c++ - 手动生成 mipmap

Question

原帖:
https://computergraphics.stackexchange.com/questions/4793/how-can-i-generate-mipmaps-manually
这是一个愚蠢的错误，我忘记设置所有纹理坐标 :P

OpenGL 相当难学。根据我对 mipmap 的理解，我可以手动设置每个 mipmap 级别，因此当我的纹理看起来更大或更小时，我可以更改要使用的图像。

我尝试了以下代码，但不管三角形的大小如何，它总是采用第一个 mipmap 级别。为什么？如果三角形更接近任何其他 mipmap 级别，为什么不接受它？

我真的很讨厌在我的问题中放一堆代码，因为我强制别人浪费时间分析代码而不是放最相关的代码片段，但我不知道问题出在哪里，我也别无选择。对不起:(

#include <iostream>

#define GLEW_STATIC
#include <GL/glew.h>

#include <GLFW/glfw3.h>

const GLchar* VERTEX_SHADER_SOURCE =
        "#version 330 core                           \n"
        "layout (location = 0) in vec2 position;     \n"
        "layout (location = 1) in vec2 myTexCoord;   \n"
        "                                            \n"
        "out vec2 TexCoord;                          \n"
        "                                            \n"
        "void main()                                 \n"
        "{                                           \n"
        "    gl_Position = vec4(position,0.0f, 1.0f);\n"
        "    TexCoord = myTexCoord;                  \n"
        "}                                           \n";

const GLchar* FRAGMENT_SHADER_SOURCE =
        "#version 330 core                         \n"
        "in vec2 TexCoord;                         \n"
        "                                          \n"
        "out vec4 color;                           \n"
        "                                          \n"
        "uniform sampler2D ourTexture;             \n"
        "                                          \n"
        "void main()                               \n"
        "{                                         \n"
        "    color = texture(ourTexture, TexCoord);\n"
        "}                                         \n";

int main()
{
    //Change the value of size by 1,2,4,8,16,32,64,128 or 256 and see how the color of the triangle doesn't change. Why does it happen?
    GLint size = 128;

    //INIT STUFFS
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
    GLFWwindow* window = glfwCreateWindow(size,size, "", nullptr, nullptr);
    glfwMakeContextCurrent(window);
    glewExperimental = GL_TRUE;
    glewInit();
    glViewport(0, 0,size,size);



    GLuint texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);

    //Our image for the mipmap with odd level and green color
    //The dimensions are 256 x 256 and is multiplied by 3 because I defined R,G and B colors
    unsigned char imageArray[256*256*3];
    for(int i = 0; i < 256*256*3; i++){
        if((i+2)%3 == 0)
            imageArray[i] = 255;
        else
            imageArray[i] = 0;
    }

    //Our image for the mipmap with pair level and red color
    unsigned char imageArray2[256*256*3];
    for(int i = 0; i < 256*256*3; i++){
        if(i%3 == 0)
            imageArray2[i] = 255;
        else
            imageArray2[i] = 0;
    }

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 8);

    //All mipmap levels defined by hand
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 256, 256, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
    glTexImage2D(GL_TEXTURE_2D, 1, GL_RGB, 128, 128, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
    glTexImage2D(GL_TEXTURE_2D, 2, GL_RGB, 64,  64,  0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
    glTexImage2D(GL_TEXTURE_2D, 3, GL_RGB, 32,  32,  0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
    glTexImage2D(GL_TEXTURE_2D, 4, GL_RGB, 16,  16,  0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
    glTexImage2D(GL_TEXTURE_2D, 5, GL_RGB, 8,   8,   0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
    glTexImage2D(GL_TEXTURE_2D, 6, GL_RGB, 4,   4,   0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
    glTexImage2D(GL_TEXTURE_2D, 7, GL_RGB, 2,   2,   0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
    glTexImage2D(GL_TEXTURE_2D, 8, GL_RGB, 1,   1,   0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);

    GLfloat vertices[] = {
            -1.0f, -1.0f, 1.0f, -1.0f, 0.0f, 1.0f,  //vertex coordinates
            0.0f, 0.0f                              //Triangle's texture coordinates
    };



    //VAOs AND VBOs
    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);

    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), (GLvoid*)0);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), (GLvoid*)(sizeof(GLfloat)*3*2));

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);



    //SHADERS
    GLuint program;
    GLuint vertex, fragment;

    vertex = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex, 1, &VERTEX_SHADER_SOURCE, NULL);
    glCompileShader(vertex);

    fragment = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment, 1, &FRAGMENT_SHADER_SOURCE, NULL);
    glCompileShader(fragment);

    program = glCreateProgram();
    glAttachShader(program, vertex);
    glAttachShader(program, fragment);
    glLinkProgram(program);

    glDeleteShader(vertex);
    glDeleteShader(fragment);
    glUseProgram(program);



    //DRAWING OUR TRIANGLE
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawArrays(GL_TRIANGLES, 0,3);
    glfwSwapBuffers(window);
    while (!glfwWindowShouldClose(window))
        glfwPollEvents();



    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glfwTerminate();
    return 0;
}

Answer 1

您的 mipmap 设置看起来不错。但我看到您有这个:

  GLfloat vertices[] = {
        -1.0f, -1.0f, 1.0f, -1.0f, 0.0f, 1.0f,  //vertex coordinates
        0.0f, 0.0f                              //Triangle's texture coordinates
  };

看起来您缺少 2 个其他顶点的 UV。另外，除非您想完全控制过滤技术等，否则我不会为手动生成 mipmap 而烦恼。