Geometry program does not work on iPad Mini 2 iOS 9

Question

I cannot run my program with shaders in node geometry in iOS 9. Here is the test code:

import SceneKit

class Test: NSObject, SCNProgramDelegate {

    private static let SIZE = 10

    private static let RES = 256

    var node: SCNNode!

    override init() {
        super.init()

        setup()
    }

    func program(program: SCNProgram, handleError error: NSError) {
        NSLog("program error: %@", error)
    }

    private func setup() {
        node = SCNNode()
        node.rotation = SCNVector4Make(1, 0, 0, -Float(M_PI) / 2)

        node.geometry = createGeometry()
    }

    private func createGeometry() -> SCNGeometry {
        let size = CGFloat(GpuHeightFieldWater.SIZE)
        let geometry = SCNPlane(width: size, height: size)
        geometry.widthSegmentCount = GpuHeightFieldWater.RES
        geometry.heightSegmentCount = GpuHeightFieldWater.RES

        let program = SCNProgram()
        program.delegate = self
        program.vertexShader = loadShader("test.vsh")
        program.fragmentShader = loadShader("test.fsh")

        program.setSemantic(SCNGeometrySourceSemanticVertex, forSymbol: "a_position", options: nil)
        program.setSemantic(SCNModelViewProjectionTransform, forSymbol: "u_mvpMatrix", options: nil)

        geometry.program = program

        return geometry
    }

    private func loadShader(name: String) -> String! {
        let file = NSString(string: name)
        let url = NSBundle.mainBundle().URLForResource(file.stringByDeletingPathExtension, withExtension: file.pathExtension)
        let data = NSData(contentsOfURL: url!)
        return String(data: data!, encoding: NSUTF8StringEncoding)
    }
}

test.vsh:

attribute vec4 a_position;
uniform mat4 u_mvpMatrix;

void main()
{
    vec4 a = a_position;
    a.x = 0;

    gl_Position = u_mvpMatrix * a;
}

test.fsh:

void main()
{
    gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0);
}

Node is added to the root of the scene node, and I see a plane (with a strange purple color), but my program never starts, and I see no errors for my program. So it looks like my program is being ignored.

What is wrong and how to run the program for geometry?

Update # 1

When I ran the application on the iPhone 5 simulator, it printed an error about my vertex shader code on line 7.

ERROR: 0: 7: Incompatible types (float and int) in assignment (and there is no implicit conversion available)

When I fix this error, it works. It is strange that when I launch this application on my iPad Mini 2 (iOS 9.0), I do not see any errors.

# 2

, , , iPhone 5s . iPad Mini 2 iOS 9.

, Metal (Mt):

iPhone GL:

, -.

Answer 1

Rendering API SCNView. Game, API- Default.

, Metal, , . API Open GL ES, .

, OpenGL ES API . , , . :

enum SCNRenderingAPI : UInt {
    case Metal
    case OpenGLES2
}

Default , iOS API- ? .

Answer 2

7:

    a.x = 0;

    a.x = 0.0;

(0:7) , int, float.