Add preview-half-page-down and preview-half-page-up (#2145)

src/options.go

@@ -854,6 +854,10 @@ func parseKeymap(keymap map[int][]action, str string) {
 				appendAction(actPreviewPageUp)
 			case "preview-page-down":
 				appendAction(actPreviewPageDown)
+			case "preview-half-page-up":
+				appendAction(actPreviewHalfPageUp)
+			case "preview-half-page-down":
+				appendAction(actPreviewHalfPageDown)
 			default:
 				t := isExecuteAction(specLower)
 				if t == actIgnore {

src/terminal.go

@@ -236,6 +236,8 @@ const (
 	actPreviewDown
 	actPreviewPageUp
 	actPreviewPageDown
+	actPreviewHalfPageUp
+	actPreviewHalfPageDown
 	actPreviousHistory
 	actNextHistory
 	actExecute
@@ -1953,6 +1955,14 @@ func (t *Terminal) Loop() {
 				if t.hasPreviewWindow() {
 					scrollPreview(t.pwindow.Height())
 				}
+			case actPreviewHalfPageUp:
+				if t.hasPreviewWindow() {
+					scrollPreview(-t.pwindow.Height()/2)
+				}
+			case actPreviewHalfPageDown:
+				if t.hasPreviewWindow() {
+					scrollPreview(t.pwindow.Height()/2)
+				}
 			case actBeginningOfLine:
 				t.cx = 0
 			case actBackwardChar: