readerview: add get/set methods for view context

frontend/apps/reader/modules/readerview.lua

@@ -557,6 +557,36 @@ function ReaderView:SetZoomCenter(x, y)
     end
 end
 
+function ReaderView:getViewContext()
+    if self.page_scroll then
+        return self.page_states
+    else
+        return {
+            {
+                page = self.state.page,
+                pos = self.state.pos,
+                zoom = self.state.zoom,
+                rotation = self.state.rotation,
+                gamma = self.state.gamma,
+                offset = self.state.offset:copy(),
+                bbox = self.state.bbox,
+            },
+            self.visible_area:copy(),
+            self.page_area:copy(),
+        }
+    end
+end
+
+function ReaderView:restoreViewContext(ctx)
+    if self.page_scroll then
+        self.page_states = ctx
+    else
+        self.state = ctx[1]
+        self.visible_area = ctx[2]
+        self.page_area = ctx[3]
+    end
+end
+
 function ReaderView:onSetScreenMode(new_mode, rotation)
     if new_mode == "landscape" or new_mode == "portrait" then
         self.screen_mode = new_mode

spec/unit/readerview_spec.lua

@@ -39,4 +39,50 @@ describe("Readerview module", function()
             end
         end
     end)
+
+    it("should return and restore view context", function()
+        local sample_pdf = "spec/front/unit/data/2col.pdf"
+        local readerui = ReaderUI:new{
+            document = DocumentRegistry:openDocument(sample_pdf),
+        }
+        local view = readerui.view
+        local ctx = view:getViewContext()
+        local zoom = ctx[1].zoom
+        ctx[1].zoom = nil
+        local saved_ctx = {
+            {
+                page = 1,
+                pos = 0,
+                gamma = 1,
+                offset = {
+                    x = 17, y = 0,
+                    h = 0, w = 0,
+                },
+                rotation = 0,
+            },
+            -- visible_area
+            {
+                x = 0, y = 0,
+                h = 800, w = 566,
+            },
+            -- page_area
+            {
+                x = 0, y = 0,
+                h = 800, w = 566,
+            },
+        }
+        assert.are.same(ctx, saved_ctx)
+        assertAlmostEquals(zoom, 0.95011876484561, 0.0001)
+
+        assert.is.same(view.state.page, 1)
+        assert.is.same(view.visible_area.x, 0)
+        assert.is.same(view.visible_area.y, 0)
+        saved_ctx[1].page = 2
+        saved_ctx[1].zoom = zoom
+        saved_ctx[2].y = 10
+        view:restoreViewContext(saved_ctx)
+        assert.is.same(view.state.page, 2)
+        assert.is.same(view.visible_area.x, 0)
+        assert.is.same(view.visible_area.y, 10)
+    end)
 end)