opengl es 如何将图片的RGB格式转换成unsigned char*并且保存成jpg完整例子

下面是一个完整的示例代码，它使用OpenGL ES将纹理转换为RGB格式的像素数据，并使用libjpeg-turbo库将像素数据保存为JPG格式的图像文件。

#include <EGL/egl.h>
#include <GLES2/gl2.h>
#include <jpeglib.h>
#include <turbojpeg.h>

#include <stdio.h>
#include <stdlib.h>

#define WINDOW_WIDTH 640
#define WINDOW_HEIGHT 480

#define TEXTURE_FILE "texture.jpg"
#define IMAGE_FILE "image.jpg"

static const char *vertexShaderSource =
    "attribute vec4 a_position;\n"
    "attribute vec2 a_texcoord;\n"
    "varying vec2 v_texcoord;\n"
    "void main() {\n"
    "  gl_Position = a_position;\n"
    "  v_texcoord = a_texcoord;\n"
    "}\n";

static const char *fragmentShaderSource =
    "precision mediump float;\n"
    "uniform sampler2D u_texture;\n"
    "varying vec2 v_texcoord;\n"
    "void main() {\n"
    "  gl_FragColor = texture2D(u_texture, v_texcoord);\n"
    "}\n";

static const GLfloat vertices[] = {
    -1.0f,  1.0f, 0.0f,  // top left
    -1.0f, -1.0f, 0.0f,  // bottom left
     1.0f, -1.0f, 0.0f,  // bottom right
     1.0f,  1.0f, 0.0f,  // top right
};

static const GLfloat texcoords[] = {
    0.0f, 0.0f,  // top left
    0.0f, 1.0f,  // bottom left
    1.0f, 1.0f,  // bottom right
    1.0f, 0.0f,  // top right
};

static const GLushort indices[] = {
    0, 1, 2,
    0, 2, 3,
};

int main(int argc, char *argv[])
{
    // Initialize EGL display and context
    EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
    EGLint major, minor;
    eglInitialize(display, &major, &minor);
    EGLint attributes[] = {
        EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
        EGL_NONE
    };
    EGLConfig config;
    EGLint num_configs;
    eglChooseConfig(display, attributes, &config, 1, &num_configs);
    EGLint context_attributes[] = {
        EGL_CONTEXT_CLIENT_VERSION, 2,
        EGL_NONE
    };
    EGLContext context = eglCreateContext(display, config, EGL_NO_CONTEXT, context_attributes);

    // Create window surface
    EGLSurface surface;
    EGLint surface_attributes[] = {
        EGL_WIDTH, WINDOW_WIDTH,
        EGL_HEIGHT, WINDOW_HEIGHT,
        EGL_NONE
    };
    surface = eglCreateWindowSurface(display, config, NULL, surface_attributes);

    // Make the context current
    eglMakeCurrent(display, surface, surface, context);

    // Load texture from file
    unsigned char *texture_data;
    int texture_width, texture_height;
    tjhandle tj = tjInitDecompress();
    FILE *fp = fopen(TEXTURE_FILE, "rb");
    fseek(fp, 0, SEEK_END);
    long file_size = ftell(fp);
    fseek(fp, 0, SEEK_SET);
    texture_data = (unsigned char *)malloc(file_size);
    fread(texture_data, 1, file_size, fp);
    fclose(fp);
    int tj_width, tj_height, tj_subsamp;
    tjDecompressHeader2(tj, texture_data, file_size, &tj_width, &tj_height, &tj_subsamp);
    texture_width = tj_width;
    texture_height = tj_height;
    unsigned char *texture_pixels = (unsigned char *)malloc(texture_width * texture_height * 3);
    tjDecompress2(tj, texture_data, file_size, texture_pixels, texture_width, 0, texture_height, TJPF_RGB, TJFLAG_FASTDCT);
    tjDestroy(tj);

    // Create texture
    GLuint texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, texture_width, texture_height, 0, GL_RGB, GL_UNSIGNED_BYTE, texture_pixels);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    // Create program
    GLuint program;
    GLint success;
    char info_log[512];
    GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex_shader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertex_shader);
    glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(vertex_shader, 512, NULL, info_log);
        fprintf(stderr, "Failed to compile vertex shader: %s\n", info_log);
        exit(1);
    }
    GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment_shader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragment_shader);
    glGetShaderiv(fragment_shader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragment_shader, 512, NULL, info_log);
        fprintf(stderr, "Failed to compile fragment shader: %s\n", info_log);
        exit(1);
    }
    program = glCreateProgram();
    glAttachShader(program, vertex_shader);
    glAttachShader(program, fragment_shader);
    glLinkProgram(program);
    glGetProgramiv(program, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(program, 512, NULL, info_log);
        fprintf(stderr, "Failed to link program: %s\n", info_log);
        exit(1);
    }
    glUseProgram(program);

    // Set up vertex attributes
    GLint position_attrib = glGetAttribLocation(program, "a_position");
    glVertexAttribPointer(position_attrib, 3, GL_FLOAT, GL_FALSE, 0, vertices);
    glEnableVertexAttribArray(position_attrib);
    GLint texcoord_attrib = glGetAttribLocation(program, "a_texcoord");
    glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, texcoords);
    glEnableVertexAttribArray(texcoord_attrib);

    // Set up texture uniform
    GLint texture_uniform = glGetUniformLocation(program, "u_texture");
    glUniform1i(texture_uniform, 0);

    // Render to framebuffer
    GLuint framebuffer, renderbuffer;
    glGenFramebuffers(1, &framebuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
    glGenRenderbuffers(1, &renderbuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, renderbuffer);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8, WINDOW_WIDTH, WINDOW_HEIGHT);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, renderbuffer);
    glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices);

    // Read framebuffer pixels
    unsigned char *pixels = (unsigned char *)malloc(WINDOW_WIDTH * WINDOW_HEIGHT * 3);
    glReadPixels(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT, GL_RGB, GL_UNSIGNED_BYTE, pixels);

    // Save image to file
    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_compress(&cinfo);
    FILE *fp2 = fopen(IMAGE_FILE, "wb");
    jpeg_stdio_dest(&cinfo, fp2);
    cinfo.image_width = WINDOW_WIDTH;
    cinfo.image_height = WINDOW_HEIGHT;
    cinfo.input_components = 3;
    cinfo.in_color_space = JCS_RGB;
    jpeg_set_defaults(&cinfo);
    jpeg_start_compress(&cinfo, TRUE);
    JSAMPROW row_pointer[1];
    while (cinfo.next_scanline < cinfo.image_height) {
        row_pointer[0] = &pixels[(cinfo.image_height - cinfo.next_scanline - 1) * cinfo.image_width * 3];
        jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }
    jpeg_finish_compress(&cinfo);
    fclose(fp2);

    // Clean up
    free(texture_data);
    free(texture_pixels);
    free(pixels);
    glDeleteProgram(program);
    glDeleteShader(vertex_shader);
    glDeleteShader(fragment_shader);
    glDeleteTextures(1, &texture);
    glDeleteFramebuffers(1, &framebuffer);
    glDeleteRenderbuffers(1, &renderbuffer);
    eglDestroySurface(display, surface);
    eglDestroyContext(display, context);
    eglTerminate(display);

    return 0;
}

注意：此示例代码仅支持RGB格式的图像文件，如果要处理其他格式的图像文件，请根据需要进行适当修改。