appy scrollback-ringbuffer patch

5 files changed, 979 insertions, 122 deletions

diff --git a/config.def.h b/config.def.h
index 5fad72a..1660264 100644
--- a/config.def.h
+++ b/config.def.h
@@ -228,6 +228,8 @@ static Shortcut shortcuts[] = {
 	{ ShiftMask,            XK_Insert,      selpaste,       {.i =  0} },
 	{ TERMMOD,              XK_Num_Lock,    numlock,        {.i =  0} },
 	{ MODKEY,               XK_l,           copyurl,        {.i =  0} },
+        { ShiftMask,            XK_Page_Up,     kscrollup,      {.i = -1} },
+        { ShiftMask,            XK_Page_Down,   kscrolldown,    {.i = -1} },
 };
 
 /*
diff --git a/patches/st-scrollback-ringbuffer-0.8.5.diff b/patches/st-scrollback-ringbuffer-0.8.5.diff
new file mode 100644
index 0000000..7c060c5
--- /dev/null
+++ b/patches/st-scrollback-ringbuffer-0.8.5.diff
@@ -0,0 +1,730 @@
+commit 0663bdf11a409961da5b1120741a69814da8ce65
+Author: Timo Röhling <timo@gaussglocke.de>
+Date:   Tue Nov 23 19:45:33 2021 +0100
+
+    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.
+
+diff --git a/config.def.h b/config.def.h
+index 91ab8ca..e3b469b 100644
+--- a/config.def.h
++++ b/config.def.h
+@@ -201,6 +201,8 @@ static Shortcut shortcuts[] = {
+ 	{ TERMMOD,              XK_Y,           selpaste,       {.i =  0} },
+ 	{ ShiftMask,            XK_Insert,      selpaste,       {.i =  0} },
+ 	{ TERMMOD,              XK_Num_Lock,    numlock,        {.i =  0} },
++	{ ShiftMask,            XK_Page_Up,     kscrollup,      {.i = -1} },
++	{ ShiftMask,            XK_Page_Down,   kscrolldown,    {.i = -1} },
+ };
+ 
+ /*
+diff --git a/st.c b/st.c
+index 51049ba..f9e24ba 100644
+--- a/st.c
++++ b/st.c
+@@ -43,6 +43,10 @@
+ #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,
+@@ -109,12 +113,21 @@ 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 */
+@@ -202,6 +215,8 @@ static void tdeftran(char);
+ static void tstrsequence(uchar);
+ 
+ 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);
+@@ -415,11 +430,12 @@ 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;
+@@ -528,7 +544,7 @@ 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;
+@@ -543,14 +559,14 @@ 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)))
+@@ -571,14 +587,14 @@ 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;
+ 				}
+@@ -609,13 +625,13 @@ 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;
+ 
+@@ -956,12 +972,15 @@ 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;
+@@ -983,14 +1002,17 @@ 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;
+ 	}
+ }
+ 
+@@ -1003,27 +1025,19 @@ 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)
+@@ -1035,17 +1049,37 @@ 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();
+ }
+@@ -1053,14 +1087,42 @@ 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)
++{
++	int n = a->i;
++
++	if (IS_SET(MODE_ALTSCREEN))
++		return;
++
++	if (n < 0) n = (-n) * term.row;
++	if (n > TSCREEN.size - term.row - TSCREEN.off) n = TSCREEN.size - term.row - TSCREEN.off;
++	while (!TLINE(-n)) --n;
++	TSCREEN.off += n;
++	selscroll(0, n);
++	tfulldirt();
++}
++
++void
++kscrolldown(const Arg *a)
++{
++
++	int n = a->i;
++
++	if (IS_SET(MODE_ALTSCREEN))
++		return;
++
++	if (n < 0) n = (-n) * term.row;
++	if (n > TSCREEN.off) n = TSCREEN.off;
++	TSCREEN.off -= n;
++	selscroll(0, -n);
++	tfulldirt();
++}
++
+ void
+ tscrolldown(int orig, int n)
+ {
+@@ -1069,15 +1131,29 @@ 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);
+ }
+ 
+@@ -1089,15 +1165,29 @@ 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);
+ }
+ 
+@@ -1201,6 +1291,7 @@ 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.
+@@ -1209,25 +1300,25 @@ 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)
+@@ -1235,15 +1326,16 @@ 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;
+@@ -1251,6 +1343,7 @@ tclearregion(int x1, int y1, int x2, int y2)
+ 			gp->mode = 0;
+ 			gp->u = ' ';
+ 		}
++		L = (L + 1) % TSCREEN.size;
+ 	}
+ }
+ 
+@@ -1265,7 +1358,7 @@ 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);
+@@ -1282,7 +1375,7 @@ 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);
+@@ -2103,7 +2196,7 @@ 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)
+@@ -2486,11 +2579,11 @@ 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)
+@@ -2498,7 +2591,7 @@ check_control_code:
+ 
+ 	if (term.c.x+width > term.col) {
+ 		tnewline(1);
+-		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);
+@@ -2529,6 +2622,11 @@ 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 */
+@@ -2555,56 +2653,85 @@ 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;
+ 
+@@ -2614,26 +2741,16 @@ 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
+@@ -2645,14 +2762,15 @@ 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;
+ 	}
+ }
+ 
+@@ -2667,14 +2785,15 @@ 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]);
++	if (TSCREEN.off == 0)
++		xdrawcursor(cx, term.c.y, TLINE(term.c.y)[cx],
++				term.ocx, term.ocy, TLINE(term.ocy)[term.ocx]);
+ 	term.ocx = cx;
+ 	term.ocy = term.c.y;
+ 	xfinishdraw();
+diff --git a/st.h b/st.h
+index 519b9bd..b48e810 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 8a16faa..1bb5853 100644
+--- a/x.c
++++ b/x.c
+@@ -59,6 +59,8 @@ 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"
diff --git a/st.c b/st.c
index 34347ce..62a9944 100644
--- a/st.c
+++ b/st.c
@@ -43,6 +43,10 @@
 #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,
@@ -109,12 +113,21 @@ 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 */
@@ -208,6 +221,8 @@ 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);
@@ -413,11 +428,12 @@ 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;
@@ -526,7 +542,7 @@ 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;
@@ -541,14 +557,14 @@ 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)))
@@ -569,14 +585,14 @@ 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;
 				}
@@ -607,13 +623,13 @@ 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;
 
