[Spice-devel] [PATCH 5/6] LZ4: Fix the row alignment when it is not on a 32bit boundary

[Javier Celaya]

El Lunes, 26 de enero de 2015 16:52:42 Christophe Fergeau escribió:
> On Mon, Jan 26, 2015 at 03:20:23PM +0100, Javier Celaya wrote:
> > Hello,
> > 
> > El Lunes, 26 de enero de 2015 15:13:57 Christophe Fergeau escribió:
> > > Hey,
> > > 
> > > On Thu, Jan 22, 2015 at 05:21:23PM +0100, Javier Celaya wrote:
> > > > ---
> > > > 
> > > >  common/canvas_base.c | 25 +++++++++++++++++++++++--
> > > >  1 file changed, 23 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/common/canvas_base.c b/common/canvas_base.c
> > > > index c45d535..170def1 100644
> > > > --- a/common/canvas_base.c
> > > > +++ b/common/canvas_base.c
> > > > @@ -563,8 +563,7 @@ static pixman_image_t *canvas_get_lz4(CanvasBase
> > > > *canvas, SpiceImage *image, int>
> > > > 
> > > >  {
> > > >  
> > > >      pixman_image_t *surface = NULL;
> > > >      int dec_size, enc_size, available;
> > > > 
> > > > -    int stride;
> > > > -    int stride_abs;
> > > > +    int stride, stride_abs, stride_encoded;
> > > > 
> > > >      uint8_t *dest, *data, *data_end;
> > > >      int width, height, top_down;
> > > >      LZ4_streamDecode_t *stream;
> > > > 
> > > > @@ -575,19 +574,23 @@ static pixman_image_t *canvas_get_lz4(CanvasBase
> > > > *canvas, SpiceImage *image, int>
> > > > 
> > > >      data = image->u.lz4.data->chunk[0].data;
> > > >      data_end = data + image->u.lz4.data->chunk[0].len;
> > > >      width = image->descriptor.width;
> > > > 
> > > > +    stride_encoded = width;
> > > > 
> > > >      height = image->descriptor.height;
> > > >      top_down = *(data++);
> > > >      spice_format = *(data++);
> > > >      switch (spice_format) {
> > > >      
> > > >          case SPICE_BITMAP_FMT_16BIT:
> > > >              format = PIXMAN_x1r5g5b5;
> > > > 
> > > > +            stride_encoded *= 2;
> > > > 
> > > >              break;
> > > >          
> > > >          case SPICE_BITMAP_FMT_24BIT:
> > > >          
> > > >          case SPICE_BITMAP_FMT_32BIT:
> > > >              format = PIXMAN_x8r8g8b8;
> > > > 
> > > > +            stride_encoded *= 4;
> > > > 
> > > >              break;
> > > >          
> > > >          case SPICE_BITMAP_FMT_RGBA:
> > > >              format = PIXMAN_a8r8g8b8;
> > > > 
> > > > +            stride_encoded *= 4;
> > > > 
> > > >              break;
> > > >          
> > > >          default:
> > > >              spice_warning("Unsupported bitmap format %d with LZ4\n",
> > > >              spice_format);
> > > > 
> > > > @@ -631,6 +634,24 @@ static pixman_image_t *canvas_get_lz4(CanvasBase
> > > > *canvas, SpiceImage *image, int>
> > > > 
> > > >          data += enc_size;
> > > >      
> > > >      } while (data < data_end);
> > > > 
> > > > +    if (stride_abs > stride_encoded) {
> > > 
> > > My understanding is that this will only trigger in the 24bpp case when
> > > the next commit adds
> > > 
> > >           case SPICE_BITMAP_FMT_24BIT:
> > >               stride_encoded *= 3;
> > > 
> > > ?
> > > If so, it should be mentioned in the commit log that this only add some
> > > helper code which will be used when 24bpp support is added or something
> > > like this.
> > 
> > It also triggers with 16bpp when width is an odd number, so the commit
> > makes sense by itself. But I can say something about the "future" support
> > to 24bpp.
> If width is an odd number, the code in this patch ends up doing 'weird'
> since it copies 32 bit at a time, so it will copy 16 bit extra at the
> end of each line.

I know, but that extra 16 bits are ignored. They end up in the padding area, 
which does not need to be all 0 or anything. Anyway, I just changed the code 
to use memmove, so it is not weird anymore ;)

> 
> Christophe