fix(plot_canvas): support rounded borders in canvas style sheets

A canvas style sheet with rounded borders, e.g.
plot.canvas().setStyleSheet("border: 2px solid black; border-radius: 8px;"),
raised a TypeError on each style change, resize and paint event. As these
exceptions are raised in Qt virtual methods, PyQt aborts the process with
its default exception hook (0xC0000409 on Windows).

Three porting bugs were on this code path, which the Qwt C++ code avoids
with implicit conversions:
- QwtStyleSheetRecorder.drawPath built QRectF(QPointF, QSize): the size is
  now converted to a QSizeF;
- qwtCombinePathList used `rect.bottom` instead of `rect.bottom()` and
  None placeholders instead of empty paths (so that any border without
  all its corners failed), and reverted the input sub-paths in place: it
  now works on a QRectF, empty paths and copies of the sub-paths, as in
  Qwt C++;
- qwtFillBackground passed the QRectF corner rectangles of the style sheet
  to QRegion.intersects, QPixmap and QWidget.mapTo, which expect integer
  types: they are now converted with QRectF.toAlignedRect(), as in Qwt
  C++. QRect rectangles (plain canvas with a border radius) are left
  unchanged by this conversion.

Canvases without rounded style sheet borders render exactly as before:
same images, pixel for pixel, with and without backing store, for
canvases without style sheet, with non-rounded style sheets and with a
border radius set by setBorderRadius.

- Regression tests: incomplete and complete rounded corners combined
  without modifying the input paths; canvases with three rounded style
  sheets, with and without backing store, rendered without exception
  (exceptions raised in Qt virtual methods are collected), with a border
  path and a rounded corner filled with the plot background.
- Changelog entry.

Refs #115

Assisted-by: Claude Opus 5.5

Author: PierreRaybaut

CHANGELOG.md

@@ -17,6 +17,7 @@
 - Fixed painting into a `QwtGraphic` with clipping enabled, which raised a `TypeError` on each paint operation (aborting the process with PyQt's default exception hook): clipped paint operations are now recorded, and the bounding rectangle of the graphic is clipped as in Qwt ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 - Fixed the `QwtPainterCommand` copy constructor (`QwtPainterCommand(other)`), which raised an `AttributeError` for state commands and a `TypeError` (Qt objects cannot be pickled) for pixmap and image commands: commands of every type can now be copied, the copy being independent of the original ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 - Fixed `QwtDynGridLayout` (used by `QwtLegend`), whose `numRows()` returned a float (e.g. `2.5` for 3 items on 2 columns) and which raised a `TypeError` when laying out its items with vertical expansion (`setExpandingDirections(Qt.Vertical)`) ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
+- Fixed canvas style sheets with rounded borders (e.g. `plot.canvas().setStyleSheet("border: 2px solid black; border-radius: 8px;")`), which raised a `TypeError` on each style change, resize and paint event (aborting the process with PyQt's default exception hook): the rounded border of the style sheet is now taken into account to clip the plot items and to fill the corners with the background of the parent widget, as in Qwt ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 
 ## Version 0.16.3
 

qwt/plot_canvas.py

@@ -16,7 +16,17 @@
 import weakref
 from collections.abc import Sequence
 
-from qtpy.QtCore import QEvent, QObject, QPoint, QPointF, QRect, QRectF, QSize, Qt
+from qtpy.QtCore import (
+    QEvent,
+    QObject,
+    QPoint,
+    QPointF,
+    QRect,
+    QRectF,
+    QSize,
+    QSizeF,
+    Qt,
+)
 from qtpy.QtGui import (
     QBrush,
     QGradient,
@@ -81,7 +91,7 @@ def drawRects(self, rects, count):
             )
 
     def drawPath(self, path):
-        rect = QRectF(QPointF(0.0, 0.0), self.__size)
+        rect = QRectF(QPointF(0.0, 0.0), QSizeF(self.__size))
         if path.controlPointRect().contains(rect.center()):
             self.setCornerRects(path)
             self.alignCornerRects(rect)
@@ -188,9 +198,11 @@ def qwtCombinePathList(rect, pathList):
     if not pathList:
         return QPainterPath()
 
