diff --git a/sys/src/libdraw/alloc.c b/sys/src/libdraw/alloc.c
index 256378f36..7cb6e2d5c 100644
--- a/sys/src/libdraw/alloc.c
+++ b/sys/src/libdraw/alloc.c
@@ -5,10 +5,10 @@
 Image*
 allocimage(Display *d, Rectangle r, ulong chan, int repl, ulong val)
 {
-	Image*	i;
+	Image *i;
 
-	i =  _allocimage(nil, d, r, chan, repl, val, 0, 0);
-	if (i)
+	i = _allocimage(nil, d, r, chan, repl, val, 0, 0);
+	if(i != nil)
 		setmalloctag(i, getcallerpc(&d));
 	return i;
 }
@@ -23,8 +23,8 @@ _allocimage(Image *ai, Display *d, Rectangle r, ulong chan, int repl, ulong val,
 	int id;
 	int depth;
 
-	err = 0;
-	i = 0;
+	err = nil;
+	i = nil;
 
 	if(badrect(r)){
 		werrstr("bad rectangle");
@@ -39,18 +39,18 @@ _allocimage(Image *ai, Display *d, Rectangle r, ulong chan, int repl, ulong val,
 	if(depth == 0){
 		err = "bad channel descriptor";
     Error:
-		if(err)
+		if(err != nil)
 			werrstr("allocimage: %s", err);
 		else
 			werrstr("allocimage: %r");
 		free(i);
-		return 0;
+		return nil;
 	}
 
 	/* flush pending data so we don't get error allocating the image */
 	flushimage(d, 0);
 	a = bufimage(d, 1+4+4+1+4+1+4*4+4*4+4);
-	if(a == 0)
+	if(a == nil)
 		goto Error;
 	d->imageid++;
 	id = d->imageid;
@@ -77,13 +77,13 @@ _allocimage(Image *ai, Display *d, Rectangle r, ulong chan, int repl, ulong val,
 	if(flushimage(d, 0) < 0)
 		goto Error;
 
-	if(ai)
+	if(ai != nil)
 		i = ai;
 	else{
 		i = malloc(sizeof(Image));
 		if(i == nil){
 			a = bufimage(d, 1+4);
-			if(a){
+			if(a != nil){
 				a[0] = 'f';
 				BPLONG(a+1, id);
 				flushimage(d, 0);
@@ -98,8 +98,8 @@ _allocimage(Image *ai, Display *d, Rectangle r, ulong chan, int repl, ulong val,
 	i->r = r;
 	i->clipr = clipr;
 	i->repl = repl;
-	i->screen = 0;
-	i->next = 0;
+	i->screen = nil;
+	i->next = nil;
 	return i;
 }
 
@@ -112,25 +112,24 @@ namedimage(Display *d, char *name)
 	int id, n;
 	ulong chan;
 
-	err = 0;
-	i = 0;
+	err = nil;
+	i = nil;
 
 	n = strlen(name);
 	if(n >= 256){
 		err = "name too long";
     Error:
-		if(err)
+		if(err != nil)
 			werrstr("namedimage: %s", err);
 		else
 			werrstr("namedimage: %r");
-		if(i)
-			free(i);
-		return 0;
+		free(i);
+		return nil;
 	}
 	/* flush pending data so we don't get error allocating the image */
 	flushimage(d, 0);
 	a = bufimage(d, 1+4+1+n);
-	if(a == 0)
+	if(a == nil)
 		goto Error;
 	d->imageid++;
 	id = d->imageid;
@@ -149,7 +148,7 @@ namedimage(Display *d, char *name)
 	if(i == nil){
 	Error1:
 		a = bufimage(d, 1+4);
-		if(a){
+		if(a != nil){
 			a[0] = 'f';
 			BPLONG(a+1, id);
 			flushimage(d, 0);
@@ -173,8 +172,8 @@ namedimage(Display *d, char *name)
 	i->clipr.min.y = atoi(buf+9*12);
 	i->clipr.max.x = atoi(buf+10*12);
 	i->clipr.max.y = atoi(buf+11*12);
-	i->screen = 0;
-	i->next = 0;
+	i->screen = nil;
+	i->next = nil;
 	return i;
 }
 
@@ -186,7 +185,7 @@ nameimage(Image *i, char *name, int in)
 
 	n = strlen(name);
 	a = bufimage(i->display, 1+4+1+1+n);
-	if(a == 0)
+	if(a == nil)
 		return 0;
 	a[0] = 'N';
 	BPLONG(a+1, i->id);
@@ -205,23 +204,16 @@ _freeimage1(Image *i)
 	Display *d;
 	Image *w;
 
-	if(i == 0 || i->display == 0)
+	if(i == nil || i->display == nil)
 		return 0;
-	/* make sure no refresh events occur on this if we block in the write */
 	d = i->display;
-	/* flush pending data so we don't get error deleting the image */
 	flushimage(d, 0);
-	a = bufimage(d, 1+4);
-	if(a == 0)
-		return -1;
-	a[0] = 'f';
-	BPLONG(a+1, i->id);
-	if(i->screen){
+	if(i->screen != nil){
 		w = d->windows;
 		if(w == i)
 			d->windows = i->next;
 		else
-			while(w){
+			while(w != nil){
 				if(w->next == i){
 					w->next = i->next;
 					break;
@@ -229,7 +221,12 @@ _freeimage1(Image *i)
 				w = w->next;
 			}
 	}
-	if(flushimage(d, i->screen!=0) < 0)
+	a = bufimage(d, 1+4);
+	if(a == nil)
+		return -1;
+	a[0] = 'f';
+	BPLONG(a+1, i->id);
+	if(flushimage(d, i->screen!=nil) < 0)
 		return -1;
 
 	return 0;
diff --git a/sys/src/libdraw/creadimage.c b/sys/src/libdraw/creadimage.c
index 351177e8d..67fd59ba4 100644
--- a/sys/src/libdraw/creadimage.c
+++ b/sys/src/libdraw/creadimage.c
@@ -54,7 +54,7 @@ creadimage(Display *d, int fd, int dolock)
 		return nil;
 	}
 
-	if(d){
+	if(d != nil){
 		if(dolock)
 			lockdisplay(d);
 		i = allocimage(d, r, chan, 0, 0);
@@ -97,7 +97,7 @@ creadimage(Display *d, int fd, int dolock)
 		}
 		if(readn(fd, buf, nb)!=nb)
 			goto Errout;
-		if(d){
+		if(d != nil){
 			if(dolock)
 				lockdisplay(d);
 			a = bufimage(i->display, 21+nb);
diff --git a/sys/src/libdraw/debug.c b/sys/src/libdraw/debug.c
index 3a6788a83..c90da09e8 100644
--- a/sys/src/libdraw/debug.c
+++ b/sys/src/libdraw/debug.c
@@ -7,7 +7,7 @@ drawsetdebug(int v)
 {
 	uchar *a;
 	a = bufimage(display, 1+1);
-	if(a == 0){
+	if(a == nil){
 		fprint(2, "drawsetdebug: %r\n");
 		return;
 	}
diff --git a/sys/src/libdraw/draw.c b/sys/src/libdraw/draw.c
index d3f83e885..966d30c24 100644
--- a/sys/src/libdraw/draw.c
+++ b/sys/src/libdraw/draw.c
@@ -9,7 +9,7 @@ _setdrawop(Display *d, Drawop op)
 
 	if(op != SoverD){
 		a = bufimage(d, 1+1);
-		if(a == 0)
+		if(a == nil)
 			return;
 		a[0] = 'O';
 		a[1] = op;
@@ -24,7 +24,7 @@ draw1(Image *dst, Rectangle *r, Image *src, Point *p0, Image *mask, Point *p1, D
 	_setdrawop(dst->display, op);
 
