OpenGL程序无法绘制三角形？

Question

我将 OpenGL 与 GLEW 和 GLFW 一起使用。我创建了两个着色器，它们编译得很好：

#include <iostream>
#include <GL/glew.h>
#include <OpenGL/OpenGL.h>
#include <GLFW/glfw3.h>

static unsigned int CompileShader( unsigned int type, const std::string source){
    unsigned int id = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);
    
    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE){
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout <<"failed to compile " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader" <<"\n";
        std::cout << message << "\n";
        glDeleteShader(id);
        return 0;
    }
    return id;
}

static int CreateShader(const std::string& VertexShader, const std::string& FragmentShader){
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, VertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, FragmentShader);
    
    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);
    
    glDeleteShader(vs);
    glDeleteShader(fs);
    
    return program;
}

int main(void){
    /* Initialize the library */
    GLFWwindow* window;

    if (!glfwInit()){return -1;}
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
  #ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
  #endif

  /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Gaston", NULL, NULL);
    if (!window){
        glfwTerminate();
        return -1;
    }
    
    /* Make the window's context current */
    glfwMakeContextCurrent(window);
   
    if (glewInit() != GLEW_OK){ std::cout <<"glewunit(); failed\n"; }
    
    float positions[6] = {
        -0.5f, -0.5f,
        -.9f, .5f,
        0.5f, 0.5f
    };
    
    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(positions) * sizeof(float), positions, GL_STATIC_DRAW);
        
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float)*2, 0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

    std::string vertexshader =
    "#version 330 core\n"
     "\n"
     "layout(location = 0) in vec4 position;\n"
     "\n"
     "void main()\n"
     "{\n"
     "   gl_Position = position;\n"
     "}\n";

    std::string fragmentshader =
    "#version 330 core\n"
    "\n"
    "layout(location = 0) out vec4 colour;\n"
    "\n"
    "void main()\n"
    "{\n"
    "   colour = vec4(1.0, 0.0, 0.0, 1.0);\n"
    "}\n";
    unsigned int shader = CreateShader(vertexshader, fragmentshader);
    glUseProgram(shader);
    
    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window)){
           /* Render here */
        
        glClear(GL_COLOR_BUFFER_BIT);
        glDrawArrays(GL_TRIANGLES, 0, 3);
           /* Swap front and back buffers */
           glfwSwapBuffers(window);

           /* Poll for and process events */
           glfwPollEvents();
       
       }

    glfwTerminate();
    return 0;
}

...但是三角形没有出现。我得到的只是一个空白屏幕。

理想的结果是红色三角形。

Answer 1

一些事情：

• 作为@G.M.指出您需要绑定和填充顶点数组对象（VAO）（使用 VBO 绑定和顶点属性启用）才能在 Core 上下文中渲染事物。 例如：

  GLuint vao = 0;
  glCreateVertexArrays(1, &vao);
  glBindVertexArray(vao);
  

• 着色器链接也可能失败，请务必通过

  glGetProgramiv()

  & co.
  检查这一点

• 调试上下文和调试消息回调将显示

  glDrawArrays()

  调用抛出

  GL_INVALID_OPERATION

  :

  if( glewIsSupported( "GL_ARB_debug_output" ) )
  {
      glEnable( GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB );
      glDebugMessageControlARB( GL_DONT_CARE, GL_DONT_CARE, GL_DONT_CARE, 0, NULL, GL_TRUE );
      glDebugMessageCallbackARB( []( GLenum, GLenum, GLuint,  GLenum, GLsizei, const GLchar* message, const void* )
      {
          std::cerr << "GL: " << message << std::endl;
      }, 0 );
  }
  

