如何在单独的 opengl 数组对象中正确渲染网格？

Question

我正在尝试使用单独的顶点数组对象渲染两个三角形。我在 C# 上使用 OpenTK（与定义的 OpenGL API 相比，它提供几乎相同的 API）。这是我的代码：

我从声明我的变量开始。

    public partial class Form1 : Form
{
    public Form1() {
        InitializeComponent();
    }
    bool loaded = false; //do not use glcontrol before it is not loaded
    private uint VAO1; 
    private uint object1_vertex_buffer; private uint object1_vertices_size; private uint object1_index_buffer;
    private uint object2_vertex_buffer; private uint object2_vertices_size; private uint object2_index_buffer;
    private uint VAO2;
    private uint VBO;
    int VertexShader;
    int FragmentShader;
    int ShaderProgram;
    private float[] object1_vertices = new float[] {
       -0.2f, 0.0f, 0.0f, 
        0.2f, 0.0f, 0.0f, 
        0.0f, 0.2f, 0.0f
    };
    private float[] object2_vertices = new float[] {
        -0.5f, 0.0f, 0.0f,
        0.5f, 0.0f, 0.0f,
        0.0f, 0.4f, 0.0f
    };
    private int[] object1_indices = new int[] { 0, 1, 2 };
    private int[] object2_indices = new int[] { 0, 1, 2 };

我在这里画每一帧：

    private void glControl1_Paint(object sender, PaintEventArgs e)
    {
        if (!loaded)//<--------------------------------------
            return;//<--------------------------------------
        // Clear the color buffer.
        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
        GL.UseProgram(ShaderProgram);
        // Object 1
        GL.BindVertexArray(VAO1);
        // drawelements requires count of elements, not bytes
        GL.DrawElements(PrimitiveType.Triangles, object1_indices.Length, DrawElementsType.UnsignedInt, 0);

        // Object 2
        GL.BindVertexArray(VAO2);
        GL.DrawElements(PrimitiveType.Triangles, object2_indices.Length, DrawElementsType.UnsignedInt, 0);

       ErrorCode miauw = GL.GetError(); /// AND I GET HERE NO ERROR!
        /// at the end I have a screen filled by a background color, which is set in GL.ClearColor()
        glControl1.SwapBuffers();
    }

这里我对 OpenGL 数组和缓冲区进行了初始化。我在这里初始化了两个顶点数组对象（每个三角形一个）和两个缓冲区（每个）：顶点和索引。我为它们设置了合适的字节长度

    private void glControl1_Load(object sender, EventArgs e) {
        loaded = true;
        GL.ClearColor(Color.SkyBlue);
        GL.Enable(EnableCap.DepthTest);
        GL.DepthFunc(DepthFunction.Less);

        // Load the source of the vertex shader and compile it.
        VertexShader = GL.CreateShader(ShaderType.VertexShader);
        GL.ShaderSource(VertexShader, MyOpenglThings.VertexShaderSource);
        GL.CompileShader(VertexShader);

        // Load the source of the fragment shader and compile it.
        FragmentShader = GL.CreateShader(ShaderType.FragmentShader);
        GL.ShaderSource(FragmentShader, MyOpenglThings.FragmentShaderSource);
        GL.CompileShader(FragmentShader);

        // Create the shader program, attach the vertex and fragment shaders and link the program.
        ShaderProgram = GL.CreateProgram();
        GL.AttachShader(ShaderProgram, VertexShader);
        GL.AttachShader(ShaderProgram, FragmentShader);
        GL.LinkProgram(ShaderProgram);


        // 
        // 
        GL.GenVertexArrays(1, out VAO1);
        GL.BindVertexArray(VAO1);
        GL.GenVertexArrays(1, out VAO2);
        GL.BindVertexArray(VAO2);

        // Object 1 vertex positions
        GL.GenBuffers(1, out object1_vertex_buffer);
        GL.BindBuffer(BufferTarget.ArrayBuffer, object1_vertex_buffer);
        GL.BufferData(BufferTarget.ArrayBuffer, object1_vertices.Length * sizeof(float), object1_vertices,BufferUsageHint.StaticDraw);
        GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
        // Object 1 vertex indices
        GL.GenBuffers(1, out object1_index_buffer);
        GL.BindBuffer(BufferTarget.ElementArrayBuffer, object1_index_buffer);
        GL.BufferData(BufferTarget.ElementArrayBuffer, object1_indices.Length * sizeof(int), object1_indices, BufferUsageHint.StaticDraw);

        GL.BindVertexArray(VAO2);
        // Object 2 vertex positions
        GL.GenBuffers(1, out object2_vertex_buffer);
        GL.BindBuffer(BufferTarget.ArrayBuffer, object2_vertex_buffer);
        GL.BufferData(BufferTarget.ArrayBuffer, object2_vertices.Length * sizeof(float), object2_vertices, BufferUsageHint.StaticDraw);
        GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
        // Object 2 vertex indices
        GL.GenBuffers(1, out object2_index_buffer);
        GL.BindBuffer(BufferTarget.ElementArrayBuffer, object2_index_buffer);
        GL.BufferData(BufferTarget.ElementArrayBuffer, object2_indices.Length*sizeof(int), object2_indices, BufferUsageHint.StaticDraw);

    }

我释放了分配的opengl资源（这与我的问题无关，现在甚至都没有调用嘿嘿）

    private void CleanupOpenGL() {
          // ...
    }

}

我已经复制了着色器代码：

class MyOpenglThings
{

    // A simple vertex shader possible. Just passes through the position vector.
    public const string VertexShaderSource = @"
        #version 330
        layout(location = 0) in vec4 position;
        void main(void)
        {
            gl_Position = position;
        }
    ";

    // A simple fragment shader. Just a constant red color.
    public const string FragmentShaderSource = @"
        #version 330
        out vec4 outputColor;
        void main(void)
        {
            outputColor = vec4(1.0, 0.0, 0.0, 1.0);
        }
    ";
}

但是当我启动一个程序时，我只得到一个 window 充满天蓝色的。至少，opengl 能够渲染背景颜色。但我也想得到两个红色三角形。

里面有什么问题吗？如何在顶点数组对象中渲染两个网格？

Answer 1

当您定义一个通用顶点属性数据数组时（GL.VertexAttribPointer), the Vertex array object 必须绑定存储定义的数组。
VAO2 的规范是这样，但 VAO1 的规范不是这样，因为在

之后

GL.GenVertexArrays(1, out VAO1);
GL.BindVertexArray(VAO1);
GL.GenVertexArrays(1, out VAO2);
GL.BindVertexArray(VAO2);

顶点数组对象VAO2已绑定。

此外，通用顶点属性数组必须由 GL.EnableVertexAttribArray 启用。启用或禁用顶点数组的状态也存储在顶点数组对象中：

GL.GenVertexArrays(1, out VAO1);
GL.BindVertexArray(VAO1);

// Object 1 vertex positions
GL.GenBuffers(1, out object1_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object1_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object1_vertices.Length * sizeof(float), object1_vertices,BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
GL.EnableVertexAttribArray(0);
// [...]

GL.GenVertexArrays(1, out VAO2);
GL.BindVertexArray(VAO2);

// Object 2 vertex positions
GL.GenBuffers(1, out object2_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object2_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object2_vertices.Length * sizeof(float), object2_vertices, BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
GL.EnableVertexAttribArray(0);
// [...]

Answer 2

上面的回答真的很有帮助。（我在这里发帖，因为评论不适合代码。）所以，我的加载代码现在看起来像：

        private void glControl1_Load(object sender, EventArgs e) {
        loaded = true;
        GL.ClearColor(Color.SkyBlue);
        GL.Enable(EnableCap.DepthTest);
        GL.DepthFunc(DepthFunction.Less);

        // Load the source of the vertex shader and compile it.
            // ....
        // Load the source of the fragment shader and compile it.
            // ....
        // Create the shader program, attach the vertex and fragment shaders and link the program.
            // ....
        GL.GenVertexArrays(1, out VAO1);
        GL.BindVertexArray(VAO1);

        // Object 1 vertex positions
        GL.GenBuffers(1, out object1_vertex_buffer);
        GL.BindBuffer(BufferTarget.ArrayBuffer, object1_vertex_buffer);
        GL.BufferData(BufferTarget.ArrayBuffer, object1_vertices.Length * sizeof(float), object1_vertices,BufferUsageHint.StaticDraw);
        GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
        GL.EnableVertexAttribArray(0);
        // Object 1 vertex indices
        GL.GenBuffers(1, out object1_index_buffer);
        GL.BindBuffer(BufferTarget.ElementArrayBuffer, object1_index_buffer);
        GL.BufferData(BufferTarget.ElementArrayBuffer, object1_indices.Length * sizeof(int), object1_indices, BufferUsageHint.StaticDraw);

        GL.GenVertexArrays(1, out VAO2);
        GL.BindVertexArray(VAO2);
        // Object 2 vertex positions
        GL.GenBuffers(1, out object2_vertex_buffer);
        GL.BindBuffer(BufferTarget.ArrayBuffer, object2_vertex_buffer);
        GL.BufferData(BufferTarget.ArrayBuffer, object2_vertices.Length * sizeof(float), object2_vertices, BufferUsageHint.StaticDraw);
        GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
        GL.EnableVertexAttribArray(0);
        // Object 2 vertex indices
        GL.GenBuffers(1, out object2_index_buffer);
        GL.BindBuffer(BufferTarget.ElementArrayBuffer, object2_index_buffer);
        GL.BufferData(BufferTarget.ElementArrayBuffer, object2_indices.Length*sizeof(int), object2_indices, BufferUsageHint.StaticDraw);

    }

GL.EnableVertexAttribArray 的参数应与着色器程序中的值匹配。

还更改了一点几何坐标，因为三角形曾经重叠。

如何在单独的 opengl 数组对象中正确渲染网格？

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