 	a = bufimage(dst->display, 1+4+4+4+4*4+2*4+2*4);
-	if(a == 0)
+	if(a == nil)
 		return;
 	if(src == nil)
 		src = dst->display->black;
diff --git a/sys/src/libdraw/ellipse.c b/sys/src/libdraw/ellipse.c
index 7a063f115..799cd6766 100644
--- a/sys/src/libdraw/ellipse.c
+++ b/sys/src/libdraw/ellipse.c
@@ -11,7 +11,7 @@ doellipse(int cmd, Image *dst, Point *c, int xr, int yr, int thick, Image *src,
 	_setdrawop(dst->display, op);
 
 	a = bufimage(dst->display, 1+4+4+2*4+4+4+4+2*4+2*4);
-	if(a == 0){
+	if(a == nil){
 		fprint(2, "image ellipse: %r\n");
 		return;
 	}
diff --git a/sys/src/libdraw/font.c b/sys/src/libdraw/font.c
index ed996e448..20eec17d3 100644
--- a/sys/src/libdraw/font.c
+++ b/sys/src/libdraw/font.c
@@ -24,7 +24,7 @@ cachechars(Font *f, char **ss, Rune **rr, ushort *cp, int max, int *wp, char **s
 		rp = *rr;
 	}
 	wid = 0;
-	*subfontname = 0;
+	*subfontname = nil;
 	for(i=0; i<max && (*sp || *rp); sp+=w, rp+=rw){
 		if(ss){
 			r = *(uchar*)sp;
@@ -153,7 +153,7 @@ cf2subfont(Cachefont *cf, Font *f)
 
 	name = cf->subfontname;
 	if(name == nil){
-		if(f->display && f->display->screenimage)
+		if(f->display != nil && f->display->screenimage != nil)
 			depth = f->display->screenimage->depth;
 		else
 			depth = 8;
@@ -298,7 +298,7 @@ loadchar(Font *f, Rune r, Cacheinfo *c, int h, int noflush, char **subfontname)
 		return 1;
 	flushimage(f->display, 0);	/* flush any pending errors */
 	b = bufimage(f->display, 37);
-	if(b == 0)
+	if(b == nil)
 		return 0;
 	b[0] = 'l';
 	BPLONG(b+1, f->cacheimage->id);
@@ -342,7 +342,7 @@ fontresize(Font *f, int wid, int ncache, int depth)
 	}
 	flushimage(d, 0);	/* flush any pending errors */
 	b = bufimage(d, 1+4+4+1);
-	if(b == 0){
+	if(b == nil){
 		freeimage(new);
 		goto Return;
 	}
diff --git a/sys/src/libdraw/init.c b/sys/src/libdraw/init.c
index b65ade357..cc88ff6b0 100644
--- a/sys/src/libdraw/init.c
+++ b/sys/src/libdraw/init.c
@@ -10,7 +10,7 @@ int	_drawdebug = 0;
 static char deffontname[] = "*default*";
 Screen	*_screen;
 
-int		debuglockdisplay = 0;
+int	debuglockdisplay = 0;
 
 static void _closedisplay(Display*, int);
 
@@ -21,7 +21,7 @@ drawshutdown(void)
 	Display *d;
 
