commit 308bc705a0482ddc18020ab584c11a9f37723cf9
parent b68b11fb5b9332ecd1f1d5173a2294a43c73dbbb
Author: Milos Nikic <nikic.milos@gmail.com>
Date: Tue, 13 Jan 2026 16:35:38 -0800
Alternative standalone scrollback, reflow using ring buffer and view offset
Implement scrollback as a fixed-size ring buffer and render
history by offsetting the view instead of copying screen
contents.
Implement reflow of history and screen content on resize
if it is needed.
Tradeoffs / differences vs other scrollback patches:
- One patch vs many to get the same functionality
- Scrollback is disabled on the alternate screen
- Simpler model than the existing scrollback patch set
- Mouse wheel scrolling enabled by default
- When using vim, mouse movement will no longer move
the cursor.
- There can be visual artifacts if width of the window is
shrank to the size smaller than the shell promp.
Diffstat:
2 files changed, 1153 insertions(+), 0 deletions(-)
diff --git a/st.suckless.org/patches/scrollback-reflow-standalone/index.md b/st.suckless.org/patches/scrollback-reflow-standalone/index.md
@@ -0,0 +1,114 @@
+scrollback-reflow-standalone
+============================
+
+Description
+-----------
+A standalone scrollback and reflow implementation for st that integrates history storage,
+mouse scrolling, selection handling, and resize reflow into a single cohesive
+patch.
+
+This implementation achieves this by modifying st’s resize and screen buffer handling.
+It is intended as an alternative design, not as a patch stack to be combined
+with other scrollback-related patches.
+
+---
+
+Why another scrollback patch?
+-----------------------------
+
+*TLDR*
+Because one patch should be easier to integrate than many.
+
+Existing scrollback patches for st tend to address individual features in
+isolation (history storage, mouse scrolling, resize behavior, or selection).
+When combined, these patches often interact in subtle ways, particularly during
+terminal resize operations.
+
+This patch explores a unified approach where scrollback storage, rendering,
+selection, and resize handling are driven through a single abstraction.
+By routing all visible content through the same view layer, it avoids common
+issues such as selection drift, incorrect wrapping after resize, and conflicting
+mouse behavior.
+
+The goal is not to replace existing solutions, but to provide a standalone
+alternative that emphasizes correctness and predictable behavior.
+
+---
+
+Key Features
+------------
+
+* Ring buffer scrollback with O(1) insertion
+* Text reflow on resize (O(N) in scrollback size)
+* Mouse wheel and touchpad scrolling
+* Altscreen-aware mouse handling (applications like vim and tmux receive mouse
+ events when requested)
+* No more text clipping when shrinking st's window
+* Visual cursor is hidden while viewing scrollback history
+* Stable selection while scrolling through history
+
+---
+
+Resize Reflow
+-------------
+
+When the terminal width changes, scrollback content is reflowed to match the new
+column width. Wrapped lines are flattened and rewrapped so that text is neither
+clipped nor lost when shrinking the window.
+
+To reduce overhead, reflow is skipped when not needed.
+
+---
+
+Patch Compatibility
+-------------------
+
+This patch modifies `tresize()` and related resize handling to support scrollback
+reflow and history preservation across window size changes.
+
+As a result, it is **not intended to be combined** with other scrollback patches
+or patches that modify `tresize()` or rely on its stock side effects.
+It should be treated as a standalone alternative for the existing scrollback
+model.
+
+Patches that do not modify scrollback or resize behavior (e.g. transparency,
+clipboard helpers, key bindings) are generally easier to integrate.
+
+---
+
+Notes & Caveats
+---------------
+
+* **Screen-bound selection:** Selection is tied to visible screen coordinates.
+ If a selection is scrolled completely off-screen while viewing history, it is
+ cleared. This is a deliberate design choice to avoid rewriting the selection
+ engine.
+
+* **Shell prompt artifacts:** During resize in which the window becomes very narrow,
+ shell prompts may appear duplicated or briefly "ghosted".
+ This is normal behavior caused by the shell reacting to `SIGWINCH` while st
+ simultaneously reflows historical content.
+
+---
+
+Configuration
+-------------
+
+* **Scrollback size:** Configurable via `scrollback_lines` in `config.h`
+ (default: 5000).
