Server: Use overlay buttons as next/prev on boo details page

See #1845417 ([Enhancement] Book details on calibre-server)

src/pyj/book_list/book_details.pyj

@@ -16,7 +16,7 @@ from book_list.library_data import (
     set_book_metadata
 )
 from book_list.router import back, home, open_book, report_a_load_failure
-from book_list.theme import get_color, get_font_size
+from book_list.theme import get_color, get_color_as_rgba, get_font_size
 from book_list.top_bar import add_button, clear_buttons, create_top_bar, set_title
 from book_list.ui import query_as_href, set_panel_handler, show_panel
 from book_list.views import search_query_for
@@ -382,6 +382,7 @@ def basic_table_rules(sel):
 add_extra_css(def():
     sel = '.' + CLASS_NAME + ' '
     style = basic_table_rules(sel)
+    style += build_rule(sel + ' .next-book-button:hover', transform='scale(1.5)')
 
     sel = '.' + SEARCH_INTERNET_CLASS
     style += build_rule(sel, margin='1ex 1em')
@@ -440,15 +441,40 @@ def render_book(container_id, book_id):
     set_title(c, metadata.title)
     authors = metadata.authors.join(' & ') if metadata.authors else _('Unknown')
     alt = _('{} by {}\nClick to read').format(metadata.title, authors)
-    imgdiv = E.div(
+    bsrgb = get_color_as_rgba('button-start')
+
+    def next_book(delta):
+        next_book_id = book_after(book_id, delta)
+        if next_book_id:
+            q = parse_url_params()
+            q.book_id = next_book_id + ''
+            show_panel('book_details', query=q, replace=True)
+
+    def prev_next_button(is_prev):
+        return E.div(
+            style=f'border-radius: {border_radius//5}px; background-color:rgba({bsrgb[0]}, {bsrgb[1]}, {bsrgb[2]}, 0.75);',
+            title=_('Previous book') if is_prev else _('Next book'),
+            class_='simple-link next-book-button',
+            svgicon('chevron-left' if is_prev else 'chevron-right'),
+            onclick=next_book.bind(None, (-1 if is_prev else 1))
+        )
+
+    border_radius = 20
+    imgdiv = E.div(style='position: relative',
         E.img(
             alt=alt, title=alt, data_title=metadata.title, data_authors=authors,
             onclick=read_book.bind(None, book_id),
-            style='cursor: pointer; border-radius: 20px; max-width: calc(100vw - 2em); max-height: calc(100vh - 4ex - {}); display: block; width:auto; height:auto; border-radius: 20px'.format(get_font_size('title')
-        ))
+            style='cursor: pointer; border-radius: 20px; max-width: calc(100vw - 2em); max-height: calc(100vh - 4ex - {}); display: block; width:auto; height:auto; border-radius: {}px'.format(get_font_size('title'), border_radius
+        )),
+        E.div(
+            style=f'position: absolute; top:0; width: 100%; padding: {border_radius//2}px; box-sizing: border-box; font-size: 2rem; display: flex; justify-content: space-between; color: {get_color("button-text")}',
+            prev_next_button(True),
+            prev_next_button(),
+        ),
     )
-    imgdiv.firstChild.onerror = on_img_err
-    imgdiv.firstChild.src = cover_url(book_id)
+    img = imgdiv.getElementsByTagName('img')[0]
+    img.onerror = on_img_err
+    img.src = cover_url(book_id)
     c = c.lastChild
     c.appendChild(E.div(
         style='display:flex; padding: 1ex 1em; align-items: flex-start; justify-content: flex-start; flex-wrap: wrap',
@@ -470,20 +496,6 @@ def render_book(container_id, book_id):
     container.appendChild(md)
     md.appendChild(table)
 
-    def next_book(delta):
-        next_book_id = book_after(book_id, delta)
-        if next_book_id:
-            q = parse_url_params()
-            q.book_id = next_book_id + ''
-            show_panel('book_details', query=q, replace=True)
-
-    md.appendChild(E.div(
-        style='margin-top: 1.5ex',
-        create_button(_('Previous'), 'arrow-left', next_book.bind(None, -1)),
-        '\xa0\xa0\xa0',
-        create_button(_('Next'), 'arrow-right', next_book.bind(None, 1)),
-    ))
-
     render_metadata(metadata, table, book_id)
 
 

src/pyj/book_list/theme.pyj

@@ -50,9 +50,30 @@ DEFAULT_FONTS = {
     'main': 'sans-serif'
 }
 
+
 def get_color(name):
     return DEFAULT_COLORS[name]
 
+
+def color_to_rgba(color):
+    # take an arbitrary color spec and return it as [r, g, b, a]
+    cvs = document.createElement('canvas')
+    cvs.height = 1
+    cvs.width = 1
+    ctx = cvs.getContext('2d')
+    ctx.fillStyle = color
+    ctx.fillRect(0, 0, 1, 1)
+    return ctx.getImageData(0, 0, 1, 1).data
+
+
+def get_color_as_rgba(name):
+    cache = get_color_as_rgba.cache
+    if not cache[name]:
+        cache[name] = color_to_rgba(get_color(name))
+    return cache[name]
+get_color_as_rgba.cache = {}
+
+
 def get_font_size(name):
     return DEFAULT_SIZES[name]
 

src/pyj/read_book/view.pyj

@@ -8,7 +8,7 @@ from gettext import gettext as _
 import read_book.iframe  # noqa
 from ajax import ajax_send
 from book_list.globals import get_session_data
-from book_list.theme import get_color
+from book_list.theme import color_to_rgba, get_color
 from dom import add_extra_css, build_rule, set_css, svgicon, unique_id
 from iframe_comm import IframeWrapper
 from modals import error_dialog, warning_dialog
@@ -30,8 +30,7 @@ from read_book.toc import get_current_toc_nodes, update_visible_toc_nodes
 from read_book.touch import set_left_margin_handler, set_right_margin_handler
 from session import get_device_uuid, get_interface_data
 from utils import (
-    color_to_rgba, html_escape, is_ios, parse_url_params, safe_set_inner_html,
-    username_key
+    html_escape, is_ios, parse_url_params, safe_set_inner_html, username_key
 )
 from viewer.constants import READER_BACKGROUND_URL
 

src/pyj/utils.pyj

@@ -242,17 +242,6 @@ def sandboxed_html(html, style, sandbox):
     return ans
 
 
-def color_to_rgba(color):
-    # take an arbitrary color spec and return it as [r, g, b, a]
-    cvs = document.createElement('canvas')
-    cvs.height = 1
-    cvs.width = 1
-    ctx = cvs.getContext('2d')
-    ctx.fillStyle = color
-    ctx.fillRect(0, 0, 1, 1)
-    return ctx.getImageData(0, 0, 1, 1).data
-
-
 if __name__ is '__main__':
     from pythonize import strings
     strings()