当我尝试从 vbo 获取颜色时，glDrawElements 没有输出

Question

我是 OpenGL 的新手，正在尝试扩展我当前的代码，该代码使用作为统一变量提供的颜色来显示正方形，而该代码将根据 vbo 中给定的颜色显示正方形。

int main(int argc, char **argv)
{
    //! The pointer to the GLFW window
    GLFWwindow *window;

    //! Initialize GLFW
    if (!glfwInit())
        return -1;

    glfwWindowHint(GLFW_SAMPLES, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 4);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    window = glfwCreateWindow(512, 512, "Testing COde", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    glewExperimental = GL_TRUE;
    GLenum err = glewInit();
    if (GLEW_OK != err)
    {
        std::cerr << "GLEW Init Failed : %s" << std::endl;
    }

    std::cout << "Vendor: " << glGetString(GL_VENDOR) << std::endl;
    std::cout << "Renderer: " << glGetString(GL_RENDERER) << std::endl;
    std::cout << "Version: " << glGetString(GL_VERSION) << std::endl;
    std::cout << "GLSL Version: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << std::endl;

    // Ensure we can capture the escape key being pressed below
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

    // Format (x,y,r,g,b,a)
    float position[] = {
        -0.5f ,  0.5f,  1.0f ,  0.0f,  1.0f, 1.0f,
        -0.5f , -0.5f,  0.0f ,  1.0f,  1.0f, 1.0f,
         0.5f , -0.5f,  1.0f ,  1.0f,  0.0f, 1.0f,
         0.5f ,  0.5f,  1.0f ,  1.0f,  1.0f, 1.0f
    };     

    uint indeces[] = {
        0, 1, 2,
        0, 2, 3
    };

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

    GLuint buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 4 * 6 * sizeof(float), position, GL_STATIC_DRAW);
    
    GLuint ibo;
    glGenBuffers(1, &ibo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, 3 * 2 * sizeof(uint), indeces, GL_STATIC_DRAW);

    struct shaderbundle* str_shader = parseShader("res/shaders/vertexshader.glsl","res/shaders/fragmentshader.glsl");

    uint shader = CreateShader(str_shader->vertex, str_shader->fragment);
    glUseProgram(shader);

    uint vPosition = glGetAttribLocation( shader, "position" );
    glEnableVertexAttribArray(vPosition);
    glVertexAttribPointer(vPosition, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 6, (GLvoid*)(0));

    uint inColor = glGetAttribLocation( shader, "in_color" );
    if (inColor != -1) {
        glEnableVertexAttribArray(inColor);
        glVertexAttribPointer(inColor  , 4, GL_FLOAT, GL_FALSE, sizeof(float) * 6, (GLvoid*)(2*sizeof(float)));
    }
    else {
        "no color recieved";
    }

    uint u_color = glGetUniformLocation( shader, "u_color" );
    if (u_color != -1) {
        glUniform4f(u_color,1.0f, 0.4f, 0.6f ,1.0f);
    }
    else {
        "no color recieved";
    }
    
    while (glfwWindowShouldClose(window) == 0)
    {
        glClear(GL_COLOR_BUFFER_BIT);

        // glDrawArrays(GL_TRIANGLES, 0, 3 * 2);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

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

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

    glDeleteProgram(shader);

    glfwTerminate();
    return 0;
}

为此，我使用了以下片段着色器：

#version 330 core
out vec4 color;
uniform vec4 u_color;
in  vec4 in_color;
void main() {
    // color = in_color;
    color = u_color;
};

但是当我使用 in_color 而不是 u_color 时，屏幕上什么也没有显示。位置数组的内容采用格式（x 位置、y 位置、r 颜色、g 颜色、b 颜色、alpha）。因此，在 glGetVertexAttribPointer 中，我将步幅用作 6*sizeof(float)，偏移量为 0 位置和 2*float 颜色。我尝试使用 glGetError() 进行调试，但它没有 return 任何东西。请帮我找出我到底做错了什么。

Answer 1

您不能直接设置片段着色器输入。 in_color 需要是顶点着色器输入（属性）。将顶点着色器输入传递给片段着色器。例如：

顶点着色器

#version 330 core

layout(location = 0) in vec4 position;
layout(location = 1) in vec4 in_color;

out vec4 vert_color;

void main()
{
    vert_color  = in_color;
    gl_Position = position;
}

片段着色器

#version 330 core

out vec4 color;
in vec4 vert_color;

void main() 
{
    color = vert_color;
}

当我尝试从 vbo 获取颜色时，glDrawElements 没有输出

No output from glDrawElements when I try to take color from vbo

c++

opengl

shader

glsl

fragment-shader