+
+* **Key bindings:** Defaults to `MouseWheel`
+
+---
+
+Download
+--------
+
+* [st-scrollback-reflow-standalone-0.9.3.diff](st-scrollback-reflow-standalone-0.9.3.diff)
+
+---
+
+Author
+------
+
+* Loshmi <nloshmi@gmail.com>
diff --git a/st.suckless.org/patches/scrollback-reflow-standalone/st-scrollback-reflow-standalone-0.9.3.diff b/st.suckless.org/patches/scrollback-reflow-standalone/st-scrollback-reflow-standalone-0.9.3.diff
@@ -0,0 +1,1039 @@
+From 6d7584cc382fd24e5da92baf3ac333b5dda12f3c Mon Sep 17 00:00:00 2001
+From: Milos Nikic <nikic.milos@gmail.com>
+Date: Thu, 8 Jan 2026 22:04:25 -0800
+Subject: [PATCH] st: alternative scrollback using ring buffer and view offset
+
+Implement scrollback as a fixed-size ring buffer and render history
+by offsetting the view instead of copying screen contents.
+Implement reflow of history and screen content on resizeif it is needed.
+
+Tradeoffs / differences:
+- Scrollback is disabled on the alternate screen
+- Simpler model than the existing scrollback patch set
+- Mouse wheel scrolling enabled by default
+- When using vim, mouse movement will no longer move the cursor.
+- There can be visual artifacts if width of the window is shrank to the size smaller than the shell promp.
+---
+ config.def.h | 5 +
+ st.c | 710 ++++++++++++++++++++++++++++++++++++++++++++-------
+ st.h | 5 +
+ x.c | 17 ++
+ 4 files changed, 644 insertions(+), 93 deletions(-)
+
+diff --git a/config.def.h b/config.def.h
+index 2cd740a..a0b14e9 100644
+--- a/config.def.h
++++ b/config.def.h
+@@ -472,3 +472,8 @@ static char ascii_printable[] =
+ " !\"#$%&'()*+,-./0123456789:;<=>?"
+ "@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_"
+ "`abcdefghijklmnopqrstuvwxyz{|}~";
++
++/*
++ * The amount of lines scrollback can hold before it wraps around.
++ */
++unsigned int scrollback_lines = 5000;
+diff --git a/st.c b/st.c
+index e55e7b3..3f6b4a8 100644
+--- a/st.c
++++ b/st.c
+@@ -5,6 +5,7 @@
+ #include <limits.h>
+ #include <pwd.h>
+ #include <stdarg.h>
++#include <stdint.h>
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <string.h>
+@@ -178,7 +179,7 @@ static void tdeletechar(int);
+ static void tdeleteline(int);
+ static void tinsertblank(int);
+ static void tinsertblankline(int);
+-static int tlinelen(int);
++static int tlinelen(Line);
+ static void tmoveto(int, int);
+ static void tmoveato(int, int);
+ static void tnewline(int);
+@@ -232,6 +233,379 @@ static const uchar utfmask[UTF_SIZ + 1] = {0xC0, 0x80, 0xE0, 0xF0, 0xF8};
+ static const Rune utfmin[UTF_SIZ + 1] = { 0, 0, 0x80, 0x800, 0x10000};
+ static const Rune utfmax[UTF_SIZ + 1] = {0x10FFFF, 0x7F, 0x7FF, 0xFFFF, 0x10FFFF};
+
++typedef struct
++{
++ Line *buf; /* ring of Line pointers */
++ int cap; /* max number of lines */
++ int len; /* current number of valid lines (<= cap) */
++ int head; /* physical index of logical oldest (valid when len>0) */
++ uint64_t base; /* Can overflow in the extreme */
++ /*
++ * max_width tracks the widest line ever pushed to scrollback.
++ * It may be conservative (stale) if that line has since been
++ * evicted from the ring buffer, which is acceptable - it just
++ * means we might reflow when not strictly necessary, which is
++ * better than skipping a needed reflow.
++ */
++ int max_width;
++ int view_offset; /* 0 means live screen */
++} Scrollback;
++
++static Scrollback sb;
++
++static int
++sb_phys_index(int logical_idx)
++{
++ /* logical_idx: 0..sb.len-1 (0 = oldest) */
++ return (sb.head + logical_idx) % sb.cap;
++}
++
++static Line
++lineclone(Line src)
++{
++ Line dst;
++
++ if (!src)
++ return NULL;
++
++ dst = xmalloc(term.col * sizeof(Glyph));
++ memcpy(dst, src, term.col * sizeof(Glyph));
++ return dst;
++}
++
++static void
++sb_init(int lines)
++{
++ int i;
++
++ sb.buf = xmalloc(sizeof(Line) * lines);
++ sb.cap = lines;
++ sb.len = 0;
++ sb.head = 0;
++ sb.base = 0;
++ for (i = 0; i < sb.cap; i++)
++ sb.buf[i] = NULL;
++
++ sb.view_offset = 0;
++ sb.max_width = 0;
++}
++
++/* Push one screen line into scrollback.
