Question

在 SDL2 窗口中，我绘制了一个矩形，我打算在其上显示图像。我现在的问题是窗口完全是黑色的。它既不显示彩色矩形，也不显示应该放置在矩形上的图像。

#define SDL_MAIN_HANDLED
#include <GL\glew.h>
#include <GL\gl.h>
#include <SDL2\SDL.h>
#include "stb_image.h"
#include <cstdio>

const GLchar *vertexSource =
        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 *fragmentSource =
        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";

int main()
{
    if (SDL_Init(SDL_INIT_VIDEO) < 0)
    {
        std::puts("Could not initialize SDL2!");
        exit(1);
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK,
            SDL_GL_CONTEXT_PROFILE_CORE);

    SDL_Window *mainWindow = SDL_CreateWindow("Main Window",
            SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 800, 600,
            SDL_WINDOW_OPENGL);

    if (nullptr == mainWindow)
    {
        std::puts("Could not create window!");
        SDL_Quit();
        exit(1);
    }

    if (!SDL_GL_CreateContext(mainWindow))
    {
        std::puts("Could not create context!");
        SDL_Quit();
        exit(1);
    }

    glewExperimental = GL_TRUE;
    if (glewInit() != GLEW_OK)
    {
        std::puts("Could not initialize GLEW!");
        SDL_Quit();
        exit(1);
    }

    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    GLuint vbo;
    glGenBuffers(1, &vbo);

    GLfloat vertices[] = {
            -0.5f, 0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f,
            0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f,
            0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f,
            -0.5f, -0.5f, 0.5f, 0.5f, 0.5f, 0.0f, 1.0f
    };

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

    GLuint ebo;
    glGenBuffers(1, &ebo);

    GLuint elements[] =
    { 0, 1, 2, 2, 3, 0 };

    glBindBuffer(GL_ARRAY_BUFFER, ebo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW);

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexSource, 0);
    glCompileShader(vertexShader);

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSource, 0);
    glCompileShader(fragmentShader);

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glBindFragDataLocation(shaderProgram, 0, "outColor");
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

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

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

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

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

    int width, height, noOfChannels;
    unsigned char *imageData = stbi_load("path",
            &width, &height, &noOfChannels, 0);
    if (imageData)
    {
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB,
        GL_UNSIGNED_BYTE, imageData);
        stbi_image_free(imageData);
    }
    else
    {
        std::puts("Could not load image");
        SDL_Quit();
        exit(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);

    SDL_Event event;
    bool running = true;

    while (running)
    {
        while (SDL_PollEvent(&event) != 0)
        {
            if (event.type == SDL_QUIT)
            {
                running = false;
            }
        }
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

        SDL_GL_SwapWindow(mainWindow);

    }

    glDeleteTextures(1, &texture);
    glDeleteProgram(shaderProgram);
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

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

    glDeleteVertexArrays(1, &vao);

    SDL_Quit();
    return 0;
}

是不是主循环无法正确显示图像？我的理解是，对于每个循环，我都应该清除屏幕，绘制形状，然后加载包含我的图像的后台缓冲区。

Answer 1

glDrawElements 旨在与 Index buffer (GL_ELEMENT_ARRAY_BUFFER) 一起使用。您不小心指定了 2 Vertex Buffers (GL_ARRAY_BUFFER)，但没有索引缓冲区：

~~glBindBuffer(GL_ARRAY_BUFFER, ebo);~~
~~glBufferData(GL_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW);~~

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW);

如何在 SDL2 中显示 OpenGL 纹理

1 个答案: