Allow reseting ratio manually for linked ratio lock buttons

python/gui/qgsratiolockbutton.sip

@@ -67,6 +67,12 @@ class QgsRatioLockButton : QToolButton
 .. seealso:: setWidthSpinBox()
 %End
 
+    void resetRatio();
+%Docstring
+ Resets the current width/height ratio, taking the width and height
+ from the current values of the width and height spin boxes.
+%End
+
   signals:
 
     void lockChanged( const bool locked );

src/gui/qgsratiolockbutton.cpp

@@ -156,3 +156,9 @@ void QgsRatioLockButton::setHeightSpinBox( QDoubleSpinBox *widget )
   mPrevHeight = widget->value();
   connect( mHeightSpinBox, static_cast<void ( QDoubleSpinBox::* )( double )>( &QDoubleSpinBox::valueChanged ), this, &QgsRatioLockButton::heightSpinBoxChanged );
 }
+
+void QgsRatioLockButton::resetRatio()
+{
+  mPrevWidth = mWidthSpinBox ? mWidthSpinBox->value() : 0.0;
+  mPrevHeight = mHeightSpinBox ? mHeightSpinBox->value() : 0.0;
+}

src/gui/qgsratiolockbutton.h

@@ -82,6 +82,12 @@ class GUI_EXPORT QgsRatioLockButton : public QToolButton
      */
     void setHeightSpinBox( QDoubleSpinBox *widget );
 
+    /**
+     * Resets the current width/height ratio, taking the width and height
+     * from the current values of the width and height spin boxes.
+     */
+    void resetRatio();
+
   signals:
 
     /**

tests/src/python/test_qgsratiolockbutton.py

@@ -99,6 +99,37 @@ class TestQgsRatioLockButton(unittest.TestCase):
         self.assertEqual(spin_width.value(), 200)
         self.assertEqual(spin_height.value(), 1000)
 
+    def testResetRatio(self):
+        w = qgis.gui.QgsRatioLockButton()
+
+        spin_width = QDoubleSpinBox()
+        spin_width.setMaximum(100000)
+        spin_height = QDoubleSpinBox()
+        spin_height.setMaximum(100000)
+
+        spin_width.setValue(1000)
+        w.setWidthSpinBox(spin_width)
+        spin_height.setValue(500)
+        w.setHeightSpinBox(spin_height)
+
+        w.setLocked(True)
+        spin_width.setValue(2000)
+        self.assertEqual(spin_height.value(), 1000)
+
+        spin_width.blockSignals(True)
+        spin_width.setValue(1000)
+        spin_width.blockSignals(False)
+
+        spin_height.setValue(2000)
+        self.assertEqual(spin_width.value(), 4000)  # signals were blocked, so ratio wasn't updated
+
+        spin_width.blockSignals(True)
+        spin_width.setValue(2000)
+        spin_width.blockSignals(False)
+        w.resetRatio() # since signals were blocked, we need to manually reset ratio
+        spin_height.setValue(1000)
+        self.assertEqual(spin_width.value(), 1000)
+
 
 if __name__ == '__main__':
     unittest.main()