Terminal scrollback with ring buffer

This patch adds a ring buffer for scrollback to the terminal.  The
advantage of using a ring buffer is that the common case, scrolling with
no static screen content, can be achieved very efficiently by
incrementing and decrementing the starting line (modulo buffer size).

The scrollback buffer is limited to HISTSIZE lines in order to bound
memory usage. As the lines are allocated on demand, it is possible to
implement unlimited scrollback with few changes.  If the terminal is
reset, the scroll back buffer is reset, too.

4 files changed, 246 insertions, 122 deletions

diff --git a/config.def.h b/config.def.h
index 83aee0e..459690c 100644
--- a/config.def.h
+++ b/config.def.h
@@ -221,6 +221,8 @@ static Shortcut shortcuts[] = {
 	{ TERMMOD,              XK_Num_Lock,    numlock,        {.i =  0} },
 	{ MODKEY,               XK_l,           copyurl,        {.i =  0} },
 	{ MODKEY|ShiftMask,     XK_L,           copyurl,        {.i =  1} },
+	{ ShiftMask,            XK_Page_Up,     kscrollup,      {.f = -0.1} },
+	{ ShiftMask,            XK_Page_Down,   kscrolldown,    {.f = -0.1} },
 };
 
 /*
diff --git a/st.c b/st.c
index f3f7beb..50997ec 100644
--- a/st.c
+++ b/st.c
@@ -44,6 +44,10 @@
 #define ISCONTROL(c)		(ISCONTROLC0(c) || ISCONTROLC1(c))
 #define ISDELIM(u)		(u && wcschr(worddelimiters, u))
 
+#define TSCREEN term.screen[IS_SET(MODE_ALTSCREEN)]
+#define TLINEOFFSET(y) (((y) + TSCREEN.cur - TSCREEN.off + TSCREEN.size) % TSCREEN.size)
+#define TLINE(y) (TSCREEN.buffer[TLINEOFFSET(y)])
+
 enum term_mode {
 	MODE_WRAP        = 1 << 0,
 	MODE_INSERT      = 1 << 1,
@@ -110,12 +114,21 @@ typedef struct {
 	int alt;
 } Selection;
 
+/* Screen lines */
+typedef struct {
+	Line* buffer;  /* ring buffer */
+	int size;      /* size of buffer */
+	int cur;       /* start of active screen */
+	int off;       /* scrollback line offset */
+	TCursor sc;    /* saved cursor */
+} LineBuffer;
+
 /* Internal representation of the screen */
 typedef struct {
 	int row;      /* nb row */
 	int col;      /* nb col */
-	Line *line;   /* screen */
-	Line *alt;    /* alternate screen */
+	LineBuffer screen[2]; /* screen and alternate screen */
+	int linelen;  /* allocated line length */
 	int *dirty;   /* dirtyness of lines */
 	TCursor c;    /* cursor */
 	int ocx;      /* old cursor col */
@@ -212,6 +225,8 @@ static void tstrsequence(uchar);
 static int daddch(URLdfa *, char);
 
 static void drawregion(int, int, int, int);
+static void clearline(Line, Glyph, int, int);
+static Line ensureline(Line);
 
 static void selnormalize(void);
 static void selscroll(int, int);
@@ -417,11 +432,12 @@ int
 tlinelen(int y)
 {
 	int i = term.col;
+	Line line = TLINE(y);
 
-	if (term.line[y][i - 1].mode & ATTR_WRAP)
+	if (line[i - 1].mode & ATTR_WRAP)
 		return i;
 
-	while (i > 0 && term.line[y][i - 1].u == ' ')
+	while (i > 0 && line[i - 1].u == ' ')
 		--i;
 
 	return i;
@@ -530,7 +546,7 @@ selsnap(int *x, int *y, int direction)
 		 * Snap around if the word wraps around at the end or
 		 * beginning of a line.
 		 */
-		prevgp = &term.line[*y][*x];
+		prevgp = &TLINE(*y)[*x];
 		prevdelim = ISDELIM(prevgp->u);
 		for (;;) {
 			newx = *x + direction;
@@ -545,14 +561,14 @@ selsnap(int *x, int *y, int direction)
 					yt = *y, xt = *x;
 				else
 					yt = newy, xt = newx;
-				if (!(term.line[yt][xt].mode & ATTR_WRAP))
+				if (!(TLINE(yt)[xt].mode & ATTR_WRAP))
 					break;
 			}
 
 			if (newx >= tlinelen(newy))
 				break;
 
