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I've created an input handler for NASA Worldwind that I'm trying to replicate Google Earth like zooming with.
I'm trying to make zoom towards the mouse cursor, instead of the center of the screen (like it does by default).
I've got it somewhat working -- except it doesn't zoom towards the lat/long under the cursor consistently, it seems to drift too far. What I want to happen is that the same lat/long is held under the cursor during the duration of the zoom. So, for instance, if you are hovering the cursor over a particular landmark (like a body of water), it will stay under the cursor as the wheel is scrolled.
The code I'm using is based heavily on this: https://forum.worldwindcentral.com/forum/world-wind-java-forums/development-help/11977-zoom-at-mouse-cursor?p=104793#post104793
Here is my Input Handler:
import java.awt.event.MouseWheelEvent;
import gov.nasa.worldwind.awt.AbstractViewInputHandler;
import gov.nasa.worldwind.awt.ViewInputAttributes;
import gov.nasa.worldwind.geom.Position;
import gov.nasa.worldwind.geom.Vec4;
import gov.nasa.worldwind.view.orbit.BasicOrbitView;
import gov.nasa.worldwind.view.orbit.OrbitViewInputHandler;
public class ZoomToCursorViewInputHandler extends OrbitViewInputHandler {
protected class ZoomActionHandler extends VertTransMouseWheelActionListener {
@Override
public boolean inputActionPerformed(AbstractViewInputHandler inputHandler, MouseWheelEvent mouseWheelEvent,
ViewInputAttributes.ActionAttributes viewAction) {
double zoomInput = mouseWheelEvent.getWheelRotation();
Position position = getView().computePositionFromScreenPoint(mousePoint.x, mousePoint.y);
// Zoom toward the cursor if we're zooming in. Move straight out when zooming
// out.
if (zoomInput < 0 && position != null)
return this.zoomToPosition(position, zoomInput, viewAction);
else
return super.inputActionPerformed(inputHandler, mouseWheelEvent, viewAction);
}
protected boolean zoomToPosition(Position position, double zoomInput,
ViewInputAttributes.ActionAttributes viewAction) {
double zoomChange = zoomInput * getScaleValueZoom(viewAction);
BasicOrbitView view = (BasicOrbitView) getView();
System.out.println("================================");
System.out.println("Center Position: \t\t"+view.getCenterPosition());
System.out.println("Mouse is on Position: \t\t"+position);
Vec4 centerVector = view.getCenterPoint();
Vec4 cursorVector = view.getGlobe().computePointFromLocation(position);
Vec4 delta = cursorVector.subtract3(centerVector);
delta = delta.multiply3(-zoomChange);
centerVector = centerVector.add3(delta);
Position newPosition = view.getGlobe().computePositionFromPoint(centerVector);
System.out.println("New Center Position is: \t"+newPosition);
setCenterPosition(view, uiAnimControl, newPosition, viewAction);
onVerticalTranslate(zoomChange, viewAction);
return true;
}
}
public ZoomToCursorViewInputHandler() {
ViewInputAttributes.ActionAttributes actionAttrs = this.getAttributes()
.getActionMap(ViewInputAttributes.DEVICE_MOUSE_WHEEL)
.getActionAttributes(ViewInputAttributes.VIEW_VERTICAL_TRANSLATE);
actionAttrs.setMouseActionListener(new ZoomActionHandler());
}
}
To enable, set this property in the worldwind.xml to point to this class:
<Property name="gov.nasa.worldwind.avkey.ViewInputHandlerClassName"
value="gov.nasa.worldwindx.examples.ZoomToCursorViewInputHandler"/>
813
After some thinking over this problem I believe there is no closed form analytical solution for it. You just have to take into account to many things: shape of the Earth, how the "eye" moves when you move the center. So the best trick I think you can do is to "follow" the main "zoom" animation and do small adjustments after each animation step. As animation steps are small, calculation errors should also be smaller and they should accumulate less because on next step you take into account all the previous errors. So my idea in the code is roughly following: create a FixZoomPositionAnimator class as
static class FixZoomPositionAnimator extends BasicAnimator
{
static final String VIEW_ANIM_KEY = "FixZoomPositionAnimator";
static final double EPS = 0.005;
private final java.awt.Point mouseControlPoint;
private final Position mouseGeoLocation;
private final Vec4 mouseGeoPoint;
private final BasicOrbitView orbitView;
private final Animator zoomAnimator;
private int lastDxSign = 0;
private int lastDySign = 0;
int stepNumber = 0;
int stepsNoAdjustments = 0;
FixZoomPositionAnimator(BasicOrbitView orbitView, Animator zoomAnimator, java.awt.Point mouseControlPoint, Position mouseGeoLocation)
{
this.orbitView = orbitView;
this.zoomAnimator = zoomAnimator;
this.mouseControlPoint = mouseControlPoint;
this.mouseGeoLocation = mouseGeoLocation;
mouseGeoPoint = orbitView.getGlobe().computePointFromLocation(mouseGeoLocation);
}
public Point getMouseControlPoint()
{
return mouseControlPoint;
}
public Position getMouseGeoLocation()
{
return mouseGeoLocation;
}
private static int sign(double d)
{
if (Math.abs(d) < EPS)
return 0;
else if (d > 0)
return 1;
else
return -1;
}
double calcAccelerationK(double dSign, double lastDSign)
{
// as we are following zoom trying to catch up - accelerate adjustment
// but slow down if we overshot the target last time
if (!zoomAnimator.hasNext())
return 1.0;
else if (dSign != lastDSign)
return 0.5;
else
{
// reduce acceleration over time
if (stepNumber < 10)
return 5;
else if (stepNumber < 20)
return 3;
else
return 2;
}
}
static boolean isBetween(double checkedValue, double target1, double target2)
{
return ((target1 < checkedValue) && (checkedValue < target2))
|| ((target1 > checkedValue) && (checkedValue > target2));
}
static boolean isValid(Position position)
{
return isBetween(position.longitude.degrees, -180, 180)
&& isBetween(position.latitude.degrees, -90, 90);
}
@Override
public void next()
{
// super.next(); // do not call super to avoid NullPointerException!
