Implement change-preview and change-preview-window actions

The new actions are named with 'change-' prefix to differentiate from
the pre-existing, one-off 'preview(...)' action.

Fix #2360
Fix #2505
Fix #2666

Related #2435
Related #2376
  - Can set up multiple bindings with different change-preview-window actions
  - Not possible to "rotate" through the options with a single binding
  - Enlarge or shrink not possible

5 files changed, 367 insertions, 221 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2b2d20ce..84754022 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,13 @@
 CHANGELOG
 =========
 
+0.29.0
+------
+- Added `change-preview(...)` action to change the `--preview` command
+    - cf. `preview(...)` is a one-off action that doesn't change the default
+      preview command
+- Added `change-preview-window(...)` action
+
 0.28.0
 ------
 - Added `--header-first` option to print header before the prompt line
diff --git a/man/man1/fzf.1 b/man/man1/fzf.1
index 5f5eb91e..c87d2c73 100644
--- a/man/man1/fzf.1
+++ b/man/man1/fzf.1
@@ -21,7 +21,7 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 ..
-.TH fzf 1 "Nov 2021" "fzf 0.28.0" "fzf - a command-line fuzzy finder"
+.TH fzf 1 "Dec 2021" "fzf 0.29.0" "fzf - a command-line fuzzy finder"
 
 .SH NAME
 fzf - a command-line fuzzy finder
@@ -810,77 +810,79 @@ e.g.
 A key or an event can be bound to one or more of the following actions.
 
   \fBACTION:                   DEFAULT BINDINGS (NOTES):
-    \fBabort\fR                     \fIctrl-c  ctrl-g  ctrl-q  esc\fR
-    \fBaccept\fR                    \fIenter   double-click\fR
-    \fBaccept-non-empty\fR          (same as \fBaccept\fR except that it prevents fzf from exiting without selection)
-    \fBbackward-char\fR             \fIctrl-b  left\fR
-    \fBbackward-delete-char\fR      \fIctrl-h  bspace\fR
-    \fBbackward-delete-char/eof\fR  (same as \fBbackward-delete-char\fR except aborts fzf if query is empty)
-    \fBbackward-kill-word\fR        \fIalt-bs\fR
-    \fBbackward-word\fR             \fIalt-b   shift-left\fR
-    \fBbeginning-of-line\fR         \fIctrl-a  home\fR
-    \fBcancel\fR                    (clear query string if not empty, abort fzf otherwise)
-    \fBchange-prompt(...)\fR        (change prompt to the given string)
-    \fBclear-screen\fR              \fIctrl-l\fR
-    \fBclear-selection\fR           (clear multi-selection)
-    \fBclose\fR                     (close preview window if open, abort fzf otherwise)
-    \fBclear-query\fR               (clear query string)
-    \fBdelete-char\fR               \fIdel\fR
-    \fBdelete-char/eof\fR           \fIctrl-d\fR (same as \fBdelete-char\fR except aborts fzf if query is empty)
+    \fBabort\fR                      \fIctrl-c  ctrl-g  ctrl-q  esc\fR
+    \fBaccept\fR                     \fIenter   double-click\fR
+    \fBaccept-non-empty\fR           (same as \fBaccept\fR except that it prevents fzf from exiting without selection)
+    \fBbackward-char\fR              \fIctrl-b  left\fR
+    \fBbackward-delete-char\fR       \fIctrl-h  bspace\fR
+    \fBbackward-delete-char/eof\fR   (same as \fBbackward-delete-char\fR except aborts fzf if query is empty)
+    \fBbackward-kill-word\fR         \fIalt-bs\fR
+    \fBbackward-word\fR              \fIalt-b   shift-left\fR
+    \fBbeginning-of-line\fR          \fIctrl-a  home\fR
+    \fBcancel\fR                     (clear query string if not empty, abort fzf otherwise)
+    \fBchange-preview(...)\fR        (change \fB--preview\fR option)
+    \fBchange-preview-window(...)\fR (change \fB--preview-window\fR option)
+    \fBchange-prompt(...)\fR         (change prompt to the given string)
+    \fBclear-screen\fR               \fIctrl-l\fR
+    \fBclear-selection\fR            (clear multi-selection)
+    \fBclose\fR                      (close preview window if open, abort fzf otherwise)
+    \fBclear-query\fR                (clear query string)
+    \fBdelete-char\fR                \fIdel\fR
+    \fBdelete-char/eof\fR            \fIctrl-d\fR (same as \fBdelete-char\fR except aborts fzf if query is empty)
     \fBdeselect\fR
-    \fBdeselect-all\fR              (deselect all matches)
-    \fBdisable-search\fR            (disable search functionality)
-    \fBdown\fR                      \fIctrl-j  ctrl-n  down\fR
-    \fBenable-search\fR             (enable search functionality)
-    \fBend-of-line\fR               \fIctrl-e  end\fR
-    \fBexecute(...)\fR              (see below for the details)
-    \fBexecute-silent(...)\fR       (see below for the details)
-    \fBfirst\fR                     (move to the first match)
-    \fBforward-char\fR              \fIctrl-f  right\fR
-    \fBforward-word\fR              \fIalt-f   shift-right\fR
+    \fBdeselect-all\fR               (deselect all matches)
+    \fBdisable-search\fR             (disable search functionality)
+    \fBdown\fR                       \fIctrl-j  ctrl-n  down\fR
+    \fBenable-search\fR              (enable search functionality)
+    \fBend-of-line\fR                \fIctrl-e  end\fR
+    \fBexecute(...)\fR               (see below for the details)
+    \fBexecute-silent(...)\fR        (see below for the details)
+    \fBfirst\fR                      (move to the first match)
+    \fBforward-char\fR               \fIctrl-f  right\fR
+    \fBforward-word\fR               \fIalt-f   shift-right\fR
     \fBignore\fR
-    \fBjump\fR                      (EasyMotion-like 2-keystroke movement)
-    \fBjump-accept\fR               (jump and accept)
+    \fBjump\fR                       (EasyMotion-like 2-keystroke movement)
+    \fBjump-accept\fR                (jump and accept)
     \fBkill-line\fR
-    \fBkill-word\fR                 \fIalt-d\fR
-    \fBlast\fR                      (move to the last match)
-    \fBnext-history\fR              (\fIctrl-n\fR on \fB--history\fR)
-    \fBpage-down\fR                 \fIpgdn\fR
-    \fBpage-up\fR                   \fIpgup\fR
+    \fBkill-word\fR                  \fIalt-d\fR
+    \fBlast\fR                       (move to the last match)
+    \fBnext-history\fR               (\fIctrl-n\fR on \fB--history\fR)
+    \fBpage-down\fR                  \fIpgdn\fR
+    \fBpage-up\fR                    \fIpgup\fR
     \fBhalf-page-down\fR
     \fBhalf-page-up\fR
-    \fBpreview(...)\fR              (see below for the details)
-    \fBpreview-down\fR              \fIshift-down\fR
-    \fBpreview-up\fR                \fIshift-up\fR
+    \fBpreview(...)\fR               (see below for the details)
+    \fBpreview-down\fR               \fIshift-down\fR
+    \fBpreview-up\fR                 \fIshift-up\fR
     \fBpreview-page-down\fR
     \fBpreview-page-up\fR
     \fBpreview-half-page-down\fR
     \fBpreview-half-page-up\fR
     \fBpreview-bottom\fR
     \fBpreview-top\fR
-    \fBprevious-history\fR          (\fIctrl-p\fR on \fB--history\fR)
-    \fBprint-query\fR               (print query and exit)
-    \fBput\fR                       (put the character to the prompt)
+    \fBprevious-history\fR           (\fIctrl-p\fR on \fB--history\fR)
+    \fBprint-query\fR                (print query and exit)
+    \fBput\fR                        (put the character to the prompt)
     \fBrefresh-preview\fR
-    \fBreload(...)\fR               (see below for the details)
-    \fBreplace-query\fR             (replace query string with the current selection)
+    \fBreload(...)\fR                (see below for the details)
+    \fBreplace-query\fR              (replace query string with the current selection)
     \fBselect\fR
-    \fBselect-all\fR                (select all matches)
-    \fBtoggle\fR                    (\fIright-click\fR)
-    \fBtoggle-all\fR                (toggle all matches)
-    \fBtoggle+down\fR               \fIctrl-i  (tab)\fR
-    \fBtoggle-in\fR                 (\fB--layout=reverse*\fR ? \fBtoggle+up\fR : \fBtoggle+down\fR)
-    \fBtoggle-out\fR                (\fB--layout=reverse*\fR ? \fBtoggle+down\fR : \fBtoggle+up\fR)
+    \fBselect-all\fR                 (select all matches)
+    \fBtoggle\fR                     (\fIright-click\fR)
+    \fBtoggle-all\fR                 (toggle all matches)
+    \fBtoggle+down\fR                \fIctrl-i  (tab)\fR
+    \fBtoggle-in\fR                  (\fB--layout=reverse*\fR ? \fBtoggle+up\fR : \fBtoggle+down\fR)
+    \fBtoggle-out\fR                 (\fB--layout=reverse*\fR ? \fBtoggle+down\fR : \fBtoggle+up\fR)
     \fBtoggle-preview\fR
     \fBtoggle-preview-wrap\fR
-    \fBtoggle-search\fR             (toggle search functionality)
+    \fBtoggle-search\fR              (toggle search functionality)
     \fBtoggle-sort\fR
-    \fBtoggle+up\fR                 \fIbtab    (shift-tab)\fR
-    \fBunbind(...)\fR               (unbind bindings)
-    \fBunix-line-discard\fR         \fIctrl-u\fR
-    \fBunix-word-rubout\fR          \fIctrl-w\fR
-    \fBup\fR                        \fIctrl-k  ctrl-p  up\fR
-    \fByank\fR                      \fIctrl-y\fR
+    \fBtoggle+up\fR                  \fIbtab    (shift-tab)\fR
+    \fBunbind(...)\fR                (unbind bindings)
+    \fBunix-line-discard\fR          \fIctrl-u\fR
+    \fBunix-word-rubout\fR           \fIctrl-w\fR
+    \fBup\fR                         \fIctrl-k  ctrl-p  up\fR
+    \fByank\fR                       \fIctrl-y\fR
 
