Widen dock separators to make them easier to grab (#277) (#595)

* Widen dock separators to make them easier to grab (#277)

* Reword the dock separator comment

* Widen the separators with a style proxy instead of a stylesheet

A stylesheet on the main window moves its whole widget subtree to
QStyleSheetStyle, which drops palette based theming (the syntax
highlighting regression seen in review).

* Reuse the main_clean fixture in the separator test

---------

Co-authored-by: Haozhe Zhang <HaozheZhang6@users.noreply.github.com>

Author: HaozheZhang6

cq_editor/main_window.py

@@ -12,6 +12,8 @@
     QAction,
     QApplication,
     QMenu,
+    QProxyStyle,
+    QStyle,
 )
 from logbook import Logger
 import cadquery as cq
@@ -63,6 +65,23 @@ def new_stdout_write(text: str):
 PRINT_REDIRECTOR = _PrintRedirectorSingleton()
 
 
+class DockSeparatorStyle(QProxyStyle):
+    """Widens the dock separators so that they are easier to grab (#277).
+
+    A style proxy is used instead of a stylesheet because setting a stylesheet
+    on the main window moves its whole widget subtree to QStyleSheetStyle,
+    which discards palette based theming (e.g. editor syntax highlighting).
+    """
+
+    def pixelMetric(self, metric, option=None, widget=None):
+
+        extent = super().pixelMetric(metric, option, widget)
+        if metric == QStyle.PM_DockWidgetSeparatorExtent:
+            return max(extent, 6)
+
+        return extent
+
+
 class MainWindow(QMainWindow, MainMixin):
 
     name = "CQ-Editor"
@@ -100,6 +119,11 @@ def __init__(self, parent=None, filename=None):
         self.viewer = OCCViewer(self)
         self.setCentralWidget(self.viewer.canvas)
 
+        # Make sure the dock separators are wide enough to grab on high-DPI displays.
+        # setStyle does not take ownership, so keep a reference on self.
+        self._separator_style = DockSeparatorStyle()
+        self.setStyle(self._separator_style)
+
         self.prepare_panes()
         self.registerComponent("viewer", self.viewer)
         self.prepare_toolbar()

tests/test_app.py

@@ -12,10 +12,17 @@
 import cadquery as cq
 
 from PyQt5.QtCore import Qt, QSettings, QPoint, QEvent, QSize
-from PyQt5.QtWidgets import QFileDialog, QMessageBox
+from PyQt5.QtWidgets import (
+    QApplication,
+    QFileDialog,
+    QMessageBox,
+    QStyle,
+    QStyleFactory,
+)
 from PyQt5.QtGui import QMouseEvent
 
 from cq_editor.__main__ import MainWindow
+from cq_editor.main_window import DockSeparatorStyle
 from cq_editor.widgets.editor import Editor
 from cq_editor.cq_utils import export, get_occ_color
 
@@ -1708,6 +1715,30 @@ def test_launch_syntax_error(tmp_path):
     assert win.isVisible()
 
 
+def test_dock_separator_width(main_clean):
+
+    qtbot, win = main_clean
+
+    # separators are widened through a style proxy, not a stylesheet: a
+    # stylesheet on the main window would break palette based theming (#595)
+    assert win.styleSheet() == ""
+    assert win.style().pixelMetric(QStyle.PM_DockWidgetSeparatorExtent, None, win) >= 6
+
+    # child widgets keep the application style
+    editor = win.components["editor"]
+    assert editor.style().objectName() == QApplication.instance().style().objectName()
+
+
+def test_dock_separator_style_widens_small_extents(qtbot):
+
+    base = QStyleFactory.create("Windows")
+    assert base.pixelMetric(QStyle.PM_DockWidgetSeparatorExtent) < 6
+
+    style = DockSeparatorStyle(base)
+
+    assert style.pixelMetric(QStyle.PM_DockWidgetSeparatorExtent) == 6
+
+
 code_import_module_makebox = """
 from module_makebox import *
 z = 1