add scrollup scrolldown builtin cmd (#764)

* add scrollup scrolldown builtin cmd

Scrollup/down move window pane without moving current cursor position.
Default keybinding would be <c-y> for scrollup and <c-e> for scrolldown
just like in vim.

* limit scrolldown when reached bottom

scrolodown will not allow empty space

Fix typo

complete.go

@@ -17,9 +17,11 @@ var (
 		"up",
 		"half-up",
 		"page-up",
+		"scrollup",
 		"down",
 		"half-down",
 		"page-down",
+		"scrolldown",
 		"updir",
 		"open",
 		"quit",

doc.go

@@ -19,9 +19,11 @@ The following commands are provided by lf:
     up                       (default 'k' and '<up>')
     half-up                  (default '<c-u>')
     page-up                  (default '<c-b>' and '<pgup>')
+    scrollup                 (default '<c-y>')
     down                     (default 'j' and '<down>')
     half-down                (default '<c-d>')
     page-down                (default '<c-f>' and '<pgdn>')
+    scrolldown               (default '<c-e>')
     updir                    (default 'h' and '<left>')
     open                     (default 'l' and '<right>')
     top                      (default 'gg' and '<home>')
@@ -242,9 +244,11 @@ Quit lf and return to the shell.
     up                       (default 'k' and '<up>')
     half-up                  (default '<c-u>')
     page-up                  (default '<c-b>' and '<pgup>')
+    scrollup                 (default '<c-y>')
     down                     (default 'j' and '<down>')
     half-down                (default '<c-d>')
     page-down                (default '<c-f>' and '<pgdn>')
+    scrolldown               (default '<c-e>')
 
 Move the current file selection upwards/downwards by one/half a page/full page.
 

docstring.go

@@ -23,9 +23,11 @@ The following commands are provided by lf:
     up                       (default 'k' and '<up>')
     half-up                  (default '<c-u>')
     page-up                  (default '<c-b>' and '<pgup>')
+    scrollup                 (default '<c-y>')
     down                     (default 'j' and '<down>')
     half-down                (default '<c-d>')
     page-down                (default '<c-f>' and '<pgdn>')
+    scrolldown               (default '<c-e>')
     updir                    (default 'h' and '<left>')
     open                     (default 'l' and '<right>')
     top                      (default 'gg' and '<home>')
@@ -249,9 +251,11 @@ Quit lf and return to the shell.
     up                       (default 'k' and '<up>')
     half-up                  (default '<c-u>')
     page-up                  (default '<c-b>' and '<pgup>')
+    scrollup                 (default '<c-y>')
     down                     (default 'j' and '<down>')
     half-down                (default '<c-d>')
     page-down                (default '<c-f>' and '<pgdn>')
+    scrolldown               (default '<c-e>')
 
 Move the current file selection upwards/downwards by one/half a page/full
 page.

eval.go

@@ -807,6 +807,11 @@ func (e *callExpr) eval(app *app, args []string) {
 			app.ui.loadFile(app.nav, true)
 			app.ui.loadFileInfo(app.nav)
 		}
+	case "scrollup":
+		if app.nav.scrollup(e.count) {
+			app.ui.loadFile(app.nav, true)
+			app.ui.loadFileInfo(app.nav)
+		}
 	case "down":
 		if app.nav.down(e.count) {
 			app.ui.loadFile(app.nav, true)
@@ -822,6 +827,11 @@ func (e *callExpr) eval(app *app, args []string) {
 			app.ui.loadFile(app.nav, true)
 			app.ui.loadFileInfo(app.nav)
 		}
+	case "scrolldown":
+		if app.nav.scrolldown(e.count) {
+			app.ui.loadFile(app.nav, true)
+			app.ui.loadFileInfo(app.nav)
+		}
 	case "updir":
 		resetIncCmd(app)
 		preChdir(app)

lf.1

@@ -35,9 +35,11 @@ The following commands are provided by lf:
     up                       (default 'k' and '<up>')
     half-up                  (default '<c-u>')
     page-up                  (default '<c-b>' and '<pgup>')
+    scrollup                 (default '<c-y>')
     down                     (default 'j' and '<down>')
     half-down                (default '<c-d>')
     page-down                (default '<c-f>' and '<pgdn>')
+    scrolldown               (default '<c-e>')
     updir                    (default 'h' and '<left>')
     open                     (default 'l' and '<right>')
     top                      (default 'gg' and '<home>')
@@ -279,9 +281,11 @@ Quit lf and return to the shell.
     up                       (default 'k' and '<up>')
     half-up                  (default '<c-u>')
     page-up                  (default '<c-b>' and '<pgup>')
+    scrollup                 (default '<c-y>')
     down                     (default 'j' and '<down>')
     half-down                (default '<c-d>')
     page-down                (default '<c-f>' and '<pgdn>')
+    scrolldown               (default '<c-e>')
 .EE
 .PP
 Move the current file selection upwards/downwards by one/half a page/full page.

nav.go

@@ -805,6 +805,64 @@ func (nav *nav) down(dist int) bool {
 	return old != dir.ind
 }
 
+func (nav *nav) scrollup(dist int) bool {
+	dir := nav.currDir()
+
+	// when reached top do nothing
+	if istop := dir.ind == dir.pos; istop {
+		return false
+	}
+
+	old := dir.ind
+
+	minedge := min(nav.height/2, gOpts.scrolloff)
+
+	dir.pos += dist
+
+	// jump to ensure minedge when edge < minedge
+	edge := nav.height - dir.pos
+	delta := min(0, edge-minedge-1)
+	dir.pos = min(dir.pos, nav.height-minedge-1)
+	// update dir.ind accordingly
+	dir.ind = dir.ind + delta
+
+	dir.ind = min(dir.ind, dir.ind-(dir.pos-nav.height+1))
+
+	// prevent cursor disappearing downwards
+	dir.pos = min(dir.pos, nav.height-1)
+
+	return old != dir.ind
+}
+
+func (nav *nav) scrolldown(dist int) bool {
+	dir := nav.currDir()
+	maxind := len(dir.files) - 1
+
+	// reached bottom
+	if dir.ind-dir.pos > maxind-nav.height {
+		return false
+	}
+
+	old := dir.ind
+
+	minedge := min(nav.height/2, gOpts.scrolloff)
+
+	dir.pos -= dist
+
+	// jump to ensure minedge when edge < minedge
+	delta := min(0, dir.pos-minedge)
+	dir.pos = max(dir.pos, minedge)
+	// update dir.ind accordingly
+	dir.ind = dir.ind - delta
+	dir.ind = max(dir.ind, dir.ind-(dir.pos-minedge))
+
+	dir.ind = min(maxind, dir.ind)
+	// prevent disappearing
+	dir.pos = max(dir.pos, 0)
+
+	return old != dir.ind
+}
+
 func (nav *nav) updir() error {
 	if len(nav.dirs) <= 1 {
 		return nil

opts.go

@@ -128,11 +128,13 @@ func init() {
 	gOpts.keys["<c-u>"] = &callExpr{"half-up", nil, 1}
 	gOpts.keys["<c-b>"] = &callExpr{"page-up", nil, 1}
 	gOpts.keys["<pgup>"] = &callExpr{"page-up", nil, 1}
+	gOpts.keys["<c-y>"] = &callExpr{"scrollup", nil, 1}
 	gOpts.keys["j"] = &callExpr{"down", nil, 1}
 	gOpts.keys["<down>"] = &callExpr{"down", nil, 1}
 	gOpts.keys["<c-d>"] = &callExpr{"half-down", nil, 1}
 	gOpts.keys["<c-f>"] = &callExpr{"page-down", nil, 1}
 	gOpts.keys["<pgdn>"] = &callExpr{"page-down", nil, 1}
+	gOpts.keys["<c-e>"] = &callExpr{"scrolldown", nil, 1}
 	gOpts.keys["h"] = &callExpr{"updir", nil, 1}
 	gOpts.keys["<left>"] = &callExpr{"updir", nil, 1}
 	gOpts.keys["l"] = &callExpr{"open", nil, 1}