Make zoomLevel refer to a default 256^2 tile size

Currently the zoomLevel is the power of 2 reflecting how many tiles
are in a map edge.

This means that two plugins with two different tileSize will show a
map of different size at the same zoomLevel.

With this patch the zoomLevel is "normalized" upon a tileSize of 256,
regardless of the tile size in use.
In this way, the new 256 based zoom level can be a consistent parameter
also for plugins that are not tile based.

CameraCapabilities therefore now offers two new methods,
m[in,ax]imumZoomLevelAt256, that return the respective value for
the normalized 256^2 tilesize.

It also gets a setTileSize, which is currently not used as all our
plugins use a tile size of 256 (which is the camera capabilities
default tilesize value).

Change-Id: Ib12092fd14faf7fc85f8be5fb799dbd5496b760b
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

3 files changed, 74 insertions, 6 deletions

diff --git a/src/location/maps/qgeocameracapabilities.cpp b/src/location/maps/qgeocameracapabilities.cpp
index 7b4a014a..97ff5790 100644
--- a/src/location/maps/qgeocameracapabilities.cpp
+++ b/src/location/maps/qgeocameracapabilities.cpp
@@ -37,6 +37,14 @@
 #include "qgeocameracapabilities_p.h"
 
 #include <QSharedData>
+#include <cmath>
+
+static const double invLog2 = 1.0 / std::log(2.0);
+
+static double zoomLevelTo256(double zoomLevelForTileSize, double tileSize)
+{
+    return std::log( std::pow(2.0, zoomLevelForTileSize) * tileSize / 256.0 ) * invLog2;
+}
 
 QT_BEGIN_NAMESPACE
 
@@ -60,6 +68,7 @@ public:
     double maxZoom_;
     double minTilt_;
     double maxTilt_;
+    int tileSize_;
 };
 
 QGeoCameraCapabilitiesPrivate::QGeoCameraCapabilitiesPrivate()
@@ -70,7 +79,8 @@ QGeoCameraCapabilitiesPrivate::QGeoCameraCapabilitiesPrivate()
       minZoom_(0.0),
       maxZoom_(0.0),
       minTilt_(0.0),
-      maxTilt_(0.0) {}
+      maxTilt_(0.0),
+      tileSize_(256) {}
 
 
 QGeoCameraCapabilitiesPrivate::QGeoCameraCapabilitiesPrivate(const QGeoCameraCapabilitiesPrivate &other)
@@ -82,7 +92,8 @@ QGeoCameraCapabilitiesPrivate::QGeoCameraCapabilitiesPrivate(const QGeoCameraCap
       minZoom_(other.minZoom_),
       maxZoom_(other.maxZoom_),
       minTilt_(other.minTilt_),
-      maxTilt_(other.maxTilt_) {}
+      maxTilt_(other.maxTilt_),
+      tileSize_(other.tileSize_) {}
 
 QGeoCameraCapabilitiesPrivate::~QGeoCameraCapabilitiesPrivate() {}
 
@@ -99,6 +110,7 @@ QGeoCameraCapabilitiesPrivate &QGeoCameraCapabilitiesPrivate::operator = (const
     maxZoom_ = other.maxZoom_;
     minTilt_ = other.minTilt_;
     maxTilt_ = other.maxTilt_;
+    tileSize_ = other.tileSize_;
 
     return *this;
 }
@@ -149,6 +161,18 @@ QGeoCameraCapabilities &QGeoCameraCapabilities::operator = (const QGeoCameraCapa
     return *this;
 }
 
+void QGeoCameraCapabilities::setTileSize(int tileSize)
+{
+    if (tileSize < 1)
+        return;
+    d->tileSize_ = tileSize;
+}
+
+int QGeoCameraCapabilities::tileSize() const
+{
+    return d->tileSize_;
+}
+
 /*!
     Returns whether this instance of the class is considered "valid". To be
     valid, the instance must have had at least one capability set (to either
@@ -183,6 +207,13 @@ double QGeoCameraCapabilities::minimumZoomLevel() const
     return d->minZoom_;
 }
 
+double QGeoCameraCapabilities::minimumZoomLevelAt256() const
+{
+    if (d->tileSize_ == 256)
+        return d->minZoom_;
+    return zoomLevelTo256(d->minZoom_, d->tileSize_);
+}
+
 /*!
     Sets the maximum zoom level supported by the associated plugin to \a maximumZoomLevel.
 