@@ -954,12 +970,15 @@ 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;
@@ -981,14 +1000,17 @@ 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;
 	}
 }
 
@@ -1001,27 +1023,19 @@ 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)
@@ -1033,17 +1047,37 @@ 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();
 }
@@ -1051,15 +1085,43 @@ 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)
+{
+	int n = a->i;
+
+	if (IS_SET(MODE_ALTSCREEN))
+		return;
+
+	if (n < 0) n = (-n) * term.row;
+	if (n > TSCREEN.size - term.row - TSCREEN.off) n = TSCREEN.size - term.row - TSCREEN.off;
+	while (!TLINE(-n)) --n;
+	TSCREEN.off += n;
+	selscroll(0, n);
+	tfulldirt();
+}
+
+void
+kscrolldown(const Arg *a)
+{
+
+	int n = a->i;
+
+	if (IS_SET(MODE_ALTSCREEN))
+		return;
+
+	if (n < 0) n = (-n) * term.row;
+	if (n > TSCREEN.off) n = TSCREEN.off;
+	TSCREEN.off -= n;
+	selscroll(0, -n);
+	tfulldirt();
+}
+
+void
 tscrolldown(int orig, int n)
 {
 	int i;
@@ -1067,15 +1129,29 @@ 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);
 }
 
@@ -1087,15 +1163,29 @@ 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);
 }
 
@@ -1199,6 +1289,7 @@ 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.
@@ -1207,28 +1298,28 @@ 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;
 
 	if (isboxdraw(u))
-		term.line[y][x].mode |= ATTR_BOXDRAW;
+		line[x].mode |= ATTR_BOXDRAW;
 }
 
 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)
@@ -1236,15 +1327,16 @@ 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;
@@ -1252,6 +1344,7 @@ tclearregion(int x1, int y1, int x2, int y2)
 			gp->mode = 0;
 			gp->u = ' ';
 		}
+		L = (L + 1) % TSCREEN.size;
 	}
 }
 
@@ -1266,7 +1359,7 @@ 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);
@@ -1283,7 +1376,7 @@ 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);
@@ -2104,7 +2197,7 @@ 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)
@@ -2488,11 +2581,11 @@ 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)
@@ -2500,7 +2593,7 @@ check_control_code:
 
 	if (term.c.x+width > term.col) {
 		tnewline(1);
-		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);
@@ -2531,6 +2624,11 @@ 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 */
@@ -2557,56 +2655,85 @@ 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);
+		}
+	}
+	/* 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]);
 	}
-	for (i += row; i < term.row; i++) {
-		free(term.line[i]);
-		free(term.alt[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;
 
@@ -2616,26 +2743,16 @@ 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
@@ -2647,14 +2764,15 @@ 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;
 	}
 }
 
@@ -2669,14 +2787,15 @@ 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]);
+	if (TSCREEN.off == 0)
+		xdrawcursor(cx, term.c.y, TLINE(term.c.y)[cx],
+				term.ocx, term.ocy, TLINE(term.ocy)[term.ocx]);
 	term.ocx = cx;
 	term.ocy = term.c.y;
 	xfinishdraw();
@@ -2742,6 +2861,9 @@ copyurl(const Arg *arg) {
 		 *match = NULL;
 	URLdfa dfa = { 0 };
 
+	int y = TLINEOFFSET(0);
+	Line line = TSCREEN.buffer[y];
+
 	row = (sel.ob.x >= 0 && sel.nb.y > 0) ? sel.nb.y : term.bot;
 	LIMIT(row, term.top, term.bot);
 
@@ -2757,7 +2879,7 @@ 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, line[col].u < 128 ? line[col].u : ' '))
 				break;
 
 		if (col >= 0)
diff --git a/st.h b/st.h
index f085e62..94293f9 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 6f2ddff..ff736f7 100644
--- a/x.c
+++ b/x.c
@@ -60,6 +60,8 @@ 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"