-			gp = &term.line[newy][newx];
+			gp = &TLINE(newy)[newx];
 			delim = ISDELIM(gp->u);
 			if (!(gp->mode & ATTR_WDUMMY) && (delim != prevdelim
 					|| (delim && gp->u != prevgp->u)))
@@ -573,14 +589,14 @@ selsnap(int *x, int *y, int direction)
 		*x = (direction < 0) ? 0 : term.col - 1;
 		if (direction < 0) {
 			for (; *y > 0; *y += direction) {
-				if (!(term.line[*y-1][term.col-1].mode
+				if (!(TLINE(*y-1)[term.col-1].mode
 						& ATTR_WRAP)) {
 					break;
 				}
 			}
 		} else if (direction > 0) {
 			for (; *y < term.row-1; *y += direction) {
-				if (!(term.line[*y][term.col-1].mode
+				if (!(TLINE(*y)[term.col-1].mode
 						& ATTR_WRAP)) {
 					break;
 				}
@@ -611,13 +627,13 @@ getsel(void)
 		}
 
 		if (sel.type == SEL_RECTANGULAR) {
-			gp = &term.line[y][sel.nb.x];
+			gp = &TLINE(y)[sel.nb.x];
 			lastx = sel.ne.x;
 		} else {
-			gp = &term.line[y][sel.nb.y == y ? sel.nb.x : 0];
+			gp = &TLINE(y)[sel.nb.y == y ? sel.nb.x : 0];
 			lastx = (sel.ne.y == y) ? sel.ne.x : term.col-1;
 		}
-		last = &term.line[y][MIN(lastx, linelen-1)];
+		last = &TLINE(y)[MIN(lastx, linelen-1)];
 		while (last >= gp && last->u == ' ')
 			--last;
 
@@ -958,12 +974,15 @@ int
 tattrset(int attr)
 {
 	int i, j;
+	int y = TLINEOFFSET(0);
 
 	for (i = 0; i < term.row-1; i++) {
+		Line line = TSCREEN.buffer[y];
 		for (j = 0; j < term.col-1; j++) {
-			if (term.line[i][j].mode & attr)
+			if (line[j].mode & attr)
 				return 1;
 		}
+		y = (y+1) % TSCREEN.size;
 	}
 
 	return 0;
@@ -985,14 +1004,17 @@ void
 tsetdirtattr(int attr)
 {
 	int i, j;
+	int y = TLINEOFFSET(0);
 
 	for (i = 0; i < term.row-1; i++) {
+		Line line = TSCREEN.buffer[y];
 		for (j = 0; j < term.col-1; j++) {
-			if (term.line[i][j].mode & attr) {
+			if (line[j].mode & attr) {
 				tsetdirt(i, i);
 				break;
 			}
 		}
+		y = (y+1) % TSCREEN.size;
 	}
 }
 
@@ -1005,27 +1027,19 @@ tfulldirt(void)
 void
 tcursor(int mode)
 {
-	static TCursor c[2];
-	int alt = IS_SET(MODE_ALTSCREEN);
-
 	if (mode == CURSOR_SAVE) {
-		c[alt] = term.c;
+		TSCREEN.sc = term.c;
 	} else if (mode == CURSOR_LOAD) {
-		term.c = c[alt];
-		tmoveto(c[alt].x, c[alt].y);
+		term.c = TSCREEN.sc;
+		tmoveto(term.c.x, term.c.y);
 	}
 }
 
 void
 treset(void)
 {
-	uint i;
-
-	term.c = (TCursor){{
-		.mode = ATTR_NULL,
-		.fg = defaultfg,
-		.bg = defaultbg
-	}, .x = 0, .y = 0, .state = CURSOR_DEFAULT};
+	int i, j;
+	Glyph g = (Glyph){ .fg = defaultfg, .bg = defaultbg};
 
