[PATCH 1/2] XCB: Fix clip-fill-{eo,nz}-unbounded tests [v2]

[Uli Schlachter]

The X server calculates the bounding box for traps and then allocates a
temporary picture for this. When the X server calculates different values than
cairo got in extents->bounded, unbounded operators will have wrong results. The
X server only ever calculates bounds that are larger than the real value.

Fix this by explicitly clipping the drawing to the expected bounds.

Thanks to Andrea Canciani for pointing out how to avoid a memory allocation by
using _cairo_region_init_rectangle and a lot more feedback.

Signed-off-by: Uli Schlachter <psychon at znc.in>
---
 src/cairo-xcb-surface-render.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/src/cairo-xcb-surface-render.c b/src/cairo-xcb-surface-render.c
index f712818..8044e33 100644
--- a/src/cairo-xcb-surface-render.c
+++ b/src/cairo-xcb-surface-render.c
@@ -2391,6 +2391,7 @@ _clip_and_composite (cairo_xcb_surface_t	*dst,
 {
     cairo_status_t status;
     cairo_region_t *clip_region = NULL;
+    cairo_region_t extents_region;
     cairo_bool_t need_clip_surface = FALSE;
 
     if (clip != NULL) {
@@ -2414,6 +2415,14 @@ _clip_and_composite (cairo_xcb_surface_t	*dst,
 	    if (unlikely (is_empty && extents->is_bounded))
 		return CAIRO_STATUS_SUCCESS;
 	}
+    } else if (!extents->is_bounded) {
+	/* The X server will estimate the affected region of the unbounded
+	 * operation and will apply the operation to that rectangle.
+	 * However, there are cases where this estimate is too high (e.g.
+	 * the test suite's clip-fill-{eo,nz}-unbounded tests).
+	 */
+	_cairo_region_init_rectangle (&extents_region, &extents->unbounded);
+	clip_region = &extents_region;
     }
 
     status = _cairo_xcb_connection_acquire (dst->connection);
@@ -2482,6 +2491,8 @@ _clip_and_composite (cairo_xcb_surface_t	*dst,
 
     if (clip_region != NULL)
 	_cairo_xcb_surface_clear_clip_region (dst);
+    if (clip == &extents_region)
+	_cairo_region_fini (&extents_region);
 
     _cairo_xcb_connection_release (dst->connection);
 
-- 
1.7.2.3


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