++ * Overwrites oldest when full (ring buffer).
++ */
++static void
++sb_push(Line line)
++{
++ Line copy;
++ int tail;
++ int width;
++
++ if (sb.cap <= 0)
++ return;
++
++ copy = lineclone(line);
++
++ if (sb.len < sb.cap) {
++ tail = sb_phys_index(sb.len);
++ sb.buf[tail] = copy;
++ sb.len++;
++ } else {
++ /* We might've just evicted the widest line... */
++ free(sb.buf[sb.head]);
++ sb.buf[sb.head] = copy;
++ sb.head = (sb.head + 1) % sb.cap;
++ sb.base++;
++ }
++ width = tlinelen(copy);
++ /* ...so max_width might be stale. */
++ if (width > sb.max_width)
++ sb.max_width = width;
++}
++
++static Line
++sb_get(int idx)
++{
++ /* idx is logical: 0..sb.len-1 */
++ if (idx < 0 || idx >= sb.len)
++ return NULL;
++ return sb.buf[sb_phys_index(idx)];
++}
++
++static void
++sb_clear(void)
++{
++ int i;
++ int p;
++
++ if (!sb.buf)
++ return;
++
++ for (i = 0; i < sb.len; i++) {
++ p = sb_phys_index(i);
++ if (sb.buf[p]) {
++ free(sb.buf[p]);
++ sb.buf[p] = NULL;
++ }
++ }
++
++ sb.len = 0;
++ sb.head = 0;
++ sb.base = 0;
++ sb.view_offset = 0;
++ sb.max_width = 0;
++}
++
++/*
++ * Reflows the scrollback buffer to fit a new terminal width.
++ *
++ * The algorithm works in three steps:
++ * 1) Unwrap: It iterates through the existing history, joining physical lines
++ * marked with ATTR_WRAP into a single continuous 'logical' line.
++ * 2) Reflow: It slices this logical line into new chunks of size 'col'.
++ * - New wrap flags are applied where the text exceeds the new width.
++ * - Trailing spaces are trimmed to prevent ghost padding.
++ * 3) Rebuild: The new lines are pushed into a fresh ring buffer.
++ * - Uses O(1) ring insertion (updating head/tail) to avoid expensive
++ * memmoves during resize, but it is still O(N) where N is the existing
++ * history.
++ *
++ * Note: During reflow we reset sb to match the rebuilt buffer
++ * (head, base and len might change).
++ */
++static void
++sb_resize(int col)
++{
++ Line *new_buf;
++ int i, j;
++ int new_len, logical_cap, logical_len, is_wrapped, cursor;
++ int copy_width, tail, current_width;
++ Line logical, line, nl;
++ uint64_t new_base = 0;
++ int new_head = 0;
++ int new_max_width = 0;
++ Glyph *g;
++
++ new_len = 0;
++
++ if (sb.len == 0)
++ return;
++
++ new_buf = xmalloc(sizeof(Line) * sb.cap);
++ for (i = 0; i < sb.cap; i++)
++ new_buf[i] = NULL;
++
++ logical_cap = term.col * 2;
++ logical = xmalloc(logical_cap * sizeof(Glyph));
++ logical_len = 0;
++
++ for (i = 0; i < sb.len; i++) {
++ /* Unwrap: Accumulate physical lines into one logical line. */
++ line = sb_get(i);
++ is_wrapped = (line[term.col - 1].mode & ATTR_WRAP);
++ if (logical_len + term.col > logical_cap) {
++ logical_cap *= 2;
++ logical = xrealloc(logical, logical_cap * sizeof(Glyph));
++ }
++
++ memcpy(logical + logical_len, line, term.col * sizeof(Glyph));
++ for (j = 0; j < term.col; j++) {
++ logical[logical_len + j].mode &= ~ATTR_WRAP;
++ }
++ logical_len += term.col;
++ /* If the line was wrapped, continue accumulating before reflowing. */
++ if (is_wrapped) {
++ continue;
++ }
++ /* Trim trailing spaces from the fully unwrapped line. */
++ while (logical_len > 0) {
++ g = &logical[logical_len - 1];
++ if (g->u == ' ' && g->bg == defaultbg
++ && (g->mode & ATTR_BOLD) == 0) {
++ logical_len--;
++ } else {
++ break;
++ }
++ }
++ if (logical_len == 0)
++ logical_len = 1;
++
++ /* Reflow: Split the logical line into new chunks. */
++ cursor = 0;
++ while (cursor < logical_len) {
++ nl = xmalloc(col * sizeof(Glyph));
++ for (j = 0; j < col; j++) {
++ nl[j].fg = defaultfg;
++ nl[j].bg = defaultbg;
++ nl[j].mode = 0;
++ nl[j].u = ' ';
++ }
++
++ copy_width = logical_len - cursor;
++ if (copy_width > col)
++ copy_width = col;
++
++ memcpy(nl, logical + cursor, copy_width * sizeof(Glyph));
++
++ for (j = 0; j < copy_width; j++) {
++ nl[j].mode &= ~ATTR_WRAP;
++ }
++
++ if (cursor + copy_width < logical_len) {
++ nl[col - 1].mode |= ATTR_WRAP;
++ } else {
++ nl[col - 1].mode &= ~ATTR_WRAP;
++ }
++
++ /* Rebuild: Push new lines into the ring buffer. */
++ if (new_len < sb.cap) {
++ tail = (new_head + new_len) % sb.cap;
++ new_buf[tail] = nl;
++ new_len++;
++ } else {
++ free(new_buf[new_head]);
++ new_buf[new_head] = nl;
++ new_head = (new_head + 1) % sb.cap;
++ new_base++;
++ }
++ current_width = (cursor + copy_width < logical_len) ? col : copy_width;
++ if (current_width > new_max_width)
++ new_max_width = current_width;
++ cursor += copy_width;
++ }
++ logical_len = 0;
++ }
++ free(logical);
++ sb_clear();
++ free(sb.buf);
++ sb.buf = new_buf;
++ sb.len = new_len;
++ sb.head = new_head;
++ sb.base = new_base;
++ sb.view_offset = 0;
++ sb.max_width = new_max_width;
++}
++
++static void
++sb_pop_screen(int loaded, int new_cols)
++{
++ int i, p;
++ int start_logical;
++ Line line;
++
++ loaded = MIN(loaded, sb.len);
++ start_logical = sb.len - loaded;
++ new_cols = MIN(new_cols, term.col);
++ for (i = 0; i < loaded; i++) {
++ p = sb_phys_index(start_logical + i);
++ line = sb.buf[p];
++
++ memcpy(term.line[i], line, new_cols * sizeof(Glyph));
++
++ free(line);
++ sb.buf[p] = NULL;
++ }
++
++ sb.len -= loaded;
++}
++
++static uint64_t
++sb_view_start(void)
++{
++ return sb.base + sb.len - sb.view_offset;
++}
++
++static void
++sb_view_changed(void)
++{
++ if (!term.dirty || term.row <= 0)
++ return;
++ tfulldirt();
++}
++
++static void
++selscrollback(int delta)
++{
++ if (delta == 0)
++ return;
++
++ if (sel.ob.x == -1 || sel.mode == SEL_EMPTY)
++ return;
++
++ if (sel.alt != IS_SET(MODE_ALTSCREEN))
++ return;
++
++ sel.nb.y += delta;
++ sel.ne.y += delta;
++ sel.ob.y += delta;
++ sel.oe.y += delta;
++
++ if (sel.ne.y < 0 || sel.nb.y >= term.row)
++ selclear();
++
++ sb_view_changed();
++}
++
++static Line
++emptyline(void)
++{
++ static Line empty;
++ static int empty_cols;
++ int i = 0;
++
++ if (empty_cols != term.col) {
++ free(empty);
++ empty = xmalloc(term.col * sizeof(Glyph));
++ empty_cols = term.col;
++ }
++
++ for (i = 0; i < term.col; i++) {
++ empty[i] = term.c.attr;
++ empty[i].u = ' ';
++ empty[i].mode = 0;
++ }
++ return empty;
++}
++
++static Line
++renderline(int y)
++{
++ int start, v;
++
++ if (sb.view_offset <= 0)
++ return term.line[y];
++
++ start = sb.len - sb.view_offset; /* can be negative */
++ v = start + y;
++
++ if (v < 0)
++ return emptyline();
++
++ if (v < sb.len)
++ return sb_get(v);
++
++ /* past scrollback -> into current screen */
++ v -= sb.len;
++ if (v >= 0 && v < term.row)
++ return term.line[v];
++
++ return emptyline();
++}
++
++static void
++sb_reset_on_clear(void)
++{
++ sb_clear();
++ sb_view_changed();
++ if (sel.ob.x != -1 && term.row > 0)
++ selclear();
++}
++
++int
++tisaltscreen(void)
++{
++ return IS_SET(MODE_ALTSCREEN);
++}
++
+ ssize_t
+ xwrite(int fd, const char *s, size_t len)
+ {
+@@ -404,20 +778,23 @@ selinit(void)
+ sel.ob.x = -1;
+ }
+
+-int
+-tlinelen(int y)
++static int
++tlinelen(Line line)
+ {
+ int i = term.col;
+-
+- 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;
+ }
+
++static int
++tlinelen_render(int y)
++{
++ return tlinelen(renderline(y));
++}
++
+ void
+ selstart(int col, int row, int snap)
+ {
+@@ -485,10 +862,10 @@ selnormalize(void)
+ /* expand selection over line breaks */
+ if (sel.type == SEL_RECTANGULAR)
+ return;
+- i = tlinelen(sel.nb.y);
++ i = tlinelen_render(sel.nb.y);
+ if (i < sel.nb.x)
+ sel.nb.x = i;
+- if (tlinelen(sel.ne.y) <= sel.ne.x)
++ if (tlinelen_render(sel.ne.y) <= sel.ne.x)
+ sel.ne.x = term.col - 1;
+ }
+
+@@ -514,6 +891,7 @@ selsnap(int *x, int *y, int direction)
+ int newx, newy, xt, yt;
+ int delim, prevdelim;
+ const Glyph *gp, *prevgp;
++ Line line;
+
+ switch (sel.snap) {
+ case SNAP_WORD:
+@@ -521,7 +899,7 @@ 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 = &renderline(*y)[*x];
+ prevdelim = ISDELIM(prevgp->u);
+ for (;;) {
+ newx = *x + direction;
+@@ -536,14 +914,15 @@ selsnap(int *x, int *y, int direction)
+ yt = *y, xt = *x;
+ else
+ yt = newy, xt = newx;
+- if (!(term.line[yt][xt].mode & ATTR_WRAP))
++ line = renderline(yt);
++ if (!(line[xt].mode & ATTR_WRAP))
+ break;
+ }
+
+- if (newx >= tlinelen(newy))
++ if (newx >= tlinelen_render(newy))
+ break;
+
+- gp = &term.line[newy][newx];
++ gp = &renderline(newy)[newx];
+ delim = ISDELIM(gp->u);
+ if (!(gp->mode & ATTR_WDUMMY) && (delim != prevdelim
+ || (delim && gp->u != prevgp->u)))
+@@ -564,14 +943,14 @@ 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 (!(renderline(*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 (!(renderline(*y)[term.col-1].mode
+ & ATTR_WRAP)) {
+ break;
+ }
+@@ -585,8 +964,9 @@ char *
+ getsel(void)
+ {
+ char *str, *ptr;
+- int y, bufsize, lastx, linelen;
++ int y, bufsize, lastx, linelen, end_idx, insert_newline, is_wrapped;
+ const Glyph *gp, *last;
++ Line line;
+
+ if (sel.ob.x == -1)
+ return NULL;
+@@ -596,29 +976,33 @@ getsel(void)
+
+ /* append every set & selected glyph to the selection */
+ for (y = sel.nb.y; y <= sel.ne.y; y++) {
+- if ((linelen = tlinelen(y)) == 0) {
++ line = renderline(y);
++ linelen = tlinelen_render(y);
++
++ if (linelen == 0) {
+ *ptr++ = '\n';
+ continue;
+ }
+
+ if (sel.type == SEL_RECTANGULAR) {
+- gp = &term.line[y][sel.nb.x];
++ gp = &line[sel.nb.x];
+ lastx = sel.ne.x;
+ } else {
+- gp = &term.line[y][sel.nb.y == y ? sel.nb.x : 0];
++ gp = &line[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)];
+- while (last >= gp && last->u == ' ')
++ end_idx = MIN(lastx, linelen-1);
++ is_wrapped = (line[end_idx].mode & ATTR_WRAP) != 0;
++ last = &line[end_idx];
++ while (last >= gp && last->u == ' ') {
+ --last;
++ }
+
+ for ( ; gp <= last; ++gp) {
+ if (gp->mode & ATTR_WDUMMY)
+ continue;
+-
+ ptr += utf8encode(gp->u, ptr);
+ }
+-
+ /*
+ * Copy and pasting of line endings is inconsistent
+ * in the inconsistent terminal and GUI world.
+@@ -628,8 +1012,13 @@ getsel(void)
+ * st.
