add half-up/half-down/page-up/page-down commands

doc/reference.md

@@ -3,7 +3,11 @@
 ## Keys
 
     up                (default "k" and "<up>")
+    half-up           (default "<c-u>")
+    page-up           (default "<c-b>")
     down              (default "j" and "<down>")
+    half-down         (default "<c-d>")
+    page-down         (default "<c-f>")
     updir             (default "h" and "<left>")
     open              (default "l" and "<right>")
     quit              (default "q")

eval.go

@@ -124,10 +124,22 @@ func (e *CallExpr) eval(app *App, args []string) {
 	// TODO: check for extra toks in each case
 	switch e.name {
 	case "up":
-		app.nav.up()
+		app.nav.up(1)
+		app.ui.echoFileInfo(app.nav)
+	case "half-up":
+		app.nav.up(app.nav.height / 2)
+		app.ui.echoFileInfo(app.nav)
+	case "page-up":
+		app.nav.up(app.nav.height)
 		app.ui.echoFileInfo(app.nav)
 	case "down":
-		app.nav.down()
+		app.nav.down(1)
+		app.ui.echoFileInfo(app.nav)
+	case "half-down":
+		app.nav.down(app.nav.height / 2)
+		app.ui.echoFileInfo(app.nav)
+	case "page-down":
+		app.nav.down(app.nav.height)
 		app.ui.echoFileInfo(app.nav)
 	case "updir":
 		if err := app.nav.updir(); err != nil {

nav.go

@@ -233,21 +233,22 @@ func (nav *Nav) renew(height int) {
 	}
 }
 
-func (nav *Nav) up() {
+func (nav *Nav) up(dist int) {
 	dir := nav.currDir()
 
 	if dir.ind == 0 {
 		return
 	}
 
-	dir.ind--
+	dir.ind -= dist
+	dir.ind = max(0, dir.ind)
 
-	dir.pos--
+	dir.pos -= dist
 	edge := min(gOpts.scrolloff, dir.ind)
 	dir.pos = max(dir.pos, edge)
 }
 
-func (nav *Nav) down() {
+func (nav *Nav) down(dist int) {
 	dir := nav.currDir()
 
 	maxind := len(dir.fi) - 1
@@ -256,9 +257,10 @@ func (nav *Nav) down() {
 		return
 	}
 
-	dir.ind++
+	dir.ind += dist
+	dir.ind = min(maxind, dir.ind)
 
-	dir.pos++
+	dir.pos += dist
 	edge := min(gOpts.scrolloff, maxind-dir.ind)
 
 	// use a smaller value when the height is even and scrolloff is maxed
@@ -349,7 +351,7 @@ func (nav *Nav) toggle() {
 		nav.marks[path] = true
 	}
 
-	nav.down()
+	nav.down(1)
 }
 
 func (nav *Nav) save(keep bool) error {

opts.go

@@ -31,8 +31,12 @@ func init() {
 
 	gOpts.keys["k"] = &CallExpr{"up", nil}
 	gOpts.keys["<up>"] = &CallExpr{"up", nil}
+	gOpts.keys["<c-u>"] = &CallExpr{"half-up", nil}
+	gOpts.keys["<c-b>"] = &CallExpr{"page-up", nil}
 	gOpts.keys["j"] = &CallExpr{"down", nil}
 	gOpts.keys["<down>"] = &CallExpr{"down", nil}
+	gOpts.keys["<c-d>"] = &CallExpr{"half-down", nil}
+	gOpts.keys["<c-f>"] = &CallExpr{"page-down", nil}
 	gOpts.keys["h"] = &CallExpr{"updir", nil}
 	gOpts.keys["<left>"] = &CallExpr{"updir", nil}
 	gOpts.keys["l"] = &CallExpr{"open", nil}