Opengl矩形不会渲染

Posted 2023-02-22

【中文标题】Opengl矩形不会渲染

【英文标题】：Opengl Rectangle wont render

【发布时间】：2016-11-20 13:56:44

【问题描述】：

要么我很愚蠢，要么非常缺乏经验（可能两者兼有），但我不知何故被困在使用 opengl 绘制一个简单的彩色矩形上。这应该不是问题，因为我刚刚完成了一个简单的 opengl 模型加载器（但这是我的第一个项目，所以我只做了一次参考）。无论如何，除了蓝色背景之外什么都没有出现。

我尝试为基本形状创建简单的类。这是矩形类：

class AVRect
private:
    AVcolor Color;
    GLuint VBO, VAO, EBO;
    GLuint indices[6] =   // Note that we start from 0!
        0, 1, 3,   // First Triangle
        1, 2, 3    // Second Triangle
    ;
public:
    GLfloat geometry[12];
    AVRect(int Drawmode, GLfloat x, GLfloat y, GLfloat x2, GLfloat y2,GLfloat x3, GLfloat y3, GLfloat x4, GLfloat y4,GLfloat r,GLfloat b,GLfloat g,GLfloat a);
    void Draw(Shader shader);
;

不用担心颜色。我只在源代码中设置了它，但在其他任何地方都没有使用过。我将在矩形使用固定颜色后立即实现它。

rect类的来源：

#include "stdafx.h"
#include "Shapes.h"

AVRect::AVRect(int Drawmode,GLfloat x, GLfloat y, GLfloat x2, GLfloat y2, GLfloat x3, GLfloat y3, GLfloat x4, GLfloat y4, GLfloat r, GLfloat b, GLfloat g, GLfloat a) 
    geometry[0] = x;
    geometry[1] = y;
    geometry[2] = 0.0f;
    geometry[3] = x2;
    geometry[4] = y2;
    geometry[5] = 0.0f;
    geometry[6] = x3;
    geometry[7] = y3;
    geometry[8] = 0.0f;
    geometry[9] = x4;
    geometry[10] = y4;
    geometry[11] = 0.0f;
    Color.r = r;
    Color.b = b;
    Color.g = g;
    Color.a = a;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);
    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(geometry), geometry, Drawmode);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, Drawmode);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);



void AVRect::Draw(Shader shader) 
    glUseProgram(shader.Program);
    glBindVertexArray(VAO);
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
    glBindVertexArray(0);

主要是不言自明的：

// Bullethell.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <GL/glew.h>
#include <SDL.h>
#include <SDL_opengl.h>
#include <GLTextures.h>
#include <Shaders.h>
#include <ctime>
#include "Shapes.h"
#define HEIGHT 600
#define WIDTH 600

int main(int argc, char* args[])

    SDL_Window *window;
    SDL_Renderer *renderer;
    window = SDL_CreateWindow("BulletHell", 100, 100, HEIGHT, WIDTH, SDL_WINDOW_OPENGL);
    SDL_GLContext glcontext = SDL_GL_CreateContext(window);

    glewExperimental = GL_TRUE;
    if (GLEW_OK != glewInit())
    
        // GLEW failed!
        printf("GLEW INIT FAILED!");
    
    Shader basic("./shaders/colorTest/colorTest.vs", "./shaders/colorTest/colorTest.frag");
    AVRect test(GL_STATIC_DRAW,0.5f,0.5f,0.5f,-0.5f,-0.5f,-0.5f,0.5f,-0.5f,0.5f,0.9f,0.2f,0.5f);
    int error = 0;
    while (SDL_PollEvent(NULL))
    
        clock_t start = clock();
        glClearColor(0.2, 0.2, 0.5, 1);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        test.Draw(basic);
        SDL_GL_SwapWindow(window);
        error = glGetError();
        if (error != GL_NO_ERROR)
            printf("GL ERROR:%d ", error);
        while (((clock() - start) * 1000 / CLOCKS_PER_SEC) <16)
            ;

        float MS = (float)((clock() - start) * 1000 / CLOCKS_PER_SEC);
        // Frames per seconds
        float FPS = 1000.0f / MS;
        //printf("%f \n",FPS);
        //    printf( "Status: Using GLEW %s\n", glewGetString(GLEW_VERSION));
    
    return 1;

