diff --git a/ubb-la/gui.c b/ubb-la/gui.c
new file mode 100644
index 0000000..c0482aa
--- /dev/null
+++ b/ubb-la/gui.c
@@ -0,0 +1,179 @@
+/*
+ * gui.c - Graphical output for ubb-la
+ *
+ * Written 2013 by Werner Almesberger
+ * Copyright 2013 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "SDL.h"
+#include "SDL_gfxPrimitives.h"
+
+#include "gui.h"
+
+
+#define XRES	320	/* canvas width */
+#define YRES	240	/* canvas height */
+
+#define	LEVEL_RGBA	0xffff00ff
+#define	BOUNCE_RGBA	0xff8080ff
+
+#define	CH_XOFF		30
+#define	CH_YOFF		30
+#define	CH_SKIP		16
+#define	CH_HEIGHT	8
+
+#define	MAX_ZOOM	8
+
+
+static SDL_Surface *surf;
+
+
+void gui_init(void)
+{
+	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
+		fprintf(stderr, "SDL_init: %s\n", SDL_GetError());
+		exit(1);
+	}
+	atexit(SDL_Quit);
+
+	surf = SDL_SetVideoMode(XRES, YRES, 0, SDL_SWSURFACE);
+	if (!surf) {
+		fprintf(stderr, "SDL_SetVideoMode: %s\n", SDL_GetError());
+		exit(1);
+	}
+}
+
+
+static void clear(void)
+{
+	SDL_LockSurface(surf);
+	SDL_FillRect(surf, NULL, SDL_MapRGB(surf->format, 0, 0, 0));
+}
+
+
+static inline int ch_y(int ch, int v)
+{
+	return CH_YOFF+CH_SKIP*ch+(v ? 0 : CH_HEIGHT);
+}
+
+
+static void bounce(int x, int ch)
+{
+	vlineColor(surf, x, ch_y(ch, 0), ch_y(ch, 1), BOUNCE_RGBA);
+}
+
+
+static void change(int x, int ch)
+{
+	vlineColor(surf, x, ch_y(ch, 0), ch_y(ch, 1), LEVEL_RGBA);
+}
+
+
+static void level(int x, int ch, int v)
+{
+	pixelColor(surf, x, ch_y(ch, v), LEVEL_RGBA);
+}
+
+
+static void show_buffer(const uint8_t *buf, int skip, int nibbles,
+    int x0, int x1)
+{
+	double f = (nibbles-skip)/(x1-x0+1.0);
+	int x;
+	int i = skip-1, n, j;
+	int changes[4], last[4] = { -1, -1, -1, -1}, next[4];
+	uint8_t v, bit;
+
+	for (x = x0; x != x1+1; x++) {
+		n = (x-x0)*f+skip;
+		if (i == n) {
+			for (j = 0; j != 4; j++)
+				level(x, j, last[j]);
+			continue;
+		}
+		for (j = 0; j != 4; j++) {
+			next[j] = last[j];
+			changes[j] = 0;
+		}
+		while (i != n) {
+			i++;
+			v = (buf[i >> 1] >> 4*(~i & 1)) & 0xf;
+			for (j = 0; j != 4; j++) {
+				bit = (v >> j) & 1;
+				if (bit != next[j]) {
+					changes[j]++;
+					next[j] = bit;
+				}
+			}
+		}
+		for (j = 0; j != 4; j++) {
+			if (changes[j] > 1)
+				bounce(x, j);
+			else if (!changes[j] || last[j] == -1)
+				level(x, j, next[j]);
+			else
+				change(x, j);
+			last[j] = next[j];
+		}
+	}
+}
+
+
+static void update(void)
+{
+	SDL_UnlockSurface(surf);
+	SDL_UpdateRect(surf, 0, 0, 0, 0);
+}
+
+
+void gui(const uint8_t *buf, int skip, int nibbles)
+{
+	SDL_Event event;
+	int zoom = 0;
+	int m, w;
+
+	while (1) {
+		m = (nibbles-skip) >> 1;
+		w = (nibbles-skip) >> zoom;
+		clear();
+		show_buffer(buf, m-(w >> 1), m+(w >> 1), CH_XOFF, XRES-1);
+		update();
+
+		do {
+			SDL_WaitEvent(&event);
+			switch (event.type) {
+			case SDL_KEYDOWN:
+				switch (event.key.keysym.sym) {
+				case SDLK_UP:
+					if (zoom < MAX_ZOOM)
+						zoom++;
+					break;
+				case SDLK_DOWN:
+					if (zoom)
+						zoom--;
+					break;
+				case SDLK_RETURN:
+				case SDLK_q:
+					return;
+				default:
+					printf("%x\n", event.key.keysym.sym);
+					continue;
+				}
+				break;
+			case SDL_QUIT:
+				return;
+			default:
+				continue;
+			}	
+		}
+		while (0);
+	}
+}
diff --git a/ubb-la/gui.h b/ubb-la/gui.h
new file mode 100644
index 0000000..f3b552a
--- /dev/null
+++ b/ubb-la/gui.h
@@ -0,0 +1,23 @@
+/*
+ * gui.h - Graphical output for ubb-la
+ *
+ * Written 2013 by Werner Almesberger
+ * Copyright 2013 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#ifndef GUI_H
+#define	GUI_H
+
+#include <stdint.h>
+
+
+void gui_init(void);
+void gui(const uint8_t *buf, int skip, int nibbles);
+
+#endif /* !GUI_H */