 	d = display;
-	if(d){
+	if(d != nil){
 		display = nil;
 		_closedisplay(d, 1);
 	}
@@ -86,7 +86,7 @@ geninitdraw(char *devdir, void(*error)(Display*, char*), char *fontname, char *l
 	/*
 	 * Write label; ignore errors (we might not be running under rio)
 	 */
-	if(label){
+	if(label != nil){
 		snprint(buf, sizeof buf, "%s/label", display->windir);
 		fd = open(buf, OREAD);
 		if(fd >= 0){
@@ -148,7 +148,7 @@ retry:
 		close(fd);
 		buf[n] = '\0';
 		image = namedimage(d, buf);
-		if(image == 0){
+		if(image == nil){
 			/*
 			 * theres a race where the winname can change after
 			 * we read it, so keep trying as long as the name
@@ -166,7 +166,7 @@ retry:
 			freescreen(*scrp);
 			*scrp = nil;
 		}
-		if(image == 0){
+		if(image == nil){
 			*winp = nil;
 			d->screenimage = nil;
 			return -1;
@@ -221,9 +221,9 @@ initdisplay(char *dev, char *win, void(*error)(Display*, char*))
 
 	fmtinstall('P', Pfmt);
 	fmtinstall('R', Rfmt);
-	if(dev == 0)
+	if(dev == nil)
 		dev = "/dev";
-	if(win == 0)
+	if(win == nil)
 		win = "/dev";
 	if(strlen(dev)>sizeof buf-25 || strlen(win)>sizeof buf-25){
 		werrstr("initdisplay: directory name too long");
@@ -240,7 +240,7 @@ initdisplay(char *dev, char *win, void(*error)(Display*, char*))
     Error1:
 			free(t);
 			werrstr("initdisplay: %s: %r", buf);
-			return 0;
+			return nil;
 		}
 		ctlfd = open(buf, ORDWR|OCEXEC);
 	}
@@ -269,7 +269,7 @@ initdisplay(char *dev, char *win, void(*error)(Display*, char*))
 		goto Error2;
 	}
 	disp = mallocz(sizeof(Display), 1);
-	if(disp == 0){
+	if(disp == nil){
     Error4:
 		close(reffd);
 		goto Error3;
@@ -418,8 +418,8 @@ drawerror(Display *d, char *s)
 {
 	char err[ERRMAX];
 
-	if(d && d->error)
-		d->error(d, s);
+	if(d != nil && d->error != nil)
+		(*d->error)(d, s);
 	else{
 		errstr(err, sizeof err);
 		fprint(2, "draw: %s: %s\n", s, err);
@@ -469,11 +469,11 @@ bufimage(Display *d, int n)
 
 	if(n<0 || n>d->bufsize){
 		werrstr("bad count in bufimage");
-		return 0;
+		return nil;
 	}
 	if(d->bufp+n > d->buf+d->bufsize)
 		if(doflush(d) < 0)
-			return 0;
+			return nil;
 	p = d->bufp;
 	d->bufp += n;
 	return p;
diff --git a/sys/src/libdraw/line.c b/sys/src/libdraw/line.c
index a06b5927e..f62921cfb 100644
--- a/sys/src/libdraw/line.c
+++ b/sys/src/libdraw/line.c
@@ -16,7 +16,7 @@ lineop(Image *dst, Point p0, Point p1, int end0, int end1, int radius, Image *sr
 	_setdrawop(dst->display, op);
 
 	a = bufimage(dst->display, 1+4+2*4+2*4+4+4+4+4+2*4);
-	if(a == 0){
+	if(a == nil){
 		fprint(2, "image line: %r\n");
 		return;
 	}
diff --git a/sys/src/libdraw/loadimage.c b/sys/src/libdraw/loadimage.c
index d5d599a2a..9f1938d54 100644
--- a/sys/src/libdraw/loadimage.c
+++ b/sys/src/libdraw/loadimage.c
@@ -38,7 +38,7 @@ loadimage(Image *i, Rectangle r, uchar *data, int ndata)
 			n = dy*bpl;
 		a = bufimage(i->display, 21+n);
 		if(a == nil){
-			werrstr("bufimage failed");
+			werrstr("loadimage: %r");
 			return -1;
 		}
 		a[0] = 'y';
diff --git a/sys/src/libdraw/poly.c b/sys/src/libdraw/poly.c
index 96effaec8..15febe09b 100644
--- a/sys/src/libdraw/poly.c
+++ b/sys/src/libdraw/poly.c
@@ -44,7 +44,7 @@ dopoly(int cmd, Image *dst, Point *pp, int np, int end0, int end1, int radius, I
 	_setdrawop(dst->display, op);
 
 	a = bufimage(dst->display, 1+4+2+4+4+4+4+2*4+(u-t));
-	if(a == 0){
+	if(a == nil){
 		free(t);
 		fprint(2, "image poly: %r\n");
 		return;
diff --git a/sys/src/libdraw/readimage.c b/sys/src/libdraw/readimage.c
index 5745bad9b..66fac9656 100644
--- a/sys/src/libdraw/readimage.c
+++ b/sys/src/libdraw/readimage.c
@@ -27,7 +27,7 @@ readimage(Display *d, int fd, int dolock)
 		
 	if(readn(fd, hdr+11, 5*12-11) != 5*12-11)
 		return nil;
-	if(d)
+	if(d != nil)
 		chunk = d->bufsize - 32;	/* a little room for header */
 	else
 		chunk = 8192;
@@ -78,7 +78,7 @@ readimage(Display *d, int fd, int dolock)
 	l = bytesperline(r, chantodepth(chan));
 	if(l > chunk)
 		chunk = l;
-	if(d){
+	if(d != nil){
 		if(dolock)
 			lockdisplay(d);
 		i = allocimage(d, r, chan, 0, -1);
@@ -116,7 +116,7 @@ readimage(Display *d, int fd, int dolock)
 			for(j=0; j<chunk; j++)
 				tmp[j] ^= 0xFF;
 
-		if(d){
+		if(d != nil){
 			if(dolock)
 				lockdisplay(d);
 			if(loadimage(i, Rect(r.min.x, miny, r.max.x, miny+dy), tmp, chunk) <= 0)
diff --git a/sys/src/libdraw/replclipr.c b/sys/src/libdraw/replclipr.c
index ffd24b47b..00667e283 100644
--- a/sys/src/libdraw/replclipr.c
+++ b/sys/src/libdraw/replclipr.c
@@ -8,6 +8,10 @@ replclipr(Image *i, int repl, Rectangle clipr)
 	uchar *b;
 
 	b = bufimage(i->display, 22);
+	if(b == nil){
+		fprint(2, "replclipr: %r\n");
+		return;
+	}
 	b[0] = 'c';
 	BPLONG(b+1, i->id);
 	repl = repl!=0;
diff --git a/sys/src/libdraw/string.c b/sys/src/libdraw/string.c
index c15bf2777..1918a7f09 100644
--- a/sys/src/libdraw/string.c
+++ b/sys/src/libdraw/string.c
@@ -112,7 +112,7 @@ _string(Image *dst, Point pt, Image *src, Point sp, Font *f, char *s, Rune *r, i
 		if(bg)
 			m += 4+2*4;
 		b = bufimage(dst->display, m);
-		if(b == 0){
+		if(b == nil){
 			fprint(2, "string: %r\n");
 			break;
 		}
diff --git a/sys/src/libdraw/unloadimage.c b/sys/src/libdraw/unloadimage.c
index 741c73b6b..107a3a786 100644
--- a/sys/src/libdraw/unloadimage.c
+++ b/sys/src/libdraw/unloadimage.c
@@ -37,7 +37,7 @@ unloadimage(Image *i, Rectangle r, uchar *data, int ndata)
 			n = bpl*dy;
 		}
 		a = bufimage(d, 1+4+4*4);
-		if(a == 0){
+		if(a == nil){
 			werrstr("unloadimage: %r");
 			return -1;
 		}
diff --git a/sys/src/libdraw/window.c b/sys/src/libdraw/window.c
index d36b132bd..3f006405c 100644
--- a/sys/src/libdraw/window.c
+++ b/sys/src/libdraw/window.c
@@ -17,17 +17,17 @@ allocscreen(Image *image, Image *fill, int public)
 	d = image->display;
 	if(d != fill->display){
 		werrstr("allocscreen: image and fill on different displays");
-		return 0;
+		return nil;
 	}
 	s = malloc(sizeof(Screen));
-	if(s == 0)
-		return 0;
+	if(s == nil)
+		return nil;
 	if(!screenid)
 		screenid = getpid();
 	for(try=0; try<25; try++){
 		/* loop until find a free id */
 		a = bufimage(d, 1+4+4+4+1);
-		if(a == 0)
+		if(a == nil)
 			break;
 		id = ++screenid & 0xffff;	/* old devdraw bug */
 		a[0] = 'A';
@@ -39,13 +39,13 @@ allocscreen(Image *image, Image *fill, int public)
 			goto Found;
 	}
 	free(s);
-	return 0;
+	return nil;
 