Shader 类已经过测试并且正在运行。着色器很简单，也应该可以工作（只传递值并分配固定颜色）。

我可能只是瞎了眼，因为我看不到错误。请帮我解决这个问题。

---

为了完整起见，这里是着色器源代码：

#include "stdafx.h"
#include "Shaders.h"

Shader::Shader(const GLchar* vertexPath, const GLchar* fragmentPath)

    // 1. Retrieve the vertex/fragment source code from filePath
    std::string vertexCode;
    std::string fragmentCode;
    std::ifstream vShaderFile;
    std::ifstream fShaderFile;

    // ensures ifstream objects can throw exceptions:
    vShaderFile.exceptions (std::ifstream::badbit);
    fShaderFile.exceptions (std::ifstream::badbit);
    try
    
        // Open files
        vShaderFile.open(vertexPath);
        fShaderFile.open(fragmentPath);
        std::stringstream vShaderStream, fShaderStream;
        // Read file's buffer contents into streams
        vShaderStream << vShaderFile.rdbuf();
        fShaderStream << fShaderFile.rdbuf();
        // close file handlers
        vShaderFile.close();
        fShaderFile.close();
        // Convert stream into string
        vertexCode = vShaderStream.str();
        fragmentCode = fShaderStream.str();
    
    catch (std::ifstream::failure e)
    
        std::cout << "ERROR::SHADER::FILE_NOT_SUCCESFULLY_READ" << std::endl;
    
    const GLchar* vShaderCode = vertexCode.c_str();
    const GLchar * fShaderCode = fragmentCode.c_str();
    // 2. Compile shaders
    GLuint vertex, fragment;
    GLint success;
    GLchar infoLog[512];
    // Vertex Shader
    vertex = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex, 1, &vShaderCode, NULL);
    glCompileShader(vertex);
    // Print compile errors if any
    glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);
    if (!success)
    
        glGetShaderInfoLog(vertex, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    
    // Fragment Shader
    fragment = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment, 1, &fShaderCode, NULL);
    glCompileShader(fragment);
    // Print compile errors if any
    glGetShaderiv(fragment, GL_COMPILE_STATUS, &success);
    if (!success)
    
        glGetShaderInfoLog(fragment, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    
    // Shader Program
    this->Program = glCreateProgram();
    glAttachShader(this->Program, vertex);
    glAttachShader(this->Program, fragment);
    glLinkProgram(this->Program);
    // Print linking errors if any
    glGetProgramiv(this->Program, GL_LINK_STATUS, &success);
    if (!success)
    
        glGetProgramInfoLog(this->Program, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    
    // Delete the shaders as they're linked into our program now and no longer necessery
    glDeleteShader(vertex);
    glDeleteShader(fragment);


// Uses the current shader
void Shader::Use()

    glUseProgram(this->Program);

【问题讨论】：

我在主帖中添加了源代码。我在我的另一个项目中使用了相同的源（一个带有纹理和基本照明的简单模型加载器）并且效果也很好。

【参考方案1】：

您正在绘制退化三角形，因此不会渲染任何像素。如果您查看“矩形”的坐标，为了便于阅读，它们之间的间距是：

 0.5f,  0.5f,
 0.5f, -0.5f,
-0.5f, -0.5f,
 0.5f, -0.5f

您可以看到第 2 和第 4 个顶点具有相同的坐标。您的顶点排列如下所示：

      0

2     1/3

将其与您的索引进行比较：

0, 1, 3,   // First Triangle
1, 2, 3    // Second Triangle

你会看到两个三角形都是退化的，因为它们的两个顶点是相同的。

您可能打算使用的坐标是：

 0.5f,  0.5f,
 0.5f, -0.5f,
-0.5f, -0.5f,
-0.5f,  0.5f

我实际上建议对几何图形使用逆时针方向，因为这是 OpenGL 中的默认缠绕顺序。尽管这并不重要，除非您计划启用剔除。