vis: improve cursor positioning after scrolling

Make cursor placement after scrolling (half) pages up/down less arbitrary.

Close #390, fix #391

3 files changed, 64 insertions, 15 deletions

diff --git a/main.c b/main.c
index 83b6910..8e76429 100644
--- a/main.c
+++ b/main.c
@@ -1916,35 +1916,43 @@ static const char *insert_verbatim(Vis *vis, const char *keys, const Arg *arg) {
 	return keys;
 }
 
-static int argi2lines(Vis *vis, const Arg *arg) {
+static const char *wscroll(Vis *vis, const char *keys, const Arg *arg) {
+	View *view = vis_view(vis);
 	int count = vis_count_get(vis);
 	switch (arg->i) {
 	case -PAGE:
+		view_scroll_page_up(view);
+		break;
 	case +PAGE:
-		return view_height_get(vis_view(vis));
+		view_scroll_page_down(view);
+		break;
 	case -PAGE_HALF:
+		view_scroll_halfpage_up(view);
+		break;
 	case +PAGE_HALF:
-		return view_height_get(vis_view(vis))/2;
+		view_scroll_halfpage_down(view);
+		break;
 	default:
-		if (count != VIS_COUNT_UNKNOWN)
-			return count;
-		return arg->i < 0 ? -arg->i : arg->i;
+		if (count == VIS_COUNT_UNKNOWN)
+			count = arg->i < 0 ? -arg->i : arg->i;
+		if (arg->i < 0)
+			view_scroll_up(view, count);
+		else
+			view_scroll_down(view, count);
+		break;
 	}
-}
-
-static const char *wscroll(Vis *vis, const char *keys, const Arg *arg) {
-	if (arg->i >= 0)
-		view_scroll_down(vis_view(vis), argi2lines(vis, arg));
-	else
-		view_scroll_up(vis_view(vis), argi2lines(vis, arg));
 	return keys;
 }
 
 static const char *wslide(Vis *vis, const char *keys, const Arg *arg) {
+	View *view = vis_view(vis);
+	int count = vis_count_get(vis);
+	if (count == VIS_COUNT_UNKNOWN)
+		count = arg->i < 0 ? -arg->i : arg->i;
 	if (arg->i >= 0)
-		view_slide_down(vis_view(vis), argi2lines(vis, arg));
+		view_slide_down(view, count);
 	else
-		view_slide_up(vis_view(vis), argi2lines(vis, arg));
+		view_slide_up(view, count);
 	return keys;
 }
 
diff --git a/view.c b/view.c
index 8f37dcc..1d620de 100644
--- a/view.c
+++ b/view.c
@@ -738,6 +738,43 @@ size_t view_scroll_up(View *view, int lines) {
 	return cursor->pos;
 }
 
+size_t view_scroll_page_up(View *view) {
+	Cursor *cursor = view->cursor;
+	if (view->start == 0) {
+		view_cursor_to(view, 0);
+	} else {
+		view_cursor_to(view, view->start-1);
+		view_redraw_bottom(view);
+		view_screenline_begin(cursor);
+	}
+	return cursor->pos;
+}
+
+size_t view_scroll_page_down(View *view) {
+	view_scroll_down(view, view->height);
+	return view_screenline_begin(view->cursor);
+}
+
+size_t view_scroll_halfpage_up(View *view) {
+	Cursor *cursor = view->cursor;
+	if (view->start == 0) {
+		view_cursor_to(view, 0);
+	} else {
+		view_cursor_to(view, view->start-1);
+		view_redraw_center(view);
+		view_screenline_begin(cursor);
+	}
+	return cursor->pos;
+}
+
+size_t view_scroll_halfpage_down(View *view) {
+	size_t end = view->end;
+	size_t pos = view_scroll_down(view, view->height/2);
+	if (pos < text_size(view->text))
+		view_cursor_to(view, end);
+	return view->cursor->pos;
+}
+
 size_t view_scroll_down(View *view, int lines) {
 	Cursor *cursor = view->cursor;
 	if (view_viewport_down(view, lines)) {
diff --git a/view.h b/view.h
index 8cd2ce3..07fedf4 100644
--- a/view.h
+++ b/view.h
@@ -73,6 +73,10 @@ size_t view_slide_down(View*, int lines);
  * visible line, try to preserve the column position */
 size_t view_scroll_up(View*, int lines);
 size_t view_scroll_down(View*, int lines);
+size_t view_scroll_page_up(View*);
+size_t view_scroll_page_down(View*);
+size_t view_scroll_halfpage_up(View*);
+size_t view_scroll_halfpage_down(View*);
 /* place the cursor at the start ot the n-th window line, counting from 1 */
 size_t view_screenline_goto(View*, int n);