xlib/shm: Limit use of the impromptu fallback pixmap for uploads

We want to avoid unnecessary readback and so only want to use the
ShmPixmap when uploading the complete surface.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/cairo-xlib-surface-shm.c b/src/cairo-xlib-surface-shm.c
index 7d9a3e1b3..cdb91c836 100644
--- a/src/cairo-xlib-surface-shm.c
+++ b/src/cairo-xlib-surface-shm.c
@@ -791,7 +791,8 @@ static void dec_idle (cairo_surface_t *surface)
 }
 
 cairo_surface_t *
-_cairo_xlib_surface_get_shm (cairo_xlib_surface_t *surface)
+_cairo_xlib_surface_get_shm (cairo_xlib_surface_t *surface,
+			     cairo_bool_t overwrite)
 {
     if (surface->fallback) {
 	assert (surface->base.damage);
@@ -836,6 +837,11 @@ _cairo_xlib_surface_get_shm (cairo_xlib_surface_t *surface)
 	surface->shm->damage = _cairo_damage_create ();
     }
 
+    if (overwrite) {
+	_cairo_damage_destroy (surface->base.damage);
+	surface->base.damage = _cairo_damage_create ();
+    }
+
     if (!surface->base.is_clear && surface->base.damage->dirty)
 	_cairo_xlib_surface_update_shm (surface);