 .SS ACTION COMPOSITION
 
diff --git a/src/options.go b/src/options.go
index b93fd972..63b385cd 100644
--- a/src/options.go
+++ b/src/options.go
@@ -176,6 +176,14 @@ type previewOpts struct {
 	headerLines int
 }
 
+func (a previewOpts) sameLayout(b previewOpts) bool {
+	return a.size == b.size && a.position == b.position && a.border == b.border && a.hidden == b.hidden
+}
+
+func (a previewOpts) sameContentLayout(b previewOpts) bool {
+	return a.wrap == b.wrap && a.headerLines == b.headerLines
+}
+
 // Options stores the values of command-line options
 type Options struct {
 	Fuzzy       bool
@@ -787,7 +795,7 @@ func init() {
 	// Backreferences are not supported.
 	// "~!@#$%^&*;/|".each_char.map { |c| Regexp.escape(c) }.map { |c| "#{c}[^#{c}]*#{c}" }.join('|')
 	executeRegexp = regexp.MustCompile(
-		`(?si)[:+](execute(?:-multi|-silent)?|reload|preview|change-prompt|unbind):.+|[:+](execute(?:-multi|-silent)?|reload|preview|change-prompt|unbind)(\([^)]*\)|\[[^\]]*\]|~[^~]*~|![^!]*!|@[^@]*@|\#[^\#]*\#|\$[^\$]*\$|%[^%]*%|\^[^\^]*\^|&[^&]*&|\*[^\*]*\*|;[^;]*;|/[^/]*/|\|[^\|]*\|)`)
+		`(?si)[:+](execute(?:-multi|-silent)?|reload|preview|change-prompt|change-preview-window|change-preview|unbind):.+|[:+](execute(?:-multi|-silent)?|reload|preview|change-prompt|change-preview-window|change-preview|unbind)(\([^)]*\)|\[[^\]]*\]|~[^~]*~|![^!]*!|@[^@]*@|\#[^\#]*\#|\$[^\$]*\$|%[^%]*%|\^[^\^]*\^|&[^&]*&|\*[^\*]*\*|;[^;]*;|/[^/]*/|\|[^\|]*\|)`)
 }
 
