIRO_FIXED_FRAC_BITS
+//#define GRID_X_BITS CAIRO_FIXED_FRAC_BITS
+//#define GRID_Y 15
+#define GRID_X_BITS 2
+#define GRID_Y_BITS 2
+
+/* Set glitter up to use a cairo span renderer to do the coverage
+ * blitting. */
+struct pool;
+struct cell_list;
+
+/*-------------------------------------------------------------------------
+ * glitter-paths.h
+ */
+
+/* "Input scaled" numbers are fixed precision reals with multiplier
+ * 2**GLITTER_INPUT_BITS.  Input coordinates are given to glitter as
+ * pixel scaled numbers.  These get converted to the internal grid
+ * scaled numbers as soon as possible. Internal overflow is possible
+ * if GRID_X/Y inside glitter-paths.c is larger than
+ * 1<<GLITTER_INPUT_BITS. */
+#ifndef GLITTER_INPUT_BITS
+#  define GLITTER_INPUT_BITS 8
+#endif
+#define GLITTER_INPUT_SCALE (1<<GLITTER_INPUT_BITS)
+typedef int glitter_input_scaled_t;
+
+#if !GLITTER_HAVE_STATUS_T
+typedef enum {
+    GLITTER_STATUS_SUCCESS = 0,
+    GLITTER_STATUS_NO_MEMORY
+} glitter_status_t;
+#endif
+
+#ifndef I
+# define I /*static*/
+#endif
+
+/* Opaque type for scan converting. */
+typedef struct glitter_scan_converter glitter_scan_converter_t;
+
+/* Reset a scan converter to accept polygon edges and set the clip box
+ * in pixels.  Allocates O(ymax-ymin) bytes of memory.	The clip box
+ * is set to integer pixel coordinates xmin <= x < xmax, ymin <= y <
+ * ymax. */
+I glitter_status_t
+glitter_scan_converter_reset(
+    glitter_scan_converter_t *converter,
+    int xmin, int ymin,
+    int xmax, int ymax);
+
+/* Render the polygon in the scan converter to the given A8 format
+ * image raster.  Only the pixels accessible as pixels[y*stride+x] for
+ * x,y inside the clip box are written to, where xmin <= x < xmax,
+ * ymin <= y < ymax.  The image is assumed to be clear on input.
+ *
+ * If nonzero_fill is true then the interior of the polygon is
+ * computed with the non-zero fill rule.  Otherwise the even-odd fill
+ * rule is used.
+ *
+ * The scan converter must be reset or destroyed after this call. */
+
+/*-------------------------------------------------------------------------
+ * glitter-paths.c: Implementation internal types
+ */
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+
+/* All polygon coordinates are snapped onto a subsample grid. "Grid
+ * scaled" numbers are fixed precision reals with multiplier GRID_X or
+ * GRID_Y. */
+typedef int grid_scaled_t;
+typedef int grid_scaled_x_t;
+typedef int grid_scaled_y_t;
+
+/* Default x/y scale factors.
+ *  You can either define GRID_X/Y_BITS to get a power-of-two scale
+ *  or define GRID_X/Y separately. */
+#if !defined(GRID_X) && !defined(GRID_X_BITS)
+#  define GRID_X_BITS 8
+#endif
+#if !defined(GRID_Y) && !defined(GRID_Y_BITS)
+#  define GRID_Y 15
+#endif
+
+/* Use GRID_X/Y_BITS to define GRID_X/Y if they're available. */
+#ifdef GRID_X_BITS
+#  define GRID_X (1 << GRID_X_BITS)
+#endif
+#ifdef GRID_Y_BITS
+#  define GRID_Y (1 << GRID_Y_BITS)
+#endif
+
+/* The GRID_X_TO_INT_FRAC macro splits a grid scaled coordinate into
+ * integer and fractional parts. The integer part is floored. */
+#if defined(GRID_X_TO_INT_FRAC)
+  /* do nothing */
+#elif defined(GRID_X_BITS)
+#  define GRID_X_TO_INT_FRAC(x, i, f) \
+	_GRID_TO_INT_FRAC_shift(x, i, f, GRID_X_BITS)
+#else
+#  define GRID_X_TO_INT_FRAC(x, i, f) \
+	_GRID_TO_INT_FRAC_general(x, i, f, GRID_X)
+#endif
+
+#define _GRID_TO_INT_FRAC_general(t, i, f, m) do {	\
+    (i) = (t) / (m);					\
+    (f) = (t) % (m);					\
+    if ((f) < 0) {					\
+	--(i);						\
+	(f) += (m);					\
+    }							\
+} while (0)
+
+#define _GRID_TO_INT_FRAC_shift(t, i, f, b) do {	\
+    (f) = (t) & ((1 << (b)) - 1);			\
+    (i) = (t) >> (b);					\
+} while (0)
+
+/* A grid area is a real in [0,1] scaled by 2*GRID_X*GRID_Y.  We want
+ * to be able to represent exactly areas of subpixel trapezoids whose
+ * vertices are given in grid scaled coordinates.  The scale factor
+ * comes from needing to accurately represent the area 0.5*dx*dy of a
+ * triangle with base dx and height dy in grid scaled numbers. */
+#define GRID_XY (2*GRID_X*GRID_Y) /* Unit area on the grid. */
+
+/* GRID_AREA_TO_ALPHA(area): map [0,GRID_XY] to [0,255]. */
+#if GRID_XY == 510
+#  define GRID_AREA_TO_ALPHA(c)	  (((c)+1) >> 1)
+#elif GRID_XY == 255
+#  define  GRID_AREA_TO_ALPHA(c)  (c)
+#elif GRID_XY == 64
+#  define  GRID_AREA_TO_ALPHA(c)  (((c) << 2) | -(((c) & 0x40) >> 6))
+#elif GRID_XY == 32
+#  define  GRID_AREA_TO_ALPHA(c)  (((c) << 3) | -(((c) & 0x20) >> 5))
+#elif GRID_XY == 128
+#  define  GRID_AREA_TO_ALPHA(c)  ((((c) << 1) | -((c) >> 7)) & 255)
+#elif GRID_XY == 256
+#  define  GRID_AREA_TO_ALPHA(c)  (((c) | -((c) >> 8)) & 255)
+#elif GRID_XY == 15
+#  define  GRID_AREA_TO_ALPHA(c)  (((c) << 4) + (c))
+#elif GRID_XY == 2*256*15
+#  define  GRID_AREA_TO_ALPHA(c)  (((c) + ((c)<<4) + 256) >> 9)
+#else
+#  define  GRID_AREA_TO_ALPHA(c)  (((c)*255 + GRID_XY/2) / GRID_XY)
+#endif
+
+#define UNROLL3(x) x x x
+
+struct quorem {
+    int32_t quo;
+    int32_t rem;
+};
+
+/* Header for a chunk of memory in a memory pool. */
+struct _pool_chunk {
+    /* # bytes used in this chunk. */
+    size_t size;
+
+    /* # bytes total in this chunk */
+    size_t capacity;
+
+    /* Pointer to the previous chunk or %NULL if this is the sentinel
+     * chunk in the pool header. */
+    struct _pool_chunk *prev_chunk;
+
+    /* Actual data starts here.	 Well aligned for pointers. */
+};
+
+/* A memory pool.  This is supposed to be embedded on the stack or
+ * within some other structure.	 It may optionally be followed by an
+ * embedded array from which requests are fulfilled until
+ * malloc needs to be called to allocate a first real chunk. */
+struct pool {
+    /* Chunk we're allocating from. */
+    struct _pool_chunk *current;
+
+    jmp_buf *jmp;
+
+    /* Free list of previously allocated chunks.  All have >= default
+     * capacity. */
+    struct _pool_chunk *first_free;
+
+    /* The default capacity of a chunk. */
+    size_t default_capacity;
+
+    /* Header for the sentinel chunk.  Directly following the pool
+     * struct should be some space for embedded elements from which
+     * the sentinel chunk allocates from. */
+    struct _pool_chunk sentinel[1];
+};
+
+/* A polygon edge. */
+struct edge {
+    /* Next in y-bucket or active list. */
+    struct edge *next, *prev;
+
+    /* Number of subsample rows remaining to scan convert of this
+     * edge. */
+    grid_scaled_y_t height_left;
+
+    /* Original sign of the edge: +1 for downwards, -1 for upwards
+     * edges.  */
+    int dir;
+    int vertical;
+
+    /* Current x coordinate while the edge is on the active
+     * list. Initialised to the x coordinate of the top of the
+     * edge. The quotient is in grid_scaled_x_t units and the
+     * remainder is mod dy in grid_scaled_y_t units.*/
+    struct quorem x;
+
+    /* Advance of the current x when moving down a subsample line. */
+    struct quorem dxdy;
+
+    /* The clipped y of the top of the edge. */
+    grid_scaled_y_t ytop;
+
+    /* y2-y1 after orienting the edge downwards.  */
+    grid_scaled_y_t dy;
+};
+
+#define EDGE_Y_BUCKET_INDEX(y, ymin) (((y) - (ymin))/GRID_Y)
+
+/* A collection of sorted and vertically clipped edges of the polygon.
+ * Edges are moved from the polygon to an active list while scan
+ * converting. */
+struct polygon {
+    /* The vertical clip extents. */
+    grid_scaled_y_t ymin, ymax;
+
+    /* Array of edges all starting in the same bucket.	An edge is put
+     * into bucket EDGE_BUCKET_INDEX(edge->ytop, polygon->ymin) when
+     * it is added to the polygon. */
+    struct edge **y_buckets;
+    struct edge *y_buckets_embedded[64];
+
+    struct {
+	struct pool base[1];
+	struct edge embedded[32];
+    } edge_pool;
+};
+
+/* A cell records the effect on pixel coverage of polygon edges
+ * passing through a pixel.  It contains two accumulators of pixel
+ * coverage.
+ *
+ * Consider the effects of a polygon edge on the coverage of a pixel
+ * it intersects and that of the following one.  The coverage of the
+ * following pixel is the height of the edge multiplied by the width
+ * of the pixel, and the coverage of the pixel itself is the area of
+ * the trapezoid formed by the edge and the right side of the pixel.
+ *
+ * +-----------------------+-----------------------+
+ * |                       |                       |
+ * |                       |                       |
+ * |_______________________|_______________________|
+ * |   \...................|.......................|\
+ * |    \..................|.......................| |
+ * |     \.................|.......................| |
+ * |      \....covered.....|.......................| |
+ * |       \....area.......|.......................| } covered height
+ * |        \..............|.......................| |
+ * |uncovered\.............|.......................| |
+ * |  area    \............|.......................| |
+ * |___________\...........|.......................|/
+ * |                       |                       |
+ * |                       |                       |
+ * |                       |                       |
+ * +-----------------------+-----------------------+
+ *
+ * Since the coverage of the following pixel will always be a multiple
+ * of the width of the pixel, we can store the height of the covered
+ * area instead.  The coverage of the pixel itself is the total
+ * coverage minus the area of the uncovered area to the left of the
+ * edge.  As it's faster to compute the uncovered area we only store
+ * that and subtract it from the total coverage later when forming
+ * spans to blit.
+ *
+ * The heights and areas are signed, with left edges of the polygon
+ * having positive sign and right edges having negative sign.  When
+ * two edges intersect they swap their left/rightness so their
+ * contribution above and below the intersection point must be
+ * computed separately. */
+struct cell {
+    struct cell		*next;
+    int			 x;
+    int16_t		 uncovered_area;
+    int16_t		 covered_height;
+};
+
+/* A cell list represents the scan line sparsely as cells ordered by
+ * ascending x.  It is geared towards scanning the cells in order
+ * using an internal cursor. */
+struct cell_list {
+    /* Sentinel nodes */
+    struct cell head, tail;
+
+    /* Cursor state for iterating through the cell list. */
+    struct cell *cursor, *rewind;
+
+    /* Cells in the cell list are owned by the cell list and are
+     * allocated from this pool.  */
+    struct {
+	struct pool base[1];
+	struct cell embedded[32];
+    } cell_pool;
+};
+
+struct cell_pair {
+    struct cell *cell1;
+    struct cell *cell2;
+};
+
+/* The active list contains edges in the current scan line ordered by
+ * the x-coordinate of the intercept of the edge and the scan line. */
