show_overlap inverts part of page visible in previous view

This is nice feature of Sony e-book readers which is very useful when
reading since it shows previous part of visible page and provides
hint where to continue reading after page refresh

crereader.lua

@@ -102,6 +102,14 @@ function CREReader:goto(pos, pos_type)
 
 	self.doc:drawCurrentPage(self.nulldc, fb.bb)
 
+	print("## self.show_overlap "..self.show_overlap)
+	if self.show_overlap < 0 then
+		fb.bb:invertRect(0,0, width, -self.show_overlap)
+	elseif self.show_overlap > 0 then
+		fb.bb:invertRect(0,height - self.show_overlap, width, self.show_overlap)
+	end
+	self.show_overlap = 0
+
 	if self.rcount == self.rcountmax then
 		print("full refresh")
 		self.rcount = 1
@@ -127,10 +135,12 @@ function CREReader:gotoTocEntry(entry)
 end
 
 function CREReader:nextView()
+	self.show_overlap = -self.pan_overlap_vertical
 	return self.pos + G_height - self.pan_overlap_vertical
 end
 
 function CREReader:prevView()
+	self.show_overlap = self.pan_overlap_vertical
 	return self.pos - G_height + self.pan_overlap_vertical
 end
 

unireader.lua

@@ -54,6 +54,7 @@ UniReader = {
 	pan_y = 0,
 	pan_margin = 20, -- horizontal margin for two-column zoom
 	pan_overlap_vertical = 30,
+	show_overlap = 0,
 
 	-- the document:
 	doc = nil,
@@ -552,6 +553,14 @@ function UniReader:show(no)
 		"width:"..width..", height:"..height)
 	fb.bb:blitFrom(bb, dest_x, dest_y, offset_x, offset_y, width, height)
 
+	print("## self.show_overlap "..self.show_overlap)
+	if self.show_overlap < 0 then
+		fb.bb:invertRect(0,0, width, dest_y - self.show_overlap)
+	elseif self.show_overlap > 0 then
+		fb.bb:invertRect(0,dest_y + height - self.show_overlap, width, self.show_overlap)
+	end
+	self.show_overlap = 0
+
 	-- render highlights to page
 	if self.highlight[no] then
 		self:toggleTextHighLight(self.highlight[no])
@@ -668,6 +677,7 @@ function UniReader:nextView()
 			-- goto next view of current page
 			self.offset_y = self.offset_y - G_height
 							+ self.pan_overlap_vertical
+			self.show_overlap = -self.pan_overlap_vertical -- top < 0
 		end
 	else
 		-- not in fit to content width pan mode, just do a page turn
@@ -695,6 +705,7 @@ function UniReader:prevView()
 			-- goto previous view of current page
 			self.offset_y = self.offset_y + G_height
 							- self.pan_overlap_vertical
+			self.show_overlap = self.pan_overlap_vertical -- bottom > 0
 		end
 	else
 		-- not in fit to content width pan mode, just do a page turn
@@ -1183,8 +1194,8 @@ function UniReader:addAllCommands()
 					x = unireader.shift_x / 5
 					y = unireader.shift_y / 5
 				elseif unireader.pan_by_page then
-					x = G_width;
-					y = G_height - unireader.pan_overlap_vertical; -- overlap for lines which didn't fit
+					x = G_width
+					y = G_height
 				else
 					x = unireader.shift_x
 					y = unireader.shift_y
@@ -1223,14 +1234,18 @@ function UniReader:addAllCommands()
 						unireader.offset_x = unireader.min_offset_x
 					end
 				elseif keydef.keycode == KEY_FW_UP then
-					unireader.offset_y = unireader.offset_y + y
+					unireader.offset_y = unireader.offset_y + y - unireader.pan_overlap_vertical
 					if unireader.offset_y > 0 then
 						unireader.offset_y = 0
+					elseif unireader.pan_by_page then
+						unireader.show_overlap = unireader.pan_overlap_vertical -- bottom
 					end
 				elseif keydef.keycode == KEY_FW_DOWN then
-					unireader.offset_y = unireader.offset_y - y
+					unireader.offset_y = unireader.offset_y - y + unireader.pan_overlap_vertical
 					if unireader.offset_y < unireader.min_offset_y then
 						unireader.offset_y = unireader.min_offset_y
+					elseif unireader.pan_by_page then
+						unireader.show_overlap = -unireader.pan_overlap_vertical -- top
 					end
 				elseif keydef.keycode == KEY_FW_PRESS then
 					if keydef.modifier==MOD_SHIFT then