+ * FIXME: Fix the computer world.
+ */
++ insert_newline = 0;
+ if ((y < sel.ne.y || lastx >= linelen) &&
+- (!(last->mode & ATTR_WRAP) || sel.type == SEL_RECTANGULAR))
++ (!is_wrapped || sel.type == SEL_RECTANGULAR)) {
++ insert_newline = 1;
++ }
++
++ if (insert_newline)
+ *ptr++ = '\n';
+ }
+ *ptr = 0;
+@@ -845,6 +1234,12 @@ ttywrite(const char *s, size_t n, int may_echo)
+ {
+ const char *next;
+
++ if (sb.view_offset > 0) {
++ selclear();
++ sb.view_offset = 0;
++ sb_view_changed();
++ }
++
+ if (may_echo && IS_SET(MODE_ECHO))
+ twrite(s, n, 1);
+
+@@ -965,6 +1360,8 @@ tsetdirt(int top, int bot)
+ {
+ int i;
+
++ if (term.row < 1)
++ return;
+ LIMIT(top, 0, term.row-1);
+ LIMIT(bot, 0, term.row-1);
+
+@@ -1030,15 +1427,21 @@ treset(void)
+ for (i = 0; i < 2; i++) {
+ tmoveto(0, 0);
+ tcursor(CURSOR_SAVE);
+- tclearregion(0, 0, term.col-1, term.row-1);
++ if (term.col > 0 && term.row > 0 && term.line > 0)
++ tclearregion(0, 0, term.col-1, term.row-1);
+ tswapscreen();
+ }
++ sb_clear();
++ if (sel.ob.x != -1 && term.row > 0)
++ selclear();
+ }
+
++
+ void
+ tnew(int col, int row)
+ {
+ term = (Term){ .c = { .attr = { .fg = defaultfg, .bg = defaultbg } } };
++ sb_init(scrollback_lines);
+ tresize(col, row);
+ treset();
+ }
+@@ -1078,10 +1481,37 @@ void
+ tscrollup(int orig, int n)
+ {
+ int i;
++ uint64_t newstart;
++ uint64_t oldstart;
++
++ int attop;
+ Line temp;
+
++ oldstart = sb_view_start();
+ LIMIT(n, 0, term.bot-orig+1);
+
++ if (!IS_SET(MODE_ALTSCREEN) && orig == term.top) {
++ /* At top of history only if history exists */
++ attop = (sb.len != 0 && sb.view_offset == sb.len);
++
++ if (sb.view_offset > 0 && !attop)
++ sb.view_offset += n;
++
++ for (i = 0; i < n; i++)
++ sb_push(term.line[orig + i]);
++
++ /* if at the top, keep me there */
++ if (attop)
++ sb.view_offset = sb.len;
++ /* otherwise clamp me */
++ else if (sb.view_offset > sb.len)
++ sb.view_offset = sb.len;
++ }
++
++ newstart = sb_view_start();
++ if (sb.view_offset > 0)
++ selscrollback(oldstart - newstart);
++
+ tclearregion(0, orig, term.col-1, orig+n-1);
+ tsetdirt(orig+n, term.bot);
+
+@@ -1097,6 +1527,8 @@ tscrollup(int orig, int n)
+ void
+ selscroll(int orig, int n)
+ {
++ if (sb.view_offset != 0)
++ return;
+ if (sel.ob.x == -1 || sel.alt != IS_SET(MODE_ALTSCREEN))
+ return;
+
+@@ -1717,6 +2149,12 @@ csihandle(void)
+ break;
+ case 2: /* all */
+ tclearregion(0, 0, term.col-1, term.row-1);
++ if (!IS_SET(MODE_ALTSCREEN))
++ sb_reset_on_clear();
++ break;
++ case 3:
++ if (!IS_SET(MODE_ALTSCREEN))
++ sb_reset_on_clear();
+ break;
+ default:
+ goto unknown;
+@@ -2106,7 +2544,7 @@ tdumpline(int n)
+ const Glyph *bp, *end;
+
+ bp = &term.line[n][0];
+- end = &bp[MIN(tlinelen(n), term.col) - 1];
++ end = &bp[MIN(tlinelen_render(n), term.col) - 1];
+ if (bp != end || bp->u != ' ') {
+ for ( ; bp <= end; ++bp)
+ tprinter(buf, utf8encode(bp->u, buf));
+@@ -2163,6 +2601,36 @@ tdeftran(char ascii)
+ }
+ }
+
++static void
++kscroll(const Arg *arg)
++{
++ uint64_t oldstart;
++ uint64_t newstart;
++
++ oldstart = sb_view_start();
++ sb.view_offset += arg->i;
++ LIMIT(sb.view_offset, 0, sb.len);
++ newstart = sb_view_start();
++
++ selscrollback(oldstart - newstart);
++ redraw();
++}
++
++void