+struct active_list {
+    /* Leftmost edge on the current scan line. */
+    struct edge head, tail;
+
+    /* A lower bound on the height of the active edges is used to
+     * estimate how soon some active edge ends.	 We can't advance the
+     * scan conversion by a full pixel row if an edge ends somewhere
+     * within it. */
+    grid_scaled_y_t min_height;
+    int is_vertical;
+};
+
+struct glitter_scan_converter {
+    struct polygon	polygon[1];
+    struct active_list	active[1];
+    struct cell_list	coverages[1];
+
+    cairo_half_open_span_t *spans;
+    cairo_half_open_span_t spans_embedded[64];
+
+    /* Clip box. */
+    grid_scaled_x_t xmin, xmax;
+    grid_scaled_y_t ymin, ymax;
+};
+
+/* Compute the floored division a/b. Assumes / and % perform symmetric
+ * division. */
+inline static struct quorem
+floored_divrem(int a, int b)
+{
+    struct quorem qr;
+    qr.quo = a/b;
+    qr.rem = a%b;
+    if ((a^b)<0 && qr.rem) {
+	qr.quo -= 1;
+	qr.rem += b;
+    }
+    return qr;
+}
+
+/* Compute the floored division (x*a)/b. Assumes / and % perform symmetric
+ * division. */
+static struct quorem
+floored_muldivrem(int x, int a, int b)
+{
+    struct quorem qr;
+    long long xa = (long long)x*a;
+    qr.quo = xa/b;
+    qr.rem = xa%b;
+    if ((xa>=0) != (b>=0) && qr.rem) {
+	qr.quo -= 1;
+	qr.rem += b;
+    }
+    return qr;
+}
+
+static struct _pool_chunk *
+_pool_chunk_init(
+    struct _pool_chunk *p,
+    struct _pool_chunk *prev_chunk,
+    size_t capacity)
+{
+    p->prev_chunk = prev_chunk;
+    p->size = 0;
+    p->capacity = capacity;
+    return p;
+}
+
+static struct _pool_chunk *
+_pool_chunk_create(struct pool *pool, size_t size)
+{
+    struct _pool_chunk *p;
+
+    p = _cairo_malloc (size + sizeof(struct _pool_chunk));
+    if (unlikely (NULL == p))
+	longjmp (*pool->jmp, _cairo_error (CAIRO_STATUS_NO_MEMORY));
+
+    return _pool_chunk_init(p, pool->current, size);
+}
+
+static void
+pool_init(struct pool *pool,
+	  jmp_buf *jmp,
+	  size_t default_capacity,
+	  size_t embedded_capacity)
+{
+    pool->jmp = jmp;
+    pool->current = pool->sentinel;
+    pool->first_free = NULL;
+    pool->default_capacity = default_capacity;
+    _pool_chunk_init(pool->sentinel, NULL, embedded_capacity);
+}
+
+static void
+pool_fini(struct pool *pool)
+{
+    struct _pool_chunk *p = pool->current;
+    do {
+	while (NULL != p) {
+	    struct _pool_chunk *prev = p->prev_chunk;
+	    if (p != pool->sentinel)
+		free(p);
+	    p = prev;
+	}
+	p = pool->first_free;
+	pool->first_free = NULL;
+    } while (NULL != p);
+}
+
+/* Satisfy an allocation by first allocating a new large enough chunk
+ * and adding it to the head of the pool's chunk list. This function
+ * is called as a fallback if pool_alloc() couldn't do a quick
+ * allocation from the current chunk in the pool. */
+static void *
+_pool_alloc_from_new_chunk(
+    struct pool *pool,
+    size_t size)
+{
+    struct _pool_chunk *chunk;
+    void *obj;
+    size_t capacity;
+
+    /* If the allocation is smaller than the default chunk size then
+     * try getting a chunk off the free list.  Force alloc of a new
+     * chunk for large requests. */
+    capacity = size;
+    chunk = NULL;
+    if (size < pool->default_capacity) {
+	capacity = pool->default_capacity;
+	chunk = pool->first_free;
+	if (chunk) {
+	    pool->first_free = chunk->prev_chunk;
+	    _pool_chunk_init(chunk, pool->current, chunk->capacity);
+	}
+    }
+
+    if (NULL == chunk)
+	chunk = _pool_chunk_create (pool, capacity);
+    pool->current = chunk;
+
+    obj = ((unsigned char*)chunk + sizeof(*chunk) + chunk->size);
+    chunk->size += size;
+    return obj;
+}
+
+/* Allocate size bytes from the pool.  The first allocated address
+ * returned from a pool is aligned to sizeof(void*).  Subsequent
+ * addresses will maintain alignment as long as multiples of void* are
+ * allocated.  Returns the address of a new memory area or %NULL on
+ * allocation failures.	 The pool retains ownership of the returned
+ * memory. */
+inline static void *
+pool_alloc (struct pool *pool, size_t size)
+{
+    struct _pool_chunk *chunk = pool->current;
+
+    if (size <= chunk->capacity - chunk->size) {
+	void *obj = ((unsigned char*)chunk + sizeof(*chunk) + chunk->size);
+	chunk->size += size;
+	return obj;
+    } else {
+	return _pool_alloc_from_new_chunk(pool, size);
+    }
+}
+
+/* Relinquish all pool_alloced memory back to the pool. */
+static void
+pool_reset (struct pool *pool)
+{
+    /* Transfer all used chunks to the chunk free list. */
+    struct _pool_chunk *chunk = pool->current;
+    if (chunk != pool->sentinel) {
+	while (chunk->prev_chunk != pool->sentinel) {
+	    chunk = chunk->prev_chunk;
+	}
+	chunk->prev_chunk = pool->first_free;
+	pool->first_free = pool->current;
+    }
+    /* Reset the sentinel as the current chunk. */
+    pool->current = pool->sentinel;
+    pool->sentinel->size = 0;
+}
+
+/* Rewinds the cell list's cursor to the beginning.  After rewinding
+ * we're good to cell_list_find() the cell any x coordinate. */
+inline static void
+cell_list_rewind (struct cell_list *cells)
+{
+    cells->cursor = &cells->head;
+}
+
+inline static void
+cell_list_maybe_rewind (struct cell_list *cells, int x)
+{
+    if (x < cells->cursor->x) {
+	cells->cursor = cells->rewind;
+	if (x < cells->cursor->x)
+	    cells->cursor = &cells->head;
+    }
+}
+
+inline static void
+cell_list_set_rewind (struct cell_list *cells)
+{
+    cells->rewind = cells->cursor;
+}
+
+static void
+cell_list_init(struct cell_list *cells, jmp_buf *jmp)
+{
+    pool_init(cells->cell_pool.base, jmp,
+	      256*sizeof(struct cell),
+	      sizeof(cells->cell_pool.embedded));
+    cells->tail.next = NULL;
+    cells->tail.x = INT_MAX;
+    cells->head.x = INT_MIN;
+    cells->head.next = &cells->tail;
+    cell_list_rewind (cells);
+}
+
+static void
+cell_list_fini(struct cell_list *cells)
+{
+    pool_fini (cells->cell_pool.base);
+}
+
+/* Empty the cell list.  This is called at the start of every pixel
+ * row. */
+inline static void
+cell_list_reset (struct cell_list *cells)
+{
+    cell_list_rewind (cells);
+    cells->head.next = &cells->tail;
+    pool_reset (cells->cell_pool.base);
+}
+
+inline static struct cell *
+cell_list_alloc (struct cell_list *cells,
+		 struct cell *tail,
+		 int x)
+{
+    struct cell *cell;
+
+    cell = pool_alloc (cells->cell_pool.base, sizeof (struct cell));
+    cell->next = tail->next;
+    tail->next = cell;
+    cell->x = x;
+    *(uint32_t *)&cell->uncovered_area = 0;
+
+    return cell;
+}
+
+/* Find a cell at the given x-coordinate.  Returns %NULL if a new cell
+ * needed to be allocated but couldn't be.  Cells must be found with
+ * non-decreasing x-coordinate until the cell list is rewound using
+ * cell_list_rewind(). Ownership of the returned cell is retained by
+ * the cell list. */
+inline static struct cell *
+cell_list_find (struct cell_list *cells, int x)
+{
+    struct cell *tail = cells->cursor;
+
+    if (tail->x == x)
+	return tail;
+
+    while (1) {
+	UNROLL3({
+		if (tail->next->x > x)
+			break;
+		tail = tail->next;
+	});
+    }
+
+    if (tail->x != x)
+	tail = cell_list_alloc (cells, tail, x);
+    return cells->cursor = tail;
+
+}
+
+/* Find two cells at x1 and x2.	 This is exactly equivalent
+ * to
+ *
+ *   pair.cell1 = cell_list_find(cells, x1);
+ *   pair.cell2 = cell_list_find(cells, x2);
+ *
+ * except with less function call overhead. */
+inline static struct cell_pair
+cell_list_find_pair(struct cell_list *cells, int x1, int x2)
+{
+    struct cell_pair pair;
+
+    pair.cell1 = cells->cursor;
+    while (1) {
+	UNROLL3({
+		if (pair.cell1->next->x > x1)
+			break;
+		pair.cell1 = pair.cell1->next;
+	});
+    }
+    if (pair.cell1->x != x1)
+	pair.cell1 = cell_list_alloc (cells, pair.cell1, x1);
+
+    pair.cell2 = pair.cell1;
+    while (1) {
+	UNROLL3({
+		if (pair.cell2->next->x > x2)
+			break;
+		pair.cell2 = pair.cell2->next;
+	});
+    }
+    if (pair.cell2->x != x2)
+	pair.cell2 = cell_list_alloc (cells, pair.cell2, x2);
+
+    cells->cursor = pair.cell2;
+    return pair;
+}
+
+/* Add a subpixel span covering [x1, x2) to the coverage cells. */
+inline static void
+cell_list_add_subspan(struct cell_list *cells,
+		      grid_scaled_x_t x1,
+		      grid_scaled_x_t x2)
+{
+    int ix1, fx1;
+    int ix2, fx2;
+
+    if (x1 == x2)
+	return;
+
+    GRID_X_TO_INT_FRAC(x1, ix1, fx1);
+    GRID_X_TO_INT_FRAC(x2, ix2, fx2);
+
+    if (ix1 != ix2) {
+	struct cell_pair p;
+	p = cell_list_find_pair(cells, ix1, ix2);
+	p.cell1->uncovered_area += 2*fx1;
+	++p.cell1->covered_height;
+	p.cell2->uncovered_area -= 2*fx2;
+	--p.cell2->covered_height;
+    } else {
+	struct cell *cell = cell_list_find(cells, ix1);
+	cell->uncovered_area += 2*(fx1-fx2);
+    }
+}
+
+/* Adds the analytical coverage of an edge crossing the current pixel
+ * row to the coverage cells and advances the edge's x position to the
+ * following row.
+ *
+ * This function is only called when we know that during this pixel row:
+ *
+ * 1) The relative order of all edges on the active list doesn't
+ * change.  In particular, no edges intersect within this row to pixel
+ * precision.
+ *
+ * 2) No new edges start in this row.
+ *
+ * 3) No existing edges end mid-row.
+ *
+ * This function depends on being called with all edges from the
+ * active list in the order they appear on the list (i.e. with
+ * non-decreasing x-coordinate.)  */
+static void
+cell_list_render_edge(struct cell_list *cells,
+		      struct edge *edge,
+		      int sign)
+{
+    grid_scaled_x_t fx;
+    struct cell *cell;
+    int ix;
+
+    GRID_X_TO_INT_FRAC(edge->x.quo, ix, fx);
+
+    /* We always know that ix1 is >= the cell list cursor in this
+     * case due to the no-intersections precondition.  */
+    cell = cell_list_find(cells, ix);
+    cell->covered_height += sign*GRID_Y;
+    cell->uncovered_area += sign*2*fx*GRID_Y;
+}
+
+static void
+polygon_init (struct polygon *polygon, jmp_buf *jmp)
+{
+    polygon->ymin = polygon->ymax = 0;
+    polygon->y_buckets = polygon->y_buckets_embedded;
+    pool_init (polygon->edge_pool.base, jmp,
+	       8192 - sizeof (struct _pool_chunk),
+	       sizeof (polygon->edge_pool.embedded));
+}
+
+static void
+polygon_fini (struct polygon *polygon)
+{
+    if (polygon->y_buckets != polygon->y_buckets_embedded)
+	free (polygon->y_buckets);
+
+    pool_fini (polygon->edge_pool.base);
+}
+
+/* Empties the polygon of all edges. The polygon is then prepared to
+ * receive new edges and clip them to the vertical range
+ * [ymin,ymax). */
+static glitter_status_t
+polygon_reset (struct polygon *polygon,
+	       grid_scaled_y_t ymin,
+	       grid_scaled_y_t ymax)
+{
+    unsigned h = ymax - ymin;
+    unsigned num_buckets = EDGE_Y_BUCKET_INDEX(ymax + GRID_Y-1, ymin);
+
+    pool_reset(polygon->edge_pool.base);
