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"/>
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
FixZoomPositionAnimatorclass asUpdate
FixZoomPositionAnimatorwas 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
nextOldand addednextWithTilt. 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 insidenextWithTiltbecause 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