Add tabs->favicon-scale setting

This allows users to change the size of the favicon independently from
the size of the font/tab, in order to adjust the balance between
favicons and text. The drawing code is also adjusted to place the icon
relative to the text center, rather than the text top.

Works as expected even for values of 0.0 (which is equivalent to hiding
the favicon completely).

Closes #2549.

doc/help/settings.asciidoc

@@ -126,6 +126,7 @@
 |<<tabs-close-mouse-button,close-mouse-button>>|On which mouse button to close tabs.
 |<<tabs-position,position>>|The position of the tab bar.
 |<<tabs-show-favicons,show-favicons>>|Whether to show favicons in the tab bar.
+|<<tabs-favicon-scale,favicon-scale>>|Scale for favicons in the tab bar. The tab size is unchanged, so big favicons also require extra `tabs->padding`.
 |<<tabs-width,width>>|The width of the tab bar if it's vertical, in px or as percentage of the window.
 |<<tabs-indicator-width,indicator-width>>|Width of the progress indicator (0 to disable).
 |<<tabs-tabs-are-windows,tabs-are-windows>>|Whether to open windows instead of tabs.
@@ -1206,6 +1207,12 @@ Valid values:
 
 Default: +pass:[true]+
 
+[[tabs-favicon-scale]]
+=== favicon-scale
+Scale for favicons in the tab bar. The tab size is unchanged, so big favicons also require extra `tabs->padding`.
+
+Default: +pass:[1.0]+
+
 [[tabs-width]]
 === width
 The width of the tab bar if it's vertical, in px or as percentage of the window.

qutebrowser/config/configdata.py

@@ -680,6 +680,11 @@ def data(readonly=False):
              SettingValue(typ.Bool(), 'true'),
              "Whether to show favicons in the tab bar."),
 
+            ('favicon-scale',
+             SettingValue(typ.Float(minval=0.0), '1.0'),
+             "Scale for favicons in the tab bar. The tab size is unchanged, "
+             "so big favicons also require extra `tabs->padding`."),
+
             ('width',
              SettingValue(typ.PercOrInt(minperc=0, maxperc=100, minint=1),
                           '20%'),

qutebrowser/mainwindow/tabwidget.py

@@ -22,7 +22,8 @@
 import collections
 import functools
 
-from PyQt5.QtCore import pyqtSignal, pyqtSlot, Qt, QSize, QRect, QTimer, QUrl
+from PyQt5.QtCore import (pyqtSignal, pyqtSlot, Qt, QSize, QRect, QPoint,
+                          QTimer, QUrl)
 from PyQt5.QtWidgets import (QTabWidget, QTabBar, QSizePolicy, QCommonStyle,
                              QStyle, QStylePainter, QStyleOptionTab)
 from PyQt5.QtGui import QIcon, QPalette, QColor
@@ -273,6 +274,7 @@ class TabBar(QTabBar):
         self.set_font()
         config_obj = objreg.get('config')
         config_obj.changed.connect(self.set_font)
+        config_obj.changed.connect(self.set_icon_size)
         self.vertical = False
         self._page_fullscreen = False
         self._auto_hide_timer = QTimer()
@@ -374,7 +376,13 @@ class TabBar(QTabBar):
     def set_font(self):
         """Set the tab bar font."""
         self.setFont(config.get('fonts', 'tabbar'))
+        self.set_icon_size()
+
+    @config.change_filter('tabs', 'favicon-scale')
+    def set_icon_size(self):
+        """Set the tab bar favicon size."""
         size = self.fontMetrics().height() - 2
+        size *= config.get('tabs', 'favicon-scale')
         self.setIconSize(QSize(size, size))
 
     @config.change_filter('colors', 'tabs.bg.bar')
@@ -775,7 +783,7 @@ class TabBarStyle(QCommonStyle):
             tab_icon_size = QSize(
                 min(actual_size.width(), icon_size.width()),
                 min(actual_size.height(), icon_size.height()))
-        icon_rect = QRect(text_rect.left(), text_rect.top() + 1,
-                          tab_icon_size.width(), tab_icon_size.height())
+        icon_top = text_rect.center().y() + 1 - tab_icon_size.height() / 2
+        icon_rect = QRect(QPoint(text_rect.left(), icon_top), tab_icon_size)
         icon_rect = self._style.visualRect(opt.direction, opt.rect, icon_rect)
         return icon_rect

tests/unit/mainwindow/test_tabwidget.py

@@ -44,6 +44,7 @@ class TestTabWidget:
             'select-on-remove': 1,
             'show': 'always',
             'show-favicons': True,
+            'favicon-scale': 1.0,
             'padding': configtypes.PaddingValues(0, 0, 5, 5),
             'indicator-width': 3,
             'indicator-padding': configtypes.PaddingValues(2, 2, 0, 4),