subsurface: Add guards for creating similar surface

If the target backend doesn't provide the entry points, just return NULL
(unsupported).

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

1 files changed, 8 insertions, 0 deletions

diff --git a/src/cairo-surface-subsurface.c b/src/cairo-surface-subsurface.c
index 09f49d08c..b2f7e0a10 100644
--- a/src/cairo-surface-subsurface.c
+++ b/src/cairo-surface-subsurface.c
@@ -61,6 +61,10 @@ _cairo_surface_subsurface_create_similar (void *other,
 					  int width, int height)
 {
     cairo_surface_subsurface_t *surface = other;
+
+    if (surface->target->backend->create_similar == NULL)
+	return NULL;
+
     return surface->target->backend->create_similar (surface->target, content, width, height);
 }
 
@@ -70,6 +74,10 @@ _cairo_surface_subsurface_create_similar_image (void *other,
 						int width, int height)
 {
     cairo_surface_subsurface_t *surface = other;
+
+    if (surface->target->backend->create_similar_image == NULL)
+	return NULL;
+
     return surface->target->backend->create_similar_image (surface->target,
 							   format,
 							   width, height);