 	memset(term.tabs, 0, term.col * sizeof(*term.tabs));
 	for (i = tabspaces; i < term.col; i += tabspaces)
@@ -1037,17 +1051,37 @@ treset(void)
 	term.charset = 0;
 
 	for (i = 0; i < 2; i++) {
-		tmoveto(0, 0);
-		tcursor(CURSOR_SAVE);
-		tclearregion(0, 0, term.col-1, term.row-1);
-		tswapscreen();
+		term.screen[i].sc = (TCursor){{
+			.fg = defaultfg,
+			.bg = defaultbg
+		}};
+		term.screen[i].cur = 0;
+		term.screen[i].off = 0;
+		for (j = 0; j < term.row; ++j) {
+			if (term.col != term.linelen)
+				term.screen[i].buffer[j] = xrealloc(term.screen[i].buffer[j], term.col * sizeof(Glyph));
+			clearline(term.screen[i].buffer[j], g, 0, term.col);
+		}
+		for (j = term.row; j < term.screen[i].size; ++j) {
+			free(term.screen[i].buffer[j]);
+			term.screen[i].buffer[j] = NULL;
+		}
 	}
+	tcursor(CURSOR_LOAD);
+	term.linelen = term.col;
+	tfulldirt();
 }
 
 void
 tnew(int col, int row)
 {
-	term = (Term){ .c = { .attr = { .fg = defaultfg, .bg = defaultbg } } };
+	int i;
+	term = (Term){};
+	term.screen[0].buffer = xmalloc(HISTSIZE * sizeof(Line));
+	term.screen[0].size = HISTSIZE;
+	term.screen[1].buffer = NULL;
+	for (i = 0; i < HISTSIZE; ++i) term.screen[0].buffer[i] = NULL;
+
 	tresize(col, row);
 	treset();
 }
@@ -1055,15 +1089,43 @@ tnew(int col, int row)
 void
 tswapscreen(void)
 {
-	Line *tmp = term.line;
-
-	term.line = term.alt;
-	term.alt = tmp;
 	term.mode ^= MODE_ALTSCREEN;
 	tfulldirt();
 }
 
 void
+kscrollup(const Arg *a)
+{
+	float n = a->f;
+
+	if (IS_SET(MODE_ALTSCREEN))
+		return;
+
+	if (n < 0) n = MAX((-n) * term.row, 1);
+	if (n > TSCREEN.size - term.row - TSCREEN.off) n = TSCREEN.size - term.row - TSCREEN.off;
+	while (!TLINE((int)-n)) --n;
+	TSCREEN.off += n;
+	selscroll(0, n);
+	tfulldirt();
+}
+
+void
+kscrolldown(const Arg *a)
+{
+
+	float n = a->f;
+
+	if (IS_SET(MODE_ALTSCREEN))
+		return;
+
+	if (n < 0) n = MAX((-n) * term.row, 1);
+	if (n > TSCREEN.off) n = TSCREEN.off;
+	TSCREEN.off -= n;
+	selscroll(0, -n);
+	tfulldirt();
+}
+
+void
 tscrolldown(int orig, int n)
 {
 	int i;
@@ -1071,15 +1133,29 @@ tscrolldown(int orig, int n)
 
 	LIMIT(n, 0, term.bot-orig+1);
 
-	tsetdirt(orig, term.bot-n);
-	tclearregion(0, term.bot-n+1, term.col-1, term.bot);
+	/* Ensure that lines are allocated */
+	for (i = -n; i < 0; i++) {
+		TLINE(i) = ensureline(TLINE(i));
+	}
 
-	for (i = term.bot; i >= orig+n; i--) {
-		temp = term.line[i];
-		term.line[i] = term.line[i-n];
-		term.line[i-n] = temp;
+	/* Shift non-scrolling areas in ring buffer */
+	for (i = term.bot+1; i < term.row; i++) {
+		temp = TLINE(i);
+		TLINE(i) = TLINE(i-n);
+		TLINE(i-n) = temp;
+	}
+	for (i = 0; i < orig; i++) {
+		temp = TLINE(i);
+		TLINE(i) = TLINE(i-n);
+		TLINE(i-n) = temp;
 	}
 
+	/* Scroll buffer */
+	TSCREEN.cur = (TSCREEN.cur + TSCREEN.size - n) % TSCREEN.size;
+	/* Clear lines that have entered the view */
+	tclearregion(0, orig, term.linelen-1, orig+n-1);
+	/* Redraw portion of the screen that has scrolled */
+	tsetdirt(orig+n-1, term.bot);
 	selscroll(orig, n);
 }
 
@@ -1091,15 +1167,29 @@ tscrollup(int orig, int n)
 
 	LIMIT(n, 0, term.bot-orig+1);
 
-	tclearregion(0, orig, term.col-1, orig+n-1);
-	tsetdirt(orig+n, term.bot);
+	/* Ensure that lines are allocated */
+	for (i = term.row; i < term.row + n; i++) {
+		TLINE(i) = ensureline(TLINE(i));
+	}
 
-	for (i = orig; i <= term.bot-n; i++) {
-		temp = term.line[i];
-		term.line[i] = term.line[i+n];
-		term.line[i+n] = temp;
+	/* Shift non-scrolling areas in ring buffer */
+	for (i = orig-1; i >= 0; i--) {
+		temp = TLINE(i);
+		TLINE(i) = TLINE(i+n);
+		TLINE(i+n) = temp;
+	}
+	for (i = term.row-1; i >term.bot; i--) {
+		temp = TLINE(i);
+		TLINE(i) = TLINE(i+n);
+		TLINE(i+n) = temp;
 	}
 
+	/* Scroll buffer */
+	TSCREEN.cur = (TSCREEN.cur + n) % TSCREEN.size;
+	/* Clear lines that have entered the view */
+	tclearregion(0, term.bot-n+1, term.linelen-1, term.bot);
+	/* Redraw portion of the screen that has scrolled */
+	tsetdirt(orig, term.bot-n+1);
 	selscroll(orig, -n);
 }
 
@@ -1229,6 +1319,7 @@ tsetchar(Rune u, const Glyph *attr, int x, int y)
 		"⎻", "─", "⎼", "⎽", "├", "┤", "┴", "┬", /* p - w */
 		"│", "≤", "≥", "π", "≠", "£", "·", /* x - ~ */
 	};
+	Line line = TLINE(y);
 
 	/*
 	 * The table is proudly stolen from rxvt.
@@ -1237,25 +1328,25 @@ tsetchar(Rune u, const Glyph *attr, int x, int y)
 	   BETWEEN(u, 0x41, 0x7e) && vt100_0[u - 0x41])
 		utf8decode(vt100_0[u - 0x41], &u, UTF_SIZ);
 
-	if (term.line[y][x].mode & ATTR_WIDE) {
+	if (line[x].mode & ATTR_WIDE) {
 		if (x+1 < term.col) {
-			term.line[y][x+1].u = ' ';
-			term.line[y][x+1].mode &= ~ATTR_WDUMMY;
+			line[x+1].u = ' ';
+			line[x+1].mode &= ~ATTR_WDUMMY;
 		}
-	} else if (term.line[y][x].mode & ATTR_WDUMMY) {
-		term.line[y][x-1].u = ' ';
-		term.line[y][x-1].mode &= ~ATTR_WIDE;
+	} else if (line[x].mode & ATTR_WDUMMY) {
+		line[x-1].u = ' ';
+		line[x-1].mode &= ~ATTR_WIDE;
 	}
 
 	term.dirty[y] = 1;
-	term.line[y][x] = *attr;
-	term.line[y][x].u = u;
+	line[x] = *attr;
+	line[x].u = u;
 }
 
 void
 tclearregion(int x1, int y1, int x2, int y2)
 {
-	int x, y, temp;
+	int x, y, L, S, temp;
 	Glyph *gp;
 
 	if (x1 > x2)
@@ -1263,15 +1354,16 @@ tclearregion(int x1, int y1, int x2, int y2)
 	if (y1 > y2)
 		temp = y1, y1 = y2, y2 = temp;
 
