[Spice-devel] [spice-server 3/3] dcc: Fix QUIC fallback in get_compression_for_bitmap()

[Christophe Fergeau]

There was a small regression introduced in get_compression_for_bitmap()
by f401eb07f dcc: Rewrite dcc_image_compress.
If SPICE_IMAGE_COMPRESSION_AUTO_GLZ is specified, and the bitmap has a
stride which is bigger than its width (ie it has padding), then
get_compression_for_bitmap() will return SPICE_IMAGE_COMPRESSION_OFF
while in that case, we used to use QUIC for compression.

This happens because that function in the AUTO_GLZ case first checks if
QUIC should be used, if not, it decides to use GLZ, but then decides it
can't because of the stride, so falls back to OFF, while it used to
fall back to QUIC.

This commit only slightly reworks a preexisting if (!can_lz_compress())
check so that it's unconditional rather than depending on the previous
checks having been unsuccessful.

This issue could be observed by using a spice-html5 without support for
uncompressed bitmaps with end-of-line padding by simply starting a f28
VM and connecting to it/moving the mouse cursor in it.
---
 server/dcc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/server/dcc.c b/server/dcc.c
index 44d8fdd75..0468e7213 100644
--- a/server/dcc.c
+++ b/server/dcc.c
@@ -796,8 +796,10 @@ static SpiceImageCompression get_compression_for_bitmap(SpiceBitmap *bitmap,
                     bitmap_get_graduality_level(bitmap) == BITMAP_GRADUAL_HIGH) {
                     return SPICE_IMAGE_COMPRESSION_QUIC;
                 }
-            } else if (!can_lz_compress(bitmap) ||
-                       drawable->copy_bitmap_graduality == BITMAP_GRADUAL_HIGH) {
+            } else if (drawable->copy_bitmap_graduality == BITMAP_GRADUAL_HIGH) {
+                return SPICE_IMAGE_COMPRESSION_QUIC;
+            }
+            if (!can_lz_compress(bitmap)) {
                 return SPICE_IMAGE_COMPRESSION_QUIC;
             }
         }
-- 
2.17.1