从OpenGL / OpenTK中的一个顶点缓冲区对象中绘制多个对象

Question

我正在尝试在OpenGL中使用VBO来尝试绘图方法。许多人通常使用1个vbo来存储一个对象数据阵列。我试图做一些相反的事情，即将多个对象数据存储到1个vbo然后绘制它。背后有故事我为什么要这样做。我希望有时将许多对象组合为单个对象。但是我的代码不公正。以下是我的伪代码：

//Data
int[] _vBO = new int[1]; //vertex buffer objects

_triangleVertices = new float[] 
                  { 0.0f, 1.0f, 0.0f, -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, //first triangle lineloop, positions in the middle of the screen.
                    3.0f, 1.0f, 0.0f, 2.0f, -1.0f, 0.0f, 4.0f, -1.0f, 0.0f, //second triangle lineloop, positions on the left side of the first triangle.
                    -3.0f, 1.0f, 0.0f, -4.0f, -1.0f, 0.0f, -2.0f, -1.0f, 0.0f  }; //third triangle lineloop, positions on the right side of the first triangle.

//Setting Up
void init()
{
   GL.GenBuffers(1, _vBO);
   GL.BindBuffer(BufferTarget.ArrayBuffer, _vBO[0]);
   GL.BufferData(BufferTarget.ArrayBuffer, new IntPtr(sizeof(float) * _triangleVertices.Length), _triangleVertices, BufferUsageHint.StaticDraw);
   GL.VertexPointer(3, VertexPointerType.Float, 0, 0);
   GL.EnableClientState(Array.VertexArray);
}

//Drawing
void display()
{
    GL.Clear(ClearBufferMask.ColorBufferBit);
    GL.Clear(ClearBufferMask.DepthBufferBit);

    //setting up camera and projection.
    float[] eyes = { 0.0f, 0.0f, -10.0f };
    float[] target = { 0.0f, 0.0f, 0.0f };
    Matrix4 projection = Matrix4.CreatePerspectiveFieldOfView(0.785398163f, 4.0f / 3.0f, 0.1f, 100f);  //45 degree = 0.785398163 rads
    Matrix4 view = Matrix4.LookAt(eyes[0], eyes[1], eyes[2], target[0], target[1], target[2], 0, 1, 0);
    Matrix4 model = Matrix4.Identity;
    Matrix4 MV = view * model;

    GL.MatrixMode(MatrixMode.Projection);
    GL.LoadIdentity();
    GL.LoadMatrix(ref projection);

    GL.MatrixMode(MatrixMode.Modelview);
    GL.LoadIdentity();
    GL.LoadMatrix(ref MV);


    GL.Viewport(0, 0, glControlWindow.Width, glControlWindow.Height);
    GL.Enable(EnableCap.DepthTest); //Enable correct Z Drawings
    GL.DepthFunc(DepthFunction.Less); //Enable correct Z Drawings
    GL.MatrixMode(MatrixMode.Modelview);

    //Draw
    drawTriangleLineLoops();


    //Finally...
    GraphicsContext.CurrentContext.VSync = true; //Caps frame rate as to not over run GPU
    glControlWindow.SwapBuffers(); //Takes from the 'GL' and puts into control
}


void drawTriangleLineLoops()
{
   GL.BindBuffer(BufferTarget.ArrayBuffer, _vBO[0]);
   GL.VertexPointer(3, VertexPointerType.Float, 0, 0);
   GL.EnableClientState(ArrayCap.VertexArray);
   GL.DrawArrays(BeginMode.LineLoop, 0, 3); //drawing first triangle lineloop, first vertex starts at index 0.
   GL.DrawArrays(BeginMode.LineLoop, 9, 3); //drawing second triangle lineloop, first vertex starts at index 9.
   GL.DrawArrays(BeginMode.LineLoop, 18, 3); //drawing third triangle lineloop, first vertex starts at index 18.
   GL.DisableClientState(ArrayCap.VertexArray);
}    

我希望绘制3个不同的三角形，但只绘制了一个。我不知道出了什么问题。