  输出：

  GL: GL_INVALID_OPERATION in glDrawArrays
  

大家一起：

// g++ main.cpp $(pkg-config --cflags --libs glew glfw3)
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>

void CheckStatus( GLuint obj, bool isShader )
{
    GLint status = GL_FALSE, log[ 1 << 11 ] = { 0 };
    ( isShader ? glGetShaderiv : glGetProgramiv )(
        obj, isShader ? GL_COMPILE_STATUS : GL_LINK_STATUS, &status );
    if( status == GL_TRUE )
        return;
    ( isShader ? glGetShaderInfoLog : glGetProgramInfoLog )(
        obj, sizeof( log ), NULL, (GLchar*)log );
    std::cerr << (GLchar*)log << "\n";
    std::exit( EXIT_FAILURE );
}

void AttachShader( GLuint program, GLenum type, const char* src )
{
    GLuint shader = glCreateShader( type );
    glShaderSource( shader, 1, &src, NULL );
    glCompileShader( shader );
    CheckStatus( shader, true );
    glAttachShader( program, shader );
    glDeleteShader( shader );
}

const char* const vert = R"GLSL(
#version 330 core
layout( location = 0 ) in vec4 position;
void main()
{
    gl_Position = position;
};
)GLSL";

const char* const frag = R"GLSL(
#version 330 core
layout(location = 0) out vec4 colour;
void main()
{
    colour = vec4( 1.0, 0.0, 0.0, 1.0 );
};
)GLSL";

int main( void )
{
    /* Initialize the library */
    glfwSetErrorCallback(
        []( int, const char* desc )
        {
            std::cerr << desc << "\n";
            std::exit( EXIT_FAILURE );
        } );
    if( !glfwInit() )
    {
        return -1;
    }

    glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3 );
    glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
    glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE );
#ifdef __APPLE__
    glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE );
#endif
    glfwWindowHint( GLFW_OPENGL_DEBUG_CONTEXT, GL_TRUE );

    /* Create a windowed mode window and its OpenGL context */
    GLFWwindow* window = glfwCreateWindow( 640, 480, "Gaston", NULL, NULL );
    if( !window )
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent( window );

    if( glewInit() != GLEW_OK )
    {
        std::cout << "glewunit(); failed\n";
    }

    if( glewIsSupported( "GL_ARB_debug_output" ) )
    {
        glEnable( GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB );
        glDebugMessageControlARB( GL_DONT_CARE, GL_DONT_CARE, GL_DONT_CARE, 0, NULL, GL_TRUE );
        glDebugMessageCallbackARB( []( GLenum, GLenum, GLuint,  GLenum, GLsizei, const GLchar* message, const void* )
        {
            std::cerr << "GL: " << message << std::endl;
        }, 0 );
    }

    float positions[ 6 ] = { -0.5f, -0.5f, -.9f, .5f, 0.5f, 0.5f };

    GLuint vao = 0;
    glCreateVertexArrays(1, &vao);
    glBindVertexArray(vao);

    unsigned int buffer;
    glGenBuffers( 1, &buffer );
    glBindBuffer( GL_ARRAY_BUFFER, buffer );
    glBufferData(
        GL_ARRAY_BUFFER,
        sizeof( positions ) * sizeof( float ),
        positions,
        GL_STATIC_DRAW );

    glEnableVertexAttribArray( 0 );
    glVertexAttribPointer( 0, 2, GL_FLOAT, GL_FALSE, sizeof( float ) * 2, 0 );

    glBindBuffer( GL_ARRAY_BUFFER, 0 );

    GLuint prog = glCreateProgram();
    AttachShader( prog, GL_VERTEX_SHADER, vert );
    AttachShader( prog, GL_FRAGMENT_SHADER, frag );
    glLinkProgram( prog );
    CheckStatus( prog, false );
    glUseProgram( prog );

    /* Loop until the user closes the window */
    while( !glfwWindowShouldClose( window ) )
    {
        /* Render here */
        glClear( GL_COLOR_BUFFER_BIT );
        glDrawArrays( GL_TRIANGLES, 0, 3 );

        /* Swap front and back buffers */
        glfwSwapBuffers( window );

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}