Autoscroll in pager (#1223)

Autoscroll the pager view if a new option `pager-autoscroll` is set to `on`.

[tk: tweaked the code and added doc]

doc/tigrc.5.adoc

@@ -364,6 +364,11 @@ The following variables can be set:
 	Mouse support requires that ncurses itself support mouse events and that
 	you have enabled mouse support in ~/.tigrc with `set mouse = true`.
 
+'pager-autoscroll' (bool)::
+
+	Whether to scroll automatically the pager view while loading. Move the
+	cursor out of the last line to stop scrolling and back in to resume.
+
 'pgrp' (bool)::
 
 	Make tig process-group leader when starting and clean all processes

include/tig/options.h

@@ -62,6 +62,7 @@ typedef struct view_column *view_settings;
 	_(mouse,			bool,			VIEW_NO_FLAGS) \
 	_(mouse_scroll,			int,			VIEW_NO_FLAGS) \
 	_(mouse_wheel_cursor,		bool,			VIEW_NO_FLAGS) \
+	_(pager_autoscroll,		bool,			VIEW_NO_FLAGS) \
 	_(pager_view,			view_settings,		VIEW_NO_FLAGS) \
 	_(pgrp,				bool,			VIEW_NO_FLAGS) \
 	_(reference_format,		struct ref_format **,	VIEW_NO_FLAGS) \

src/pager.c

@@ -137,6 +137,9 @@ pager_common_read(struct view *view, const char *data, enum line_type type, stru
 static bool
 pager_read(struct view *view, struct buffer *buf, bool force_stop)
 {
+	if (opt_pager_autoscroll && view->pos.offset + view->height == view->lines - 1)
+		do_scroll_view(view, 1);
+
 	if (!buf) {
 		if (!diff_done_highlight(view->private)) {
 			report("Failed run the diff-highlight program: %s", opt_diff_highlight);

tigrc

@@ -143,6 +143,7 @@ set mouse			= no		# Enable mouse support?
 set mouse-scroll		= 3		# Number of lines to scroll via the mouse
 set mouse-wheel-cursor		= no		# Prefer moving the cursor to scrolling the view?
 set pgrp			= no		# Make tig process-group leader?
+set pager-autoscroll		= no		# Scroll the pager view automatically while loading?
 
 # User-defined commands
 # ---------------------