 func parseKeymap(keymap map[tui.Event][]action, str string) {
@@ -799,6 +807,10 @@ func parseKeymap(keymap map[tui.Event][]action, str string) {
 		prefix := symbol + "execute"
 		if strings.HasPrefix(src[1:], "reload") {
 			prefix = symbol + "reload"
+		} else if strings.HasPrefix(src[1:], "change-preview-window") {
+			prefix = symbol + "change-preview-window"
+		} else if strings.HasPrefix(src[1:], "change-preview") {
+			prefix = symbol + "change-preview"
 		} else if strings.HasPrefix(src[1:], "preview") {
 			prefix = symbol + "preview"
 		} else if strings.HasPrefix(src[1:], "unbind") {
@@ -1002,6 +1014,10 @@ func parseKeymap(keymap map[tui.Event][]action, str string) {
 						offset = len("reload")
 					case actPreview:
 						offset = len("preview")
+					case actChangePreviewWindow:
+						offset = len("change-preview-window")
+					case actChangePreview:
+						offset = len("change-preview")
 					case actChangePrompt:
 						offset = len("change-prompt")
 					case actUnbind:
@@ -1028,6 +1044,9 @@ func parseKeymap(keymap map[tui.Event][]action, str string) {
 					}
 					if t == actUnbind {
 						parseKeyChords(actionArg, "unbind target required")
+					} else if t == actChangePreviewWindow {
+						opts := previewOpts{}
+						parsePreviewWindow(&opts, actionArg)
 					}
 				}
 			}
@@ -1053,6 +1072,10 @@ func isExecuteAction(str string) actionType {
 		return actUnbind
 	case "preview":
 		return actPreview
+	case "change-preview-window":
+		return actChangePreviewWindow
+	case "change-preview":
+		return actChangePreview
 	case "change-prompt":
 		return actChangePrompt
 	case "execute":
@@ -1633,10 +1656,28 @@ func postProcessOptions(opts *Options) {
 	// Extend the default key map
 	keymap := defaultKeymap()
 	for key, actions := range opts.Keymap {
+		lastChangePreviewWindow := action{t: actIgnore}
 		for _, act := range actions {
-			if act.t == actToggleSort {
+			switch act.t {
+			case actToggleSort:
+				// To display "+S"/"-S" on info line
 				opts.ToggleSort = true
+			case actChangePreviewWindow:
+				lastChangePreviewWindow = act
+			}
+		}
+		// Re-organize actions so that we only keep the last change-preview-window
+		// and it comes first in the list.
+		//  *  change-preview-window(up,+10)+preview(sleep 3; cat {})+change-preview-window(up,+20)
+		//  -> change-preview-window(up,+20)+preview(sleep 3; cat {})
+		if lastChangePreviewWindow.t == actChangePreviewWindow {
+			reordered := []action{lastChangePreviewWindow}
+			for _, act := range actions {
+				if act.t != actChangePreviewWindow {
+					reordered = append(reordered, act)
+				}
 			}
+			actions = reordered
 		}
 		keymap[key] = actions
 	}
diff --git a/src/terminal.go b/src/terminal.go
index 2bad5d75..804e2b2e 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -104,88 +104,89 @@ var emptyLine = itemLine{}
 
 // Terminal represents terminal input/output
 type Terminal struct {
-	initDelay    time.Duration
-	infoStyle    infoStyle
-	spinner      []string
-	prompt       func()
-	promptLen    int
-	pointer      string
-	pointerLen   int
-	pointerEmpty string
-	marker       string
-	markerLen    int
-	markerEmpty  string
-	queryLen     [2]int
-	layout       layoutType
-	fullscreen   bool
-	keepRight    bool
-	hscroll      bool
-	hscrollOff   int
-	scrollOff    int
-	wordRubout   string
-	wordNext     string
-	cx           int
-	cy           int
-	offset       int
-	xoffset      int
-	yanked       []rune
-	input        []rune
-	multi        int
-	sort         bool
-	toggleSort   bool
-	delimiter    Delimiter
-	expect       map[tui.Event]string
-	keymap       map[tui.Event][]action
-	pressed      string
-	printQuery   bool
-	history      *History
-	cycle        bool
-	headerFirst  bool
-	headerLines  int
-	header       []string
-	header0      []string
-	ansi         bool
-	tabstop      int
-	margin       [4]sizeSpec
-	padding      [4]sizeSpec
-	strong       tui.Attr
-	unicode      bool
-	borderShape  tui.BorderShape
-	cleanExit    bool
-	paused       bool
-	border       tui.Window
-	window       tui.Window
-	pborder      tui.Window
-	pwindow      tui.Window
-	count        int
-	progress     int
-	reading      bool
-	running      bool
-	failed       *string
-	jumping      jumpMode
-	jumpLabels   string
-	printer      func(string)
-	printsep     string
-	merger       *Merger
-	selected     map[int32]selectedItem
-	version      int64
-	reqBox       *util.EventBox
-	previewOpts  previewOpts
-	previewer    previewer
-	previewed    previewed
-	previewBox   *util.EventBox
-	eventBox     *util.EventBox
-	mutex        sync.Mutex
-	initFunc     func()
-	prevLines    []itemLine
-	suppress     bool
-	sigstop      bool
-	startChan    chan bool
-	killChan     chan int
-	slab         *util.Slab
-	theme        *tui.ColorTheme
-	tui          tui.Renderer
-	executing    *util.AtomicBool
+	initDelay          time.Duration
+	infoStyle          infoStyle
+	spinner            []string
+	prompt             func()
+	promptLen          int
+	pointer            string
+	pointerLen         int
+	pointerEmpty       string
+	marker             string
+	markerLen          int
+	markerEmpty        string
+	queryLen           [2]int
+	layout             layoutType
+	fullscreen         bool
+	keepRight          bool
+	hscroll            bool
+	hscrollOff         int
+	scrollOff          int
+	wordRubout         string
+	wordNext           string
+	cx                 int
+	cy                 int
+	offset             int
+	xoffset            int
+	yanked             []rune
+	input              []rune
+	multi              int
+	sort               bool
+	toggleSort         bool
+	delimiter          Delimiter
+	expect             map[tui.Event]string
+	keymap             map[tui.Event][]action
+	pressed            string
+	printQuery         bool
+	history            *History
+	cycle              bool
+	headerFirst        bool
+	headerLines        int
+	header             []string
+	header0            []string
+	ansi               bool
+	tabstop            int
+	margin             [4]sizeSpec
+	padding            [4]sizeSpec
+	strong             tui.Attr
+	unicode            bool
+	borderShape        tui.BorderShape
+	cleanExit          bool
+	paused             bool
+	border             tui.Window
+	window             tui.Window
+	pborder            tui.Window
+	pwindow            tui.Window
+	count              int
+	progress           int
+	reading            bool
+	running            bool
+	failed             *string
+	jumping            jumpMode
+	jumpLabels         string
+	printer            func(string)
+	printsep           string
+	merger             *Merger
+	selected           map[int32]selectedItem
+	version            int64
+	reqBox             *util.EventBox
+	initialPreviewOpts previewOpts
+	previewOpts        previewOpts
+	previewer          previewer
+	previewed          previewed
+	previewBox         *util.EventBox
+	eventBox           *util.EventBox
+	mutex              sync.Mutex
+	initFunc           func()
+	prevLines          []itemLine
+	suppress           bool
+	sigstop            bool
+	startChan          chan bool
+	killChan           chan int
+	slab               *util.Slab
+	theme              *tui.ColorTheme
+	tui                tui.Renderer
+	executing          *util.AtomicBool
 }
 
 type selectedItem struct {
@@ -286,6 +287,8 @@ const (
 	actTogglePreview
 	actTogglePreviewWrap
 	actPreview
+	actChangePreview
+	actChangePreviewWindow
 	actPreviewTop
 	actPreviewBottom
 	actPreviewUp
@@ -324,9 +327,10 @@ type searchRequest struct {
 }
 
 type previewRequest struct {
-	template string
-	pwindow  tui.Window
-	list     []*Item
+	template     string
+	pwindow      tui.Window
+	scrollOffset int
+	list         []*Item
 }
 
