From e05097c604c607d27b341cd33426001bd2d1f690 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 27 May 2009 16:45:20 +0100
Subject: [PATCH] [surface] Assign a unique id to the surface.

Allocate an ever-increasing, non-zero, unique identifier to each surface.
True for the first 4-billion...
---
 src/cairo-pattern.c         | 11 ++++++++---
 src/cairo-surface-private.h |  2 ++
 src/cairo-surface.c         | 25 +++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/src/cairo-pattern.c b/src/cairo-pattern.c
index 654989f88..cf41a8758 100644
--- a/src/cairo-pattern.c
+++ b/src/cairo-pattern.c
@@ -2424,7 +2424,10 @@ static unsigned long
 _cairo_surface_pattern_hash (unsigned long hash,
 			     const cairo_pattern_t *pattern)
 {
-    /* XXX requires cow-snapshots */
+    const cairo_surface_pattern_t *surface = (cairo_surface_pattern_t *) pattern;
+
+    hash ^= surface->surface->unique_id;
+
     return hash;
 }
 
@@ -2578,8 +2581,10 @@ static cairo_bool_t
 _cairo_surface_pattern_equal (const cairo_pattern_t *A,
 			      const cairo_pattern_t *B)
 {
-    /* XXX requires cow-snapshots */
-    return FALSE;
+    const cairo_surface_pattern_t *a = (cairo_surface_pattern_t *) A;
+    const cairo_surface_pattern_t *b = (cairo_surface_pattern_t *) B;
+
+    return a->surface->unique_id == b->surface->unique_id;
 }
 
 cairo_bool_t
diff --git a/src/cairo-surface-private.h b/src/cairo-surface-private.h
index 12b38f015..b07f7806d 100644
--- a/src/cairo-surface-private.h
+++ b/src/cairo-surface-private.h
@@ -56,6 +56,8 @@ struct _cairo_surface {
     cairo_reference_count_t ref_count;
     cairo_status_t status;
     cairo_bool_t finished;
+    unsigned int unique_id;
+
     cairo_user_data_array_t user_data;
     cairo_user_data_array_t mime_data;
 
diff --git a/src/cairo-surface.c b/src/cairo-surface.c
index d42e1ef96..d21ebf247 100644
--- a/src/cairo-surface.c
+++ b/src/cairo-surface.c
@@ -50,6 +50,7 @@ const cairo_surface_t name = {					\
     CAIRO_REFERENCE_COUNT_INVALID,	/* ref_count */		\
     status,				/* status */		\
     FALSE,				/* finished */		\
+    0,					/* unique id */		\
     { 0, 0, 0, NULL, },			/* user_data */		\
     { 0, 0, 0, NULL, },			/* mime_data */         \
     { 1.0, 0.0, 0.0, 1.0, 0.0, 0.0 },   /* device_transform */	\
@@ -180,6 +181,29 @@ cairo_surface_status (cairo_surface_t *surface)
 }
 slim_hidden_def (cairo_surface_status);
 
+static unsigned long
+_cairo_surface_allocate_unique_id (void)
+{
+    static unsigned int unique_id;
+
+#if CAIRO_NO_MUTEX
+    if (++unique_id == 0)
+	unique_id = 1;
+    return unique_id;
+#else
+    unsigned int old, id;
+
+    do {
+	old = _cairo_atomic_int_get (&unique_id);
+	id = old + 1;
+	if (id == 0)
+	    id = 1;
+    } while (! _cairo_atomic_int_cmpxchg (&unique_id, old, id));
+
+    return id;
+#endif
+}
+
 void
 _cairo_surface_init (cairo_surface_t			*surface,
 		     const cairo_surface_backend_t	*backend,
@@ -194,6 +218,7 @@ _cairo_surface_init (cairo_surface_t			*surface,
     CAIRO_REFERENCE_COUNT_INIT (&surface->ref_count, 1);
     surface->status = CAIRO_STATUS_SUCCESS;
     surface->finished = FALSE;
+    surface->unique_id = _cairo_surface_allocate_unique_id ();
 
     _cairo_user_data_array_init (&surface->user_data);
     _cairo_user_data_array_init (&surface->mime_data);