+
+    if (unlikely (h > 0x7FFFFFFFU - GRID_Y))
+	goto bail_no_mem; /* even if you could, you wouldn't want to. */
+
+    if (polygon->y_buckets != polygon->y_buckets_embedded)
+	free (polygon->y_buckets);
+
+    polygon->y_buckets =  polygon->y_buckets_embedded;
+    if (num_buckets > ARRAY_LENGTH (polygon->y_buckets_embedded)) {
+	polygon->y_buckets = _cairo_malloc_ab (num_buckets,
+					       sizeof (struct edge *));
+	if (unlikely (NULL == polygon->y_buckets))
+	    goto bail_no_mem;
+    }
+    memset (polygon->y_buckets, 0, num_buckets * sizeof (struct edge *));
+
+    polygon->ymin = ymin;
+    polygon->ymax = ymax;
+    return GLITTER_STATUS_SUCCESS;
+
+bail_no_mem:
+    polygon->ymin = 0;
+    polygon->ymax = 0;
+    return GLITTER_STATUS_NO_MEMORY;
+}
+
+static void
+_polygon_insert_edge_into_its_y_bucket(struct polygon *polygon,
+				       struct edge *e)
+{
+    unsigned ix = EDGE_Y_BUCKET_INDEX(e->ytop, polygon->ymin);
+    struct edge **ptail = &polygon->y_buckets[ix];
+    e->next = *ptail;
+    *ptail = e;
+}
+
+inline static void
+polygon_add_edge (struct polygon *polygon,
+		  const cairo_edge_t *edge)
+{
+    struct edge *e;
+    grid_scaled_x_t dx;
+    grid_scaled_y_t dy;
+    grid_scaled_y_t ytop, ybot;
+    grid_scaled_y_t ymin = polygon->ymin;
+    grid_scaled_y_t ymax = polygon->ymax;
+
+    if (unlikely (edge->top >= ymax || edge->bottom <= ymin))
+	return;
+
+    e = pool_alloc (polygon->edge_pool.base, sizeof (struct edge));
+
+    dx = edge->line.p2.x - edge->line.p1.x;
+    dy = edge->line.p2.y - edge->line.p1.y;
+    e->dy = dy;
+    e->dir = edge->dir;
+
+    ytop = edge->top >= ymin ? edge->top : ymin;
+    ybot = edge->bottom <= ymax ? edge->bottom : ymax;
+    e->ytop = ytop;
+    e->height_left = ybot - ytop;
+
+    if (dx == 0) {
+	e->vertical = TRUE;
+	e->x.quo = edge->line.p1.x;
+	e->x.rem = 0;
+	e->dxdy.quo = 0;
+	e->dxdy.rem = 0;
+    } else {
+	e->vertical = FALSE;
+	e->dxdy = floored_divrem (dx, dy);
+	if (ytop == edge->line.p1.y) {
+	    e->x.quo = edge->line.p1.x;
+	    e->x.rem = 0;
+	} else {
+	    e->x = floored_muldivrem (ytop - edge->line.p1.y, dx, dy);
+	    e->x.quo += edge->line.p1.x;
+	}
+    }
+
+    _polygon_insert_edge_into_its_y_bucket (polygon, e);
+
+    e->x.rem -= dy;		/* Bias the remainder for faster
+				 * edge advancement. */
+}
+
+static void
+active_list_reset (struct active_list *active)
+{
+    active->head.vertical = 1;
+    active->head.height_left = INT_MAX;
+    active->head.x.quo = INT_MIN;
+    active->head.prev = NULL;
+    active->head.next = &active->tail;
+    active->tail.prev = &active->head;
+    active->tail.next = NULL;
+    active->tail.x.quo = INT_MAX;
+    active->tail.height_left = INT_MAX;
+    active->tail.vertical = 1;
+    active->min_height = 0;
+    active->is_vertical = 1;
+}
+
+static void
+active_list_init(struct active_list *active)
+{
+    active_list_reset(active);
+}
+
+/*
+ * Merge two sorted edge lists.
+ * Input:
+ *  - head_a: The head of the first list.
+ *  - head_b: The head of the second list; head_b cannot be NULL.
+ * Output:
+ * Returns the head of the merged list.
+ *
+ * Implementation notes:
+ * To make it fast (in particular, to reduce to an insertion sort whenever
+ * one of the two input lists only has a single element) we iterate through
+ * a list until its head becomes greater than the head of the other list,
+ * then we switch their roles. As soon as one of the two lists is empty, we
+ * just attach the other one to the current list and exit.
+ * Writes to memory are only needed to "switch" lists (as it also requires
+ * attaching to the output list the list which we will be iterating next) and
+ * to attach the last non-empty list.
+ */
+static struct edge *
+merge_sorted_edges (struct edge *head_a, struct edge *head_b)
+{
+    struct edge *head, **next, *prev;
+    int32_t x;
+
+    prev = head_a->prev;
+    next = &head;
+    if (head_a->x.quo <= head_b->x.quo) {
+	head = head_a;
+    } else {
+	head = head_b;
+	head_b->prev = prev;
+	goto start_with_b;
+    }
+
+    do {
+	x = head_b->x.quo;
+	while (head_a != NULL && head_a->x.quo <= x) {
+	    prev = head_a;
+	    next = &head_a->next;
+	    head_a = head_a->next;
+	}
+
+	head_b->prev = prev;
+	*next = head_b;
+	if (head_a == NULL)
+	    return head;
+
+start_with_b:
+	x = head_a->x.quo;
+	while (head_b != NULL && head_b->x.quo <= x) {
+	    prev = head_b;
+	    next = &head_b->next;
+	    head_b = head_b->next;
+	}
+
+	head_a->prev = prev;
+	*next = head_a;
+	if (head_b == NULL)
+	    return head;
+    } while (1);
+}
+
+/*
+ * Sort (part of) a list.
+ * Input:
+ *  - list: The list to be sorted; list cannot be NULL.
+ *  - limit: Recursion limit.
+ * Output:
+ *  - head_out: The head of the sorted list containing the first 2^(level+1) elements of the
+ *              input list; if the input list has fewer elements, head_out be a sorted list
+ *              containing all the elements of the input list.
+ * Returns the head of the list of unprocessed elements (NULL if the sorted list contains
+ * all the elements of the input list).
+ *
+ * Implementation notes:
+ * Special case single element list, unroll/inline the sorting of the first two elements.
+ * Some tail recursion is used since we iterate on the bottom-up solution of the problem
+ * (we start with a small sorted list and keep merging other lists of the same size to it).
