From d112b2fbcc278746037badfb96619b6a87c7b7a3 Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Wed, 5 Sep 2012 10:41:42 +0200
Subject: [PATCH] spice: send updates only for changed screen content

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.

[ v2: drop redundant qemu_spice_create_one_update call ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 ui/spice-display.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 55 insertions(+), 1 deletion(-)

diff --git a/ui/spice-display.c b/ui/spice-display.c
index 973cd53..d062765 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 = 32;
+    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;
     };
@@ -253,7 +260,54 @@ static void qemu_spice_create_update(SimpleSpiceDisplay *ssd)
         ssd->ds_mirror = g_malloc0(size);
     }
 
-    qemu_spice_create_one_update(ssd, &ssd->dirty);
+    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;
+        }
+    }
+
     memset(&ssd->dirty, 0, sizeof(ssd->dirty));
 }