永远不会调用OpenTK GL.DrawElements

Question

我找到了这个C ++代码here。它绘制简单的矩形。效果很好。

#define GLEW_STATIC

#include <iostream>
#include <glew.h>
#include <freeglut.h>

const GLchar* vertexSource =
"#version 150 core\n"
"in vec2 position;"
"in vec3 color;"
"out vec3 Color;"
"void main() {"
"   Color = color;"
"   gl_Position = vec4(position, 0.0, 1.0);"
"}";
const GLchar* fragmentSource =
"#version 150 core\n"
"in vec3 Color;"
"out vec4 outColor;"
"void main() {"
"   outColor = vec4(Color, 1.0);"
"}";

void Display()
{
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

    glFlush();

    glutSwapBuffers();
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_MULTISAMPLE);
    glutInitWindowSize(800, 600);
    glutInitContextVersion(4, 4);
    glutInitContextProfile(GLUT_CORE_PROFILE);
    glutCreateWindow("OpenGL");
    glewExperimental = GL_TRUE;

    if (GLEW_OK != glewInit())
        exit(1);

    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    GLuint vbo;
    glGenBuffers(1, &vbo);

    GLfloat vertices[] = {
        -0.5f, 0.5f, 1.0f, 0.0f, 0.0f, // Top-left
        0.5f, 0.5f, 0.0f, 1.0f, 0.0f, // Top-right
        0.5f, -0.5f, 0.0f, 0.0f, 1.0f, // Bottom-right
        -0.5f, -0.5f, 1.0f, 1.0f, 1.0f  // Bottom-left
    };

    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    GLuint ebo;
    glGenBuffers(1, &ebo);

    GLuint elements[] = {
        0, 1, 2,
        2, 3, 0
    };

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW);

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexSource, NULL);
    glCompileShader(vertexShader);

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
    glCompileShader(fragmentShader);

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glBindFragDataLocation(shaderProgram, 0, "outColor");
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

    GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), 0);

    GLint colAttrib = glGetAttribLocation(shaderProgram, "color");
    glEnableVertexAttribArray(colAttrib);
    glVertexAttribPointer(colAttrib, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (void*)(2 * sizeof(GLfloat)));

    glutDisplayFunc(Display);
    glutMainLoop();

    glDeleteProgram(shaderProgram);
    glDeleteShader(fragmentShader);
    glDeleteShader(vertexShader);

    glDeleteBuffers(1, &ebo);
    glDeleteBuffers(1, &vbo);

    glDeleteVertexArrays(1, &vao);
}

所以我决定用OpenTK框架在C＃上重写它：

using OpenTK;
using OpenTK.Graphics.OpenGL;
using System;
using System.IO;

namespace OpenTKTest
{
    public class Game : GameWindow
    {
        private Int32 vao;
        private Int32 vbo;
        private Int32 ebo;
        private Int32 vertexShader;
        private Int32 fragmentShader;
        private Int32 shaderProgram;

        public Game() : base()
        {
        }

        [STAThread]
        public static void Main()
        {
            var window = new Game();
            window.Run(120, 120);
            window.Dispose();
        }

        protected override void OnLoad(EventArgs e)
        {
            GL.GenVertexArrays(1, out vao);
            GL.BindVertexArray(vao);

            GL.GenBuffers(1, out vbo);
            var vertices = new Single[]
            {
                -0.5f,  0.5f, 1.0f, 0.0f, 0.0f, // Top-left
                 0.5f,  0.5f, 0.0f, 1.0f, 0.0f, // Top-right
                 0.5f, -0.5f, 0.0f, 0.0f, 1.0f, // Bottom-right
                -0.5f, -0.5f, 1.0f, 1.0f, 1.0f  // Bottom-left
            };
            GL.BindBuffer(BufferTarget.ArrayBuffer, vbo);
            GL.BufferData(BufferTarget.ArrayBuffer, new IntPtr(sizeof(Single) * vertices.Length), vertices, BufferUsageHint.StaticDraw);


            GL.GenBuffers(1, out ebo);
            var elements = new Single[]
            {
                0, 1, 2,
                2, 3, 0
            };
            GL.BindBuffer(BufferTarget.ElementArrayBuffer, ebo);
            GL.BufferData(BufferTarget.ElementArrayBuffer, new IntPtr(sizeof(UInt32) * elements.Length), elements, BufferUsageHint.StaticDraw);


            vertexShader = GL.CreateShader(ShaderType.VertexShader);
            GL.ShaderSource(vertexShader, File.ReadAllText("vs.glsl"));
            GL.CompileShader(vertexShader);
            Console.WriteLine(GL.GetShaderInfoLog(vertexShader));


            fragmentShader = GL.CreateShader(ShaderType.FragmentShader);
            GL.ShaderSource(fragmentShader, File.ReadAllText("fs.glsl"));
            GL.CompileShader(fragmentShader);
            Console.WriteLine(GL.GetShaderInfoLog(fragmentShader));

            shaderProgram = GL.CreateProgram();

            GL.AttachShader(shaderProgram, vertexShader);
            GL.AttachShader(shaderProgram, fragmentShader);
            GL.BindFragDataLocation(shaderProgram, 0, "outColor");
            GL.LinkProgram(shaderProgram);
            GL.UseProgram(shaderProgram);

            var posAttrib = GL.GetAttribLocation(shaderProgram, "position");
            GL.EnableVertexAttribArray(posAttrib);
            GL.VertexAttribPointer(posAttrib, 2, VertexAttribPointerType.Float, false, 5 * sizeof(Single), IntPtr.Zero);

            var colAttrib = GL.GetAttribLocation(shaderProgram, "color");
            GL.EnableVertexAttribArray(colAttrib);
            GL.VertexAttribPointer(colAttrib, 3, VertexAttribPointerType.Float, false, 5 * sizeof(Single), new IntPtr(2 * sizeof(Single)));

            GL.Viewport(0, 0, Width, Height);
        }

        protected override void OnRenderFrame(FrameEventArgs e)
        {
            GL.ClearColor(0.0f, 0.0f, 0.0f, 1.0f);
            GL.Clear(ClearBufferMask.ColorBufferBit);
            GL.DrawElements(PrimitiveType.Triangles, 6, DrawElementsType.UnsignedInt, IntPtr.Zero);
            GL.Flush();
            SwapBuffers();
        }

        protected override void OnClosing(System.ComponentModel.CancelEventArgs e)
        {
            GL.DeleteProgram(shaderProgram);
            GL.DeleteShader(fragmentShader);
            GL.DeleteShader(vertexShader);

            GL.DeleteBuffers(1, ref ebo);
            GL.DeleteBuffers(1, ref vbo);

            GL.DeleteVertexArrays(1, ref vao);
        }
    }
}

顶点着色器：

#version 150 core
in vec2 position;
in vec3 color;
out vec3 Color;
void main()
{
    Color = color;
    gl_Position = vec4(position, 0.0, 1.0);
}

片段着色器：

#version 150 core
in vec3 Color;
out vec4 outColor;
void main()
{
    outColor = vec4(Color, 1.0);
}

两个来源几乎相同。但是在C＃版本GL.DrawElements中，函数永远不会被调用（我在使用gremedy中的gDEBugger进行调试时发现了它。 为什么这段代码在OpenTK中不起作用？