[Spice-devel] [PATCH spice-server] Revert "gstreamer: Avoid memory copy if strides are different"

[Frediano Ziglio]

> 
> On Fri, Mar 03, 2017 at 11:18:57AM +0000, Frediano Ziglio wrote:
> > This reverts commit c3d237075b994fe67edddd58f2b3164cb579e6f4.
> > 
> > When you call gst_buffer_add_video_meta_full GStreamer assumes
> > that buffer is contiguous. This results usually in some pixels
> > shift in the video. The pixels shift you can see are artifacts
> 
> "pixel shifts" I think (twice)
> 
> > due to how the guest send the frames but basically are bytes
> 
> "sends". I'd end the sentence after "send the frames", and then make a
> slightly more detailed sentence for "basically are bytes inside 2 chunks
> of data" (I don't understand it).
> 

Maybe this is important to explain as is not clear how a corruption
cause pixels shift.


Assume you allocate the 2 chunks with 2 malloc:

   p1 = malloc(size);
   ...
   p2 = malloc(size);

Usually the allocator tend to allocate linearly if there are space
adding a prefix to describe next block leading to a memory arrangement
as:

   +-------------------+
   | p1 prefix         |
   +-------------------+
   | p1 buffer         |
   +-------------------+
   | p2 prefix         |
   +-------------------+
   | p2 buffer         |
   +-------------------+

now if you take p1 pointer and you assume it points to a 2* size
buffer you will get p2 prefix in the middle, this prefix are the
pixel shifts.


Do you have suggestion for a shorter explanation?

Frediano

> 
> Acked-by: Christophe Fergeau <cfergeau at redhat.com>
> 
> Christophe
> 
> > inside 2 chunks of data.
> > 
> > Problems happens specifically in gst_video_frame_map_id.
> > This bug is reported in https://bugzilla.gnome.org/show_bug.cgi?id=779524.
> > 
> > Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> > ---
> >  server/gstreamer-encoder.c | 26 ++++++--------------------
> >  1 file changed, 6 insertions(+), 20 deletions(-)
> > 
> > diff --git a/server/gstreamer-encoder.c b/server/gstreamer-encoder.c
> > index 991eb51..df54cad 100644
> > --- a/server/gstreamer-encoder.c
> > +++ b/server/gstreamer-encoder.c
> > @@ -1236,6 +1236,8 @@ static void clear_zero_copy_queue(SpiceGstEncoder
> > *encoder, gboolean unref_queue
> >      /* Nothing to do */
> >  }
> >  
> > +#endif
> > +
> >  /* A helper for push_raw_frame() */
> >  static inline int line_copy(SpiceGstEncoder *encoder, const SpiceBitmap
> >  *bitmap,
> >                              uint32_t chunk_offset, uint32_t stream_stride,
> > @@ -1266,8 +1268,6 @@ static inline int line_copy(SpiceGstEncoder *encoder,
> > const SpiceBitmap *bitmap,
> >       return TRUE;
> >  }
> >  
> > -#endif
> > -
> >  /* A helper for push_raw_frame() */
> >  static inline int chunk_copy(SpiceGstEncoder *encoder, const SpiceBitmap
> >  *bitmap,
> >                               uint32_t chunk_index, uint32_t chunk_offset,
> > @@ -1350,8 +1350,8 @@ static int push_raw_frame(SpiceGstEncoder *encoder,
> >                            gpointer bitmap_opaque)
> >  {
> >      uint32_t height = src->bottom - src->top;
> > -    uint32_t len;
> > -    uint32_t chunk_index = 0;
> > +    uint32_t stream_stride = (src->right - src->left) *
> > encoder->format->bpp / 8;
> > +    uint32_t len = stream_stride * height;
> >      GstBuffer *buffer = gst_buffer_new();
> >      /* TODO Use GST_MAP_INFO_INIT once GStreamer 1.4.5 is no longer
> >      relevant */
> >      GstMapInfo map = { .memory = NULL };
> > @@ -1362,10 +1362,6 @@ static int push_raw_frame(SpiceGstEncoder *encoder,
> >      uint32_t skip_lines = top_down ? src->top : bitmap->y - (src->bottom -
> >      0);
> >      uint32_t chunk_offset = bitmap->stride * skip_lines;
> >  
> > -#ifndef DO_ZERO_COPY
> > -    uint32_t stream_stride = (src->right - src->left) *
> > encoder->format->bpp / 8;
> > -
> > -    len = stream_stride * height;
> >      if (stream_stride != bitmap->stride) {
> >          /* We have to do a line-by-line copy because for each we have to
> >           * leave out pixels on the left or right.
> > @@ -1381,19 +1377,9 @@ static int push_raw_frame(SpiceGstEncoder *encoder,
> >              return VIDEO_ENCODER_FRAME_UNSUPPORTED;
> >          }
> >      } else {
> > -#else
> > -    {
> > -        /* using GStreamer 1.0, we can avoid cropping the image by simply
> > passing
> > -         * the appropriate offset and stride as metadata */
> > -        gsize offset[] = { src->left * encoder->format->bpp / 8 };
> > -        gint stride[] = { bitmap->stride };
> > -        gst_buffer_add_video_meta_full(buffer, GST_VIDEO_FRAME_FLAG_NONE,
> > -                                       encoder->format->gst_format,
> > bitmap->x, bitmap->y,
> > -                                       1, offset, stride);
> > -
> > -        len = bitmap->stride * height;
> > -
> >          /* We can copy the bitmap chunk by chunk */
> > +        uint32_t chunk_index = 0;
> > +#ifdef DO_ZERO_COPY
> >          if (!zero_copy(encoder, bitmap, bitmap_opaque, buffer,
> >          &chunk_index,
> >                         &chunk_offset, &len)) {
> >              gst_buffer_unref(buffer);