Question
Answer and Explanation
Converting a point from the 2D screen space of an SCNView
to 3D world coordinates is a common task in SceneKit. Here's how you can achieve this:
The primary method is unprojectPoint(_:)
, a method of the SCNView
class. This method takes a CGPoint
(representing a point on the screen) and returns a SCNVector3
(representing a point in the 3D world).
Steps:
1. Obtain the Screen Point: Start with the CGPoint
that you want to convert. This might come from a tap gesture, mouse click, or some other input.
2. Use `unprojectPoint(_:)`: Call the unprojectPoint(_:)
method on your SCNView
instance. The method will transform the 2D point to a 3D point in the world coordinate system. Here is an example code:
import SceneKit
func convertScreenPointToWorldCoordinates(screenPoint: CGPoint, in scnView: SCNView) -> SCNVector3? {
let worldCoordinates = scnView.unprojectPoint(screenPoint)
return worldCoordinates
}
3. Usage Example: Let's say you have an SCNView
named mySceneView
and want to convert a screen point. Here is an example how you would use it:
let myScreenPoint = CGPoint(x: 100, y: 200) // Example screen point
if let worldPoint = convertScreenPointToWorldCoordinates(screenPoint: myScreenPoint, in: mySceneView) {
print("World Coordinates: \(worldPoint)")
// You can now use the `worldPoint` variable, which is an `SCNVector3`, in your scene.
} else {
print("Failed to convert screen point to world coordinates.")
}
Explanation:
The unprojectPoint(_:)
method performs the inverse of the projection transformation that SceneKit applies when rendering the 3D scene onto a 2D screen. It calculates the 3D point that corresponds to the given 2D screen point based on the camera's perspective and other rendering settings.
Considerations:
- The resulting world coordinates are relative to the scene's root node. If you have any transformations applied to your nodes, you might need to further transform the world point to get coordinates relative to a specific node.
- If you are working with a depth value other than the one provided by the viewport, you need to consider adding a z value before calling unprojectPoint(_:)
.
By following these steps and adapting the example, you can successfully convert a screen point to world coordinates in SceneKit. This allows you to easily interact with your 3D scene based on user inputs on the 2D screen.