Introduce cairo_mime_surface_t

The mime surface is a user-callback surface designed for interfacing
cairo with an opaque data source. For instance, in a web browser, the
incoming page may be laid out and rendered to a recording surface before
all the image data has finished being downloaded. In this circumstance
we need to pass a place holder to cairo and to supply the image data
later upon demand.

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

1 files changed, 8 insertions, 3 deletions

diff --git a/src/cairo.c b/src/cairo.c
index a9f8c6e41..6f6d00e69 100644
--- a/src/cairo.c
+++ b/src/cairo.c
@@ -212,9 +212,11 @@ _cairo_create_in_error (cairo_status_t status)
  *  with cairo_destroy() when you are done using the #cairo_t.
  *  This function never returns %NULL. If memory cannot be
  *  allocated, a special #cairo_t object will be returned on
- *  which cairo_status() returns %CAIRO_STATUS_NO_MEMORY.
- *  You can use this object normally, but no drawing will
- *  be done.
+ *  which cairo_status() returns %CAIRO_STATUS_NO_MEMORY. If
+ *  you attempt to target a surface which does not support
+ *  writing (such as #cairo_mime_surface_t) then a
+ *  %CAIRO_STATUS_WRITE_ERROR will be raised.  You can use this
+ *  object normally, but no drawing will be done.
  **/
 cairo_t *
 cairo_create (cairo_surface_t *target)
@@ -224,6 +226,9 @@ cairo_create (cairo_surface_t *target)
     if (unlikely (target->status))
 	return _cairo_create_in_error (target->status);
 
+    if (target->backend->create_context == NULL)
+	return _cairo_create_in_error (_cairo_error (CAIRO_STATUS_WRITE_ERROR));
+
     return target->backend->create_context (target);
 
 }