nextWithTilt(); // works OK on tilted Earth
// nextOld(); // IMHO better looking but stops working is user tilts the Earth
}
private void nextOld()
{
stepNumber++;
Vec4 curProjection = orbitView.project(mouseGeoPoint);
Rectangle viewport = orbitView.getViewport();
// for Y sign is inverted
double dX = (mouseControlPoint.x - curProjection.x);
double dY = (mouseControlPoint.y + curProjection.y - viewport.getHeight());
if (Math.abs(dX) > EPS || Math.abs(dY) > EPS)
{
double dCX = (mouseControlPoint.x - viewport.getCenterX());
double dCY = (mouseControlPoint.y + viewport.getCenterY() - viewport.getHeight());
final double stepPx = 10;
// As the Earth is curved and we are not guaranteed to have a frontal view on it
// latitude an longitude lines are not really parallel to X or Y. But we assume that
// locally they are parallel enough both around the mousePoint and around the center.
// So we use reference points near center to calculate how we want to move the center.
Vec4 controlPointRight = new Vec4(viewport.getCenterX() + stepPx, viewport.getCenterY());
Vec4 geoPointRight = orbitView.unProject(controlPointRight);
Position positionRight = (geoPointRight != null) ? orbitView.getGlobe().computePositionFromPoint(geoPointRight) : null;
Vec4 controlPointUp = new Vec4(viewport.getCenterX(), viewport.getCenterY() - stepPx);
Vec4 geoPointUp = orbitView.unProject(controlPointUp);
Position positionUp = (geoPointUp != null) ? orbitView.getGlobe().computePositionFromPoint(geoPointUp) : null;
Position centerPosition = orbitView.getCenterPosition();
double newCenterLongDeg;
if (Math.abs(dCX) <= 1.0) // same X => same longitude
{
newCenterLongDeg = mouseGeoLocation.longitude.degrees;
}
else if (positionRight == null) // if controlPointRight is outside of the globe - don't try to fix this coordinate
{
newCenterLongDeg = centerPosition.longitude.degrees;
}
else
{
double scaleX = -dX / stepPx;
// apply acceleration if possible
int dXSign = sign(dX);
double accScaleX = scaleX * calcAccelerationK(dXSign, lastDxSign);
lastDxSign = dXSign;
newCenterLongDeg = centerPosition.longitude.degrees * (1 - accScaleX) + positionRight.longitude.degrees * accScaleX;
// if we overshot - use non-accelerated mode
if (!isBetween(newCenterLongDeg, centerPosition.longitude.degrees, mouseGeoLocation.longitude.degrees)
|| !isBetween(newCenterLongDeg, -180, 180))
{
newCenterLongDeg = centerPosition.longitude.degrees * (1 - scaleX) + positionRight.longitude.degrees * scaleX;
}
}
double newCenterLatDeg;
if (Math.abs(dCY) <= 1.0) // same Y => same latitude
{
newCenterLatDeg = mouseGeoLocation.latitude.degrees;
}
else if (positionUp == null) // if controlPointUp is outside of the globe - don't try to fix this coordinate
{
newCenterLatDeg = centerPosition.latitude.degrees;
}
else
{
double scaleY = -dY / stepPx;
// apply acceleration if possible
int dYSign = sign(dY);
double accScaleY = scaleY * calcAccelerationK(dYSign, lastDySign);
lastDySign = dYSign;
newCenterLatDeg = centerPosition.latitude.degrees * (1 - accScaleY) + positionUp.latitude.degrees * accScaleY;
// if we overshot - use non-accelerated mode
if (!isBetween(newCenterLatDeg, centerPosition.latitude.degrees, mouseGeoLocation.latitude.degrees)
|| !isBetween(newCenterLatDeg, -90, 90))
{
newCenterLatDeg = centerPosition.latitude.degrees * (1 - scaleY) + positionUp.latitude.degrees * scaleY;
}
}
Position newCenterPosition = Position.fromDegrees(newCenterLatDeg, newCenterLongDeg);
orbitView.setCenterPosition(newCenterPosition);
}
if (!zoomAnimator.hasNext())
stop();
}
