Tag: #WPF #3D #Selection #Modifier #ScreenCoordinates

Hello SciChart team,

I wanted to implement 3DSelectionModifier that should select a point closest to the mouse pointer per mouse click.

To do this, I create a rectangle with a clicked point in the center with a mouse click and use the PickScene method of the ViewPort3D object.

List<EntityVertexId>? entityVertexIds = Viewport3D.PickScene(mousePoint.ToRectCenter(30));

Depending on the camera angle It can of course happen that several points appear in the scene. In this case I wanted to do the following:

for each determined point in 3D space, determine its 2D screen coordinates

HitTestInfo3D hitTestInfo = new HitTestInfo3D() { IsHit = true, EntityId = entityVertexId.EntityId, VertexId = entityVertexId.VertexId };
SeriesInfo3D? seriesInfo = pointsEntity.ToSeriesInfo(hitTestInfo);
//Vector3D hitVertex = seriesInfo.HitVertex; 
Vector3 vertex = seriesInfo.HitVertexCoords; 
Point point1 = ParentSurface.Camera.WorldToScreenSpace(vertex); 

Determine the distance between the point of the mouse and the 2D coordinates of the point from the scene

double newDistance = PointUtil.Distance(mousePoint, point1);

Select the point with the shortest distance.

if (distance.IsNaN() || newDistance < distance) 
{   
  distance = newDistance;   
  nearestSeriesInfo3D = seriesInfo; 
}

During the implementation I encountered the following problem:
I used following camera object method first

Point p = ParentSurface.Camera.WorldToScreenSpace(vertex);

but this gave me no plausible point.
The other method

Point p = ParentSurface.Camera.LocalCoordinateToScreenSpace(vertex);

also seemed to return a point that returned the wrong value when calculating the distance, so the wrong point was selected.

If I try to click the data point directly, I expect at least one of the methods to return a point very very close to the mouse pointer. However, both methods gave me a point on the screen (see screenshot) that did not match the mouse point.

Maybe I’m missing a step or transformation. Could you explain me what I’m doing wrong?

Example project is attached