SpriteKit: suggestions for rounding corners of unconventional grid?

Question

The goal is to round the corners of an unconventional grid similar to the following:

https://s-media-cache-ak0.pinimg.com/564x/50/bc/e0/50bce0cb908913ebc2cf630d635331ef.jpg

https://s-media-cache-ak0.pinimg.com/564x/7e/29/ee/7e29ee80e957ec22bbba630ccefbfaa2.jpg

Instead of a grid with four corners like a conventional grid, these grids have multiple corners in need of rounding.

The brute force approach would be to identify tiles with corners exposed then round those corners either with a different background image or by clipping the corners in code.

Is there a cleaner approach?

The grid is rendered for an iOS app in a SpriteKit SKScene.

Answer 1

What we did was lay out the tiles then call this function to round the nodes of exposed tiles.

// Rounds corners of exposed tiles. UIKit inverts coordinates so top is bottom and vice-versa.
fileprivate func roundTileCorners() {
    // Get all tiles
    var tiles = [TileClass]()
    tileLayer.enumerateChildNodes(withName: ".//*") { node, stop in
        if node is TileClass {
            tiles.append(node as! TileClass)
        }
    }

    // Round corners for each exposed tile
    for t in tiles {
        // Convert tile's position to root coordinates
        let convertedPos = convert(t.position, from: t.parent!)

        // Set neighbor positions
        var leftNeighborPos = convertedPos
        leftNeighborPos.x -= tileWidth
        var rightNeighborPos = convertedPos
        rightNeighborPos.x += tileWidth
        var topNeighborPos = convertedPos
        topNeighborPos.y += tileHeight
        var bottomNeighborPos = convertedPos
        bottomNeighborPos.y -= tileHeight

        // Set default value for rounding
        var cornersToRound : UIRectCorner?

        // No neighbor below & to left? Round bottom left.
        if !isTileAtPoint(point: bottomNeighborPos) && !isTileAtPoint(point: leftNeighborPos) {
            cornersToRound = cornersToRound?.union(.topLeft) ?? .topLeft
        }

        // No neighbor below & to right? Round bottom right.
        if !isTileAtPoint(point: bottomNeighborPos) && !isTileAtPoint(point: rightNeighborPos) {
            cornersToRound = cornersToRound?.union(.topRight) ?? .topRight
        }

        // No neightbor above & to left? Round top left.
        if !isTileAtPoint(point: topNeighborPos) && !isTileAtPoint(point: leftNeighborPos) {
            cornersToRound = cornersToRound?.union(.bottomLeft) ?? .bottomLeft
        }

        // No neighbor above & to right? Round top right.
        if !isTileAtPoint(point: topNeighborPos) && !isTileAtPoint(point: rightNeighborPos) {
            cornersToRound = cornersToRound?.union(.bottomRight) ?? .bottomRight
        }

        // Any corners to round?
        if cornersToRound != nil {
            t.roundCorners(cornersToRound: cornersToRound!)
        }
    }
}

// Returns true if a tile exists at <point>. Assumes <point> is in root node's coordinates.
fileprivate func isTileAtPoint(point: CGPoint) -> Bool {
    return nodes(at: point).contains(where: {$0 is BoardTileNode })
}