-    ordered = [None] * 8
+    rect = QRectF(rect)
+    ordered = [QPainterPath() for _i in range(8)]
     for subPath in pathList:
         index = -1
+        subPath = QPainterPath(subPath)
         br = subPath.controlPointRect()
         if br.center().x() < rect.center().x():
             if br.center().y() < rect.center().y():
@@ -199,7 +211,7 @@ def qwtCombinePathList(rect, pathList):
                 else:
                     index = 0
             else:
-                if abs(br.bottom() - rect.bottom) < abs(br.left() - rect.left()):
+                if abs(br.bottom() - rect.bottom()) < abs(br.left() - rect.left()):
                     index = 6
                 else:
                     index = 7
@@ -297,7 +309,8 @@ def qwtFillBackground(*args):
         else:
             clipRegion = widget.contentsRect()
         bgWidget = qwtBackgroundWidget(widget.parentWidget())
-        for rect in fillRects:
+        for fillRect in fillRects:
+            rect = QRectF(fillRect).toAlignedRect()
             if clipRegion.intersects(rect):
                 pm = QPixmap(rect.size())
                 QwtPainter.fillPixmap(

qwt/tests/test_issue115_porting_bugs.py

@@ -37,6 +37,7 @@
 from qwt.dyngrid_layout import QwtDynGridLayout
 from qwt.graphic import QwtGraphic
 from qwt.painter_command import QwtPainterCommand
+from qwt.plot_canvas import QwtPlotCanvas, qwtCombinePathList
 from qwt.plot_curve import series_to_polyline
 from qwt.transform import QwtPowerTransform
 
@@ -567,6 +568,73 @@ def test_dyngrid_layout_vertical_expanding():
     del app
 
 
+# ---------------------------------------------------------------------------
+# Canvas style sheets with rounded borders
+# ---------------------------------------------------------------------------
+
+
+def _curve_path(start, ctrl1, ctrl2, end):
+    path = QG.QPainterPath(QC.QPointF(*start))
+    path.cubicTo(QC.QPointF(*ctrl1), QC.QPointF(*ctrl2), QC.QPointF(*end))
+    return path
+
+
+@pytest.mark.parametrize("rect_type", (QC.QRect, QC.QRectF))
+def test_combine_path_list_incomplete_border(rect_type):
+    """Incomplete rounded borders are not combined (as in Qwt C++)"""
+    rect = rect_type(0, 0, 100, 100)
+    assert qwtCombinePathList(rect, []).isEmpty()
+    corner = _curve_path((0.0, 10.0), (0.0, 7.0), (0.0, 6.0), (0.0, 5.0))
+    assert qwtCombinePathList(rect, [corner]).isEmpty()
+
+
+def test_combine_path_list_rounded_corner():
+    """The sub-paths of a rounded corner are combined with the other corners"""
+    rect = QC.QRectF(0.0, 0.0, 100.0, 100.0)
+    left = _curve_path((0.0, 5.0), (0.0, 6.0), (0.0, 7.0), (0.0, 10.0))
+    top = _curve_path((5.0, 0.0), (6.0, 0.0), (7.0, 0.0), (10.0, 0.0))
+    references = [QG.QPainterPath(left), QG.QPainterPath(top)]
+    path = qwtCombinePathList(rect, [left, top])
+    assert not path.isEmpty()
+    assert path.boundingRect() == rect
+    # The sub-paths are reverted when needed, but the input ones are unchanged
+    assert [left, top] == references
+
+
+ROUNDED_STYLE_SHEETS = (
+    "border-radius: 10px; background-color: white;",
+    "border: 2px solid black; border-radius: 8px;",
+    "border: 1px solid gray; border-top-left-radius: 12px; background-color: white;",
+)
+
+
+@pytest.mark.parametrize("backing_store", (False, True), ids=("direct", "backing"))
+@pytest.mark.parametrize("style_sheet", ROUNDED_STYLE_SHEETS)
+def test_canvas_rounded_style_sheet(style_sheet, backing_store):
+    """A canvas style sheet with rounded borders is supported"""
+    app = _ensure_app()  # keep a reference alive for the duration of the test
+    plot = QwtPlot()
+    canvas = plot.canvas()
+    canvas.setPaintAttribute(QwtPlotCanvas.BackingStore, backing_store)
+    with _qt_exceptions() as errors:
+        canvas.setStyleSheet(style_sheet)
+        plot.resize(400, 300)
+        plot.show()
+        app.processEvents()
+        plot.replot()
+        image = canvas.grab().toImage()
+        border_path = canvas.borderPath(canvas.rect())
+    assert not errors, _format_exceptions(errors)
+    assert not border_path.isEmpty()
+    if "background-color: white" in style_sheet:
+        # Rounded top left corner: filled with the background of the plot
+        white = QG.QColor(QC.Qt.white).rgb()
+        assert image.pixelColor(0, 0).rgb() != white
+        assert image.pixelColor(image.width() // 2, image.height() // 2).rgb() == white
+    plot.close()
+    del app
+
+
 if __name__ == "__main__":
     for name in ("toPixmap", "toImage"):
         test_graphic_conversion_default_size(name)
@@ -586,4 +654,8 @@ def test_dyngrid_layout_vertical_expanding():
     test_painter_command_copy_is_independent()
     test_painter_command_copy_replay()
     test_dyngrid_layout_vertical_expanding()
+    test_combine_path_list_rounded_corner()
+    for sheet in ROUNDED_STYLE_SHEETS:
+        for backing in (False, True):
+            test_canvas_rounded_style_sheet(sheet, backing)
     print("OK")