Zoom/center the page map so that all locations are in view

src/CMakeLists.txt

@@ -58,6 +58,7 @@ add_library(neochat STATIC
     delegatesizehelper.cpp
     models/livelocationsmodel.cpp
     models/locationsmodel.cpp
+    locationhelper.cpp
 )
 
 ecm_qt_declare_logging_category(neochat

src/locationhelper.cpp

@@ -0,0 +1,44 @@
+// SPDX-FileCopyrightText: 2023 Volker Krause <vkrause@kde.org>
+// SPDX-License-Identifier: LGPL-2.0-or-later
+
+#include "locationhelper.h"
+
+#include <cmath>
+
+QRectF LocationHelper::unite(const QRectF &r1, const QRectF &r2)
+{
+    // this looks weird but is actually intentional as we need to handle point-like "rects" as well
+    if ((!r1.isEmpty() || r1.isNull()) && (!r2.isEmpty() || r2.isNull())) {
+        return r1 | r2;
+    }
+    return (!r1.isEmpty() || r1.isNull()) ? r1 : r2;
+}
+
+QPointF LocationHelper::center(const QRectF &r)
+{
+    return r.center();
+}
+
+constexpr inline double degToRad(double deg)
+{
+    return deg / 180.0 * M_PI;
+}
+
+static QPointF mercatorProject(double lat, double lon, double zoom)
+{
+    const auto x = (256.0 / (2.0 * M_PI)) * std::pow(2.0, zoom) * (degToRad(lon) + M_PI);
+    const auto y = (256.0 / (2.0 * M_PI)) * std::pow(2.0, zoom) * (M_PI - std::log(std::tan(M_PI / 4.0 + degToRad(lat) / 2.0)));
+    return QPointF(x, y);
+}
+
+float LocationHelper::zoomToFit(const QRectF &r, float mapWidth, float mapHeight)
+{
+    const auto p1 = mercatorProject(r.bottomLeft().y(), r.bottomLeft().x(), 1.0);
+    const auto p2 = mercatorProject(r.topRight().y(), r.topRight().x(), 1.0);
+
+    const auto zx = std::log2((mapWidth / (p2.x() - p1.x())));
+    const auto zy = std::log2((mapHeight / (p2.y() - p1.y())));
+    const auto z = std::min(zx, zy);
+
+    return std::clamp(z, 5.0, 18.0);
+}

src/locationhelper.h

@@ -0,0 +1,22 @@
+// SPDX-FileCopyrightText: 2023 Volker Krause <vkrause@kde.org>
+// SPDX-License-Identifier: LGPL-2.0-or-later
+
+#include "linkpreviewer.h"
+#include <QMetaType>
+#include <QRectF>
+
+/** Location related helper functions for QML. */
+class LocationHelper
+{
+    Q_GADGET
+public:
+    /** Unite two rectanlges. */
+    Q_INVOKABLE static QRectF unite(const QRectF &r1, const QRectF &r2);
+    /** Returns the center of @p r. */
+    Q_INVOKABLE static QPointF center(const QRectF &r);
+
+    /** Returns the highest zoom level to fit @r into a map of size @p mapWidth x @p mapHeight. */
+    Q_INVOKABLE static float zoomToFit(const QRectF &r, float mapWidth, float mapHeight);
+};
+
+Q_DECLARE_METATYPE(LocationHelper)

src/main.cpp

@@ -46,6 +46,7 @@
 #include "delegatesizehelper.h"
 #include "filetypesingleton.h"
 #include "linkpreviewer.h"
+#include "locationhelper.h"
 #include "logger.h"
 #include "login.h"
 #include "matriximageprovider.h"
@@ -288,6 +289,9 @@ int main(int argc, char *argv[])
         return engine->toScriptValue(KAboutData::applicationData());
     });
     qmlRegisterSingletonType(QUrl("qrc:/OsmLocationPlugin.qml"), "org.kde.neochat", 1, 0, "OsmLocationPlugin");
+    qmlRegisterSingletonType("org.kde.neochat", 1, 0, "LocationHelper", [](QQmlEngine *engine, QJSEngine *) -> QJSValue {
+        return engine->toScriptValue(LocationHelper());
+    });
 
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     qRegisterMetaTypeStreamOperators<Emoji>();

src/qml/Component/LocationPage.qml

@@ -23,8 +23,15 @@ Kirigami.Page {
         anchors.fill: parent
         plugin: OsmLocationPlugin.plugin
 
+        center: {
+            let c = LocationHelper.center(LocationHelper.unite(locationsModel.boundingBox, liveLocationsModel.boundingBox));
+            return QtPositioning.coordinate(c.y, c.x);
+        }
+        zoomLevel: LocationHelper.zoomToFit(LocationHelper.unite(locationsModel.boundingBox, liveLocationsModel.boundingBox), map.width, map.height)
+
         MapItemView {
             model: LocationsModel {
+                id: locationsModel
                 room: locationsPage.room
             }
             delegate: LocationMapItem {
@@ -34,6 +41,7 @@ Kirigami.Page {
 
         MapItemView {
             model: LiveLocationsModel {
+                id: liveLocationsModel
                 room: locationsPage.room
             }
             delegate: LocationMapItem {}