-	LIMIT(x1, 0, term.col-1);
-	LIMIT(x2, 0, term.col-1);
+	LIMIT(x1, 0, term.linelen-1);
+	LIMIT(x2, 0, term.linelen-1);
 	LIMIT(y1, 0, term.row-1);
 	LIMIT(y2, 0, term.row-1);
 
+	L = TLINEOFFSET(y1);
 	for (y = y1; y <= y2; y++) {
 		term.dirty[y] = 1;
 		for (x = x1; x <= x2; x++) {
-			gp = &term.line[y][x];
+			gp = &TSCREEN.buffer[L][x];
 			if (selected(x, y))
 				selclear();
 			gp->fg = term.c.attr.fg;
@@ -1279,6 +1371,7 @@ tclearregion(int x1, int y1, int x2, int y2)
 			gp->mode = 0;
 			gp->u = ' ';
 		}
+		L = (L + 1) % TSCREEN.size;
 	}
 }
 
@@ -1293,7 +1386,7 @@ tdeletechar(int n)
 	dst = term.c.x;
 	src = term.c.x + n;
 	size = term.col - src;
-	line = term.line[term.c.y];
+	line = TLINE(term.c.y);
 
 	memmove(&line[dst], &line[src], size * sizeof(Glyph));
 	tclearregion(term.col-n, term.c.y, term.col-1, term.c.y);
@@ -1310,7 +1403,7 @@ tinsertblank(int n)
 	dst = term.c.x + n;
 	src = term.c.x;
 	size = term.col - dst;
-	line = term.line[term.c.y];
+	line = TLINE(term.c.y);
 
 	memmove(&line[dst], &line[src], size * sizeof(Glyph));
 	tclearregion(src, term.c.y, dst - 1, term.c.y);
@@ -2168,7 +2261,7 @@ tdumpline(int n)
 	char buf[UTF_SIZ];
 	const Glyph *bp, *end;
 
-	bp = &term.line[n][0];
+	bp = &TLINE(n)[0];
 	end = &bp[MIN(tlinelen(n), term.col) - 1];
 	if (bp != end || bp->u != ' ') {
 		for ( ; bp <= end; ++bp)
@@ -2556,11 +2649,11 @@ check_control_code:
 	if (selected(term.c.x, term.c.y))
 		selclear();
 
-	gp = &term.line[term.c.y][term.c.x];
+	gp = &TLINE(term.c.y)[term.c.x];
 	if (IS_SET(MODE_WRAP) && (term.c.state & CURSOR_WRAPNEXT)) {
 		gp->mode |= ATTR_WRAP;
 		tnewline(1);
-		gp = &term.line[term.c.y][term.c.x];
+		gp = &TLINE(term.c.y)[term.c.x];
 	}
 
 	if (IS_SET(MODE_INSERT) && term.c.x+width < term.col) {
@@ -2573,7 +2666,7 @@ check_control_code:
 			tnewline(1);
 		else
 			tmoveto(term.col - width, term.c.y);
-		gp = &term.line[term.c.y][term.c.x];
+		gp = &TLINE(term.c.y)[term.c.x];
 	}
 
 	tsetchar(u, &term.c.attr, term.c.x, term.c.y);
@@ -2604,6 +2697,11 @@ twrite(const char *buf, int buflen, int show_ctrl)
 	Rune u;
 	int n;
 
+	if (TSCREEN.off) {
+		TSCREEN.off = 0;
+		tfulldirt();
+	}
+
 	for (n = 0; n < buflen; n += charsize) {
 		if (IS_SET(MODE_UTF8)) {
 			/* process a complete utf8 char */
@@ -2630,56 +2728,85 @@ twrite(const char *buf, int buflen, int show_ctrl)
 }
 
 void
-tresize(int col, int row)
+clearline(Line line, Glyph g, int x, int xend)
 {
 	int i;
+	g.mode = 0;
+	g.u = ' ';
+	for (i = x; i < xend; ++i) {
+		line[i] = g;
+	}
+}
+
+Line
+ensureline(Line line)
+{
+	if (!line) {
+		line = xmalloc(term.linelen * sizeof(Glyph));
+	}
+	return line;
+}
+
+void
+tresize(int col, int row)
+{
+	int i, j;
 	int minrow = MIN(row, term.row);
 	int mincol = MIN(col, term.col);
+	int linelen = MAX(col, term.linelen);
 	int *bp;
-	TCursor c;
 
-	if (col < 1 || row < 1) {
+	if (col < 1 || row < 1 || row > HISTSIZE) {
 		fprintf(stderr,
 		        "tresize: error resizing to %dx%d\n", col, row);
 		return;
 	}
 
-	/*
-	 * slide screen to keep cursor where we expect it -
-	 * tscrollup would work here, but we can optimize to
-	 * memmove because we're freeing the earlier lines
-	 */
-	for (i = 0; i <= term.c.y - row; i++) {
-		free(term.line[i]);
-		free(term.alt[i]);
+	/* Shift buffer to keep the cursor where we expect it */
+	if (row <= term.c.y) {
+		term.screen[0].cur = (term.screen[0].cur - row + term.c.y + 1) % term.screen[0].size;
+	}
+
+	/* Resize and clear line buffers as needed */
+	if (linelen > term.linelen) {
+		for (i = 0; i < term.screen[0].size; ++i) {
+			if (term.screen[0].buffer[i]) {
+				term.screen[0].buffer[i] = xrealloc(term.screen[0].buffer[i], linelen * sizeof(Glyph));
+				clearline(term.screen[0].buffer[i], term.c.attr, term.linelen, linelen);
+			}
+		}
+		for (i = 0; i < minrow; ++i) {
+			term.screen[1].buffer[i] = xrealloc(term.screen[1].buffer[i], linelen * sizeof(Glyph));
+			clearline(term.screen[1].buffer[i], term.c.attr, term.linelen, linelen);
+		}
 	}
-	/* ensure that both src and dst are not NULL */
-	if (i > 0) {
-		memmove(term.line, term.line + i, row * sizeof(Line));
-		memmove(term.alt, term.alt + i, row * sizeof(Line));
+	/* Allocate all visible lines for regular line buffer */
+	for (j = term.screen[0].cur, i = 0; i < row; ++i, j = (j + 1) % term.screen[0].size)
+	{
+		if (!term.screen[0].buffer[j]) {
+			term.screen[0].buffer[j] = xmalloc(linelen * sizeof(Glyph));
+		}
+		if (i >= term.row) {
+			clearline(term.screen[0].buffer[j], term.c.attr, 0, linelen);
+		}
 	}
-	for (i += row; i < term.row; i++) {
-		free(term.line[i]);
-		free(term.alt[i]);
+	/* Resize alt screen */
+	term.screen[1].cur = 0;
+	term.screen[1].size = row;
+	for (i = row; i < term.row; ++i) {
+		free(term.screen[1].buffer[i]);
+	}
+	term.screen[1].buffer = xrealloc(term.screen[1].buffer, row * sizeof(Line));
+	for (i = term.row; i < row; ++i) {
+		term.screen[1].buffer[i] = xmalloc(linelen * sizeof(Glyph));
+		clearline(term.screen[1].buffer[i], term.c.attr, 0, linelen);
 	}
 
 	/* resize to new height */
-	term.line = xrealloc(term.line, row * sizeof(Line));
-	term.alt  = xrealloc(term.alt,  row * sizeof(Line));
 	term.dirty = xrealloc(term.dirty, row * sizeof(*term.dirty));
 	term.tabs = xrealloc(term.tabs, col * sizeof(*term.tabs));
 
-	/* resize each row to new width, zero-pad if needed */
-	for (i = 0; i < minrow; i++) {
-		term.line[i] = xrealloc(term.line[i], col * sizeof(Glyph));
-		term.alt[i]  = xrealloc(term.alt[i],  col * sizeof(Glyph));
-	}
-
-	/* allocate any new rows */
-	for (/* i = minrow */; i < row; i++) {
-		term.line[i] = xmalloc(col * sizeof(Glyph));
-		term.alt[i] = xmalloc(col * sizeof(Glyph));
-	}
+	/* fix tabstops */
 	if (col > term.col) {
 		bp = term.tabs + term.col;
 
