From 1b0a2cff51fe179afebd2fa954fa6223851629ad Mon Sep 17 00:00:00 2001
From: Werner Almesberger <werner@almesberger.net>
Date: Wed, 30 Jan 2013 20:35:30 -0300
Subject: [PATCH] ubb-la/gui.c: use powers of two for zoom and integer
 arithmetic (WIP)

This looks better and avoids the risk of math issues.
---
 ubb-la/gui.c | 111 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 90 insertions(+), 21 deletions(-)

diff --git a/ubb-la/gui.c b/ubb-la/gui.c
index c0482aa..5c7a7c2 100644
--- a/ubb-la/gui.c
+++ b/ubb-la/gui.c
@@ -30,7 +30,7 @@
 #define	CH_SKIP		16
 #define	CH_HEIGHT	8
 
-#define	MAX_ZOOM	8
+#define	MAX_ZOOM	3
 
 
 static SDL_Surface *surf;
@@ -77,34 +77,61 @@ static void change(int x, int ch)
 }
 
 
-static void level(int x, int ch, int v)
+static void level(int x0, int x1, int ch, int v)
 {
-	pixelColor(surf, x, ch_y(ch, v), LEVEL_RGBA);
+	if (x0 == x1)
+		pixelColor(surf, x0, ch_y(ch, v), LEVEL_RGBA);
+	else
+		hlineColor(surf, x0, x1, ch_y(ch, v), LEVEL_RGBA);
 }
 
 
-static void show_buffer(const uint8_t *buf, int skip, int nibbles,
+static void show_buffer_zoom_in(const uint8_t *buf, int skip, int nibbles,
     int x0, int x1)
 {
-	double f = (nibbles-skip)/(x1-x0+1.0);
+	int f = (x1-x0)/(nibbles-skip);
+	int x, i, j;
+	int last[4] = { -1, -1, -1, -1};
+	uint8_t v, bit;
+
+fprintf(stderr, "in: %d-%d (%d) Sa %d-%d (%d) pix %d f (%d)\n",
+    skip, nibbles, nibbles-skip, x0, x1, x1-x0, f, f*(nibbles-skip));
+	x = x0;
+	for (i = skip; i != nibbles; i++) {
+		v = (buf[i >> 1] >> 4*(~i & 1)) & 0xf;
+		for (j = 0; j != 4; j++) {
+			bit = (v >> j) & 1;
+			if (bit == last[j] || last[j] == -1) {
+				level(x, x+f-1, j, bit);
+			} else {
+				change(x, j);
+				level(x+1, x+f-1, j, bit);
+			}
+			last[j] = bit;
+		}
+		x += f;
+	}
+}
+
+
+static void show_buffer_zoom_out(const uint8_t *buf, int skip, int nibbles,
+    int x0, int x1)
+{
+	int f = (nibbles-skip)/(x1-x0);
 	int x;
-	int i = skip-1, n, j;
+	int i = skip, 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;
-		}
+fprintf(stderr, "out: %d-%d (%d) Sa %d-%d (%d) pix %d f (%d)\n",
+    skip, nibbles, nibbles-skip, x0, x1, x1-x0, f, f*(x1-x0));
+	for (x = x0; x != x1; x++) {
+		n = i+f;
 		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;
@@ -113,12 +140,13 @@ static void show_buffer(const uint8_t *buf, int skip, int nibbles,
 					next[j] = bit;
 				}
 			}
+			i++;
 		}
 		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]);
+				level(x, x, j, next[j]);
 			else
 				change(x, j);
 			last[j] = next[j];
@@ -127,6 +155,45 @@ static void show_buffer(const uint8_t *buf, int skip, int nibbles,
 }
 
 
+static void show_buffer(const uint8_t *buf, int skip, int nibbles,
+    int x0, int x1, int zoom, int pos)
+{
+	int xm, w, p0, p1;
+	int d;
+
+	xm = (x0+x1) >> 1;
+	if (zoom < 0) {
+		w = (nibbles-skip) >> -zoom;
+		p0 = xm-(w >> 1);
+		p1 = xm+((w+1) >> 1);
+		if (p0 < x0) {
+			skip += (x0-p0) << -zoom;
+			p0 = x0;
+		}
+		if (p1 > x1) {
+			nibbles -= (p1-x1) << -zoom;
+			p1 = x1;
+		}
+		show_buffer_zoom_out(buf, skip, nibbles, p0, p1);
+	} else {
+		w = (nibbles-skip) << zoom;
+		p0 = xm-(w >> 1);
+		p1 = xm+((w+1) >> 1);
+		if (p0 < x0) {
+			d = ((x0-p0)+(1 << zoom)-1) >> zoom;
+			skip += d;
+			p0 += d << zoom;
+		}
+		if (p1 > x1) {
+			d = ((p1-x1)+(1 << zoom)-1) >> zoom;
+			nibbles -= d;
+			p1 -= d << zoom;
+		}
+		show_buffer_zoom_in(buf, skip, nibbles, p0, p1);
+	}
+}
+
+
 static void update(void)
 {
 	SDL_UnlockSurface(surf);
@@ -137,14 +204,16 @@ static void update(void)
 void gui(const uint8_t *buf, int skip, int nibbles)
 {
 	SDL_Event event;
-	int zoom = 0;
-	int m, w;
+	int pos = (skip+nibbles) >> 1;
+	int zoom;	/* < 0: zoom out; 0: 1 pixel = 1 sample; > 1: zoom in */
+	int min_zoom = 0;
 
+	while (XRES-CH_XOFF < (nibbles-skip) >> -min_zoom)
+		min_zoom--;
+	zoom = min_zoom;
 	while (1) {
-		m = (nibbles-skip) >> 1;
-		w = (nibbles-skip) >> zoom;
 		clear();
-		show_buffer(buf, m-(w >> 1), m+(w >> 1), CH_XOFF, XRES-1);
+		show_buffer(buf, skip, nibbles, CH_XOFF, XRES, zoom, pos);
 		update();
 
 		do {
@@ -157,7 +226,7 @@ void gui(const uint8_t *buf, int skip, int nibbles)
 						zoom++;
 					break;
 				case SDLK_DOWN:
-					if (zoom)
+					if (zoom > min_zoom)
 						zoom--;
 					break;
 				case SDLK_RETURN: