Maps: "snap" and disable linear filtering near whole zoom numbers

Near whole zoom numbers, this patch enables "snapping" behaviour,
so that zoom = 0.97 and zoom = 1.01 will display the same result on
screen. When this snapping is active, textures are now displayed with
linear filtering disabled, giving a much sharper appearance.

Depends on http://codereview.qt-project.org/21497 in Qt3d for support
for disabling bilinear filtering on already-uploaded textures.

Task-number: QTBUG-24940
Change-Id: I791e6469781ef73f53394a8d62ff61c725a5ff2a
Reviewed-by: Ian Chen <ian.1.chen@nokia.com>
Reviewed-by: Cristian Adam <cristian.adam@nokia.com>
Reviewed-by: Aaron McCarthy <aaron.mccarthy@nokia.com>

2 files changed, 50 insertions, 2 deletions

diff --git a/src/location/maps/qgeomapgeometry.cpp b/src/location/maps/qgeomapgeometry.cpp
index 215de3ff..3a10ca03 100644
--- a/src/location/maps/qgeomapgeometry.cpp
+++ b/src/location/maps/qgeomapgeometry.cpp
@@ -105,6 +105,7 @@ public:
 
     bool useVerticalLock_;
     bool verticalLock_;
+    bool linearScaling_;
 
     void addTile(const QGeoTileSpec &spec, QSharedPointer<QGeoTileTexture> texture);
 
@@ -117,6 +118,7 @@ public:
     QGLSceneNode *buildGeometry(const QGeoTileSpec &spec);
     void setTileBounds(const QSet<QGeoTileSpec> &tiles);
     void setupCamera();
+    void setScalingOnTextures();
 
     void paintGL(QGLPainter *painter);
 
@@ -157,6 +159,14 @@ void QGeoMapGeometry::setCameraData(const QGeoCameraData &cameraData)
     Q_D(QGeoMapGeometry);
     d->cameraData_ = cameraData;
     d->intZoomLevel_ = static_cast<int>(floor(d->cameraData_.zoomLevel()));
+    float delta = cameraData.zoomLevel() - d->intZoomLevel_;
+    if (qAbs(delta) < 0.05) {
+        d->linearScaling_ = false;
+        d->setScalingOnTextures();
+    } else {
+        d->linearScaling_ = true;
+        d->setScalingOnTextures();
+    }
     d->sideLength_ = 1 << d->intZoomLevel_;
 }
 
@@ -231,6 +241,7 @@ QGeoMapGeometryPrivate::QGeoMapGeometryPrivate(QGeoMapGeometry *geometry)
       screenHeight_(0.0),
       useVerticalLock_(false),
       verticalLock_(false),
+      linearScaling_(true),
       q_ptr(geometry) {}
 
 QGeoMapGeometryPrivate::~QGeoMapGeometryPrivate()
@@ -345,8 +356,31 @@ QGLSceneNode *QGeoMapGeometryPrivate::buildGeometry(const QGeoTileSpec &spec)
     return builder.finalizedSceneNode();
 }
 
+void QGeoMapGeometryPrivate::setScalingOnTextures()
+{
+    if (!linearScaling_) {
+        foreach (const QSharedPointer<QGeoTileTexture> &tex, textures_.values()) {
+            tex->texture->setBindOptions(tex->texture->bindOptions() &
+                                         (~QGLTexture2D::LinearFilteringBindOption));
+        }
+    } else {
+        foreach (const QSharedPointer<QGeoTileTexture> &tex, textures_.values()) {
+            tex->texture->setBindOptions(tex->texture->bindOptions() |
+                                         (QGLTexture2D::LinearFilteringBindOption));
+        }
+    }
+}
+
 void QGeoMapGeometryPrivate::addTile(const QGeoTileSpec &spec, QSharedPointer<QGeoTileTexture> texture)
 {
+    if (linearScaling_) {
+        texture->texture->setBindOptions(texture->texture->bindOptions() |
+                                         (QGLTexture2D::LinearFilteringBindOption));
+    } else {
+        texture->texture->setBindOptions(texture->texture->bindOptions() &
+                                         (~QGLTexture2D::LinearFilteringBindOption));
+    }
+
     QGLSceneNode *node = nodes_.value(spec, 0);
     if (!node) {
         node = buildGeometry(spec);
diff --git a/src/location/maps/qgeotiledmapdata.cpp b/src/location/maps/qgeotiledmapdata.cpp
index bf8df5f9..1ecc26e8 100644
--- a/src/location/maps/qgeotiledmapdata.cpp
+++ b/src/location/maps/qgeotiledmapdata.cpp
@@ -266,10 +266,24 @@ void QGeoTiledMapDataPrivate::changeCameraData(const QGeoCameraData &oldCameraDa
         map_->cameraData().setCenter(coord);
     }
 
-    cameraTiles_->setCamera(map_->cameraData());
+    // For zoomlevel, "snap" 0.05 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 = map_->cameraData();
+    int izl = static_cast<int>(floor(cam.zoomLevel()));
+    float delta = cam.zoomLevel() - izl;
+    if (delta > 0.5) {
+        izl++;
+        delta -= 1.0;
+    }
+    if (qAbs(delta) < 0.05) {
+        cam.setZoomLevel(izl);
+    }
+
+    cameraTiles_->setCamera(cam);
     visibleTiles_ = cameraTiles_->tiles();
 
-    mapGeometry_->setCameraData(map_->cameraData());
+    mapGeometry_->setCameraData(cam);
     mapGeometry_->setVisibleTiles(visibleTiles_);
 
     if (mapImages_) {