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mapwidget.qml: more improvements for the dynamic zoom-in/out

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The QML Map has a couple of methods - toCoordinate(someQPointF) and
fromCoordinate(someQGeoCoordinate). Ideally, if one passes a point to
toCoordinate() and then attempts to convert the resulted coordinates
back to the point, the same point in the Map view port with minimal error
should be retrieved. That's not always the case - e.g. near
47.400200 -123.142066, which means that the methods are not exactly
*reliable* and there might be Map class bugs at hand.

The new zoom-in and zoom-out improvements try to work around the above:
- for both centerOnRectangle() and centerOnCoordinate(), if no good
zoom-out level is found (newZoomOut), the zoom-out is set to the default
value of defaultZoomOut. In practice, this prevents the case where the map
does not zoom-out at all when going from one place to another
- centerOnRectangle() now uses rectangle diagonals to estimate a fit,
instead of checking if 2 points (top-left and bottom-right) are visible
in the viewport. The usage of fromCoordinate() was giving bad results
in this case and comparing distances (diagonals) is more reliable
but more expensive on the CPU.

Due to the inconsistencies of toCoordinate() and fromCoordinate()
the dynamic zoom-in and zoom-out are still not ideal, but the current
implementation is somewhat usable with decent accuracy.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
This commit is contained in:
Lubomir I. Ivanov 2017-08-08 02:10:23 +03:00 committed by Dirk Hohndel
parent 514c298600
commit f21ae69f7b
1 changed files with 16 additions and 11 deletions
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27
mobile-widgets/qml/MapWidget.qml
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@ -164,16 +164,20 @@ Item {
newZoom = 2.6
newZoomOut = newZoom
} else {
var newZoomOutFound = false
var zoomStored = zoomLevel
newZoomOut = zoomLevel
while (zoomLevel > minimumZoomLevel) {
var pt = fromCoordinate(coord)
if (pointIsVisible(pt)) {
newZoomOut = zoomLevel
newZoomOutFound = true
break
}
zoomLevel--
}
if (!newZoomOutFound)
newZoomOut = defaultZoomOut
zoomLevel = zoomStored
newZoom = defaultZoomIn
}
@ -190,29 +194,30 @@ Item {
} else {
var centerStored = QtPositioning.coordinate(center.latitude, center.longitude)
var zoomStored = zoomLevel
var ptCenter
var ptTopLeft
var ptBottomRight
var newZoomOutFound = false
// calculate zoom out
newZoomOut = zoomLevel
while (zoomLevel > minimumZoomLevel) {
ptCenter = fromCoordinate(centerStored)
ptTopLeft = fromCoordinate(topLeft)
ptBottomRight = fromCoordinate(bottomRight)
if (pointIsVisible(ptCenter) && pointIsVisible(ptTopLeft) && pointIsVisible(ptBottomRight)) {
var ptCenter = fromCoordinate(centerStored)
var ptCenterRect = fromCoordinate(centerRect)
if (pointIsVisible(ptCenter) && pointIsVisible(ptCenterRect)) {
newZoomOut = zoomLevel
newZoomOutFound = true
break
}
zoomLevel--
}
if (!newZoomOutFound)
newZoomOut = defaultZoomOut
// calculate zoom in
center = newCenter
zoomLevel = maximumZoomLevel
var diagonalRect = topLeft.distanceTo(bottomRight)
while (zoomLevel > minimumZoomLevel) {
ptTopLeft = fromCoordinate(topLeft)
ptBottomRight = fromCoordinate(bottomRight)
if (pointIsVisible(ptTopLeft) && pointIsVisible(ptBottomRight)) {
newZoom = zoomLevel
var c0 = toCoordinate(Qt.point(0.0, 0.0))
var c1 = toCoordinate(Qt.point(width, height))
if (c0.distanceTo(c1) > diagonalRect) {
newZoom = zoomLevel - 2.0
break
}
zoomLevel--