Detector2D now parameterized through width and center in phi,alpha (#854)

Some code duplication in the GUI (Axis -> Span property and form), to be revised later.

Resolves #854 (closed).

GUI/Model/Descriptor/SpanProperty.cpp

+//  ************************************************************************************************
+//
+//  BornAgain: simulate and fit reflection and scattering
+//
+//! @file      GUI/Model/Descriptor/SpanProperty.cpp
+//! @brief     Implements class SpanProperty.
+//!
+//! @homepage  http://www.bornagainproject.org
+//! @license   GNU General Public License v3 or higher (see COPYING)
+//! @copyright Forschungszentrum Jülich GmbH 2022
+//! @authors   Scientific Computing Group at MLZ (see CITATION, AUTHORS)
+//
+//  ************************************************************************************************
+
+#include "GUI/Model/Descriptor/SpanProperty.h"
+#include "Base/Axis/Scale.h"
+#include "GUI/Support/XML/UtilXML.h"
+
+namespace {
+namespace Tag {
+
+const QString Nbins("Nbins");
+const QString Width("Width");
+const QString Center("Center");
+const QString Min("Min");                       // from AxisProperty pre v22
+const QString Max("Max");                       // from AxisProperty pre v22
+const QString ExpandGroupbox("ExpandGroupbox"); // from AxisProperty pre v22
+
+} // namespace Tag
+} // namespace
+
+SpanProperty::SpanProperty() = default;
+
+void SpanProperty::initWidth(const QString& label, const QString& tooltip, double value,
+                             const RealLimits& limits, uint decimals)
+{
+    m_width.init(label, tooltip, value, decimals, limits, "width");
+}
+
+void SpanProperty::initCenter(const QString& label, const QString& tooltip, double value,
+                              const RealLimits& limits, uint decimals)
+{
+    m_center.init(label, tooltip, value, decimals, limits, "center");
+}
+
+Scale SpanProperty::createAxis(const std::string& name) const
+{
+    return EquiDivision(name, m_nbins, m_center - m_width / 2, m_center + m_width / 2);
+}
+
+void SpanProperty::writeTo(QXmlStreamWriter* w) const
+{
+    XML::writeAttribute(w, XML::Attrib::version, uint(3)); // forked from AxesProperty v3
+
+    // nbins
+    w->writeStartElement(Tag::Nbins);
+    XML::writeAttribute(w, XML::Attrib::value, m_nbins);
+    w->writeEndElement();
+
+    // width
+    w->writeStartElement(Tag::Width);
+    m_width.writeTo(w);
+    w->writeEndElement();
+
+    // center
+    w->writeStartElement(Tag::Center);
+    m_center.writeTo(w);
+    w->writeEndElement();
+}
+
+void SpanProperty::readFrom(QXmlStreamReader* r)
+{
+    const uint version = XML::readUIntAttribute(r, XML::Attrib::version);
+    Q_UNUSED(version)
+
+    while (r->readNextStartElement()) {
+        QString tag = r->name().toString();
+
+        // nbins
+        if (tag == Tag::Nbins) {
+            XML::readAttribute(r, XML::Attrib::value, &m_nbins);
+            XML::gotoEndElementOfTag(r, tag);
+
+            // width
+        } else if (tag == Tag::Width) {
+            m_width.readFrom(r);
+            XML::gotoEndElementOfTag(r, tag);
+
+            // center
+        } else if (tag == Tag::Center) {
+            m_center.readFrom(r);
+            XML::gotoEndElementOfTag(r, tag);
+
+        } else
+            r->skipCurrentElement();
+    }
+}