change backgrounds with 'background' command to wctl at runtime

echo background $home/bunny.bit >> $wctl

diff --git a/sys/src/cmd/rio/rio.c b/sys/src/cmd/rio/rio.c
--- a/sys/src/cmd/rio/rio.c
+++ b/sys/src/cmd/rio/rio.c
@@ -29,7 +29,7 @@ void		newtile(int);
 Image*	sweep(void);
 Image*	bandsize(Window*);
 Image*	drag(Window*);
-void		resized(void);
+void		resized(int);
 Channel	*exitchan;	/* chan(int) */
 Channel	*winclosechan; /* chan(Window*); */
 Channel	*kbdchan;	/* chan(char*); */
@@ -506,7 +506,7 @@ mousethread(void*)
 	for(;;)
 	    switch(alt(alts)){
 		case MReshape:
-			resized();
+			resized(1);
 			break;
 		case MMouse:
 			if(wkeyboard!=nil && (mouse->buttons & (1<<5))){
@@ -612,7 +612,7 @@ wtopcmp(void *a, void *b)
 }
 
 void
-resized(void)
+resized(int new)
 {
 	Image *im;
 	int i, j;
@@ -620,6 +620,7 @@ resized(void)
 	Point o, n;
 	Window *w;
 
+	if(new){
 	if(getwindow(display, Refnone) < 0)
 		error("failed to re-attach window");
 	freescrtemps();
@@ -628,7 +629,8 @@ resized(void)
 	wscreen = allocscreen(screen, background, 0);
 	if(wscreen == nil)
 		error("can't re-allocate screen");
-	draw(view, view->r, background, nil, ZP);
+	}
+	draw(view, view->r, background, nil, view->r.min);
 	o = subpt(viewr.max, viewr.min);
 	n = subpt(view->clipr.max, view->clipr.min);
 	qsort(window, nwindow, sizeof(window[0]), wtopcmp);
diff --git a/sys/src/cmd/rio/wctl.c b/sys/src/cmd/rio/wctl.c
--- a/sys/src/cmd/rio/wctl.c
+++ b/sys/src/cmd/rio/wctl.c
@@ -30,6 +30,7 @@ enum
 	Hide,
 	Unhide,
 	Delete,
+	Background,
 };
 
 static char *cmds[] = {
@@ -45,6 +46,7 @@ static char *cmds[] = {
 	[Hide]	= "hide",
 	[Unhide]	= "unhide",
 	[Delete]	= "delete",
+	[Background]	= "background",
 	nil
 };
 
@@ -301,7 +303,7 @@ parsewctl(char **argp, Rectangle r, Rect
 
 	while(isspace(*s))
 		s++;
-	if(cmd!=New && *s!='\0'){
+	if((cmd!=New && cmd!=Background) && *s!='\0'){
 		strcpy(err, "extraneous text in wctl message");
 		return -1;
 	}
@@ -440,6 +442,33 @@ wctlcmd(Window *w, Rectangle r, int cmd,
 	return -1;
 }
 
+static void
+wctlbackground(char *file)
+{
+	int fd;
+	char *n;
+	Image *i;
+
+	if((n = strchr(file, '\n')) != nil)
+		*n = '\0';
+
+	fd = open(file, OREAD);
+	if(fd < 0)
+		return;
+	i = readimage(display, fd, 0);
+	if(i == nil)
+		fprint(2, "readimage: %r\n");
+	close(fd);
+	if(i != nil){
+		freeimage(background);
+		background = allocimage(display, Rect(0, 0, Dx(i->r), Dy(i->r)), RGBA32, 1, DBlack);
+		draw(background, background->r, i, nil, i->r.min);
+		freeimage(i);
+		extern void resized(int);
+		resized(0);
+	}
+}
+
 int
 writewctl(Xfid *x, char *err)
 {
@@ -473,6 +502,13 @@ writewctl(Xfid *x, char *err)
 		if(pid > 0)
 			wsetpid(w, pid, 0);
 		return 1;
+	case Background:
+		if(*arg == '\0'){
+			strcpy(err, "invalid argument");
+			return -1;
+		}
+		wctlbackground(arg);
+		return 1;
 	}
 
 	incref(w);
@@ -502,6 +538,12 @@ wctlthread(void *v)
 		switch(cmd){
 		case New:
 			wctlnew(rect, arg, pid, hideit, scrollit, dir, err);
+			break;
+		case Background:
+			if(*arg == '\0')
+				break;
+			wctlbackground(arg);
+			break;
 		}
 		free(buf);
 	}