Nonoku - SpriteKit Shader

A quick one because I was having trouble with this:

let node = SKShapeNode(rectOf: CGSize(width: 100, height: 100), cornerRadius: 5)
        let dashedShader = SKShader(source: "void main() {" +
            "float diff = u_path_length / 5.0;" +
            "float stripe = u_path_length / diff;" +
            "float distance = v_path_distance;" +
            "int h = int(mod(distance / stripe, 2.0));" +
            "gl_FragColor = vec4(h, h, h, h);" +
            "}")

        node.strokeShader = dashedShader

        node.fillColor = SKColor.clear
        node.lineWidth = 2

I've not done much with shaders before so when it didn't work I was short on tools to debug it. In the end it was a bunch of little things I had to solve, from converting the original version to one that would work against the iOS GL ES version, to making sure I converted to int before setting the colour.