QwtPlot: added support for margins

Fix #82

Author: PierreRaybaut

.vscode/settings.json

@@ -24,7 +24,7 @@
     ],
     "[python]": {
         "editor.codeActionsOnSave": {
-            "source.organizeImports": true
+            "source.organizeImports": "explicit"
         },
         "editor.defaultFormatter": "ms-python.black-formatter"
     },

CHANGELOG.md

@@ -1,5 +1,12 @@
 # PythonQwt Releases
 
+## Version 0.12.0
+
+- Added support for margins in `QwtPlot` (see Issue #82):
+  - Default margins are set to 0.05 (5% of the plot area) at each side of the plot
+  - Margins are adjustable for each plot axis using `QwtPlot.setAxisMargin` (and
+    `QwtPlot.axisMargin` to get the current value)
+
 ## Version 0.11.2
 
 - Fixed `TypeError` on `QwtPlotLayout.minimumSizeHint`

qwt/__init__.py

@@ -27,7 +27,7 @@
 .. _GitHub: https://github.com/PlotPyStack/PythonQwt
 """
 
-__version__ = "0.11.2"
+__version__ = "0.12.0"
 QWT_VERSION_STR = "6.1.5"
 
 import warnings

qwt/interval.py

@@ -396,3 +396,18 @@ def extend(self, value):
         if not self.isValid():
             return self
         return QwtInterval(min([value, self.__minValue]), max([value, self.__maxValue]))
+
+    def extend_fraction(self, value):
+        """
+        Extend the interval by a fraction of its width
+
+        :param float value: Fraction
+        :return: extended interval
+        """
+        if not self.isValid():
+            return self
+        return QwtInterval(
+            self.__minValue - value * self.width(),
+            self.__maxValue + value * self.width(),
+            self.__borderFlags,
+        )

qwt/plot.py

@@ -101,6 +101,7 @@ def __init__(self):
         self.scaleDiv = None  # QwtScaleDiv
         self.scaleEngine = None  # QwtScaleEngine
         self.scaleWidget = None  # QwtScaleWidget
+        self.margin = None  # Margin (float) in %
 
 
 class QwtPlot(QFrame):
@@ -431,6 +432,7 @@ def initAxesData(self):
             d.scaleWidget.setTitle(text)
 
             d.doAutoScale = True
+            d.margin = 0.05
             d.minValue = 0.0
             d.maxValue = 1000.0
             d.stepSize = 0.0
@@ -586,6 +588,19 @@ def axisStepSize(self, axisId):
         else:
             return 0
 
+    def axisMargin(self, axisId):
+        """
+        :param int axisId: Axis index
+        :return: Margin in % of the canvas size
+
+        .. seealso::
+
+            :py:meth:`setAxisMargin()`
+        """
+        if self.axisValid(axisId):
+            return self.__axisData[axisId].margin
+        return 0.0
+
     def axisInterval(self, axisId):
         """
         :param int axisId: Axis index
@@ -857,6 +872,24 @@ def setAxisMaxMajor(self, axisId, maxMajor):
                 d.isValid = False
                 self.autoRefresh()
 
+    def setAxisMargin(self, axisId, margin):
+        """
+        Set the margin of the scale widget
+
+        :param int axisId: Axis index
+        :param float margin: Margin in % of the canvas size
+
+        .. seealso::
+
+            :py:meth:`axisMargin()`
+        """
+        if self.axisValid(axisId):
+            d = self.__axisData[axisId]
+            if margin != d.margin:
+                d.margin = margin
+                d.isValid = False
+                self.autoRefresh()
+
     def setAxisTitle(self, axisId, title):
         """
         Change the title of a specified axis
@@ -910,15 +943,20 @@ def updateAxes(self):
                     intv[item.xAxis()] |= QwtInterval(rect.left(), rect.right())
                 if rect.height() >= 0.0:
                     intv[item.yAxis()] |= QwtInterval(rect.top(), rect.bottom())
+
         for axisId in self.AXES:
             d = self.__axisData[axisId]
             minValue = d.minValue
             maxValue = d.maxValue
             stepSize = d.stepSize
-            if d.doAutoScale and intv[axisId].isValid():
+            if d.margin is not None:
+                intv_i = intv[axisId].extend_fraction(d.margin)
+            else:
+                intv_i = intv[axisId]
+            if d.doAutoScale and intv_i.isValid():
                 d.isValid = False
-                minValue = intv[axisId].minValue()
-                maxValue = intv[axisId].maxValue()
+                minValue = intv_i.minValue()
+                maxValue = intv_i.maxValue()
                 d.scaleEngine.autoScale(d.maxMajor, minValue, maxValue, stepSize)
             if not d.isValid:
                 d.scaleDiv = d.scaleEngine.divideScale(