register swipe diagonal gesture range to screenshot

for non-multitouch devices

This PR is intended to substitude #652 which needs tweaking
double tap zone for screenshot.

frontend/apps/reader/modules/readerpaging.lua

@@ -290,7 +290,6 @@ function ReaderPaging:onSwipe(arg, ges)
     else
         UIManager.full_refresh = true
     end
-    return true
 end
 
 function ReaderPaging:onPan(arg, ges)

frontend/apps/reader/modules/readerrolling.lua

@@ -188,7 +188,6 @@ function ReaderRolling:onSwipe(arg, ges)
     elseif ges.direction == "east" or ges.direction == "south" then
         self:onGotoViewRel(-1)
     end
-    return true
 end
 
 function ReaderRolling:onPan(arg, ges)

frontend/apps/reader/modules/readerscreenshot.lua

@@ -15,13 +15,20 @@ function ReaderScreenshot:init()
         math.pow(Screen:getHeight(), 2)
     )
     self.ges_events = {
-        Screenshot = {
+        TapDiagonal = {
             GestureRange:new{
                 ges = "two_finger_tap",
                 scale = {diagonal - Screen:scaleByDPI(200), diagonal},
                 rate = 1.0,
             }
         },
+        SwipeDiagonal = {
+            GestureRange:new{
+                ges = "swipe",
+                scale = {diagonal - Screen:scaleByDPI(200), diagonal},
+                rate = 1.0,
+            }
+        },
     }
 end
 
@@ -41,4 +48,12 @@ function ReaderScreenshot:onScreenshot()
     return true
 end
 
+function ReaderScreenshot:onTapDiagonal()
+    return self:onScreenshot()
+end
+
+function ReaderScreenshot:onSwipeDiagonal()
+    return self:onScreenshot()
+end
+
 return ReaderScreenshot