---------------------------------------------------
Qt3D ShaderPrograme
Qt3D GLSL 渲染器
Shader示例可參考：
    http://blog.csdn.net/candycat1992/article/details/44039077
    https://www.shadertoy.com/
http://blog.csdn.net/candycat1992/article/details/44039077
faq: shader的輸入參數怎麽各家都不一樣，到底是如何定義的
---------------------------------------------------
概念
    渲染代碼可由ShaderProgram對象封裝
    參數的傳遞比ShaderEffect復雜得多，好麻煩
    要求輸出的參數是一致的（gl_Position, gl_FragColor)
    

Qt3D默認提供的參數
    attribute highp vec4 vertexPosition;   // 頂點位置
    attribute highp vec3 vertexNormal;     // 頂點法線
    attribute highp vec2 vertexTexCoord;   // 頂點紋理坐標
    uniform highp mat4 mvp;                // ？
    uniform highp mat4 modelMatrix;        // ?
    uniform highp vec3 cameraPosition;     // 相機位置
    uniform mat4 modelView;                // ?
    uniform mat4 modelNormalMatrix;        // ?

常用的方法
   normalize
   dot
   min/mix/max/pow/
   textureCube
    highp vec4 surface = texture2D(surfaceTexture, texCoord);
    highp vec3 reflectedDirection = reflect(viewDirection, normalize(normal));
    textureCube(skyboxTexture, reflectedDirection).rgb

VertexShader
    // Qt 3D默認提供的參數  
    attribute vec3 vertexPosition;  
    attribute vec3 vertexNormal;  
    uniform mat4 modelView;  
    uniform mat4 modelNormalMatrix;  
    uniform mat4 mvp;  
    // 自己提供的參數  
    uniform vec3 lightPosition;  
    varying vec3 reflectVec;  
    varying vec3 viewVec;  
    varying float NdotL;  
    void main( void )  
    
 
{  
        vec3 ecPos = ( modelView * vec4( vertexPosition, 1.0 ) ).xyz;  
        vec3 normal = normalize( modelNormalMatrix * vec4( vertexNormal, 1.0 ) ).xyz;  
        vec3 lightVec = normalize( lightPosition - ecPos );  
        reflectVec = normalize( reflect( -lightVec, normal ) );  
        viewVec = normalize( -ecPos );  
        NdotL = ( dot( lightVec, normal ) + 1.0 ) * 0.5;  
        gl_Position = mvp * vec4( vertexPosition, 1.0 );  
    
 
}  


FragmentShader
    // 自己提供的參數  
    uniform vec3 surfaceColor;  
    uniform vec3 warmColor;  
    uniform vec3 coolColor;  
    uniform float diffuseWarm;  
    uniform float diffuseCool;  
    varying vec3 reflectVec;  
    varying vec3 viewVec;  
    varying float NdotL;  
    void main( void )  
    
 
{  
        vec3 kcool    = min( coolColor + diffuseCool * surfaceColor, 1.0 );  
        vec3 kwarm    = min( warmColor + diffuseWarm * surfaceColor, 1.0 );  
        vec3 kfinal   = mix( kcool, kwarm, NdotL );  
        float spec = max( dot( reflectVec, viewVec ), 0.0 );  
        spec = pow( spec, 32.0 );  
        gl_FragColor = vec4( min( kfinal + spec, 1.0 ), 1.0 );  
    }
    


cinematic3d/BackgroundCubeMap.qml    
    ShaderProgram {
        id: gles2SkyboxShader
        vertexShaderCode: "
            attribute vec3 vertexPosition;
            varying vec3 texCoord0;
            uniform mat4 mvp;
            void main()
            {
                texCoord0 = vertexPosition.xyz;
                gl_Position = vec4(mvp * vec4(vertexPosition, 1.0)).xyww; // Fail depth test always against any rendered pixel
            }
            "
        fragmentShaderCode: "
            varying highp vec3 texCoord0;
            uniform samplerCube skyboxTexture;
            void main()
            {
                gl_FragColor = textureCube(skyboxTexture, texCoord0);
            }
            "
    }
    
// 二維貼圖材質
Texture2D {
    property alias source: image.source
    minificationFilter: Texture.LinearMipMapLinear
    magnificationFilter: Texture.Linear
    generateMipMaps: true
    wrapMode {
        x: WrapMode.ClampToEdge
        y: WrapMode.ClampToEdge
    }
    TextureImage {id: image}
}

Qt3D Shader