SKWarpGeometryGridDeformation.swift

extension SKWarpGeometryGrid {
    func deform(at contactPoint: float2, radius: Float) -> SKWarpGeometryGrid {
        // Make a copy of current grid positions.
        let currentPositions: [float2] = {
            var positions = [float2](repeating: .zero, count: vertexCount)
            (0..<vertexCount).forEach({ positions[$0] = destPosition(at: $0) })
            return positions
        }()
        
        // Move some of the positions in the grid close to contact point.
        let destination = currentPositions.map { (gridPoint) -> float2 in
            let contactDistance = gridPoint.distance(to: contactPoint)
            guard contactDistance <= Float(radius) else { return gridPoint }
            // If contact was very close to the grid point, move it a little bit further away from the contact point.
            let gridPointChangeFactor = (Float(radius) - contactDistance) / Float(radius)
            let maxDeformation: Float = 0.1
            let gridPointDistanceChange = Float(maxDeformation) * gridPointChangeFactor // vector length
            
            // Limit angle, as otherwise the edges of the crater are too far away from the center of the node.
            let angleToCenter = contactPoint.angle(to: float2(x: 0.5, y: 0.5))
            let maxAngleOffset = Float.pi / 4.0
            let minAngle = angleToCenter - maxAngleOffset
            let maxAngle = angleToCenter + maxAngleOffset
            var gridPointOffsetAngle = contactPoint.angle(to: gridPoint)
            gridPointOffsetAngle = min(max(gridPointOffsetAngle, minAngle), maxAngle)
            
            return float2(x: gridPoint.x + gridPointDistanceChange * cos(gridPointOffsetAngle), y: gridPoint.y + gridPointDistanceChange * sin(gridPointOffsetAngle))
        }
        
        return replacingByDestinationPositions(positions: destination)
    }
}