fix(plot_directpainter): set and clear attributes as requested

QwtPlotDirectPainter.setAttribute decided whether to set or to clear the
attribute by comparing its current state with `on`, instead of using `on`:
enabling AtomicPainter twice disabled it, and FullRepaint or
CopyBackingStore could not be disabled anymore once enabled (their
non-boolean flag values never compare equal to `on`).

- Restore the Qwt C++ logic: change the attribute only when its state
  differs from `on`, set it when `on` is true and clear it otherwise, and
  reset the painter only when AtomicPainter gets enabled.
- Regression tests: set, set again, clear, clear again and default `on`
  for each attribute, other attributes unchanged; painter reset count.
- Changelog entry.

Refs #115

Assisted-by: Claude Opus 5.5

Author: PierreRaybaut

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Fixed `QwtPlotMarker.legendIcon` for markers with a symbol, which raised an `AssertionError` or a `TypeError`: such markers can now be shown in a legend ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 - Fixed `QwtPlotGrid.make`, which raised a `TypeError` when only some of the minor pen arguments (`mincolor`, `minwidth`, `minstyle`) were given: each of them is now honored, the missing ones taking their documented default value ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 - Fixed `QwtPowerTransform`, which raised a `ValueError` when drawing a curve on an axis with a power scale (curve data are mapped as NumPy arrays), and an `AttributeError` with NumPy < 2.0 (`numpy.pow` does not exist there): it now transforms scalars (with unchanged results) as well as NumPy arrays, with any supported NumPy version ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
+- Fixed `QwtPlotDirectPainter.setAttribute`, which did not set or clear attributes as requested: enabling `AtomicPainter` twice disabled it, and `FullRepaint` or `CopyBackingStore` could not be disabled anymore once enabled ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 
 ## Version 0.16.3
 

qwt/plot_directpainter.py

@@ -119,12 +119,13 @@ def setAttribute(self, attribute, on=True):
 
             :py:meth:`testAttribute()`
         """
-        if self.testAttribute(attribute) != on:
-            self.__data.attributes |= attribute
-        else:
-            self.__data.attributes &= ~attribute
-        if attribute == self.AtomicPainter and on:
-            self.reset()
+        if bool(self.testAttribute(attribute)) != on:
+            if on:
+                self.__data.attributes |= attribute
+            else:
+                self.__data.attributes &= ~attribute
+            if attribute == self.AtomicPainter and on:
+                self.reset()
 
     def testAttribute(self, attribute):
         """

qwt/tests/test_issue115_porting_bugs.py

@@ -23,6 +23,7 @@
     QwtLinearScaleEngine,
     QwtPlot,
     QwtPlotCurve,
+    QwtPlotDirectPainter,
     QwtPlotGrid,
     QwtPlotItem,
     QwtPlotMarker,
@@ -304,6 +305,69 @@ def test_power_transform_curve_rendering():
     del app
 
 
+# ---------------------------------------------------------------------------
+# QwtPlotDirectPainter.setAttribute
+# ---------------------------------------------------------------------------
+
+DIRECT_PAINTER_ATTRIBUTES = (
+    QwtPlotDirectPainter.AtomicPainter,
+    QwtPlotDirectPainter.FullRepaint,
+    QwtPlotDirectPainter.CopyBackingStore,
+)
+
+
+class _CountingDirectPainter(QwtPlotDirectPainter):
+    """Direct painter counting the calls to `reset`"""
+
+    def __init__(self):
+        super().__init__()
+        self.reset_count = 0
+
+    def reset(self):
+        self.reset_count += 1
+        super().reset()
+
+
+@pytest.mark.parametrize(
+    "attribute",
+    DIRECT_PAINTER_ATTRIBUTES,
+    ids=("AtomicPainter", "FullRepaint", "CopyBackingStore"),
+)
+def test_direct_painter_set_attribute(attribute):
+    """setAttribute sets or clears an attribute, as requested"""
+    app = _ensure_app()  # keep a reference alive for the duration of the test
+    painter = QwtPlotDirectPainter()
+    others = [attr for attr in DIRECT_PAINTER_ATTRIBUTES if attr != attribute]
+    for other in others:
+        painter.setAttribute(other, True)
+    assert not painter.testAttribute(attribute)
+    for on in (True, True, False, False, True):
+        painter.setAttribute(attribute, on)
+        assert bool(painter.testAttribute(attribute)) is on
+        assert all(painter.testAttribute(other) for other in others)
+    painter.setAttribute(attribute, False)
+    painter.setAttribute(attribute)  # `on` defaults to True
+    assert painter.testAttribute(attribute)
+    del app
+
+
+def test_direct_painter_atomic_painter_reset():
+    """Enabling AtomicPainter resets the painter, as in Qwt C++"""
+    app = _ensure_app()  # keep a reference alive for the duration of the test
+    painter = _CountingDirectPainter()
+    painter.setAttribute(QwtPlotDirectPainter.AtomicPainter, True)
+    assert painter.reset_count == 1
+    painter.setAttribute(QwtPlotDirectPainter.AtomicPainter, True)  # unchanged
+    assert painter.reset_count == 1
+    painter.setAttribute(QwtPlotDirectPainter.AtomicPainter, False)
+    assert painter.reset_count == 1
+    painter.setAttribute(QwtPlotDirectPainter.AtomicPainter, True)
+    assert painter.reset_count == 2
+    painter.setAttribute(QwtPlotDirectPainter.FullRepaint, True)
+    assert painter.reset_count == 2
+    del app
+
+
 if __name__ == "__main__":
     for name in ("toPixmap", "toImage"):
         test_graphic_conversion_default_size(name)
@@ -315,4 +379,7 @@ def test_power_transform_curve_rendering():
     test_grid_make_without_minor_pen()
     test_power_transform_scale_map()
     test_power_transform_curve_rendering()
+    for attr in DIRECT_PAINTER_ATTRIBUTES:
+        test_direct_painter_set_attribute(attr)
+    test_direct_painter_atomic_painter_reset()
     print("OK")