+ */
+static struct edge *
+sort_edges (struct edge *list,
+	    unsigned int level,
+	    struct edge **head_out)
+{
+    struct edge *head_other, *remaining;
+    unsigned int i;
+
+    head_other = list->next;
+
+    if (head_other == NULL) {
+	*head_out = list;
+	return NULL;
+    }
+
+    remaining = head_other->next;
+    if (list->x.quo <= head_other->x.quo) {
+	*head_out = list;
+	head_other->next = NULL;
+    } else {
+	*head_out = head_other;
+	head_other->prev = list->prev;
+	head_other->next = list;
+	list->prev = head_other;
+	list->next = NULL;
+    }
+
+    for (i = 0; i < level && remaining; i++) {
+	remaining = sort_edges (remaining, i, &head_other);
+	*head_out = merge_sorted_edges (*head_out, head_other);
+    }
+
+    return remaining;
+}
+
+static struct edge *
+merge_unsorted_edges (struct edge *head, struct edge *unsorted)
+{
+    sort_edges (unsorted, UINT_MAX, &unsorted);
+    return merge_sorted_edges (head, unsorted);
+}
+
+/* Test if the edges on the active list can be safely advanced by a
+ * full row without intersections or any edges ending. */
+inline static int
+can_do_full_row (struct active_list *active)
+{
+    const struct edge *e;
+
+    /* Recomputes the minimum height of all edges on the active
+     * list if we have been dropping edges. */
+    if (active->min_height <= 0) {
+	int min_height = INT_MAX;
+	int is_vertical = 1;
+
+	e = active->head.next;
+	while (NULL != e) {
+	    if (e->height_left < min_height)
+		min_height = e->height_left;
+	    is_vertical &= e->vertical;
+	    e = e->next;
+	}
+
+	active->is_vertical = is_vertical;
+	active->min_height = min_height;
+    }
+
+    if (active->min_height < GRID_Y)
+	return 0;
+
+    return active->is_vertical;
+}
+
+/* Merges edges on the given subpixel row from the polygon to the
+ * active_list. */
+inline static void
+active_list_merge_edges_from_bucket(struct active_list *active,
+				    struct edge *edges)
+{
+    active->head.next = merge_unsorted_edges (active->head.next, edges);
+}
+
+inline static void
+polygon_fill_buckets (struct active_list *active,
+		      struct edge *edge,
+		      int y,
+		      struct edge **buckets)
+{
+    grid_scaled_y_t min_height = active->min_height;
+    int is_vertical = active->is_vertical;
+
+    while (edge) {
+	struct edge *next = edge->next;
+	int suby = edge->ytop - y;
+	if (buckets[suby])
+	    buckets[suby]->prev = edge;
+	edge->next = buckets[suby];
+	edge->prev = NULL;
+	buckets[suby] = edge;
+	if (edge->height_left < min_height)
+	    min_height = edge->height_left;
+	is_vertical &= edge->vertical;
+	edge = next;
+    }
+
+    active->is_vertical = is_vertical;
+    active->min_height = min_height;
+}
+
+inline static void
+sub_row (struct active_list *active,
+	 struct cell_list *coverages,
+	 unsigned int mask)
+{
+    struct edge *edge = active->head.next;
+    int xstart = INT_MIN, prev_x = INT_MIN;
+    int winding = 0;
+
+    cell_list_rewind (coverages);
+
+    while (&active->tail != edge) {
+	struct edge *next = edge->next;
+	int xend = edge->x.quo;
+
+	if (--edge->height_left) {
+	    edge->x.quo += edge->dxdy.quo;
+	    edge->x.rem += edge->dxdy.rem;
+	    if (edge->x.rem >= 0) {
+		++edge->x.quo;
+		edge->x.rem -= edge->dy;
+	    }
+
+	    if (edge->x.quo < prev_x) {
+		struct edge *pos = edge->prev;
+		pos->next = next;
+		next->prev = pos;
+		do {
+		    pos = pos->prev;
+		} while (edge->x.quo < pos->x.quo);
+		pos->next->prev = edge;
+		edge->next = pos->next;
+		edge->prev = pos;
+		pos->next = edge;
+	    } else
+		prev_x = edge->x.quo;
+	} else {
+	    edge->prev->next = next;
+	    next->prev = edge->prev;
+	}
+
+	winding += edge->dir;
+	if ((winding & mask) == 0) {
+	    if (next->x.quo != xend) {
+		cell_list_add_subspan (coverages, xstart, xend);
+		xstart = INT_MIN;
+	    }
+	} else if (xstart == INT_MIN)
+	    xstart = xend;
+
+	edge = next;
+    }
+}
+
+inline static void dec (struct edge *e, int h)
+{
+    e->height_left -= h;
+    if (e->height_left == 0) {
+	e->prev->next = e->next;
+	e->next->prev = e->prev;
+    }
+}
+
+static void
+full_row (struct active_list *active,
+	  struct cell_list *coverages,
+	  unsigned int mask)
+{
+    struct edge *left = active->head.next;
+
+    while (&active->tail != left) {
+	struct edge *right;
+	int winding;
+
+	dec (left, GRID_Y);
+
+	winding = left->dir;
+	right = left->next;
+	do {
+	    dec (right, GRID_Y);
+
+	    winding += right->dir;
+	    if ((winding & mask) == 0 && right->next->x.quo != right->x.quo)
+		break;
+
+	    right = right->next;
+	} while (1);
+
+	cell_list_set_rewind (coverages);
+	cell_list_render_edge (coverages, left, +1);
+	cell_list_render_edge (coverages, right, -1);
+
+	left = right->next;
+    }
+}
+
+static void
+_glitter_scan_converter_init(glitter_scan_converter_t *converter, jmp_buf *jmp)
+{
+    polygon_init(converter->polygon, jmp);
+    active_list_init(converter->active);
+    cell_list_init(converter->coverages, jmp);
+    converter->xmin=0;
+    converter->ymin=0;
+    converter->xmax=0;
+    converter->ymax=0;
+}
+
+static void
+_glitter_scan_converter_fini(glitter_scan_converter_t *self)
+{
+    if (self->spans != self->spans_embedded)
+	free (self->spans);
+
+    polygon_fini(self->polygon);
+    cell_list_fini(self->coverages);
+
+    self->xmin=0;
+    self->ymin=0;
+    self->xmax=0;
+    self->ymax=0;
+}
+
+static grid_scaled_t
+int_to_grid_scaled(int i, int scale)
+{
+    /* Clamp to max/min representable scaled number. */
+    if (i >= 0) {
+	if (i >= INT_MAX/scale)
+	    i = INT_MAX/scale;
+    }
+    else {
+	if (i <= INT_MIN/scale)
+	    i = INT_MIN/scale;
+    }
+    return i*scale;
+}
+
+#define int_to_grid_scaled_x(x) int_to_grid_scaled((x), GRID_X)
+#define int_to_grid_scaled_y(x) int_to_grid_scaled((x), GRID_Y)
+
+I glitter_status_t
+glitter_scan_converter_reset(
+			     glitter_scan_converter_t *converter,
+			     int xmin, int ymin,
+			     int xmax, int ymax)
+{
+    glitter_status_t status;
+
+    converter->xmin = 0; converter->xmax = 0;
+    converter->ymin = 0; converter->ymax = 0;
+
+    if (xmax - xmin > ARRAY_LENGTH(converter->spans_embedded)) {
+	converter->spans = _cairo_malloc_ab (xmax - xmin,
+					     sizeof (cairo_half_open_span_t));
+	if (unlikely (converter->spans == NULL))
+	    return _cairo_error (CAIRO_STATUS_NO_MEMORY);
+    } else
+	converter->spans = converter->spans_embedded;
+
+    xmin = int_to_grid_scaled_x(xmin);
+    ymin = int_to_grid_scaled_y(ymin);
+    xmax = int_to_grid_scaled_x(xmax);
+    ymax = int_to_grid_scaled_y(ymax);
+
+    active_list_reset(converter->active);
+    cell_list_reset(converter->coverages);
+    status = polygon_reset(converter->polygon, ymin, ymax);
+    if (status)
+	return status;
+
+    converter->xmin = xmin;
+    converter->xmax = xmax;
+    converter->ymin = ymin;
+    converter->ymax = ymax;
+    return GLITTER_STATUS_SUCCESS;
+}
+
+/* INPUT_TO_GRID_X/Y (in_coord, out_grid_scaled, grid_scale)
+ *   These macros convert an input coordinate in the client's
+ *   device space to the rasterisation grid.
+ */
+/* Gah.. this bit of ugly defines INPUT_TO_GRID_X/Y so as to use
+ * shifts if possible, and something saneish if not.
+ */
+#if !defined(INPUT_TO_GRID_Y) && defined(GRID_Y_BITS) && GRID_Y_BITS <= GLITTER_INPUT_BITS
+#  define INPUT_TO_GRID_Y(in, out) (out) = (in) >> (GLITTER_INPUT_BITS - GRID_Y_BITS)
+#else
+#  define INPUT_TO_GRID_Y(in, out) INPUT_TO_GRID_general(in, out, GRID_Y)
+#endif
+
+#if !defined(INPUT_TO_GRID_X) && defined(GRID_X_BITS) && GRID_X_BITS <= GLITTER_INPUT_BITS
+#  define INPUT_TO_GRID_X(in, out) (out) = (in) >> (GLITTER_INPUT_BITS - GRID_X_BITS)
+#else
+#  define INPUT_TO_GRID_X(in, out) INPUT_TO_GRID_general(in, out, GRID_X)
+#endif
+
+#define INPUT_TO_GRID_general(in, out, grid_scale) do {		\
+    long long tmp__ = (long long)(grid_scale) * (in);	\
+    tmp__ >>= GLITTER_INPUT_BITS;				\
+    (out) = tmp__;						\
+} while (0)
+
+/* Add a new polygon edge from pixel (x1,y1) to (x2,y2) to the scan
+ * converter.  The coordinates represent pixel positions scaled by
+ * 2**GLITTER_PIXEL_BITS.  If this function fails then the scan
+ * converter should be reset or destroyed.  Dir must be +1 or -1,
+ * with the latter reversing the orientation of the edge. */
+I void
+glitter_scan_converter_add_edge (glitter_scan_converter_t *converter,
+				 const cairo_edge_t *edge)
+{
+    cairo_edge_t e;
+
+    INPUT_TO_GRID_Y (edge->top, e.top);
+    INPUT_TO_GRID_Y (edge->bottom, e.bottom);
+    if (e.top >= e.bottom)
+	return;
+
+    /* XXX: possible overflows if GRID_X/Y > 2**GLITTER_INPUT_BITS */
+    INPUT_TO_GRID_Y (edge->line.p1.y, e.line.p1.y);
+    INPUT_TO_GRID_Y (edge->line.p2.y, e.line.p2.y);
+    if (e.line.p1.y == e.line.p2.y)
+	e.line.p2.y++; /* Fudge to prevent div-by-zero */
+
+    INPUT_TO_GRID_X (edge->line.p1.x, e.line.p1.x);
+    INPUT_TO_GRID_X (edge->line.p2.x, e.line.p2.x);
+
+    e.dir = edge->dir;
+
+    polygon_add_edge (converter->polygon, &e);
+}
+
+static void
+step_edges (struct active_list *active, int count)
+{
+    struct edge *edge;
+
+    count *= GRID_Y;
+    for (edge = active->head.next; edge != &active->tail; edge = edge->next) {
+	edge->height_left -= count;
+	if (! edge->height_left) {
+	    edge->prev->next = edge->next;
+	    edge->next->prev = edge->prev;
+	}
+    }
+}
+
+static glitter_status_t
+blit_a8 (struct cell_list *cells,
+	 cairo_span_renderer_t *renderer,
+	 cairo_half_open_span_t *spans,
+	 int y, int height,
+	 int xmin, int xmax)
+{
+    struct cell *cell = cells->head.next;
+    int prev_x = xmin, last_x = -1;
+    int16_t cover = 0, last_cover = 0;
+    unsigned num_spans;
+
+    if (cell == &cells->tail)
+	return CAIRO_STATUS_SUCCESS;
+
+    /* Skip cells to the left of the clip region. */
+    while (cell->x < xmin) {
+	cover += cell->covered_height;
+	cell = cell->next;
+    }
+    cover *= GRID_X*2;
+
+    /* Form the spans from the coverages and areas. */
+    num_spans = 0;
+    for (; cell->x < xmax; cell = cell->next) {
+	int x = cell->x;
+	int16_t area;
+
+	if (x > prev_x && cover != last_cover) {
+	    spans[num_spans].x = prev_x;
+	    spans[num_spans].coverage = GRID_AREA_TO_ALPHA (cover);
+	    last_cover = cover;
+	    last_x = prev_x;
+	    ++num_spans;
+	}
+
+	cover += cell->covered_height*GRID_X*2;
+	area = cover - cell->uncovered_area;
+
+	if (area != last_cover) {
+	    spans[num_spans].x = x;
+	    spans[num_spans].coverage = GRID_AREA_TO_ALPHA (area);
+	    last_cover = area;
+	    last_x = x;
+	    ++num_spans;
+	}
+
+	prev_x = x+1;
+    }
+
+    if (prev_x <= xmax && cover != last_cover) {
+	spans[num_spans].x = prev_x;
+	spans[num_spans].coverage = GRID_AREA_TO_ALPHA (cover);
+	last_cover = cover;
+	last_x = prev_x;
+	++num_spans;
+    }
+
+    if (last_x < xmax && last_cover) {
+	spans[num_spans].x = xmax;
+	spans[num_spans].coverage = 0;
+	++num_spans;
+    }
+
+    /* Dump them into the renderer. */
+    return renderer->render_rows (renderer, y, height, spans, num_spans);
+}
+
+#define GRID_AREA_TO_A1(A)  ((GRID_AREA_TO_ALPHA (A) > 127) ? 255 : 0)
+static glitter_status_t
+blit_a1 (struct cell_list *cells,
+	 cairo_span_renderer_t *renderer,
+	 cairo_half_open_span_t *spans,
+	 int y, int height,
+	 int xmin, int xmax)
+{
+    struct cell *cell = cells->head.next;
+    int prev_x = xmin, last_x = -1;
+    int16_t cover = 0;
+    uint8_t coverage, last_cover = 0;
+    unsigned num_spans;
+
+    if (cell == &cells->tail)
+	return CAIRO_STATUS_SUCCESS;
+
+    /* Skip cells to the left of the clip region. */
+    while (cell->x < xmin) {
+	cover += cell->covered_height;
+	cell = cell->next;
+    }
+    cover *= GRID_X*2;
+
+    /* Form the spans from the coverages and areas. */
+    num_spans = 0;
+    for (; cell->x < xmax; cell = cell->next) {
+	int x = cell->x;
+	int16_t area;
+
+	coverage = GRID_AREA_TO_A1 (cover);
+	if (x > prev_x && coverage != last_cover) {
+	    last_x = spans[num_spans].x = prev_x;
+	    last_cover = spans[num_spans].coverage = coverage;
+	    ++num_spans;
+	}
+
+	cover += cell->covered_height*GRID_X*2;
+	area = cover - cell->uncovered_area;
+
+	coverage = GRID_AREA_TO_A1 (area);
+	if (coverage != last_cover) {
+	    last_x = spans[num_spans].x = x;
+	    last_cover = spans[num_spans].coverage = coverage;
+	    ++num_spans;
+	}
+
+	prev_x = x+1;
+    }
+
+    coverage = GRID_AREA_TO_A1 (cover);
+    if (prev_x <= xmax && coverage != last_cover) {
+	last_x = spans[num_spans].x = prev_x;
+	last_cover = spans[num_spans].coverage = coverage;
+	++num_spans;
+    }
+
+    if (last_x < xmax && last_cover) {
+	spans[num_spans].x = xmax;
+	spans[num_spans].coverage = 0;
+	++num_spans;
+    }
+    if (num_spans == 1)
+	return CAIRO_STATUS_SUCCESS;
+
+    /* Dump them into the renderer. */
+    return renderer->render_rows (renderer, y, height, spans, num_spans);
+}
+
+
+I void
+glitter_scan_converter_render(glitter_scan_converter_t *converter,
+			      unsigned int winding_mask,
+			      int antialias,
+			      cairo_span_renderer_t *renderer)
+{
+    int i, j;
+    int ymax_i = converter->ymax / GRID_Y;
+    int ymin_i = converter->ymin / GRID_Y;
+    int xmin_i, xmax_i;
+    int h = ymax_i - ymin_i;
+    struct polygon *polygon = converter->polygon;
+    struct cell_list *coverages = converter->coverages;
+    struct active_list *active = converter->active;
+    struct edge *buckets[GRID_Y] = { 0 };
+
+    xmin_i = converter->xmin / GRID_X;
+    xmax_i = converter->xmax / GRID_X;
+    if (xmin_i >= xmax_i)
+	return;
+
+    /* Render each pixel row. */
+    for (i = 0; i < h; i = j) {
+	int do_full_row = 0;
+
+	j = i + 1;
+
+	/* Determine if we can ignore this row or use the full pixel
+	 * stepper. */
+	if (! polygon->y_buckets[i]) {
+	    if (active->head.next == &active->tail) {
+		active->min_height = INT_MAX;
+		active->is_vertical = 1;
+		for (; j < h && ! polygon->y_buckets[j]; j++)
+		    ;
+		continue;
+	    }
+
+	    do_full_row = can_do_full_row (active);
+	}
+
+	if (do_full_row) {
+	    /* Step by a full pixel row's worth. */
+	    full_row (active, coverages, winding_mask);
+
+	    if (active->is_vertical) {
+		while (j < h &&
+		       polygon->y_buckets[j] == NULL &&
+		       active->min_height >= 2*GRID_Y)
+		{
+		    active->min_height -= GRID_Y;
+		    j++;
+		}
+		if (j != i + 1)
+		    step_edges (active, j - (i + 1));
+	    }
+	} else {
+	    int sub;
+
+	    polygon_fill_buckets (active,
+				  polygon->y_buckets[i],
+				  (i+ymin_i)*GRID_Y,
+				  buckets);
+
+	    /* Subsample this row. */
+	    for (sub = 0; sub < GRID_Y; sub++) {
+		if (buckets[sub]) {
+		    active_list_merge_edges_from_bucket (active, buckets[sub]);
+		    buckets[sub] = NULL;
+		}
+
+		sub_row (active, coverages, winding_mask);
+	    }
+	}
+
+	if (antialias)
+	    blit_a8 (coverages, renderer, converter->spans,
+		     i+ymin_i, j-i, xmin_i, xmax_i);
+	else
+	    blit_a1 (coverages, renderer, converter->spans,
+		     i+ymin_i, j-i, xmin_i, xmax_i);
+	cell_list_reset (coverages);
+
+	active->min_height -= GRID_Y;
+    }
+}
+
+struct _cairo_tor22_scan_converter {
+    cairo_scan_converter_t base;
+
+    glitter_scan_converter_t converter[1];
+    cairo_fill_rule_t fill_rule;
+    cairo_antialias_t antialias;
+
+    jmp_buf jmp;
+};
+
+typedef struct _cairo_tor22_scan_converter cairo_tor22_scan_converter_t;
+
+static void
+_cairo_tor22_scan_converter_destroy (void *converter)
+{
+    cairo_tor22_scan_converter_t *self = converter;
+    if (self == NULL) {
+	return;
+    }
+    _glitter_scan_converter_fini (self->converter);
+    free(self);
+}
+
+cairo_status_t
+_cairo_tor22_scan_converter_add_polygon (void		*converter,
+				       const cairo_polygon_t *polygon)
+{
+    cairo_tor22_scan_converter_t *self = converter;
+    int i;
+
+#if 0
+    FILE *file = fopen ("polygon.txt", "w");
+    _cairo_debug_print_polygon (file, polygon);
+    fclose (file);
+#endif
+
+    for (i = 0; i < polygon->num_edges; i++)
+	 glitter_scan_converter_add_edge (self->converter, &polygon->edges[i]);
+
+    return CAIRO_STATUS_SUCCESS;
+}
+
+static cairo_status_t
+_cairo_tor22_scan_converter_generate (void			*converter,
+				    cairo_span_renderer_t	*renderer)
+{
+    cairo_tor22_scan_converter_t *self = converter;
+    cairo_status_t status;
+
+    if ((status = setjmp (self->jmp)))
+	return _cairo_scan_converter_set_error (self, _cairo_error (status));
+
+    glitter_scan_converter_render (self->converter,
+				   self->fill_rule == CAIRO_FILL_RULE_WINDING ? ~0 : 1,
+				   self->antialias != CAIRO_ANTIALIAS_NONE,
+				   renderer);
+    return CAIRO_STATUS_SUCCESS;
+}
+
+cairo_scan_converter_t *
+_cairo_tor22_scan_converter_create (int			xmin,
+				  int			ymin,
+				  int			xmax,
+				  int			ymax,
+				  cairo_fill_rule_t	fill_rule,
+				  cairo_antialias_t	antialias)
+{
+    cairo_tor22_scan_converter_t *self;
+    cairo_status_t status;
+
+    self = _cairo_malloc (sizeof(struct _cairo_tor22_scan_converter));
+    if (unlikely (self == NULL)) {
+	status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
+	goto bail_nomem;
+    }
+
+    self->base.destroy = _cairo_tor22_scan_converter_destroy;
+    self->base.generate = _cairo_tor22_scan_converter_generate;
+
+    _glitter_scan_converter_init (self->converter, &self->jmp);
+    status = glitter_scan_converter_reset (self->converter,
+					   xmin, ymin, xmax, ymax);
+    if (unlikely (status))
+	goto bail;
+
+    self->fill_rule = fill_rule;
+    self->antialias = antialias;
+
+    return &self->base;
+
+ bail:
+    self->base.destroy(&self->base);
+ bail_nomem:
+    return _cairo_scan_converter_create_in_error (status);
+}