我在 OpenGL 中显示图像时遇到问题

Posted 2023-02-22

【中文标题】我在 OpenGL 中显示图像时遇到问题

【英文标题】：I am having a problem displaying a image in OpenGL

【发布时间】：2020-06-07 00:50:03

【问题描述】：

我不完全理解 OpenGL 中绑定纹理的概念，我无法用它来为我的项目渲染 jpg 图像，知道我可能做错了什么吗？

// Shader sources
const GLchar* vertexShaderSource = R"glsl(
#version 150 core
in vec2 position;
in vec3 color;
in vec2 texcoord;
out vec3 Color;
out vec2 Texcoord;
void main()

    Color = color;
    Texcoord = texcoord;
    gl_Position = vec4(position, 0.0, 1.0);

)glsl";

const GLchar* fragmentShaderSource = R"glsl(
#version 150 core
in vec3 Color;
in vec2 Texcoord;
out vec4 outColor;
uniform sampler2D tex;
void main()

    outColor = texture(tex, Texcoord) * vec4(Color, 1.0);

)glsl";

    //creating the window
    GLFWwindow *window= glfwCreateWindow(1200, 700, "NEX_Tests", NULL, NULL);

    if(nullptr== window)
        std::cout<<"ERROR HAS OCCURED WHILE LOADING THE WINDOW\n"<<"\n";
        glfwTerminate();
        return -1;
    

    else
         int screenWidth,screenHeight;
           glfwGetFramebufferSize(window, &screenWidth, &screenHeight);

           glfwMakeContextCurrent(window);

        glewExperimental=true;
        if(GLEW_OK==!glewInit())
            std::cout<<"ERROR HAS OCCURED WHILE INITILIZING THE GLEW LIBRARY\n"<<"\n";
            return EXIT_FAILURE;
        

        //set the viewing port
        glViewport(0, 0, screenWidth, screenHeight);

        //creating the vetex array object;
        GLuint vao,vbo;
        glGenVertexArrays(1,&vao);
        glGenBuffers(1,&vbo);

        glBindVertexArray(vao);
        glBindBuffer(GL_ARRAY_BUFFER,vbo);
        glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_STATIC_DRAW);

        //creating the element buffer
        GLuint ebo;
        glGenBuffers(1,&ebo);
        GLuint elements[]=
            0,1,2,
            2,3,0
        ;

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,ebo);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(elements),elements,GL_STATIC_DRAW);
        std::cout<<vbo<<"\n";

        //   glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,(3* sizeof(GLfloat)),(GLvoid*)0);
        // glEnableVertexAttribArray(0);
        //glBindBuffer(GL_VERTEX_ARRAY,0);
        // glBindVertexArray(0);



        //creating and linking the shaders
        GLuint vertexShader= glCreateShader(GL_VERTEX_SHADER);

        glShaderSource(vertexShader,1,&vertexShaderSource,NULL );
        glCompileShader(vertexShader);
        GLint success;
        GLchar infoLog[512];

        glGetShaderiv(vertexShader,GL_COMPILE_STATUS,&success);
        if(!success)
            glGetShaderInfoLog(vertexShader, 512,NULL,infoLog);
            std::cout<<"ERROR HAS OCCURED WHILE COMPILING THE SHADERS\n"<<infoLog<<std::endl;
        
        GLuint fragmentShader= glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fragmentShader,1,&fragmentShaderSource,NULL);
        glCompileShader(fragmentShader);

        glGetShaderiv(fragmentShader,GL_COMPILE_STATUS,&success);
        if(!success)
            glGetShaderInfoLog(fragmentShader,512,NULL,infoLog);
            std::cout<<"ERROR HAS OCCURED WHILE COMPILING THE SHADERS\n"<<infoLog<<std::endl;
        
        GLuint shaderProgram= glCreateProgram();
        glAttachShader(shaderProgram,vertexShader);
        glAttachShader(shaderProgram,fragmentShader);
        glLinkProgram(shaderProgram);
        glUseProgram(shaderProgram);

        glGetProgramiv(shaderProgram,GL_LINK_STATUS,&success);
        if(!success)
            glGetProgramInfoLog(shaderProgram,512,NULL,infoLog);
            std::cout<<"ERROR HAS OCCURED WHILE LINKING THE SHADERS\n"<<infoLog<<std::endl;
        
         //delete the shaders
        glDeleteShader(vertexShader);
        glDeleteShader(fragmentShader);

        //layout of the vertex shader
        GLint posAttrib = glGetAttribLocation(shaderProgram,"position");
        glEnableVertexAttribArray(posAttrib);
        glVertexAttribPointer(posAttrib,0,GL_FLOAT,GL_FALSE,7* sizeof(GLfloat),0);

        GLint colAttrib = glGetAttribLocation(shaderProgram,"color");
        glEnableVertexAttribArray(colAttrib);
        glVertexAttribPointer(colAttrib,2,GL_FLOAT,GL_FALSE,7* sizeof(GLfloat),((void*)(2*sizeof(GLfloat))));

        GLint TexAttrib= glGetAttribLocation(shaderProgram,"texcoord");
        glEnableVertexAttribArray(TexAttrib);
        glVertexAttribPointer(TexAttrib,2,GL_FLOAT,GL_FALSE,7*sizeof(GLfloat),((void*)(5*sizeof(GLfloat))));

        //loading the textures
        GLuint tex;
        glGenTextures(2, &tex);
        glBindTexture(GL_TEXTURE_2D, tex);
        std::cout<<tex<<"\n";
        glActiveTexture(GL_TEXTURE0+ 1);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);


        //loading the image
        int me=200,me2=300;
        int *width=&me,*height=&me2;

        unsigned char* Image= SOIL_load_image("IceKarl.png", width, height, 0, SOIL_LOAD_RGB);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, *width, *height, 0, GL_RGB, GL_UNSIGNED_BYTE, Image);

        SOIL_free_image_data(Image);


        if(!Image)

            std::cout<<"ERROR HAS OCCURED WHILE LOADING IN IMAGE\n";
        

        //running loop
        while(!glfwWindowShouldClose(window))
            glfwPollEvents();

            glClearColor(0.0f, 0.00f, 0.00f, 1.0f);
            glClear(GL_COLOR_BUFFER_BIT);

            glBindTexture(GL_TEXTURE_2D, 0);

            //glDrawArrays(GL_TRIANGLES, 0, 6);
            // glDrawElements(GL_TRIANGLES,6,GL_UNSIGNED_INT,0);
            // glBindTexture(GL_TEXTURE_2D,0);
            glfwSwapBuffers(window);
        
        glDeleteTextures(1,&tex);
        glDeleteProgram(shaderProgram);
        glDeleteShader(vertexShader);
        glDeleteShader(fragmentShader);

        glDeleteBuffers(1,&vbo);
        glDeleteBuffers(1,&ebo);
        glDeleteVertexArrays(1,&vao);
    

    glfwTerminate();

    return 0;

【参考方案1】：

glVertexAttribPointer 的第二个参数是属性的元组大小。在您的情况下，这是位置 (x, y) 的 2，颜色 (r, g, b) 的 3 和纹理坐标 ( u, v):

GLint posAttrib = glGetAttribLocation(shaderProgram,"position");
glEnableVertexAttribArray(posAttrib);
glVertexAttribPointer(posAttrib,  2,  GL_FLOAT,GL_FALSE,7* sizeof(GLfloat),0);

GLint colAttrib = glGetAttribLocation(shaderProgram,"color");
glEnableVertexAttribArray(colAttrib);
glVertexAttribPointer(colAttrib,  3,  GL_FLOAT,GL_FALSE,7* sizeof(GLfloat),((void*)(2*sizeof(GLfloat))));

GLint TexAttrib= glGetAttribLocation(shaderProgram,"texcoord");
glEnableVertexAttribArray(TexAttrib);
glVertexAttribPointer(TexAttrib,  2,  GL_FLOAT,GL_FALSE,7*sizeof(GLfloat),((void*)(5*sizeof(GLfloat))));

绘制网格时，必须绑定纹理和顶点数组对象。

在绑定纹理（glBindTexture）之前必须设置纹理单元（glActiveTexture）：

glActiveTexture(GL_TEXTURE0 + 1);
glBindTexture(GL_TEXTURE_2D, tex);

您必须将纹理单元索引分配给纹理采样器制服 (glUniform)：

glUniform1i(tex_loc, 1);

获取纹理采样器制服的位置索引（glGetUniformLocation）：

GLuint tex_loc = glGetUniformLocation(shaderProgram, "tex");

在绘制调用之前绑定对象：

int texture_unit = 1;
glActiveTexture(GL_TEXTURE0 + texture_unit);
glBindTexture(GL_TEXTURE_2D, tex);
glUniform1i(tex_loc, texture_unit);

glBindVertexArray(vao);

glDrawElements(GL_TRIANGLES,6,GL_UNSIGNED_INT,0);

---

生成纹理名称时还有一个问题。生成 1 个纹理名称而不是 2 个：

glGenTextures(2, &tex);

GLuint tex;
glGenTextures(1, &tex);

【讨论】：

感谢您的帮助，非常感谢。

我试过了，但现在我只得到一个黑匣子，很抱歉再次询问。

@KrishPatel 所以你犯了一个错误。当然，我已经测试了该解决方案，它对我来说效果很好。您是否确保 glActiveTexture 在 glBindTexture 之前完成（无处不在）？

是的，我有，我只是在屏幕上看到一个黑色矩形

@KrishPatel 这是我的测试示例代码：pastebin.com/qQgWChi0。它对我来说很好。