OpenGL - 无法获取顶点阵列对象和顶点缓冲区对象绘制

Question

我在MacOSX 10.10上使用OpenGL和SDL2。我一直在尝试在现代OpenGL中使用VAO和VBO，但我无法让它们绘制。我的着色器非常简单，但根据我一直试图遵循的教程，他们应该工作。我没有收到任何错误，但仍然无法正常工作。我收到的只是一个完全黑色的窗口。如果有人能够帮助我了解我的问题在哪里以及如何解决问题，我将不胜感激。我希望我不重复先前的问题，但是我已经搜索和搜索，没有找到任何解决这个问题的方法。这里是我的代码：

vertexShader.glsl：

#version 330 core 

layout(location = 0) in vec3 vertexPosition_modelspace; 

void main(){ 
    gl_Position.xyz = vertexPosition_modelspace; 
    gl_Position.w = 1.0; 
} 

fragmentShader.glsl

#version 330 core 

out vec4 color; 

void main(){ 
    color = vec4(1.0, 1.0, 0.0, 1.0); 
} 

这里是我的加载着色器代码，里面有工作，没有提供任何错误：

//Note: PXConsole is a util class for printing to the console. 
GLuint loadShaders(std::string vertexPath, std::string fragmentPath){ 

const char* vertexShaderPath = vertexPath.c_str(); 
const char* fragmentShaderPath = fragmentPath.c_str(); 
// Create the shaders 
GLuint VertexShaderID = glCreateShader(GL_VERTEX_SHADER); 
GLuint FragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER); 

// Read the Vertex Shader code from the file 
std::string VertexShaderCode; 
std::ifstream VertexShaderStream(vertexShaderPath, std::ios::in); 
if(VertexShaderStream.is_open()){ 
    std::string Line = ""; 
    while(getline(VertexShaderStream, Line)) 
     VertexShaderCode += "\n" + Line; 
    VertexShaderStream.close(); 
}else{ 
    std::string error ="Could not open vertex shader at \"" + vertexPath +"\". Is the the path written correctly? "; 
    PXConsole::err(error); 
    return 0; 
} 

// Read the Fragment Shader code from the file 
std::string FragmentShaderCode; 
std::ifstream FragmentShaderStream(fragmentShaderPath, std::ios::in); 
if(FragmentShaderStream.is_open()){ 
    std::string Line = ""; 
    while(getline(FragmentShaderStream, Line)) 
     FragmentShaderCode += "\n" + Line; 
    FragmentShaderStream.close(); 
}else{ 
    std::string error ="Could not open fragment shader at \"" + fragmentPath +"\". Is the the path written correctly? "; 
    PXConsole::err(error); 
    return 0; 
} 

GLint Result = GL_FALSE; 
int InfoLogLength; 


// Compile Vertex Shader 
PXConsole::info("Compiling Vertex Shader at: " + vertexPath); 
char const * VertexSourcePointer = VertexShaderCode.c_str(); 
glShaderSource(VertexShaderID, 1, &VertexSourcePointer , NULL); 
glCompileShader(VertexShaderID); 

// Check Vertex Shader 
glGetShaderiv(VertexShaderID, GL_COMPILE_STATUS, &Result); 
glGetShaderiv(VertexShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength); 
if (InfoLogLength > 0){ 
    std::vector<char> VertexShaderErrorMessage(InfoLogLength+1); 
    glGetShaderInfoLog(VertexShaderID, InfoLogLength, NULL, &VertexShaderErrorMessage[0]); 
    PXConsole::err(&VertexShaderErrorMessage[0]); 
} 



// Compile Fragment Shader 
PXConsole::info("Compiling Fragment Shader at: " + fragmentPath); 
char const * FragmentSourcePointer = FragmentShaderCode.c_str(); 
glShaderSource(FragmentShaderID, 1, &FragmentSourcePointer , NULL); 
glCompileShader(FragmentShaderID); 

// Check Fragment Shader 
glGetShaderiv(FragmentShaderID, GL_COMPILE_STATUS, &Result); 
glGetShaderiv(FragmentShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength); 
if (InfoLogLength > 0){ 
    std::vector<char> FragmentShaderErrorMessage(InfoLogLength+1); 
    glGetShaderInfoLog(FragmentShaderID, InfoLogLength, NULL, &FragmentShaderErrorMessage[0]); 
    PXConsole::err(&FragmentShaderErrorMessage[0]); 
} 



// Link the program 
PXConsole::info("Linking Shader Program!"); 
GLuint ProgramID = glCreateProgram(); 
glAttachShader(ProgramID, VertexShaderID); 
glAttachShader(ProgramID, FragmentShaderID); 
glLinkProgram(ProgramID); 

// Check the program 
glGetProgramiv(ProgramID, GL_LINK_STATUS, &Result); 
glGetProgramiv(ProgramID, GL_INFO_LOG_LENGTH, &InfoLogLength); 
if (InfoLogLength > 0){ 
    std::vector<char> ProgramErrorMessage(InfoLogLength+1); 
    glGetProgramInfoLog(ProgramID, InfoLogLength, NULL, &ProgramErrorMessage[0]); 
    PXConsole::err(&ProgramErrorMessage[0]); 
} 


glDetachShader(ProgramID, VertexShaderID); 
glDetachShader(ProgramID, FragmentShaderID); 

glDeleteShader(VertexShaderID); 
glDeleteShader(FragmentShaderID); 

return ProgramID; 

这是我用SDL2创建的OpenGL上下文：

SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3); 
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3); 
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE); 
SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG); 
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1); 
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24); 

appWindow = SDL_CreateWindow("Window Title", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1280, 720, SDL_WINDOW_OPENGL); 

if (!application->appWindow) { 
    PXConsole::err("Couldn't Initialize Window!!"); 
    endApp(); 
} 

appGLContext = SDL_GL_CreateContext(appWindow); 

而且最后这里是我的渲染功能，这是一个循环：

void render(){  

    GLuint vaoID; 
    GLuint posVBO; 

    GLfloat positions[] = {-0.5f, -0.5f, 1.0f, 
     0.5f, -0.5f, 1.0f, 
     0.5f, 0.5f, 1.0f, 
     -0.5f, 0.5f, 1.0f}; 


    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 

    //shaderProgramID = the function mentioned above in an initializating function and has no errors finding the shader files 

    glUseProgram(shaderProgramID); 

    glColor4f(1.0, 1.0, 0.0, 1.0); 

    glGenVertexArrays(1, &vaoID); 
    glBindVertexArray(vaoID); 

    glGenBuffers(1, &posVBO); 
    glBindBuffer(GL_ARRAY_BUFFER, posVBO); 
    glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW); 

    glEnableVertexAttribArray(0); 

    glBindBuffer(GL_ARRAY_BUFFER, posVBO); 
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0); 
    glColor4f(1.0, 0.0, 0.0, 1.0); 
    glDrawArrays(GL_QUADS, 0, 4); 
    glDisableVertexAttribArray(0); 

    SDL_GL_SwapWindow(appWindow); 
} 

我希望这是足够的代码，以便能够确定问题。谢谢你的帮助！

Answer 1

一个VAO基本上存储由glVertexAttribPointer设置的属性绑定。为了存储它们，必须在VAO绑定时设置它们。就你而言，你首先解除绑定，然后设置属性绑定。

此外，一个应该永不在每个帧中生成缓冲区或vaos。这是在初始化期间必须完成的事情。

既然你在问题中说你没有得到任何错误：每帧至少有三个。你如何检查错误？

• glColor4f已从OpenGL 3.3 Core Profile中移除。调用此应该会导致错误。 （2x）
• GL_QUADS在核心配置文件中不是有效的drawing mode，还应该生成错误。

一个修正版本可能看起来像这样

初始化

glGenVertexArrays(1, &vaoID); 
glBindVertexArray(vaoID); 

glGenBuffers(1, &posVBO); 
glBindBuffer(GL_ARRAY_BUFFER, posVBO); 
glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW); 
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0); 

glEnableVertexAttribArray(0); 

渲染

glBindVertexArray(vaoID); 
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); 

更新

当您想在每个帧中使用新的坐标时，仍然会生成缓冲区并在初始化中设置VAO。你在每一帧做的是新的数据上传到像这样的缓冲区（假设顶点的数量保持不变）：

glBindBuffer(GL_ARRAY_BUFFER, posVBO); 
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(positions), positions); 

这将覆盖缓冲区的数据，而无需分配新的GPU内存。请注意，您必须在初始化时使用正确大小调用glBufferData一次，但使用nullptr作为数据指针来为缓冲区分配内存。