Try to use the default font from mpl

src/silx/gui/plot/backends/BackendOpenGL.py

@@ -239,6 +239,7 @@ def __init__(self, plot, parent=None, f=qt.Qt.Widget):
         )
         BackendBase.BackendBase.__init__(self, plot, parent)
 
+        self._defaultFont: qt.QFont = None
         self.__isOpenGLValid = False
 
         self._backgroundColor = 1.0, 1.0, 1.0, 1.0
@@ -261,6 +262,7 @@ def __init__(self, plot, parent=None, f=qt.Qt.Widget):
             foregroundColor=(0.0, 0.0, 0.0, 1.0),
             gridColor=(0.7, 0.7, 0.7, 1.0),
             marginRatios=(0.15, 0.1, 0.1, 0.15),
+            font=self.getDefaultFont(),
         )
         self._plotFrame.size = (  # Init size with size int
             int(self.getDevicePixelRatio() * 640),
@@ -1156,6 +1158,19 @@ def addShape(
             gapcolor,
         )
 
+    def getDefaultFont(self):
+        """Returns the default font, used by raw markers and axes labels"""
+        if self._defaultFont is None:
+            from matplotlib.font_manager import findfont, FontProperties
+            font_filename = findfont(FontProperties(family=["sans-serif"]))
+            _logger.debug("Load font from mpl: %s", font_filename)
+            id = qt.QFontDatabase.addApplicationFont(font_filename)
+            family = qt.QFontDatabase.applicationFontFamilies(id)[0]
+            font = qt.QFont(family, 10, qt.QFont.Normal, False)
+            font.setStyleStrategy(qt.QFont.PreferAntialias)
+            self._defaultFont = font
+        return self._defaultFont
+
     def addMarker(
         self,
         x,
@@ -1170,7 +1185,9 @@ def addMarker(
         font,
         bgcolor: RGBAColorType | None,
     ):
-        font = qt.QApplication.instance().font() if font is None else font
+        if font is None:
+            font = self.getDefaultFont()
+
         dashoffset, dashpattern = self._lineStyleToDashOffsetPattern(linestyle)
         return _MarkerItem(
             x,

src/silx/gui/plot/backends/glutils/GLPlotFrame.py

@@ -494,7 +494,7 @@ class GLPlotFrame(object):
     # Margins used when plot frame is not displayed
     _NoDisplayMargins = _Margins(0, 0, 0, 0)
 
-    def __init__(self, marginRatios, foregroundColor, gridColor):
+    def __init__(self, marginRatios, foregroundColor, gridColor, font: qt.QFont):
         """
         :param List[float] marginRatios:
             The ratios of margins around plot area for axis and labels.
@@ -503,6 +503,7 @@ def __init__(self, marginRatios, foregroundColor, gridColor):
         :type foregroundColor: tuple with RGBA values ranging from 0.0 to 1.0
         :param gridColor: color used for grid lines.
         :type gridColor: tuple RGBA with RGBA values ranging from 0.0 to 1.0
+        :param font: Font used by the axes label
         """
         self._renderResources = None
 
@@ -517,6 +518,7 @@ def __init__(self, marginRatios, foregroundColor, gridColor):
         self._grid = False
         self._size = 0.0, 0.0
         self._title = ""
+        self._font: qt.QFont = font
 
         self._devicePixelRatio = 1.0
         self._dpi = 92
@@ -730,7 +732,7 @@ def _buildVerticesAndLabels(self):
         labels.append(
             Text2D(
                 text=self.title,
-                font=qt.QApplication.instance().font(),
+                font=self._font,
                 color=self._foregroundColor,
                 x=xTitle,
                 y=yTitle,
@@ -816,7 +818,7 @@ def renderGrid(self):
 
 
 class GLPlotFrame2D(GLPlotFrame):
-    def __init__(self, marginRatios, foregroundColor, gridColor):
+    def __init__(self, marginRatios, foregroundColor, gridColor, font: qt.QFont):
         """
         :param List[float] marginRatios:
             The ratios of margins around plot area for axis and labels.
@@ -825,9 +827,9 @@ def __init__(self, marginRatios, foregroundColor, gridColor):
         :type foregroundColor: tuple with RGBA values ranging from 0.0 to 1.0
         :param gridColor: color used for grid lines.
         :type gridColor: tuple RGBA with RGBA values ranging from 0.0 to 1.0
-
+        :param font: Font used by the axes label
         """
-        super(GLPlotFrame2D, self).__init__(marginRatios, foregroundColor, gridColor)
+        super(GLPlotFrame2D, self).__init__(marginRatios, foregroundColor, gridColor, font)
         self.axes.append(
             PlotAxis(
                 self,

src/silx/gui/utils/matplotlib.py

@@ -93,6 +93,9 @@ def qFontToFontProperties(font: qt.QFont):
         families = [f for f in families if f in availableNames]
         families.append(font_manager.fontManager.defaultFamily["ttf"])
 
+    if "Sans" in font.family():
+        families.insert(0, "sans-serif")
+
     return FontProperties(
         family=families,
         style=_FONT_STYLES[font.style()],