++kscrolldown(const Arg *arg)
++{
++ Arg a;
++
++ a.i = -arg->i;
++ kscroll(&a);
++}
++
++void
++kscrollup(const Arg *arg)
++{
++ kscroll(arg);
++}
++
+ void
+ tdectest(char c)
+ {
+@@ -2569,83 +3037,136 @@ twrite(const char *buf, int buflen, int show_ctrl)
+ void
+ tresize(int col, int row)
+ {
+- int i;
++ int i, j;
++ int min_limit;
+ int minrow = MIN(row, term.row);
+- int mincol = MIN(col, term.col);
+- int *bp;
+- TCursor c;
++ int old_row = term.row;
++ int old_col = term.col;
++ int save_end = 0; /* Track effective pushed height */
++ int loaded = 0;
++ int pop_width = 0;
++ int needs_reflow = 0;
++ int is_alt = IS_SET(MODE_ALTSCREEN);
++ Line *tmp;
+
+ if (col < 1 || row < 1) {
+ fprintf(stderr,
+- "tresize: error resizing to %dx%d\n", col, row);
++ "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]);
+- }
+- /* 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));
+- }
+- for (i += row; i < term.row; i++) {
+- free(term.line[i]);
+- free(term.alt[i]);
++ /* Operate on the currently visible screen buffer. */
++ if (is_alt) {
++ tmp = term.line;
++ term.line = term.alt;
++ term.alt = tmp;
+ }
+
+- /* 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));
++ save_end = term.row;
++ if (term.row != 0 && term.col != 0) {
++ if (!is_alt && term.c.y > 0 && term.c.y < term.row) {
++ term.line[term.c.y - 1][term.col - 1].mode &= ~ATTR_WRAP;
++ }
++ min_limit = is_alt ? 0 : term.c.y;
+
+- /* 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));
+- }
++ for (i = term.row - 1; i > min_limit; i--) {
++ if (tlinelen(term.line[i]) > 0)
++ break;
++ }
++ save_end = i + 1;
+
+- /* allocate any new rows */
+- for (/* i = minrow */; i < row; i++) {
+- term.line[i] = xmalloc(col * sizeof(Glyph));
+- term.alt[i] = xmalloc(col * sizeof(Glyph));
++ for (i = 0; i < save_end; i++) {
++ sb_push(term.line[i]);
++ }
++ /* Optimization: Only reflow if content doesn't fit in new width.
++ * This avoids expensive reflow operations when resizing doesn't
++ * affect line wrapping (e.g., when terminal is wide enough). */
++ if (col > term.col) {
++ /* Growing: Only reflow if history was wrapped at old width */
++ needs_reflow = sb.max_width >= term.col;
++ } else if (col < term.col) {
++ /* Shrinking: Only reflow if content is wider than new width. */
++ if (sb.max_width > col)
++ needs_reflow = 1;
++ }
++ if (needs_reflow) {
++ sb_resize(col);
++ } else {
++ /* If we don't reflow, we still need to reset the view
++ * because sb_pop_screen() might change the history length. */
++ sb.view_offset = 0;
++ }
+ }
+- if (col > term.col) {
+- bp = term.tabs + term.col;
+
+- memset(bp, 0, sizeof(*term.tabs) * (col - term.col));
+- while (--bp > term.tabs && !*bp)
+- /* nothing */ ;
+- for (bp += tabspaces; bp < term.tabs + col; bp += tabspaces)
+- *bp = 1;
+- }
+- /* update terminal size */
++ if (term.line) {
++ for (i = 0; i < term.row; i++) {
++ free(term.line[i]);
++ free(term.alt[i]);
++ }
++ free(term.line);
++ free(term.alt);
++ free(term.dirty);
++ free(term.tabs);
++ }
++
+ term.col = col;
+ term.row = row;
+- /* 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);
++
++ term.line = xmalloc(term.row * sizeof(Line));
++ term.alt = xmalloc(term.row * sizeof(Line));