 type previewResult struct {
@@ -416,7 +420,7 @@ func trimQuery(query string) []rune {
 func hasPreviewAction(opts *Options) bool {
 	for _, actions := range opts.Keymap {
 		for _, action := range actions {
-			if action.t == actPreview {
+			if action.t == actPreview || action.t == actChangePreview {
 				return true
 			}
 		}
@@ -496,72 +500,73 @@ func NewTerminal(opts *Options, eventBox *util.EventBox) *Terminal {
 		wordNext = fmt.Sprintf("[^%s]%s|(.$)", sep, sep)
 	}
 	t := Terminal{
-		initDelay:   delay,
-		infoStyle:   opts.InfoStyle,
-		spinner:     makeSpinner(opts.Unicode),
-		queryLen:    [2]int{0, 0},
-		layout:      opts.Layout,
-		fullscreen:  fullscreen,
-		keepRight:   opts.KeepRight,
-		hscroll:     opts.Hscroll,
-		hscrollOff:  opts.HscrollOff,
-		scrollOff:   opts.ScrollOff,
-		wordRubout:  wordRubout,
-		wordNext:    wordNext,
-		cx:          len(input),
-		cy:          0,
-		offset:      0,
-		xoffset:     0,
-		yanked:      []rune{},
-		input:       input,
-		multi:       opts.Multi,
-		sort:        opts.Sort > 0,
-		toggleSort:  opts.ToggleSort,
-		delimiter:   opts.Delimiter,
-		expect:      opts.Expect,
-		keymap:      opts.Keymap,
-		pressed:     "",
-		printQuery:  opts.PrintQuery,
-		history:     opts.History,
-		margin:      opts.Margin,
-		padding:     opts.Padding,
-		unicode:     opts.Unicode,
-		borderShape: opts.BorderShape,
-		cleanExit:   opts.ClearOnExit,
-		paused:      opts.Phony,
-		strong:      strongAttr,
-		cycle:       opts.Cycle,
-		headerFirst: opts.HeaderFirst,
-		headerLines: opts.HeaderLines,
-		header:      header,
-		header0:     header,
-		ansi:        opts.Ansi,
-		tabstop:     opts.Tabstop,
-		reading:     true,
-		running:     true,
-		failed:      nil,
-		jumping:     jumpDisabled,
-		jumpLabels:  opts.JumpLabels,
-		printer:     opts.Printer,
-		printsep:    opts.PrintSep,
-		merger:      EmptyMerger,
-		selected:    make(map[int32]selectedItem),
-		reqBox:      util.NewEventBox(),
-		previewOpts: opts.Preview,
-		previewer:   previewer{0, []string{}, 0, showPreviewWindow, false, true, false, ""},
-		previewed:   previewed{0, 0, 0, false},
-		previewBox:  previewBox,
-		eventBox:    eventBox,
-		mutex:       sync.Mutex{},
-		suppress:    true,
-		sigstop:     false,
-		slab:        util.MakeSlab(slab16Size, slab32Size),
-		theme:       opts.Theme,
-		startChan:   make(chan bool, 1),
-		killChan:    make(chan int),
-		tui:         renderer,
-		initFunc:    func() { renderer.Init() },
-		executing:   util.NewAtomicBool(false)}
+		initDelay:          delay,
+		infoStyle:          opts.InfoStyle,
+		spinner:            makeSpinner(opts.Unicode),
+		queryLen:           [2]int{0, 0},
+		layout:             opts.Layout,
+		fullscreen:         fullscreen,
+		keepRight:          opts.KeepRight,
+		hscroll:            opts.Hscroll,
+		hscrollOff:         opts.HscrollOff,
+		scrollOff:          opts.ScrollOff,
+		wordRubout:         wordRubout,
+		wordNext:           wordNext,
+		cx:                 len(input),
+		cy:                 0,
+		offset:             0,
+		xoffset:            0,
+		yanked:             []rune{},
+		input:              input,
+		multi:              opts.Multi,
+		sort:               opts.Sort > 0,
+		toggleSort:         opts.ToggleSort,
+		delimiter:          opts.Delimiter,
+		expect:             opts.Expect,
+		keymap:             opts.Keymap,
+		pressed:            "",
+		printQuery:         opts.PrintQuery,
+		history:            opts.History,
+		margin:             opts.Margin,
+		padding:            opts.Padding,
+		unicode:            opts.Unicode,
+		borderShape:        opts.BorderShape,
+		cleanExit:          opts.ClearOnExit,
+		paused:             opts.Phony,
+		strong:             strongAttr,
+		cycle:              opts.Cycle,
+		headerFirst:        opts.HeaderFirst,
+		headerLines:        opts.HeaderLines,
+		header:             header,
+		header0:            header,
+		ansi:               opts.Ansi,
+		tabstop:            opts.Tabstop,
+		reading:            true,
+		running:            true,
+		failed:             nil,
+		jumping:            jumpDisabled,
+		jumpLabels:         opts.JumpLabels,
+		printer:            opts.Printer,
+		printsep:           opts.PrintSep,
+		merger:             EmptyMerger,
+		selected:           make(map[int32]selectedItem),
+		reqBox:             util.NewEventBox(),
+		initialPreviewOpts: opts.Preview,
+		previewOpts:        opts.Preview,
+		previewer:          previewer{0, []string{}, 0, showPreviewWindow, false, true, false, ""},
+		previewed:          previewed{0, 0, 0, false},
+		previewBox:         previewBox,
+		eventBox:           eventBox,
+		mutex:              sync.Mutex{},
+		suppress:           true,
+		sigstop:            false,
+		slab:               util.MakeSlab(slab16Size, slab32Size),
+		theme:              opts.Theme,
+		startChan:          make(chan bool, 1),
+		killChan:           make(chan int),
+		tui:                renderer,
+		initFunc:           func() { renderer.Init() },
+		executing:          util.NewAtomicBool(false)}
 	t.prompt, t.promptLen = t.parsePrompt(opts.Prompt)
 	t.pointer, t.pointerLen = t.processTabs([]rune(opts.Pointer), 0)
 	t.marker, t.markerLen = t.processTabs([]rune(opts.Marker), 0)
@@ -1642,9 +1647,14 @@ func (t *Terminal) replacePlaceholder(template string, forcePlus bool, input str
 		template, t.ansi, t.delimiter, t.printsep, forcePlus, input, list)
 }
 
-func (t *Terminal) evaluateScrollOffset(list []*Item, height int) int {
+func (t *Terminal) evaluateScrollOffset() int {
+	if t.pwindow == nil {
+		return 0
+	}
+
+	// We only need the current item to calculate the scroll offset
 	offsetExpr := offsetTrimCharsRegex.ReplaceAllString(
-		t.replacePlaceholder(t.previewOpts.scroll, false, "", list), "")
+		t.replacePlaceholder(t.previewOpts.scroll, false, "", []*Item{t.currentItem(), nil}), "")
 
 	atoi := func(s string) int {
 		n, e := strconv.Atoi(s)
@@ -1655,20 +1665,21 @@ func (t *Terminal) evaluateScrollOffset(list []*Item, height int) int {
 	}
 
 	base := -1
+	height := util.Max(0, t.pwindow.Height()-t.previewOpts.headerLines)
 	for _, component := range offsetComponentRegex.FindAllString(offsetExpr, -1) {
 		if strings.HasPrefix(component, "-/") {
 			component = component[1:]
 		}
 		if component[0] == '/' {
 			denom := atoi(component[1:])
-			if denom == 0 {
-				return base
+			if denom != 0 {
+				base -= height / denom
 			}
-			return base - height/denom
+			break
 		}
 		base += atoi(component)
 	}
-	return base
+	return util.Max(0, base)
 }
 
 func replacePlaceholder(template string, stripAnsi bool, delimiter Delimiter, printsep string, forcePlus bool, query string, allItems []*Item) string {
@@ -1972,12 +1983,14 @@ func (t *Terminal) Loop() {
 				var items []*Item
 				var commandTemplate string
 				var pwindow tui.Window
+				initialOffset := 0
 				t.previewBox.Wait(func(events *util.Events) {
 					for req, value := range *events {
 						switch req {
 						case reqPreviewEnqueue:
 							request := value.(previewRequest)
 							commandTemplate = request.template
+							initialOffset = request.scrollOffset
 							items = request.list
 							pwindow = request.pwindow
 						}
@@ -1989,11 +2002,9 @@ func (t *Terminal) Loop() {
 				if items[0] != nil {
 					_, query := t.Input()
 					command := t.replacePlaceholder(commandTemplate, false, string(query), items)
-					initialOffset := 0
 					cmd := util.ExecCommand(command, true)
 					if pwindow != nil {
 						height := pwindow.Height()
-						initialOffset = util.Max(0, t.evaluateScrollOffset(items, util.Max(0, height-t.previewOpts.headerLines)))
 						env := os.Environ()
 						lines := fmt.Sprintf("LINES=%d", height)
 						columns := fmt.Sprintf("COLUMNS=%d", pwindow.Width())
@@ -2128,7 +2139,7 @@ func (t *Terminal) Loop() {
 		if len(command) > 0 && t.isPreviewEnabled() {
 			_, list := t.buildPlusList(command, false)
 			t.cancelPreview()
-			t.previewBox.Set(reqPreviewEnqueue, previewRequest{command, t.pwindow, list})
+			t.previewBox.Set(reqPreviewEnqueue, previewRequest{command, t.pwindow, t.evaluateScrollOffset(), list})
 		}
 	}
 
@@ -2253,13 +2264,16 @@ func (t *Terminal) Loop() {
 				}
 			}
 		}
-		togglePreview := func(enabled bool) {
+		togglePreview := func(enabled bool) bool {
 			if t.previewer.enabled != enabled {
 				t.previewer.enabled = enabled
+				// We need to immediately update t.pwindow so we don't use reqRedraw
 				t.tui.Clear()
 				t.resizeWindows()
 				req(reqPrompt, reqList, reqInfo, reqHeader)
+				return true
 			}
+			return false
 		}
 		toggle := func() bool {
 			current := t.currentItem()
@@ -2327,7 +2341,7 @@ func (t *Terminal) Loop() {
 						if valid {
 							t.cancelPreview()
 							t.previewBox.Set(reqPreviewEnqueue,
-								previewRequest{t.previewOpts.command, t.pwindow, list})
+								previewRequest{t.previewOpts.command, t.pwindow, t.evaluateScrollOffset(), list})
 						}
 					}
 				}
@@ -2707,6 +2721,39 @@ func (t *Terminal) Loop() {
 				for key := range keys {
 					delete(t.keymap, key)
 				}
+			case actChangePreview:
+				if t.previewOpts.command != a.a {
+					togglePreview(len(a.a) > 0)
+					t.previewOpts.command = a.a
+					refreshPreview(t.previewOpts.command)
+				}
+			case actChangePreviewWindow:
+				currentPreviewOpts := t.previewOpts
+
+				// Reset preview options and apply the additional options
+				t.previewOpts = t.initialPreviewOpts
+				parsePreviewWindow(&t.previewOpts, a.a)
+
+				if t.previewOpts.hidden {
+					togglePreview(false)
+				} else {
+					// Full redraw
+					if !currentPreviewOpts.sameLayout(t.previewOpts) {
+						if togglePreview(true) {
+							refreshPreview(t.previewOpts.command)
+						} else {
+							req(reqRedraw)
+						}
+					} else if !currentPreviewOpts.sameContentLayout(t.previewOpts) {
+						t.previewed.version = 0
+						req(reqPreviewRefresh)
+					}
+
+					// Adjust scroll offset
+					if t.hasPreviewWindow() && currentPreviewOpts.scroll != t.previewOpts.scroll {
+						scrollPreviewTo(t.evaluateScrollOffset())
+					}
+				}
 			}
 			return true
 		}
diff --git a/test/test_go.rb b/test/test_go.rb
index 20a4c923..3fc66f94 100755
--- a/test/test_go.rb
+++ b/test/test_go.rb
@@ -2142,6 +2142,55 @@ class TestGoFZF < TestBase
       assert_equal expected.chomp, lines.take(6).join("\n")
     end
   end
+
+  def test_change_preview_window
+    tmux.send_keys "seq 1000 | #{FZF} --preview 'echo [[{}]]' --preview-window border-none --bind '" \
+      'a:change-preview(echo __{}__),' \
+      'b:change-preview-window(down)+change-preview(echo =={}==)+change-preview-window(up),' \
+      'c:change-preview(),d:change-preview-window(hidden),' \
+      "e:preview(printf ::%${FZF_PREVIEW_COLUMNS}s{})+change-preview-window(up),f:change-preview-window(up,wrap)'", :Enter
+    tmux.until { |lines| assert_equal 1000, lines.item_count }
+    tmux.until { |lines| assert_includes lines[0], '[[1]]' }
+
+    # change-preview action permanently changes the preview command set by --preview
+    tmux.send_keys 'a'
+    tmux.until { |lines| assert_includes lines[0], '__1__' }
+    tmux.send_keys :Up
+    tmux.until { |lines| assert_includes lines[0], '__2__' }
+
+    # When multiple change-preview-window actions are bound to a single key,
+    # the last one wins and the updated options are immediately applied to the new preview
+    tmux.send_keys 'b'
+    tmux.until { |lines| assert_equal '==2==', lines[0] }
+    tmux.send_keys :Up
+    tmux.until { |lines| assert_equal '==3==', lines[0] }
+
+    # change-preview with an empty preview command closes the preview window
+    tmux.send_keys 'c'
+    tmux.until { |lines| refute_includes lines[0], '==' }
+
+    # change-preview again to re-open the preview window
+    tmux.send_keys 'a'
+    tmux.until { |lines| assert_equal '__3__', lines[0] }
+
+    # Hide the preview window with hidden flag
+    tmux.send_keys 'd'
+    tmux.until { |lines| refute_includes lines[0], '__3__' }
+
+    # One-off preview
+    tmux.send_keys 'e'
+    tmux.until do |lines|
+      assert_equal '::', lines[0]
+      refute_includes lines[1], '3'
+    end
+
+    # Wrapped
+    tmux.send_keys 'f'
+    tmux.until do |lines|
+      assert_equal '::', lines[0]
+      assert_equal '  3', lines[1]
+    end
+  end
 end
 
 module TestShell