make log-spacing explicit option for custom fit x values (#227)

closes #225

src/gui_qt/fit/result.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from math import isnan
 
 from pyqtgraph import mkBrush, mkPen
@@ -28,6 +30,7 @@ class QFitResult(QtWidgets.QDialog, Ui_Dialog):
         self.extrapolate_box.stateChanged.connect(lambda x: self.maxx_line.setEnabled(x))
         self.extrapolate_box.stateChanged.connect(lambda x: self.minx_line.setEnabled(x))
         self.extrapolate_box.stateChanged.connect(lambda x: self.numx_line.setEnabled(x))
+        self.extrapolate_box.stateChanged.connect(lambda x: self.newx_log_checkbox.setEnabled(x))
 
         self._previous_fits = {}
         self._opts = []
@@ -352,7 +355,7 @@ class QFitResult(QtWidgets.QDialog, Ui_Dialog):
 
             parts = self.partial_checkBox.checkState() == QtCore.Qt.CheckState.Checked
 
-            extrapolate = [None, None, None]
+            extrapolate = [None, None, None, None]
             error = []
             if self.extrapolate_box.isChecked():
                 try:
@@ -368,6 +371,8 @@ class QFitResult(QtWidgets.QDialog, Ui_Dialog):
                 except (TypeError, ValueError):
                     error.append('Number of points is missing')
 
+                extrapolate[3] = self.newx_log_checkbox.isChecked()
+
             if error:
                 msg = QtWidgets.QMessageBox.warning(self, 'Error', 'Extrapolation failed because:\n' + '\n'.join(error))
                 return
@@ -405,10 +410,13 @@ class FitExtension(QtWidgets.QDialog):
         self.num_pts.setValidator(QtGui.QIntValidator())
         gridLayout.addWidget(self.num_pts, 2, 1, 1, 1)
 
+        self.logx_checkbox = QtWidgets.QCheckBox('Log-spaced?')
+        gridLayout.addWidget(self.logx_checkbox, 3, 0, 1, 2)
+
         self.buttonBox = QtWidgets.QDialogButtonBox()
         self.buttonBox.setOrientation(QtCore.Qt.Orientation.Horizontal)
         self.buttonBox.setStandardButtons(QtWidgets.QDialogButtonBox.Cancel | QtWidgets.QDialogButtonBox.Ok)
-        gridLayout.addWidget(self.buttonBox, 3, 0, 1, 2)
+        gridLayout.addWidget(self.buttonBox, 4, 0, 1, 2)
 
         self.setLayout(gridLayout)
 
@@ -416,12 +424,13 @@ class FitExtension(QtWidgets.QDialog):
         self.buttonBox.rejected.connect(self.reject)
 
     @property
-    def values(self):
+    def values(self) -> tuple[float, float, int, bool] | None:
         try:
             xmin = float(self.min_line.text())
             xmax = float(self.max_line.text())
             nums = int(self.num_pts.text())
+            logx = self.logx_checkbox.isChecked()
         except TypeError:
             return None
 
-        return xmin, xmax, nums
+        return xmin, xmax, nums, logx