++ term.dirty = xmalloc(term.row * sizeof(int));
++ term.tabs = xmalloc(term.col * sizeof(*term.tabs));
++
++ for (i = 0; i < term.row; i++) {
++ term.line[i] = xmalloc(term.col * sizeof(Glyph));
++ term.alt[i] = xmalloc(term.col * sizeof(Glyph));
++ term.dirty[i] = 1;
++
++ for (j = 0; j < term.col; j++) {
++ term.line[i][j] = term.c.attr;
++ term.line[i][j].u = ' ';
++ term.line[i][j].mode = 0;
++
++ term.alt[i][j] = term.c.attr;
++ term.alt[i][j].u = ' ';
++ term.alt[i][j].mode = 0;
+ }
+- tswapscreen();
+- tcursor(CURSOR_LOAD);
+ }
+- term.c = c;
++
++ memset(term.tabs, 0, term.col * sizeof(*term.tabs));
++ for (i = 8; i < term.col; i += 8)
++ term.tabs[i] = 1;
++
++ tsetscroll(0, term.row - 1);
++
++ if (minrow > 0) {
++ loaded = MIN(sb.len, term.row);
++ pop_width = needs_reflow ? col : MIN(col, old_col);
++ sb_pop_screen(loaded, pop_width);
++ }
++ if (is_alt) {
++ tmp = term.line;
++ term.line = term.alt;
++ term.alt = tmp;
++ }
++ if (!is_alt && old_row > 0) {
++ term.c.y += (loaded - save_end);
++ }
++ if (term.c.y >= term.row) {
++ term.c.y = term.row - 1;
++ }
++ if (term.c.x >= term.col) {
++ term.c.x = term.col - 1;
++ }
++ if (term.c.y < 0) {
++ term.c.y = 0;
++ }
++ if (term.c.x < 0) {
++ term.c.x = 0;
++ }
++
++ tfulldirt();
++ sb_view_changed();
+ }
+
+ void
+@@ -2659,12 +3180,13 @@ drawregion(int x1, int y1, int x2, int y2)
+ {
+ int y;
+
++ Line line;
+ for (y = y1; y < y2; y++) {
+ if (!term.dirty[y])
+ continue;
+-
+ term.dirty[y] = 0;
+- xdrawline(term.line[y], x1, y, x2);
++ line = renderline(y);
++ xdrawline(line, x1, y, x2);
+ }
+ }
+
+@@ -2685,10 +3207,12 @@ draw(void)
+ 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.ocx = cx;
+- term.ocy = term.c.y;
++ if (sb.view_offset == 0) {
++ xdrawcursor(cx, term.c.y, term.line[term.c.y][cx],
++ term.ocx, term.ocy, term.line[term.ocy][term.ocx]);
++ term.ocx = cx;
++ term.ocy = term.c.y;
++ }
+ xfinishdraw();
+ if (ocx != term.ocx || ocy != term.ocy)
+ xximspot(term.ocx, term.ocy);
+diff --git a/st.h b/st.h
+index fd3b0d8..151d0c6 100644
+--- a/st.h
++++ b/st.h
+@@ -86,6 +86,7 @@ void printsel(const Arg *);
+ void sendbreak(const Arg *);
+ void toggleprinter(const Arg *);
+
++int tisaltscreen(void);
+ int tattrset(int);
+ void tnew(int, int);
+ void tresize(int, int);
+@@ -111,6 +112,9 @@ void *xmalloc(size_t);
+ void *xrealloc(void *, size_t);
+ char *xstrdup(const char *);
+
++void kscrollup(const Arg *arg);
++void kscrolldown(const Arg *arg);
++
+ /* config.h globals */
+ extern char *utmp;
+ extern char *scroll;
+@@ -124,3 +128,4 @@ extern unsigned int tabspaces;
+ extern unsigned int defaultfg;
+ extern unsigned int defaultbg;
+ extern unsigned int defaultcs;
++extern unsigned int scrollback_lines;
+diff --git a/x.c b/x.c
+index d73152b..75f3db1 100644
+--- a/x.c
++++ b/x.c
+@@ -472,6 +472,23 @@ bpress(XEvent *e)
+ struct timespec now;
+ int snap;
+
++ if (btn == Button4 || btn == Button5) {
++ Arg a;
++ if (IS_SET(MODE_MOUSE) && !(e->xbutton.state & forcemousemod)) {
++ mousereport(e);
++ return;
++ }
++ if (!tisaltscreen()) {
++ a.i = 1;
++ if (btn == Button4) {
++ kscrollup(&a);
++ } else {
++ kscrolldown(&a);
++ }
++ }
++ return;
++ }
++
+ if (1 <= btn && btn <= 11)
+ buttons |= 1 << (btn-1);
+
+--
+2.52.0
+
