[Qemu-devel] [PATCH 4/4] spice: send updates only for changed screen content

[Gerd Hoffmann <kraxel@redhat.com>]

when creating screen updates go compare the current guest screen
against the mirror (which holds the most recent update sent), then
only create updates for the screen areas which did actually change.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 ui/spice-display.c |   55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 55 insertions(+), 0 deletions(-)

diff --git a/ui/spice-display.c b/ui/spice-display.c
index 6f87099..ea87d82 100644
--- a/ui/spice-display.c
+++ b/ui/spice-display.c
@@ -239,6 +239,13 @@ static void qemu_spice_create_one_update(SimpleSpiceDisplay *ssd,
 
 static void qemu_spice_create_update(SimpleSpiceDisplay *ssd)
 {
+    static const int blksize = 42;
+    int blocks = (ds_get_width(ssd->ds) + blksize - 1) / blksize;
+    int dirty_top[blocks];
+    int y, yoff, x, xoff, blk, bw;
+    int bpp = ds_get_bytes_per_pixel(ssd->ds);
+    uint8_t *guest, *mirror;
+
     if (qemu_spice_rect_is_empty(&ssd->dirty)) {
         return;
     };
@@ -253,6 +260,54 @@ static void qemu_spice_create_update(SimpleSpiceDisplay *ssd)
         ssd->ds_mirror = g_malloc0(size);
     }
 
+    for (blk = 0; blk < blocks; blk++) {
+        dirty_top[blk] = -1;
+    }
+
+    guest = ds_get_data(ssd->ds);
+    mirror = ssd->ds_mirror;
+    for (y = ssd->dirty.top; y < ssd->dirty.bottom; y++) {
+        yoff = y * ds_get_linesize(ssd->ds);
+        for (x = ssd->dirty.left; x < ssd->dirty.right; x += blksize) {
+            xoff = x * bpp;
+            blk = x / blksize;
+            bw = MIN(blksize, ssd->dirty.right - x);
+            if (memcmp(guest + yoff + xoff,
+                       mirror + yoff + xoff,
+                       bw * bpp) == 0) {
+                if (dirty_top[blk] != -1) {
+                    QXLRect update = {
+                        .top    = dirty_top[blk],
+                        .bottom = y,
+                        .left   = x,
+                        .right  = x + bw,
+                    };
+                    qemu_spice_create_one_update(ssd, &update);
+                    dirty_top[blk] = -1;
+                }
+            } else {
+                if (dirty_top[blk] == -1) {
+                    dirty_top[blk] = y;
+                }
+            }
+        }
+    }
+
+    for (x = ssd->dirty.left; x < ssd->dirty.right; x += blksize) {
+        blk = x / blksize;
+        bw = MIN(blksize, ssd->dirty.right - x);
+        if (dirty_top[blk] != -1) {
+            QXLRect update = {
+                .top    = dirty_top[blk],
+                .bottom = ssd->dirty.bottom,
+                .left   = x,
+                .right  = x + bw,
+            };
+            qemu_spice_create_one_update(ssd, &update);
+            dirty_top[blk] = -1;
+        }
+    }
+
     qemu_spice_create_one_update(ssd, &ssd->dirty);
     memset(&ssd->dirty, 0, sizeof(ssd->dirty));
 }
-- 
1.7.1