Proper CFI calculation for paged mode

src/calibre/ebooks/oeb/display/cfi.coffee

@@ -572,29 +572,22 @@ class CanonicalFragmentIdentifier
         null
     # }}}
 
-    at_current: () -> # {{{
-        [winx, winy] = window_scroll_pos()
-        [winw, winh] = [window.innerWidth, window.innerHeight]
-        max = Math.max
-        winw = max(winw, 400)
-        winh = max(winh, 600)
-        deltay = Math.floor(winh/50)
-        deltax = Math.floor(winw/25)
-        miny = max(-winy, -winh)
-        maxy = winh
-        minx = max(-winx, -winw)
-        maxx = winw
+    at_point: (ox, oy) ->
+        # The CFI at the specified point. Different to at() in that this method
+        # returns null if there is an error, and also calculates a point from
+        # the CFI and returns null if the calculated point is far from the
+        # original point.
 
         dist = (p1, p2) ->
             Math.sqrt(Math.pow(p1[0]-p2[0], 2), Math.pow(p1[1]-p2[1], 2))
 
-        get_cfi = (ox, oy) ->
         try
             cfi = window.cfi.at(ox, oy)
             point = window.cfi.point(cfi)
         catch err
             cfi = null
 
+
         if cfi
             if point.range != null
                 r = point.range
@@ -617,12 +610,25 @@ class CanonicalFragmentIdentifier
 
         return cfi
 
-        x_loop = (cury) ->
+    at_current: () -> # {{{
+        [winx, winy] = window_scroll_pos()
+        [winw, winh] = [window.innerWidth, window.innerHeight]
+        max = Math.max
+        winw = max(winw, 400)
+        winh = max(winh, 600)
+        deltay = Math.floor(winh/50)
+        deltax = Math.floor(winw/25)
+        miny = max(-winy, -winh)
+        maxy = winh
+        minx = max(-winx, -winw)
+        maxx = winw
+
+        x_loop = (cury) =>
             for direction in [-1, 1]
                 delta = deltax * direction
                 curx = 0
                 until (direction < 0 and curx < minx) or (direction > 0 and curx > maxx)
-                    cfi = get_cfi(curx, cury)
+                    cfi = this.at_point(curx, cury)
                     if cfi
                         return cfi
                     curx += delta

src/calibre/ebooks/oeb/display/paged.coffee

@@ -67,6 +67,8 @@ class PagedDisplay
     ###
 
     constructor: () ->
+        if not this instanceof arguments.callee
+            throw new Error('PagedDisplay constructor called as function')
         this.set_geometry()
         this.page_width = 0
         this.screen_width = 0
@@ -213,11 +215,11 @@ class PagedDisplay
         # most column in the viewport is the column containing the start of the
         # element and that the scroll position is at the start of the column.
         elem = document.getElementById(name)
-        if !elem
+        if not elem
             elems = document.getElementsByName(name)
             if elems
                 elem = elems[0]
-        if !elem
+        if not elem
             return
         elem.scrollIntoView()
         if this.in_paged_mode
@@ -249,12 +251,48 @@ class PagedDisplay
                 window.scrollTo(0, y)
         )
 
+    current_cfi: () ->
+        # The Conformal Fragment Identifier at the current position, returns
+        # null if it could not be calculated. Requires the cfi.coffee library.
+        ans = null
+        if not window.cfi?
+            return ans
+        if this.in_paged_mode
+            c = this.current_column_location()
+            for x in [c, c-this.page_width, c+this.page_width]
+                # Try the current column, the previous column and the next
+                # column. Each column is tried from top to bottom.
+                [left, right] = [x, x + this.page_width]
+                if left < 0 or right > document.body.scrollWidth
+                    continue
+                deltax = Math.floor(this.page_width/25)
+                deltay = Math.floor(window.innerHeight/25)
+                cury = this.margin_top
+                until cury >= (window.innerHeight - this.margin_bottom)
+                    curx = left + this.current_margin_side
+                    until curx >= (right - this.current_margin_side)
+                        cfi = window.cfi.at_point(curx-window.pageXOffset, cury-window.pageYOffset)
+                        if cfi
+                            log('Viewport cfi:', cfi)
+                            return cfi
+                        curx += deltax
+                    cury += deltay
+        else
+            try
+                ans = window.cfi.at_current()
+                if not ans
+                    ans = null
+            catch err
+                log(err)
+        if ans
+            log('Viewport cfi:', ans)
+        return ans
+
 if window?
     window.paged_display = new PagedDisplay()
 
 # TODO:
 # css pagebreak rules
-# CFI and bookmarks
 # Go to reference positions
 # Indexing
 # Resizing of images

src/calibre/gui2/viewer/position.py

@@ -19,13 +19,10 @@ class PagePosition(object):
         ans = None
         res = self.document.mainFrame().evaluateJavaScript('''
             ans = 'undefined';
-            try {
-                ans = window.cfi.at_current();
+            if (window.paged_display) {
+                ans = window.paged_display.current_cfi();
                 if (!ans) ans = 'undefined';
-            } catch (err) {
-                window.console.log(err);
             }
-            window.console.log("Viewport cfi: " + ans);
             ans;
         ''')
         if res.isValid() and not res.isNull() and res.type() == res.String: