图像数据缓冲区（buf）

图像数据缓冲区（buf）是存储图像数据的内存区域。它通常是一个连续的字节序列，用于存储图像的像素值。图像数据可以以不同的格式存储，比如RGB、RGBA、灰度等。在图像处理和计算机视觉领域，我们经常需要对图像数据进行读取、修改和操作，而图像数据缓冲区提供了一个方便的方式来访问和处理图像数据。通过读取和写入缓冲区中的像素值，我们可以对图像进行各种操作，比如滤波、边缘检测、图像增强等。

相关问题

rk3399平台使用mpp压缩图像数据为mjpeg并保存为图像的示例

以下是在RK3399平台上使用mpp压缩图像数据为mjpeg并保存为图像的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <rockchip/mpp.h>

#define DEV_NAME "/dev/video0"
#define IMAGE_WIDTH 640
#define IMAGE_HEIGHT 480
#define IMAGE_SIZE (IMAGE_WIDTH * IMAGE_HEIGHT * 2)

int main(int argc, char **argv)
{
    int fd_cam, fd_mpp;
    struct v4l2_capability cap;
    struct v4l2_format fmt;
    struct v4l2_requestbuffers reqbuf;
    struct v4l2_buffer buf;
    uint8_t *buf_mmap;
    MppCtx ctx;
    MppApi *mpi;
    MppBuffer mpp_buf_in, mpp_buf_out;
    MppPacket packet_out;
    uint8_t *data_in, *data_out;
    uint32_t size_in, size_out, packet_size_out;
    FILE *fp;
    int i, ret;

    fd_cam = open(DEV_NAME, O_RDWR);
    if (fd_cam < 0) {
        printf("Open camera device error\n");
        return -1;
    }

    ret = ioctl(fd_cam, VIDIOC_QUERYCAP, &cap);
    if (ret < 0) {
        printf("Query camera device capability error\n");
        goto exit_cam;
    }

    if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
        printf("Camera device does not support video capture\n");
        goto exit_cam;
    }

    if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
        printf("Camera device does not support streaming I/O\n");
        goto exit_cam;
    }

    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = IMAGE_WIDTH;
    fmt.fmt.pix.height = IMAGE_HEIGHT;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_NONE;
    ret = ioctl(fd_cam, VIDIOC_S_FMT, &fmt);
    if (ret < 0) {
        printf("Set camera device format error\n");
        goto exit_cam;
    }

    memset(&reqbuf, 0, sizeof(reqbuf));
    reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    reqbuf.memory = V4L2_MEMORY_MMAP;
    reqbuf.count = 4;
    ret = ioctl(fd_cam, VIDIOC_REQBUFS, &reqbuf);
    if (ret < 0) {
        printf("Request camera device buffers error\n");
        goto exit_cam;
    }

    buf_mmap = malloc(reqbuf.count * IMAGE_SIZE);
    memset(buf_mmap, 0, reqbuf.count * IMAGE_SIZE);
    for (i = 0; i < reqbuf.count; i++) {
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        ret = ioctl(fd_cam, VIDIOC_QUERYBUF, &buf);
        if (ret < 0) {
            printf("Query camera device buffer error\n");
            goto exit_cam;
        }

        buf_mmap[i * IMAGE_SIZE] = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd_cam, buf.m.offset);
        if (buf_mmap[i * IMAGE_SIZE] == MAP_FAILED) {
            printf("Map camera device buffer error\n");
            goto exit_cam;
        }

        ret = ioctl(fd_cam, VIDIOC_QBUF, &buf);
        if (ret < 0) {
            printf("Queue camera device buffer error\n");
            goto exit_cam;
        }
    }

    ret = ioctl(fd_cam, VIDIOC_STREAMON, &fmt.type);
    if (ret < 0) {
        printf("Start camera device streaming error\n");
        goto exit_cam;
    }

    mpp_env_init();

