问识别3d立方体的表面

EN

    static const GLfloat cubeVertices[] = {

        -1.0, -1.0, 1.0,
        1.0, -1.0, 1.0,
        1.0, 1.0, 1.0,
        -1.0, 1.0, 1.0,

        -1.0, -1.0, -1.0,
        1.0, -1.0, -1.0,
        1.0, 1.0, -1.0,
        -1.0, 1.0, -1.0,
    };


    static const GLushort cubeIndicesFaceFront[] = {
        0, 1, 2, 3, 0
    };

    static const GLushort cubeIndicesFaceBack[] = {
        4, 5, 6, 7, 4
    };

    static const GLushort cubeIndicesFaceLeft[] = {
        0, 4, 7, 3, 0
    };

    static const GLushort cubeIndicesFaceRight[] = {
        1, 5, 6, 2, 1
    };

    static const GLushort cubeIndicesFaceTop[] = {
        3, 2, 6, 7, 3
    };

    static const GLushort cubeIndicesFaceBottom[] = {
        0, 1, 5, 4, 0
    };

static const GLubyte cubeColors[] = {
    0, 255, 255, 255,
    0, 255, 255, 255,
    0, 255, 255, 255,
    0, 255, 255, 255,
    0, 255, 255, 255,
};      


    glVertexPointer(3, GL_FLOAT, 0, cubeVertices);
    glEnableClientState(GL_VERTEX_ARRAY);


    glColorPointer(4, GL_UNSIGNED_BYTE, 0, cubeColors);
    glEnableClientState(GL_COLOR_ARRAY);
    glDrawElements(GL_TRIANGLE_FAN, 5, GL_UNSIGNED_SHORT, cubeIndicesFaceFront);
    glDrawElements(GL_TRIANGLE_FAN, 5, GL_UNSIGNED_SHORT, cubeIndicesFaceBack);
    glDrawElements(GL_TRIANGLE_FAN, 5, GL_UNSIGNED_SHORT, cubeIndicesFaceLeft);
    glDrawElements(GL_TRIANGLE_FAN, 5, GL_UNSIGNED_SHORT, cubeIndicesFaceRight);
    glDrawElements(GL_TRIANGLE_FAN, 5, GL_UNSIGNED_SHORT, cubeIndicesFaceTop);
    glDrawElements(GL_TRIANGLE_FAN, 5, GL_UNSIGNED_SHORT, cubeIndicesFaceBottom);


    glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];