@@ -2689,26 +2816,16 @@ tresize(int col, int row)
 		for (bp += tabspaces; bp < term.tabs + col; bp += tabspaces)
 			*bp = 1;
 	}
+
 	/* update terminal size */
 	term.col = col;
 	term.row = row;
+	term.linelen = linelen;
 	/* reset scrolling region */
 	tsetscroll(0, row-1);
 	/* make use of the LIMIT in tmoveto */
 	tmoveto(term.c.x, term.c.y);
-	/* Clearing both screens (it makes dirty all lines) */
-	c = term.c;
-	for (i = 0; i < 2; i++) {
-		if (mincol < col && 0 < minrow) {
-			tclearregion(mincol, 0, col - 1, minrow - 1);
-		}
-		if (0 < col && minrow < row) {
-			tclearregion(0, minrow, col - 1, row - 1);
-		}
-		tswapscreen();
-		tcursor(CURSOR_LOAD);
-	}
-	term.c = c;
+	tfulldirt();
 }
 
 void
@@ -2720,14 +2837,15 @@ resettitle(void)
 void
 drawregion(int x1, int y1, int x2, int y2)
 {
-	int y;
+	int y, L;
 
+	L = TLINEOFFSET(y1);
 	for (y = y1; y < y2; y++) {
-		if (!term.dirty[y])
-			continue;
-
-		term.dirty[y] = 0;
-		xdrawline(term.line[y], x1, y, x2);
+		if (term.dirty[y]) {
+			term.dirty[y] = 0;
+			xdrawline(TSCREEN.buffer[L], x1, y, x2);
+		}
+		L = (L + 1) % TSCREEN.size;
 	}
 }
 
@@ -2742,15 +2860,16 @@ draw(void)
 	/* adjust cursor position */
 	LIMIT(term.ocx, 0, term.col-1);
 	LIMIT(term.ocy, 0, term.row-1);
-	if (term.line[term.ocy][term.ocx].mode & ATTR_WDUMMY)
+	if (TLINE(term.ocy)[term.ocx].mode & ATTR_WDUMMY)
 		term.ocx--;
-	if (term.line[term.c.y][cx].mode & ATTR_WDUMMY)
+	if (TLINE(term.c.y)[cx].mode & ATTR_WDUMMY)
 		cx--;
 
 	drawregion(0, 0, term.col, term.row);
-	xdrawcursor(cx, term.c.y, term.line[term.c.y][cx],
-		term.ocx, term.ocy, term.line[term.ocy][term.ocx],
-		term.line[term.ocy], term.col);
+	if (TSCREEN.off == 0)
+		xdrawcursor(cx, term.c.y, TLINE(term.c.y)[cx],
+				term.ocx, term.ocy, TLINE(term.ocy)[term.ocx],
+				TLINE(term.ocy), term.col);
 	term.ocx = cx;
 	term.ocy = term.c.y;
 	xfinishdraw();
@@ -2831,7 +2950,7 @@ copyurl(const Arg *arg) {
 		** we hit previous occurrence of URL
 		*/
 		for (col = colend; col--;)
-			if (daddch(&dfa, term.line[row][col].u < 128 ? term.line[row][col].u : ' '))
+			if (daddch(&dfa, TLINE(row)[col].u < 128 ? TLINE(row)[col].u : ' '))
 				break;
 
 		if (col >= 0)
diff --git a/st.h b/st.h
index eee067a..03f8561 100644
--- a/st.h
+++ b/st.h
@@ -19,6 +19,7 @@
 
 #define TRUECOLOR(r,g,b)	(1 << 24 | (r) << 16 | (g) << 8 | (b))
 #define IS_TRUECOL(x)		(1 << 24 & (x))
+#define HISTSIZE            2000
 
 enum glyph_attribute {
 	ATTR_NULL       = 0,
diff --git a/x.c b/x.c
index e0eb263..a82dde9 100644
--- a/x.c
+++ b/x.c
@@ -69,6 +69,8 @@ static void zoom(const Arg *);
 static void zoomabs(const Arg *);
 static void zoomreset(const Arg *);
 static void ttysend(const Arg *);
+void kscrollup(const Arg *);
+void kscrolldown(const Arg *);
 
 /* config.h for applying patches and the configuration. */
 #include "config.h"