Center pdf manual zoom mode (#10246)

Center PDF content when its width is smaller than the screen

fix #9967

frontend/apps/reader/modules/readerpaging.lua

@@ -714,7 +714,7 @@ function ReaderPaging:onUpdateScrollPageGamma(gamma)
     return true
 end
 
-function ReaderPaging:getNextPageState(blank_area, offset)
+function ReaderPaging:getNextPageState(blank_area, image_offset)
     local page_area = self.view:getPageArea(
         self.view.state.page,
         self.view.state.zoom,
@@ -722,21 +722,25 @@ function ReaderPaging:getNextPageState(blank_area, offset)
     local visible_area = Geom:new{x = 0, y = 0}
     visible_area.w, visible_area.h = blank_area.w, blank_area.h
     visible_area.x, visible_area.y = page_area.x, page_area.y
-    visible_area = visible_area:shrinkInside(page_area, offset.x, offset.y)
+    visible_area = visible_area:shrinkInside(page_area, image_offset.x, image_offset.y)
     -- shrink blank area by the height of visible area
     blank_area.h = blank_area.h - visible_area.h
+    local page_offset = Geom:new{x = self.view.state.offset.x, y = 0}
+    if blank_area.w > page_area.w then
+        page_offset:offsetBy((blank_area.w - page_area.w) / 2, 0)
+    end
     return {
         page = self.view.state.page,
         zoom = self.view.state.zoom,
         rotation = self.view.state.rotation,
         gamma = self.view.state.gamma,
-        offset = Geom:new{ x = self.view.state.offset.x, y = 0},
+        offset = page_offset,
         visible_area = visible_area,
         page_area = page_area,
     }
 end
 
-function ReaderPaging:getPrevPageState(blank_area, offset)
+function ReaderPaging:getPrevPageState(blank_area, image_offset)
     local page_area = self.view:getPageArea(
         self.view.state.page,
         self.view.state.zoom,
@@ -745,15 +749,19 @@ function ReaderPaging:getPrevPageState(blank_area, offset)
     visible_area.w, visible_area.h = blank_area.w, blank_area.h
     visible_area.x = page_area.x
     visible_area.y = page_area.y + page_area.h - visible_area.h
-    visible_area = visible_area:shrinkInside(page_area, offset.x, offset.y)
+    visible_area = visible_area:shrinkInside(page_area, image_offset.x, image_offset.y)
     -- shrink blank area by the height of visible area
     blank_area.h = blank_area.h - visible_area.h
+    local page_offset = Geom:new{x = self.view.state.offset.x, y = 0}
+    if blank_area.w > page_area.w then
+        page_offset:offsetBy((blank_area.w - page_area.w) / 2, 0)
+    end
     return {
         page = self.view.state.page,
         zoom = self.view.state.zoom,
         rotation = self.view.state.rotation,
         gamma = self.view.state.gamma,
-        offset = Geom:new{ x = self.view.state.offset.x, y = 0},
+        offset = page_offset,
         visible_area = visible_area,
         page_area = page_area,
     }

spec/unit/readerlink_spec.lua

@@ -124,7 +124,7 @@ describe("ReaderLink module", function()
         local expected_page_states = {
             {
                 gamma = 1,
-                offset = {x = 0, y = 0},
+                offset = {x = 17, y = 0},
                 page = 3,
                 page_area = {
                   x = 0, y = 0,
@@ -139,7 +139,7 @@ describe("ReaderLink module", function()
            },
            {
                 gamma = 1,
-                offset = {x = 0, y = 0},
+                offset = {x = 17, y = 0},
                 page = 4,
                 page_area = {
                   h = 800, w = 566,

spec/unit/readerview_spec.lua

@@ -124,7 +124,7 @@ describe("Readerview module", function()
         local saved_ctx = {
             {
                  gamma = 1,
-                 offset = {x = 0, y = 0},
+                 offset = {x = 17, y = 0},
                  page = 1,
                  page_area = {
                      h = 800,