多个对象无法渲染？

Posted 2023-02-22

【中文标题】多个对象无法渲染？

【英文标题】：Multiple objects fail to render?

【发布时间】：2020-06-01 21:18:16

【问题描述】：

我应该在屏幕上显示两个方块，但是当我运行它时，我看到的只是一个虚无的屏幕。

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>




struct Shaderprogramsource

std::string VertexSouce;
std::string FragmentSource;
;

static Shaderprogramsource Parseshader(const std::string& filepath)

std::ifstream stream(filepath);

enum class Shadertype

    VERTEX = 0,
    FRAGMENT = 1,
    NONE = 5
;

std::string line;
std::stringstream ss[3];

Shadertype type = Shadertype::NONE;

while (getline(stream, line))

    if (line.find("#shader") != std::string::npos)
    
        if (line.find("vertex") != std::string::npos)
            type = Shadertype::VERTEX;

        else if (line.find("fragment") != std::string::npos)
            type = Shadertype::FRAGMENT;
    
    else
    
        ss[(int)type] << line << "\n";
    


return Shaderprogramsource ss[0].str(), ss[1].str() ;


static 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 << message;

    return 0;


return id;


static unsigned int CreateShader(
const std::string& Vertexshader,
const std::string& Fragmentshader)

unsigned int program = glCreateProgram();
unsigned int vertex = CompileShader(GL_VERTEX_SHADER, Vertexshader);
unsigned int fragment = CompileShader(GL_FRAGMENT_SHADER, Fragmentshader);

glAttachShader(program, vertex);
glAttachShader(program, fragment);

glLinkProgram(program);
glValidateProgram(program);

return program;


int main(void)

GLFWwindow* window;

/* Initialize the library */
if (!glfwInit())
    return -1;

glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);






/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(800, 800, "Hello World", NULL, NULL);
if (!window)

    glfwTerminate();
    return -1;


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

if (GLEW_OK == glewInit())



float vertices[] =  -0.1, -0.1,
                      0.1, -0.1, 
                      0.1, 0.1, 
                     -0.1, 0.1 ;



float vertices2[] =  -0.1,0.1,
                      0.1, 0.1,
                      0.1, 0.3,
                     -0.1, 0.3 ;


unsigned int indices[] = 

    0, 1, 2,
    2, 3, 0


;

unsigned int vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

unsigned int vao2;
glGenVertexArrays(1, &vao2);
glBindVertexArray(vao2);


unsigned int buffer1;

unsigned int vbo;

glGenBuffers(1, &buffer1);
glBindBuffer(GL_ARRAY_BUFFER, buffer1);
glBufferData(GL_ARRAY_BUFFER, 4 * 2 * sizeof(float), vertices, GL_STATIC_DRAW);

glEnableVertexAttribArray(0);

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

glEnableVertexAttribArray(1);

glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);



glGenBuffers(1, &vbo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(unsigned int), indices, GL_STATIC_DRAW);





Shaderprogramsource source = Parseshader("res/shaders/Basic.Shader");

unsigned int shader =
    CreateShader(source.VertexSouce, source.FragmentSource);




glUseProgram(shader);


int location = glGetUniformLocation(shader, "Color_u");
if (location > -1) 
    glUniform4f(location, 0.8f, 0.0f, 0.0f, 1.0f);





std::cout << source.VertexSouce;

glUseProgram(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))

    /* Render here */

    glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(shader);
    glBindBuffer(GL_ARRAY_BUFFER, vao);
    glBindBuffer(GL_ARRAY_BUFFER, vao2);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo);


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

    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);

    glEnableVertexAttribArray(0);

    glEnableVertexAttribArray(1);

    glUseProgram(shader);
    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;

着色器：

#shader vertex
#version 330 core

layout(location = 0) in vec3 position;



void main()

gl_Position = vec4(position.x, position.y, position.z, 1.0);
;

#shader fragment
#version 330 core

layout(location = 0) out vec4 color;

uniform vec4 Color_u;

void main()

color = Color_u;
;

【参考方案1】：

各种各样的笨蛋：

如果第一行以魔法 #shader 指令以外的任何内容开头，Parseshader() 将被破坏，因为 NONE 设置为 5 并且 ss[(int)type] 索引 + 赋值将直接从 3 元素 @987654327 的末尾走开@ 大批。将NONE 下拉至2。 您的着色器中只有一个顶点属性 (0)，但您正在尝试设置 1。

这不是 VAO 的工作方式根本。 VAO从未成为glBindBuffer() 的有效参数。 Intead，绑定一个 VAO，然后设置您的顶点属性绑定/布局：

unsigned int vao1 = 0;
glGenVertexArrays(1, &vao1);
glBindVertexArray(vao1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
glBindBuffer(GL_ARRAY_BUFFER, buffer1);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
glEnableVertexAttribArray(0);

