static void vnc_dpy_update(DisplayChangeListener *dcl, DisplayState *ds, int x, int y, int w, int h) { int i; VncDisplay *vd = ds->opaque; struct VncSurface *s = &vd->guest; int width = ds_get_width(ds); int height = ds_get_height(ds); h += y; /* round x down to ensure the loop only spans one 16-pixel block per, iteration. otherwise, if (x % 16) != 0, the last iteration may span two 16-pixel blocks but we only mark the first as dirty */ w += (x % 16); x -= (x % 16); x = MIN(x, width); y = MIN(y, height); w = MIN(x + w, width) - x; h = MIN(h, height); for (; y < h; y++) for (i = 0; i < w; i += 16) set_bit((x + i) / 16, s->dirty[y]); }