Make the number of columns per screen automatic in paged mode

src/pyj/read_book/paged_mode.pyj

@@ -106,14 +106,19 @@ def layout(is_single_page):
     nonlocal _in_paged_mode, col_width, col_and_gap, screen_height, gap, screen_width, is_full_screen_layout, cols_per_screen
     body_style = window.getComputedStyle(document.body)
     first_layout = not _in_paged_mode
+    cps = opts.columns_per_screen
+    cps = cps.landscape if window.innerWidth > window.innerHeight else cps.portrait
+    if cps is 'auto':
+        cps = int(Math.floor(window.innerWidth / 500.0))
+    cps = max(1, min(cps or 1, 20))
     if first_layout:
         handle_rtl_body(body_style)
         # Check if the current document is a full screen layout like
         # cover, if so we treat it specially.
         single_screen = (document.body.scrollHeight < window.innerHeight + 75)
         first_layout = True
-        if not single_screen and opts.cols_per_screen > 1:
-            num = opts.cols_per_screen - 1
+        if not single_screen and cps > 1:
+            num = cps - 1
             elems = document.querySelectorAll('body > *')
             if elems.length == 1:
                 # Workaround for the case when the content is wrapped in a
@@ -125,7 +130,7 @@ def layout(is_single_page):
                 num -= 1
                 create_page_div()
 
-    n = cols_per_screen = opts.cols_per_screen
+    n = cols_per_screen = cps
     # Calculate the column width so that cols_per_screen columns fit exactly in
     # the window width, with their separator margins
     ww = col_width = screen_width = window.innerWidth

src/pyj/read_book/settings.pyj

@@ -6,7 +6,7 @@ opts = {}
 
 def apply_settings(settings):
     settings = settings or {}
-    opts.cols_per_screen = max(1, settings.cols_per_screen or 1)
+    opts.columns_per_screen = settings.columns_per_screen or {'portrait':'auto', 'landscape':'auto'}
     opts.margin_left = max(0, settings.margin_left or 0)
     opts.margin_right = max(0, settings.margin_right or 0)
     opts.color_scheme = settings.color_scheme

src/pyj/read_book/view.pyj

@@ -102,7 +102,8 @@ class View:
     def show_chrome(self):
         self.overlay.show()
 
-    def set_margins(self, no_margins):
+    def set_margins(self):
+        no_margins = self.currently_showing.name is self.book.manifest.title_page_name
         sd = get_session_data()
         margin_left = 0 if no_margins else sd.get('margin_left')
         margin_right = 0 if no_margins else sd.get('margin_right')
@@ -197,7 +198,7 @@ class View:
         return ans
 
     def on_resize(self):
-        pass
+        self.set_margins()  # needed because of max text height/width
 
     def show_loading(self):
         title = self.book.metadata.title
@@ -244,7 +245,7 @@ class View:
             'margin_left': 0 if name is self.book.manifest.title_page_name else sd.get('margin_left'),
             'margin_right': 0 if name is self.book.manifest.title_page_name else sd.get('margin_right'),
             'read_mode': sd.get('read_mode'),
-            'cols_per_screen': sd.get('cols_per_screen'),
+            'columns_per_screen': sd.get('columns_per_screen'),
             'color_scheme': self.get_color_scheme(True),
         }
         initial_position = initial_position or {'replace_history':False}
@@ -254,7 +255,7 @@ class View:
         idx = spine.indexOf(name)
         if idx > -1:
             self.currently_showing.bookpos = 'epubcfi(/{})'.format(2 * (idx +1))
-        self.set_margins(name is self.book.manifest.title_page_name)
+        self.set_margins()
         load_resources(self.ui.db, self.book, name, self.loaded_resources, self.show_spine_item)
 
     def goto_doc_boundary(self, data):

src/pyj/session.pyj

@@ -25,7 +25,7 @@ defaults = {
     'read_mode': 'paged',
     'max_text_height': 0,
     'max_text_width': 0,
-    'cols_per_screen': 1,
+    'columns_per_screen': {'portrait':'auto', 'landscape':'auto'},
     'current_color_scheme': 'white',
     'user_color_schemes': {},
 }
@@ -38,7 +38,7 @@ is_local_setting = {
     'read_mode': 'paged',
     'max_text_height': True,
     'max_text_width': True,
-    'cols_per_screen': True,
+    'columns_per_screen': True,
     'current_color_scheme': True,
 }