开发笔记:为什么iOS8上的SceneKit无法编译我的自定义着色器？

我创建了一个基于游戏模板的新项目，其中SceneKit作为游戏技术，Swift作为语言。我尝试使用自定义着色器。这是设置代码：

var material = SCNMaterial()
var program = SCNProgram()
// Read the vertex shader file and set its content as our vertex shader
if let vertexShaderPath = NSBundle.mainBundle().pathForResource("VertexShader", ofType:"vsh") {
let vertexShaderAsAString = NSString(contentsOfFile: vertexShaderPath, encoding: NSUTF8StringEncoding, error: nil)
program.vertexShader = vertexShaderAsAString
}
// Read the fragment shader file and set its content as our fragment shader
if let fragmentShaderPath = NSBundle.mainBundle().pathForResource("FragmentShader", ofType:"fsh") {
let fragmentShaderAsAString = NSString(contentsOfFile: fragmentShaderPath, encoding: NSUTF8StringEncoding, error: nil)
program.fragmentShader = fragmentShaderAsAString
}
// Give a meaning to variables used in the shaders
program.setSemantic(SCNGeometrySourceSemanticVertex, forSymbol: "a_position", options: nil)
program.setSemantic(SCNModelViewProjectionTransform, forSymbol: "u_viewProjectionTransformMatrix", options: nil)
material.program = program
// retrieve the ship node
let ship = scene.rootNode.childNodeWithName("shipMesh", recursively: true)
ship.geometry.firstMaterial = material


我的顶点着色器的代码：

#version 300 es
uniform mat4 u_viewProjectionTransformMatrix;
in vec4 a_position;
out vec4 outPosition;
void main() {
outPosition = u_viewProjectionTransformMatrix * a_position;
}


我的片段着色器的代码：

#version 300 es
out vec4 outColor;
void main() {
outColor = vec4(1.0, 0.0, 0.0, 1.0)
}


很简单吧？但是当我执行此代码时，我收到以下错误：

SceneKit: error, failed to link program: ERROR: 0:1: '' : version '300' is not supported
ERROR: 0:1: '' : syntax error: #version


我做错了什么？为了您的信息，#version 200 es产生相同的结果，因此它似乎与OpenGL本身的版本无关。