private void nextWithTilt()
{
stepNumber++;
if (!zoomAnimator.hasNext() || (stepsNoAdjustments > 20))
{
System.out.println("Stop after " + stepNumber);
stop();
}
Vec4 curProjection = orbitView.project(mouseGeoPoint);
Rectangle viewport = orbitView.getViewport();
System.out.println("----------------------------------");
System.out.println("Mouse: mouseControlPoint = " + mouseControlPoint + "\t location = " + mouseGeoLocation + "\t viewSize = " + viewport);
System.out.println("Mouse: curProjection = " + curProjection);
double dX = (mouseControlPoint.x - curProjection.x);
double dY = (viewport.getHeight() - mouseControlPoint.y - curProjection.y); // Y is inverted
Vec4 dTgt = new Vec4(dX, dY);
// sometimes if you zoom close to the edge curProjection is calculated as somewhere
// way beyond where it is and it leads to overflow. This is a protection against it
if (Math.abs(dX) > viewport.width / 4 || Math.abs(dY) > viewport.height / 4)
{
Vec4 unproject = orbitView.unProject(new Vec4(mouseControlPoint.x, viewport.getHeight() - mouseControlPoint.y));
System.out.println("!!!End Mouse:"
+ " dX = " + dX + "\t" + " dY = " + dY
+ "\n" + "unprojectPt = " + unproject
+ "\n" + "unprojectPos = " + orbitView.getGlobe().computePositionFromPoint(unproject)
);
stepsNoAdjustments += 1;
return;
}
if (Math.abs(dX) <= EPS && Math.abs(dY) <= EPS)
{
stepsNoAdjustments += 1;
System.out.println("Mouse: No adjustment: " + " dX = " + dX + "\t" + " dY = " + dY);
return;
}
else
{
stepsNoAdjustments = 0;
}
// create reference points about 10px away from the center to the Up and to the Right
// and then map them to screen coordinates and geo coordinates
// Unfortunately unproject often generates points far from the Earth surface (and
// thus with significantly less difference in lat/long)
// So this longer but more fool-proof calculation is used
final double stepPx = 10;
Position centerPosition = orbitView.getCenterPosition();
Position eyePosition = orbitView.getEyePosition();
double pixelGeoSize = orbitView.computePixelSizeAtDistance(eyePosition.elevation - centerPosition.elevation);
Vec4 geoCenterPoint = orbitView.getCenterPoint();
Vec4 geoRightPoint = geoCenterPoint.add3(new Vec4(pixelGeoSize * stepPx, 0, 0));
Vec4 geoUpPoint = geoCenterPoint.add3(new Vec4(0, pixelGeoSize * stepPx, 0));
Position geoRightPosition = orbitView.getGlobe().computePositionFromPoint(geoRightPoint);
Position geoUpPosition = orbitView.getGlobe().computePositionFromPoint(geoUpPoint);
Vec4 controlCenter = orbitView.project(geoCenterPoint);
Vec4 controlRight = orbitView.project(geoRightPoint);
Vec4 controlUp = orbitView.project(geoUpPoint);
Vec4 controlRightDif = controlRight.subtract3(controlCenter);
controlRightDif = new Vec4(controlRightDif.x, controlRightDif.y); // ignore z for scale calculation
Vec4 controlUpDif = controlUp.subtract3(controlCenter);
controlUpDif = new Vec4(controlUpDif.x, controlUpDif.y); // ignore z for scale calculation
double scaleRight = -dTgt.dot3(controlRightDif) / controlRightDif.getLengthSquared3();
double scaleUp = -dTgt.dot3(controlUpDif) / controlUpDif.getLengthSquared3();
Position posRightDif = geoRightPosition.subtract(centerPosition);
Position posUpDif = geoUpPosition.subtract(centerPosition);
double totalLatDifDeg = posRightDif.latitude.degrees * scaleRight + posUpDif.latitude.degrees * scaleUp;
double totalLongDifDeg = posRightDif.longitude.degrees * scaleRight + posUpDif.longitude.degrees * scaleUp;
Position totalDif = Position.fromDegrees(totalLatDifDeg, totalLongDifDeg);
// don't copy elevation!
