layoutx/capture_fb.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <xf86drm.h>
#include <xf86drmMode.h>
#include <drm_fourcc.h>

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

    drmModeRes *res = drmModeGetResources(fd);
    if (!res) { perror("getResources"); return 1; }

    drmModeCrtc *crtc = NULL;
    uint32_t crtc_id = 0;
    for (int i = 0; i < res->count_crtcs; i++) {
        crtc = drmModeGetCrtc(fd, res->crtcs[i]);
        if (crtc && crtc->buffer_id) { crtc_id = crtc->crtc_id; break; }
        if (crtc) { drmModeFreeCrtc(crtc); crtc = NULL; }
    }
    if (!crtc || !crtc->buffer_id) {
        fprintf(stderr, "No active CRTC\n");
        drmModeFreeResources(res);
        return 1;
    }

    fprintf(stderr, "CRTC %u -> FB %u, %ux%u\n",
            crtc_id, crtc->buffer_id, crtc->width, crtc->height);

    drmModeFB2 *fb = drmModeGetFB2(fd, crtc->buffer_id);
    if (!fb) {
        fprintf(stderr, "drmModeGetFB2 failed, trying FB...\n");
        drmModeFB *fb1 = drmModeGetFB(fd, crtc->buffer_id);
        if (!fb1) { perror("getFB"); return 1; }
        fprintf(stderr, "FB: %ux%u pitch=%u handle=%u\n",
                fb1->width, fb1->height, fb1->pitch, fb1->handle);

        uint32_t size = fb1->pitch * fb1->height;
        void *map = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
        if (map == MAP_FAILED) {
            struct drm_mode_map_dumb mreq = { .handle = fb1->handle };
            if (ioctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &mreq)) { perror("map"); return 1; }
            map = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, mreq.offset);
            if (map == MAP_FAILED) { perror("mmap2"); return 1; }
        }
        FILE *fp = fopen("/tmp/frame.bin", "wb");
        fwrite(map, 1, size, fp);
        fclose(fp);
        fprintf(stderr, "Dumped %u bytes to /tmp/frame.bin\n", size);
        munmap(map, size);
        drmModeFreeFB(fb1);
        drmModeFreeCrtc(crtc);
        drmModeFreeResources(res);
        return 0;
    }

    fprintf(stderr, "FB2: %ux%u format=0x%x\n", fb->width, fb->height, fb->pixel_format);
    for (int i = 0; i < 4; i++)
        fprintf(stderr, "  plane[%d]: handle=%u pitch=%u offset=%u\n",
                i, fb->handles[i], fb->pitches[i], fb->offsets[i]);

    if (fb->handles[0] == 0) {
        fprintf(stderr, "No handle on plane 0\n");
        drmModeFreeFB2(fb); drmModeFreeCrtc(crtc); drmModeFreeResources(res);
        return 1;
    }

    uint32_t w = fb->width, h = fb->height;
    uint32_t pitch = fb->pitches[0];
    uint32_t size = pitch * h;

    struct drm_mode_map_dumb mreq = { .handle = fb->handles[0] };
    if (ioctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &mreq)) { perror("map_dumb"); return 1; }

    void *map = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, mreq.offset);
    if (map == MAP_FAILED) { perror("mmap"); return 1; }

    FILE *fp = fopen("/tmp/frame.bin", "wb");
    fwrite(map, 1, size, fp);
    fclose(fp);
    fprintf(stderr, "Dumped %ux%u (pitch=%u, %u bytes) to /tmp/frame.bin\n", w, h, pitch, size);

    munmap(map, size);
    drmModeFreeFB2(fb);
    drmModeFreeCrtc(crtc);
    drmModeFreeResources(res);
    return 0;
}