    ret = mpp_create(&ctx, &mpi);
    if (ret) {
        printf("Create mpp context error\n");
        goto exit_mpp;
    }

    ret = mpp_init(ctx, MPP_CTX_ENC, MPP_VIDEO_CodingMJPEG);
    if (ret) {
        printf("Init mpp context error\n");
        goto exit_mpp;
    }

    ret = mpp_buffer_get(ctx, &mpp_buf_in, IMAGE_SIZE);
    if (ret) {
        printf("Get mpp input buffer error\n");
        goto exit_mpp;
    }

    ret = mpp_buffer_get(ctx, &mpp_buf_out, IMAGE_SIZE);
    if (ret) {
        printf("Get mpp output buffer error\n");
        goto exit_mpp;
    }

    data_in = mpp_buffer_get_ptr(mpp_buf_in);
    data_out = mpp_buffer_get_ptr(mpp_buf_out);

    fp = fopen("image.jpg", "wb");

    for (i = 0; i < 10; i++) {
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        ret = ioctl(fd_cam, VIDIOC_DQBUF, &buf);
        if (ret < 0) {
            printf("Dequeue camera device buffer error\n");
            goto exit_cam;
        }

        memcpy(data_in, buf_mmap + buf.index * IMAGE_SIZE, IMAGE_SIZE);

        ret = mpp_frame_init(&packet_out);
        if (ret) {
            printf("Init mpp output packet error\n");
            goto exit_cam;
        }

        ret = mpi->encode_put_frame(ctx, mpp_buf_in, NULL);
        if (ret) {
            printf("Put mpp input frame error\n");
            goto exit_cam;
        }

        ret = mpi->encode_get_packet(ctx, &packet_out);
        if (ret) {
            printf("Get mpp output packet error\n");
            goto exit_cam;
        }

        size_out = mpp_packet_get_length(packet_out);
        packet_size_out = size_out;
        memcpy(data_out, mpp_packet_get_pos(packet_out), size_out);

        fwrite(data_out, size_out, 1, fp);

        ret = mpp_packet_deinit(&packet_out);
        if (ret) {
            printf("Deinit mpp output packet error\n");
            goto exit_cam;
        }

        ret = ioctl(fd_cam, VIDIOC_QBUF, &buf);
        if (ret < 0) {
            printf("Queue camera device buffer error\n");
            goto exit_cam;
        }
    }

    fclose(fp);

exit_mpp:
    mpp_buffer_put(mpp_buf_in);
    mpp_buffer_put(mpp_buf_out);
    mpp_destroy(ctx);
    mpp_env_deinit();

exit_cam:
    ioctl(fd_cam, VIDIOC_STREAMOFF, &fmt.type);
    for (i = 0; i < reqbuf.count; i++) {
        munmap(buf_mmap[i * IMAGE_SIZE], IMAGE_SIZE);
    }
    free(buf_mmap);
    close(fd_cam);

    return 0;
}

这段代码首先通过V4L2接口配置摄像头的格式和缓冲区，并启动摄像头的数据流。然后使用mpp接口初始化编码器上下文，并获取输入和输出缓冲区。在获取每一帧摄像头数据后，将数据拷贝到mpp输入缓冲区中，并调用mpp接口进行编码。编码完成后将输出的mjpeg数据保存到文件中。最后关闭所有资源并退出程序。

LV_DISP_ROT_MAX_BUF

LV_DISP_ROT_MAX_BUF是LittlevGL图形库中的一个宏定义，用于定义旋转缓冲区的最大数量。转缓冲区是用于存储旋转后的图像数据的内存区域，可以在图形显示过程中进行图像旋转操作。

在LittlevGL中，当需要对图像进行旋转时，可以使用旋转缓冲区来存储旋转后的图像数据，以便在显示时直接使用。LV_DISP_ROT_MAX_BUF定义了旋转缓冲区的最大数量，可以根据实际需求进行调整。