然后当您想绘制时，您可以重新绑定 VAO 并立即绘制，跳过所有 glBindBuffer()/glVertexAttribPointer()/glEnableVertexAttribArray() 设置。

大家一起：

// g++ -g main.cpp `pkg-config --cflags --libs glfw3 glew`
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <sstream>
#include <string>

const char* const shaderSource = R"GLSL(
#shader vertex
#version 330 core
layout(location = 0) in vec3 position;
void main()

    gl_Position = vec4(position.x, position.y, position.z, 1.0);
;

#shader fragment
#version 330 core
layout(location = 0) out vec4 color;
uniform vec4 Color_u;
void main()

    color = Color_u;
;
)GLSL";

struct Shaderprogramsource

    std::string VertexSouce;
    std::string FragmentSource;
;

static Shaderprogramsource Parseshader(const std::string& shaderString)

    std::stringstream stream( shaderString );

    enum class Shadertype
    
        VERTEX = 0,
        FRAGMENT = 1,
        NONE = 2
    ;

    std::string line;
    std::stringstream ss[3];

    Shadertype type = Shadertype::NONE;

    while( std::getline(stream, line) )
    
        if (line.find("#shader") != std::string::npos)
        
            if (line.find("vertex") != std::string::npos)
                type = Shadertype::VERTEX;

            else if (line.find("fragment") != std::string::npos)
                type = Shadertype::FRAGMENT;
        
        else
        
            ss[(int)type] << line << '\n';
        
    

    return Shaderprogramsource ss[0].str(), ss[1].str() ;
    

static 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 << message;

        return 0;
    

    return id;


static unsigned int CreateShader( const std::string& Vertexshader, const std::string& Fragmentshader )

    unsigned int program = glCreateProgram();
    unsigned int vertex = CompileShader(GL_VERTEX_SHADER, Vertexshader);
    unsigned int fragment = CompileShader(GL_FRAGMENT_SHADER, Fragmentshader);

    glAttachShader(program, vertex);
    glAttachShader(program, fragment);

    glLinkProgram(program);
    glValidateProgram(program);

    return program;


int main( int argc, char** argv )

    if (!glfwInit())
        return -1;

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    GLFWwindow* window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    
        glfwTerminate();
        return -1;
    

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

    if (GLEW_OK == glewInit())
    
    

    unsigned int buffer1;
    glGenBuffers(1, &buffer1);
    glBindBuffer(GL_ARRAY_BUFFER, buffer1);
    float vertices1[] =
    
        -0.1, -0.1,
        0.1, -0.1, 
        0.1, 0.1, 
        -0.1, 0.1,
    ;
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices1), vertices1, GL_STATIC_DRAW);

    unsigned int buffer2;
    glGenBuffers(1, &buffer2);
    glBindBuffer(GL_ARRAY_BUFFER, buffer2);
    float vertices2[] =
    
        -0.1, 0.1,
        0.1, 0.1,
        0.1, 0.3,
        -0.1, 0.3,
    ;
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices2), vertices2, GL_STATIC_DRAW);

    unsigned int ebo;
    glGenBuffers(1, &ebo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    unsigned int indices[] =
    
        0, 1, 2,
        2, 3, 0,
    ;
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    unsigned int vao1 = 0;
    glGenVertexArrays(1, &vao1);
    glBindVertexArray(vao1);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBindBuffer(GL_ARRAY_BUFFER, buffer1);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
    glEnableVertexAttribArray(0);

    unsigned int vao2 = 0;
    glGenVertexArrays(1, &vao2);
    glBindVertexArray(vao2);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBindBuffer(GL_ARRAY_BUFFER, buffer2);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
    glEnableVertexAttribArray(0);

    Shaderprogramsource source = Parseshader( shaderSource );
    unsigned int shader = CreateShader(source.VertexSouce, source.FragmentSource);
    glUseProgram(shader);
    int location = glGetUniformLocation(shader, "Color_u");

    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    
        glfwPollEvents();

        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shader);

        if (location > -1)
        
            glUniform4f(location, 0.8f, 0.0f, 0.0f, 1.0f);
        
        glBindVertexArray(vao1);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

        if (location > -1)
        
            glUniform4f(location, 0.0f, 0.8f, 0.0f, 1.0f);
        
        glBindVertexArray(vao2);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

        glfwSwapBuffers(window);
    

    glDeleteProgram(shader);

    glfwTerminate();
    return 0;

【讨论】：

为什么必须用 VAO 重新绑定所有内容？只是好奇。

@Jerryoff：“重新绑定一切”是什么意思？您是说在 VAO 设置期间重新绑定 buffer1/buffer2/ebo 吗？

是的缓冲区。

@Jerryoff：您必须重新绑定，因为 glBindVertexArray() 调用会将绑定点重置为 VAO 中的任何内容。由于在这些绑定点默认为零之前尚未绑定 VAO，这意味着从客户端内存（兼容性上下文）或无效缓冲区对象（核心上下文）中提取。