颜色设置在碎片着色器中，未显示GLSL 1.30

Question

我正在学习OpenGl，我只是看到了如何编写着色器。但是第一个问题是，在本课程中，支持GLSL 3.30 （OpenGL 4），但是我的驱动程序（MESA）不允许我使用GLSL 1.30或ES 3.20的版本。因此，我更改了着色器中的#version预处理器，然后继续。但是，不幸的是，当我尝试使用颜色时，它无效。

这是我的代码：

#include "colors.h"
#include <iostream>
#include <fstream>
#include <regex>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
unsigned int CompileShader(unsigned int type, std::string& source);
unsigned int CreateShader(std::string& vertexShader, std::string& fragmentShader);
int main(int argc, char* argv[]) {
    GLFWwindow* window;
    /* Initialize the library */
    if (!glfwInit()) {
        std::cerr << "Couldn't initialize GLFW" << std::endl;
        exit(1);
    }
    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Hello World", nullptr, nullptr);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }
    /* Make the window's context current */
    glfwMakeContextCurrent(window);
    if(glewInit() != GLEW_OK) {
        std::cerr << "Couldn't initialize GLEW" << std::endl;
        exit(1);
    }
    float positions[6] = {
        -0.5f, -0.5f,
        0.0f, 0.5f,
        0.5f, -0.5f
    };
    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), 0);
    // Compiling Shader
    std::string vertexShader = "#version 130n"
                               "n"
                               "in vec4 position;n"
                               "n"
                               "void main () {n"
                               "    gl_Position = position;n"
                               "}";
    std::string fragmentShader = "#version 130n"
                                 "n"
                                 "uniform vec4 color = vec4(1.0, 0.0, 0.0, 1.0);n"
                                 "n"
                                 "out vec4 outputF;n"
                                 "n"
                                 "void main () {n"
                                 "    outputF = color;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;
}
unsigned int CompileShader(unsigned int type, 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::cerr << "Failed to compile "
                  << (type == GL_VERTEX_SHADER ? "vertex" : "fragment")
                  << " shader. Error message:" << std::endl;
        std::cerr << "t" << FG_ERROR << message << std::endl;
    }
    return id;
}
unsigned int CreateShader(std::string& vertexShader, 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, vs);
    glLinkProgram(program);
    glValidateProgram(program);
    glDeleteShader(vs);
    glDeleteShader(fs);
    return program;
}

Answer 1

我有一些时间来看看这个，发现您有一个小的复制糊错误：

unsigned int CreateShader(std::string& vertexShader, 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, vs); //<--should be fs

您两次连接顶点着色器。这将设置一个OpenGL错误，实际上我发现它是使用我通常使用的OpenGL调试方法的方式。当我更深入地测试您的代码时，我将所有OpenGL调用用Define包围，如果OpenGL设置错误，则停止执行。我将其放在来源的顶部，并建议使用以下内容：

#include <cstdlib>
#include <iostream>
#include <iomanip>
void CheckOpenGLError(const char *stmt, const char *fname, int line);
#define GL_CHECK(stmt)                               
    do                                               
    {                                                
        stmt;                                        
        CheckOpenGLError(#stmt, __FILE__, __LINE__); 
    } while (0)
void CheckOpenGLError(const char *stmt, const char *fname, int line)
{
    GLenum err = glGetError();
    if (err != GL_NO_ERROR)
    {
        std::cout << "OpenGL error 0x" << std::setfill('0') << std::setw(8) << std::hex << err << std::dec << ": " << gluErrorString(err) << ", at " << fname << ":" << line << " - for " << stmt << std::endl;
        abort();
    }
}

如果您希望以人类可读的形式打印出openGL错误，则需要在Glu库中链接到GluErrorString函数（linux上的glu32.lib或linux上的libglu.so），否则需要去查找错误代码。在这种情况下，我将您的电话包围着：

unsigned int CreateShader(std::string& vertexShader, std::string& fragmentShader) {
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);
    GL_CHECK(glAttachShader(program, vs));
    GL_CHECK(glAttachShader(program, vs)); //<--should be fs

当我运行代码时，它将此错误丢弃：

OpenGL error 0x00000502: invalid operation, at main.cpp:147 - for glAttachShader(program, vs)

---

也很少的音符，完成链接后，您可能应该分离着着色器：

https://gamedev.stackexchange.com/a/47912

unsigned int CreateShader(std::string& vertexShader, 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);
    glDetachShader(program, vs);
    glDetachShader(program, fs);
    glDeleteShader(vs);
    glDeleteShader(fs);
    return program;
}