@@ -206,6 +237,13 @@ double QGeoCameraCapabilities::maximumZoomLevel() const
     return d->maxZoom_;
 }
 
+double QGeoCameraCapabilities::maximumZoomLevelAt256() const
+{
+    if (d->tileSize_ == 256)
+        return d->maxZoom_;
+    return zoomLevelTo256(d->maxZoom_, d->tileSize_);
+}
+
 /*!
     Sets whether the associated plugin can render a map when the camera
     has an arbitrary bearing to \a supportsBearing.
diff --git a/src/location/maps/qgeocameracapabilities_p.h b/src/location/maps/qgeocameracapabilities_p.h
index 4e498b1d..7de6ece0 100644
--- a/src/location/maps/qgeocameracapabilities_p.h
+++ b/src/location/maps/qgeocameracapabilities_p.h
@@ -65,11 +65,16 @@ public:
 
     QGeoCameraCapabilities &operator = (const QGeoCameraCapabilities &other);
 
+    void setTileSize(int tileSize);
+    int tileSize() const;
+
     void setMinimumZoomLevel(double minimumZoomLevel);
     double minimumZoomLevel() const;
+    double minimumZoomLevelAt256() const;
 
     void setMaximumZoomLevel(double maximumZoomLevel);
     double maximumZoomLevel() const;
+    double maximumZoomLevelAt256() const;
 
     void setSupportsBearing(bool supportsBearing);
     bool supportsBearing() const;
diff --git a/src/location/maps/qgeotiledmap.cpp b/src/location/maps/qgeotiledmap.cpp
index f2c1d4d3..0916c7b7 100644
--- a/src/location/maps/qgeotiledmap.cpp
+++ b/src/location/maps/qgeotiledmap.cpp
@@ -49,6 +49,18 @@
 QT_BEGIN_NAMESPACE
 #define PREFETCH_FRUSTUM_SCALE 2.0
 
+static const double invLog2 = 1.0 / std::log(2.0);
+
+static double zoomLevelFrom256(double zoomLevelFor256, double tileSize)
+{
+    return std::log( std::pow(2.0, zoomLevelFor256) * 256.0 / tileSize ) * invLog2;
+}
+
+static double zoomLevelTo256(double zoomLevelForTileSize, double tileSize)
+{
+    return std::log( std::pow(2.0, zoomLevelForTileSize) * tileSize / 256.0 ) * invLog2;
+}
+
 QGeoTiledMap::QGeoTiledMap(QGeoTiledMappingManagerEngine *engine, QObject *parent)
     : QGeoMap(*new QGeoTiledMapPrivate(engine), parent)
 {
@@ -150,13 +162,16 @@ void QGeoTiledMap::evaluateCopyrights(const QSet<QGeoTileSpec> &visibleTiles)
 }
 
 // This method returns the minimum zoom level that this specific qgeomap type allows
-// at a given canvas size (width,height) and for a given tile size (usually 256).
+// at a given canvas size (width,height) and for the default tile size of 256^2
 double QGeoTiledMap::minimumZoomAtViewportSize(int width, int height) const
 {
     Q_D(const QGeoTiledMap);
+    double tileSize = d->m_visibleTiles->tileSize();
     double maxSize = qMax(width,height);
-    double numTiles = maxSize / d->m_visibleTiles->tileSize();
-    return std::log(numTiles) / std::log(2.0);
+    double numTiles = maxSize / tileSize;
+    if (tileSize == 256.0)
+        return std::log(numTiles) * invLog2;
+    return zoomLevelTo256(std::log(numTiles) * invLog2, tileSize);
 }
 
 // This method recalculates the "no-trespassing" limits for the map center.
@@ -275,10 +290,18 @@ void QGeoTiledMapPrivate::changeCameraData(const QGeoCameraData &cameraData)
 {
     Q_Q(QGeoTiledMap);
 
+    QGeoCameraData cam = cameraData;
+
+    // The incoming zoom level is intended for a tileSize of 256.
+    // Adapt it to the current tileSize
+    double zoomLevel = cameraData.zoomLevel();
+    if (m_visibleTiles->tileSize() != 256)
+        zoomLevel = zoomLevelFrom256(zoomLevel, m_visibleTiles->tileSize());
+    cam.setZoomLevel(zoomLevel);
+
     // For zoomlevel, "snap" 0.01 either side of a whole number.
     // This is so that when we turn off bilinear scaling, we're
     // snapped to the exact pixel size of the tiles
-    QGeoCameraData cam = cameraData;
     int izl = static_cast<int>(std::floor(cam.zoomLevel()));
     float delta = cam.zoomLevel() - izl;
 
@@ -286,6 +309,8 @@ void QGeoTiledMapPrivate::changeCameraData(const QGeoCameraData &cameraData)
         izl++;
         delta -= 1.0;
     }
+
+    // TODO: Don't do this if there's tilt or bearing.
     if (qAbs(delta) < 0.01) {
         cam.setZoomLevel(izl);
     }