Position newCenterPosition = Position.fromDegrees(centerPosition.latitude.degrees + totalLatDifDeg,
centerPosition.longitude.degrees + totalLongDifDeg);
// if we overshot - try to slow down
if (!isValid(newCenterPosition))
{
newCenterPosition = Position.fromDegrees(centerPosition.latitude.degrees + totalLatDifDeg / 2,
centerPosition.longitude.degrees + totalLongDifDeg / 2);
if (!isValid(newCenterPosition))
{
System.out.println("Too much overshot: " + newCenterPosition);
stepsNoAdjustments += 1;
return;
}
}
System.out.println("Mouse:"
+ " dX = " + dX + "\t" + " dY = " + dY
+ "\n"
+ " centerPosition = " + centerPosition
+ "\n"
+ " geoUpPoint = " + geoUpPoint + "\t " + " geoUpPosition = " + geoUpPosition
+ "\n"
+ " geoRightPoint = " + geoRightPoint + "\t " + " geoRightPosition = " + geoRightPosition
+ "\n"
+ " posRightDif = " + posRightDif
+ "\t"
+ " posUpDif = " + posUpDif
+ "\n"
+ " scaleRight = " + scaleRight + "\t" + " scaleUp = " + scaleUp);
System.out.println("Mouse: oldCenterPosition = " + centerPosition);
System.out.println("Mouse: newCenterPosition = " + newCenterPosition);
orbitView.setCenterPosition(newCenterPosition);
}
}
Update
FixZoomPositionAnimator was updated to take into account the fact that one a large scale you can't assume that longitude and latitude lines go parallel to X and Y. To work this around reference points around the center are used to calculate adjustment. This means that the code will not work if the globe size is less than about 20px (2*stepPx) or if the user has tilted the Earth making latitude/longitude significantly non-parallel to X/Y.
End of Update
Update #2
I've moved previous logic to nextOld and added nextWithTilt. The new function should work even if the world is tilted but as the base logic is more complicated now, there is no acceleration anymore which IMHO makes it a bit worse for more typical cases. Also there are still a log of logging inside nextWithTilt because I'm not quite sure it really works OK. Use at your own risk.
End of Update #2
and then you may use it as
public class ZoomToCursorViewInputHandler extends OrbitViewInputHandler
{
public ZoomToCursorViewInputHandler()
{
ViewInputAttributes.ActionAttributes actionAttrs = this.getAttributes()
.getActionMap(ViewInputAttributes.DEVICE_MOUSE_WHEEL)
.getActionAttributes(ViewInputAttributes.VIEW_VERTICAL_TRANSLATE);
actionAttrs.setMouseActionListener(new ZoomActionHandler());
}
protected class ZoomActionHandler extends VertTransMouseWheelActionListener
{
@Override
public boolean inputActionPerformed(AbstractViewInputHandler inputHandler, MouseWheelEvent mouseWheelEvent,
final ViewInputAttributes.ActionAttributes viewAction)
{
double zoomInput = mouseWheelEvent.getWheelRotation();
Position position = wwd.getCurrentPosition();
Point mouseControlPoint = mouseWheelEvent.getPoint();
// Zoom toward the cursor if we're zooming in. Move straight out when zooming
// out.
if (zoomInput < 0 && position != null)
{
boolean res = super.inputActionPerformed(inputHandler, mouseWheelEvent, viewAction);
BasicOrbitView view = (BasicOrbitView) getView();
OrbitViewMoveToZoomAnimator zoomAnimator = (OrbitViewMoveToZoomAnimator) uiAnimControl.get(VIEW_ANIM_ZOOM);
// for continuous scroll preserve the original target if mouse was not moved
FixZoomPositionAnimator old = (FixZoomPositionAnimator) uiAnimControl.get(FixZoomPositionAnimator.VIEW_ANIM_KEY);
if (old != null && old.getMouseControlPoint().equals(mouseControlPoint))
{
position = old.getMouseGeoLocation();
}
FixZoomPositionAnimator fixZoomPositionAnimator = new FixZoomPositionAnimator(view, zoomAnimator, mouseControlPoint, position);
fixZoomPositionAnimator.start();
uiAnimControl.put(FixZoomPositionAnimator.VIEW_ANIM_KEY, fixZoomPositionAnimator);
return res;
}
else
{
uiAnimControl.remove(FixZoomPositionAnimator.VIEW_ANIM_KEY); // when zoom direction changes we don't want to make position adjustments anymore
return super.inputActionPerformed(inputHandler, mouseWheelEvent, viewAction);
}
}
}
// here goes aforementioned FixZoomPositionAnimator
}
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