     Found:
 	s->display = d;
 	s->id = id;
 	s->image = image;
-	assert(s->image && s->image->chan != 0);
+	assert(s->image != nil && s->image->chan != 0);
 
 	s->fill = fill;
 	return s;
@@ -58,13 +58,13 @@ publicscreen(Display *d, int id, ulong chan)
 	Screen *s;
 
 	s = malloc(sizeof(Screen));
-	if(s == 0)
-		return 0;
+	if(s == nil)
+		return nil;
 	a = bufimage(d, 1+4+4);
-	if(a == 0){
-    Error:
+	if(a == nil){
+Error:
 		free(s);
-		return 0;
+		return nil;
 	}
 	a[0] = 'S';
 	BPLONG(a+1, id);
@@ -74,8 +74,8 @@ publicscreen(Display *d, int id, ulong chan)
 
 	s->display = d;
 	s->id = id;
-	s->image = 0;
-	s->fill = 0;
+	s->image = nil;
+	s->fill = nil;
 	return s;
 }
 
@@ -85,12 +85,15 @@ freescreen(Screen *s)
 	uchar *a;
 	Display *d;
 
-	if(s == 0)
+	if(s == nil)
 		return 0;
 	d = s->display;
 	a = bufimage(d, 1+4);
-	if(a == 0)
+	if(a == nil){
+Error:
+		free(s);
 		return -1;
+	}
 	a[0] = 'F';
 	BPLONG(a+1, s->id);
 	/*
@@ -98,7 +101,7 @@ freescreen(Screen *s)
 	 * window, and want it to disappear visually.
 	 */
 	if(flushimage(d, 1) < 0)
-		return -1;
+		goto Error;
 	free(s);
 	return 1;
 }
@@ -116,8 +119,8 @@ _allocwindow(Image *i, Screen *s, Rectangle r, int ref, ulong val)
 
 	d = s->display;
 	i = _allocimage(i, d, r, d->screenimage->chan, 0, val, s->id, ref);
-	if(i == 0)
-		return 0;
+	if(i == nil)
+		return nil;
 	i->screen = s;
 	i->next = s->display->windows;
 	s->display->windows = i;
@@ -157,6 +160,8 @@ topbottom(Image **w, int n, int top)
 	if(n==0)
 		return;
 	b = bufimage(d, 1+1+2+4*n);
+	if(b == nil)
+		return;
 	b[0] = 't';
 	b[1] = top;
 	BPSHORT(b+2, n);
@@ -167,17 +172,15 @@ topbottom(Image **w, int n, int top)
 void
 bottomwindow(Image *w)
 {
-	if(w->screen == 0)
-		return;
-	topbottom(&w, 1, 0);
+	if(w->screen != nil)
+		topbottom(&w, 1, 0);
 }
 
 void
 topwindow(Image *w)
 {
-	if(w->screen == 0)
-		return;
-	topbottom(&w, 1, 1);
+	if(w->screen != nil)
+		topbottom(&w, 1, 1);
 }
 
 void