c - 使用顶点缓冲区和纹理缓冲区的 OpenGL C++ 顺序

Question

我在将纹理加载到三角形 strip 上时遇到问题。我正在关注Anton Gerdelan's tutorial ，在我的主程序失败后，我回到了基础知识，只是尝试制作一个简单的正方形并在其上放置他的纹理(骷髅和交叉骨)。

我完全复制并粘贴了他的 "Hello Triangle" 中的代码页面，它有效，但是一旦尝试适应上面纹理教程中的代码(并将三角形更改为正方形)，我得到的只是一个没有纹理的大白色正方形。

我已经使用 glGetShaderiv() 检查了着色器的状态，它们返回了正值，我检查了加载的图像以查看像素数据是否合理，所以我相信我的错误在于声明我的 VBO 或顺序/我在其中使用它们的参数。

这是我复制的完整代码，它可以在 Visual Studio 2013 中正常编译，但输出不是预期的结果。

我正在使用 GLEW 和 GLFW 的静态库以及 STBI 图像 header

#include <GL/glew.h> // include GLEW and new version of GL on Windows
#include <GL/glfw3.h> // GLFW helper library
#include <stdio.h>
#define STB_IMAGE_IMPLEMENTATION
#include <stb/stb_image.h>

const char* vertex_shader =
"#version 400\n"
"in vec3 vp;"
"layout (location=1) in vec2 vt; // per-vertex texture co-ords"
"out vec2 texture_coordinates; "
"void main () {"
"  gl_Position = vec4 (vp, 1.0);"
"  texture_coordinates = vt; "
"}";

const char* fragment_shader =
"#version 400\n"
"in vec2 texture_coordinates;"
"uniform sampler2D basic_texture;"
"out vec4 frag_colour;"
"void main () {"
"vec4 texel = texture(basic_texture, texture_coordinates);"
"frag_colour = texel; "
"}";

float points[] = {
    -0.5f, -0.5f, 0.0f,
    -0.5f, 0.5f, 0.0f,
    0.5f, -0.5f, 0.0f,
    0.5f, 0.5f, 0.0f

};

float texcoords[] = {
    0.0f, 1.0f,
    0.0f, 0.0f,
    1.0, 0.0,
    1.0, 0.0,
    1.0, 1.0,
    0.0, 1.0
};

GLFWwindow* window;
unsigned int vt_vbo;
unsigned int tex = 0;
GLuint vao = 0;
GLuint vbo = 0;
GLuint shader_programme;

void initializeGL(){
    // start GL context and O/S window using the GLFW helper library
    if (!glfwInit()) {
        printf("ERROR: could not start GLFW3\n");
        return;
    }

    window = glfwCreateWindow(640, 480, "Texture Test", NULL, NULL);
    if (!window) {
        printf("ERROR: could not open window with GLFW3\n");
        glfwTerminate();
        return;
    }
    glfwMakeContextCurrent(window);

    // start GLEW extension handler
    glewExperimental = GL_TRUE;
    glewInit();

    // get version info
    const GLubyte* renderer = glGetString(GL_RENDERER); // get renderer string
    const GLubyte* version = glGetString(GL_VERSION); // version as a string
    printf("Renderer: %s\n", renderer);
    printf("OpenGL version supported %s\n", version);

    // tell GL to only draw onto a pixel if the shape is closer to the viewer
    glEnable(GL_DEPTH_TEST); // enable depth-testing
    glDepthFunc(GL_LESS); // depth-testing interprets a smaller value as "closer"
}

void startShaders(){

    GLuint vs = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vs, 1, &vertex_shader, NULL);
    glCompileShader(vs);
    GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fs, 1, &fragment_shader, NULL);
    glCompileShader(fs);

    shader_programme = glCreateProgram();
    glAttachShader(shader_programme, fs);
    glAttachShader(shader_programme, vs);
    glLinkProgram(shader_programme);
    GLint vsstat;
    glGetShaderiv(vs, GL_COMPILE_STATUS, &vsstat);
    GLint fsstat;
    glGetShaderiv(fs, GL_COMPILE_STATUS, &fsstat);
    printf("%i\n%i\n", vsstat, fsstat);
}

void loadImage(){
    int x, y, n;
    int force_channels = 4;
    unsigned char* image_data = stbi_load("skulluvmap.png", &x, &y, &n, force_channels);
    if (!image_data) {
        printf("ERROR: could not load %s\n", "skulluvmap.png");
    }

    int width_in_bytes = x * 4;
    unsigned char *top = NULL;
    unsigned char *bottom = NULL;
    unsigned char temp = 0;
    int half_height = y / 2;


    for (int row = 0; row < half_height; row++) {
        top = image_data + row * width_in_bytes;
        bottom = image_data + (y - row - 1) * width_in_bytes;
        for (int col = 0; col < width_in_bytes; col++) {
            temp = *top;
            *top = *bottom;
            *bottom = temp;
            top++;
            bottom++;
        }
    }
    printf("first 4 bytes are: %i %i %i %i\n",
        image_data[0], image_data[1], image_data[2], image_data[3]
        );
    glGenTextures(1, &tex);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, x, y, 0, GL_RGBA, GL_UNSIGNED_BYTE, image_data);
    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_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
}

void generateBuffers(){
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, 12 * sizeof(float), points, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);
    glEnableVertexAttribArray(0); // don't forget this!

    glGenBuffers(1, &vt_vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vt_vbo);
    glBufferData(GL_ARRAY_BUFFER, 12 * sizeof(float), texcoords, GL_STATIC_DRAW);

    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, NULL);
    glEnableVertexAttribArray(1); // don't forget this!
}

void mainLoop(){
    while (!glfwWindowShouldClose(window)) {
        // wipe the drawing surface clear
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
        int tex_loc = glGetUniformLocation(shader_programme, "basic_texture");
        glUseProgram(shader_programme);
        glUniform1i(tex_loc, 0); // use active texture 0
        // draw points 0-4 from the currently bound VAO with current in-use shader
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
        // update other events like input handling 
        glfwPollEvents();
        // put the stuff we've been drawing onto the display
        glfwSwapBuffers(window);
    }
}

int main() {

    initializeGL();
    startShaders();
    loadImage();
    generateBuffers();
    mainLoop();

    // close GL context and any other GLFW resources
    glfwTerminate();
    return 0;
}

Answer 1

您滥用了第二个缓冲区，它应该是带有 texcoords 的缓冲区。所以你真正想要实现的是每个顶点都有一对纹理坐标。这意味着 texcoords 数组实际上应该存储 4 对，因为点数组中有 4 个三元组。这是第一个修复。您可能希望它看起来像:

float texcoords[] = {
0.0f, 1.0f,
0.0f, 0.0f,
1.0, 0.0,
1.0, 1.0,
};

然后在generateBuffers中，您的vt_vbo是错误的。数据应该这样传递:

glBufferData(GL_ARRAY_BUFFER, 8 * sizeof(float), texcoords, GL_STATIC_DRAW);

因为您只想在那里传递 8 个值。每个顶点 2 个纹理坐标。

编辑:

然而，这并不能完全解释为什么你的纹理根本不出现。我主要认为您的 texcoords 指针可能有问题，但事实似乎并非如此。