使用drm api显示NV12数据的C语言代码

以下是一个简单的使用drm api显示NV12数据的C语言代码示例：

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <drm/drm_fourcc.h>
#include <drm/drm_mode.h>

#define WIDTH 640
#define HEIGHT 480

int main() {
    int fd = open("/dev/dri/card0", O_RDWR);
    if (fd < 0) {
        perror("open /dev/dri/card0 failed");
        return -1;
    }

    struct drm_mode_create_dumb create_dumb = {
        .width = WIDTH,
        .height = HEIGHT,
        .bpp = 8,
    };
    if (ioctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb) < 0) {
        perror("DRM_IOCTL_MODE_CREATE_DUMB failed");
        return -1;
    }

    uint32_t handle = create_dumb.handle;

    struct drm_mode_map_dumb map_dumb = {
        .handle = handle,
    };
    if (ioctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb) < 0) {
        perror("DRM_IOCTL_MODE_MAP_DUMB failed");
        return -1;
    }

    size_t size = create_dumb.size;
    uint8_t *buffer = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, map_dumb.offset);
    if (buffer == MAP_FAILED) {
        perror("mmap failed");
        return -1;
    }

    // fill the buffer with NV12 data
    for (int y = 0; y < HEIGHT; y++) {
        for (int x = 0; x < WIDTH; x++) {
            int uv_x = x / 2;
            int uv_y = y / 2 + HEIGHT;
            buffer[y * WIDTH + x] = (uint8_t)(0.2126 * x + 0.7152 * y + 0.0722 * (x + y) / 2);
            buffer[uv_y * WIDTH + uv_x * 2] = (uint8_t)(128 + 0.5 * x - 0.4187 * y - 0.0813 * (x + y) / 2);
            buffer[uv_y * WIDTH + uv_x * 2 + 1] = (uint8_t)(128 - 0.1687 * x - 0.3313 * y + 0.5 * (x + y) / 2);
        }
    }

    struct drm_mode_create_dumb create_dumb2 = {
        .width = WIDTH,
        .height = HEIGHT * 3 / 2,
        .bpp = 8,
    };
    if (ioctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb2) < 0) {
        perror("DRM_IOCTL_MODE_CREATE_DUMB failed");
        return -1;
    }

    uint32_t handle2 = create_dumb2.handle;

    struct drm_mode_map_dumb map_dumb2 = {
        .handle = handle2,
    };
    if (ioctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb2) < 0) {
        perror("DRM_IOCTL_MODE_MAP_DUMB failed");
        return -1;
    }

    size_t size2 = create_dumb2.size;
    uint8_t *buffer2 = mmap(NULL, size2, PROT_READ | PROT_WRITE, MAP_SHARED, fd, map_dumb2.offset);
    if (buffer2 == MAP_FAILED) {
        perror("mmap failed");
        return -1;
    }

    // convert NV12 to YUV420
    for (int y = 0; y < HEIGHT; y++) {
        memcpy(buffer2 + y * WIDTH, buffer + y * WIDTH, WIDTH);
    }
    for (int y = 0; y < HEIGHT / 2; y++) {
        for (int x = 0; x < WIDTH / 2; x++) {
            int uv_x = x * 2;
            int uv_y = y * 2 + HEIGHT;
            buffer2[uv_y * WIDTH + uv_x] = buffer[y * WIDTH + x * 2 + WIDTH * HEIGHT];
            buffer2[uv_y * WIDTH + uv_x + 1] = buffer[y * WIDTH + x * 2 + WIDTH * HEIGHT + 1];
            buffer2[(uv_y + 1) * WIDTH + uv_x] = buffer[y * WIDTH + x * 2 + WIDTH * HEIGHT];
            buffer2[(uv_y + 1) * WIDTH + uv_x + 1] = buffer[y * WIDTH + x * 2 + WIDTH * HEIGHT + 1];
        }
    }

    struct drm_mode_create_plane create_plane = {
        .fb_id = 0,
        .crtc_id = 0,
        .format = DRM_FORMAT_YUV420,
        .plane_id = 0,
        .flags = 0,
    };
    if (ioctl(fd, DRM_IOCTL_MODE_CREATE_PLANES, &create_plane) < 0) {
        perror("DRM_IOCTL_MODE_CREATE_PLANES failed");
        return -1;
    }

    struct drm_mode_set_plane set_plane = {
        .plane_id = create_plane.plane_id,
        .crtc_id = 0,
        .fb_id = create_plane.fb_id,
        .src_x = 0,
        .src_y = 0,
        .src_w = WIDTH << 16,
        .src_h = HEIGHT * 3 / 2 << 16,
        .crtc_x = 0,
        .crtc_y = 0,
        .crtc_w = WIDTH,
        .crtc_h = HEIGHT,
    };
    if (ioctl(fd, DRM_IOCTL_MODE_SETPLANE, &set_plane) < 0) {
        perror("DRM_IOCTL_MODE_SETPLANE failed");
        return -1;
    }

    getchar(); // wait for user input

    if (ioctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &create_dumb2) < 0) {
        perror("DRM_IOCTL_MODE_DESTROY_DUMB failed");
        return -1;
    }

    if (ioctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &create_dumb) < 0) {
        perror("DRM_IOCTL_MODE_DESTROY_DUMB failed");
        return -1;
    }

    close(fd);

    return 0;
}

该示例代码假设你有一个名为 `/dev/dri/card0` 的DRM设备，并且它支持 `DRM_FORMAT_YUV420` 格式。它使用两个dumb buffer，一个用于存储原始的NV12数据，另一个用于存储转换后的YUV420数据。它还使用一个DRM plane将YUV420数据显示在屏幕上。