片段着色器中设置的颜色未显示GLSL 1.30

Question

我正在学习OpenGL，我刚刚看到了如何编写着色器。但第一个问题是，在课程中，支持GLSL 3.30+（OpenGL 4），但我的驱动程序（mesa）不允许我使用GLSL 1.30或ES 3.20之上的版本。所以我在着色器中更改了#version预处理器，然后我继续说道。但是，不幸的是，当我尝试使用颜色时，它没有用。

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 130\n"
                               "\n"
                               "in vec4 position;\n"
                               "\n"
                               "void main () {\n"
                               "    gl_Position = position;\n"
                               "}";
    std::string fragmentShader = "#version 130\n"
                                 "\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

我有时间看一下这个，发现你有一个小的复制粘贴错误：

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

您正在连接顶点着色器两次。这将设置一个OpenGL错误，实际上我发现它的方式是我经常使用的OpenGL调试方法。当我更深入地测试你的代码时，我用一个定义来包围所有OpenGL调用，如果OpenGL设置了错误，它会停止执行。我把它放在源代码的顶部并建议使用它：

#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();
    }
}

如果你想要以人类可读的形式打印出OpenGL错误，你需要另外链接glu库（windows上的glu32.lib或linux上的libGLU.so）中的gluErrorString函数，否则你需要查找错误代码。在这种情况下，我像这样包围你的电话：

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

然后在运行代码时抛出此错误：

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

---

另外一个小注意事项，您应该在完成链接后分离着色器：

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;
}