main.c

#include <stdio.h>
#include <syslog.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <sys/time.h>

#include <bcm_host.h>

DISPMANX_DISPLAY_HANDLE_T display;
DISPMANX_MODEINFO_T display_info;
DISPMANX_RESOURCE_HANDLE_T screen_resource;
VC_IMAGE_TRANSFORM_T transform;
uint32_t image_prt;
VC_RECT_T rect1;
int ret;
int fbfd = 0;
char *fbp = 0;

struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;

unsigned char locked = 0;

void copy_screen(DISPMANX_UPDATE_HANDLE_T handle, void* arg) {
    if (!locked) {
      locked = 1;
      vc_dispmanx_snapshot(display, screen_resource, 0);
      vc_dispmanx_resource_read_data(screen_resource, &rect1, fbp, vinfo.xres * vinfo.bits_per_pixel / 8);
      locked = 0;
    }
}

int main(int argc, char **argv) {
    bcm_host_init();

    display = vc_dispmanx_display_open(0);
    if (!display) {
        syslog(LOG_ERR, "Unable to open primary display");
        return -1;
    }
    ret = vc_dispmanx_display_get_info(display, &display_info);
    if (ret) {
        syslog(LOG_ERR, "Unable to get primary display information");
        return -1;
    }
    syslog(LOG_INFO, "Primary display is %d x %d", display_info.width, display_info.height);

    fbfd = open("/dev/fb1", O_RDWR);
    if (fbfd == -1) {
        syslog(LOG_ERR, "Unable to open secondary display");
        return -1;
    }
    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
        syslog(LOG_ERR, "Unable to get secondary display information");
        return -1;
    }
    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
        syslog(LOG_ERR, "Unable to get secondary display information");
        return -1;
    }

    syslog(LOG_INFO, "Second display is %d x %d %dbps\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);

    screen_resource = vc_dispmanx_resource_create(VC_IMAGE_RGB565, vinfo.xres, vinfo.yres, &image_prt);
    if (!screen_resource) {
        syslog(LOG_ERR, "Unable to create screen buffer");
        close(fbfd);
        vc_dispmanx_display_close(display);
        return -1;
    }

    fbp = (char*) mmap(0, finfo.smem_len, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
    if (fbp <= 0) {
        syslog(LOG_ERR, "Unable to create memory mapping");
        close(fbfd);
        ret = vc_dispmanx_resource_delete(screen_resource);
        vc_dispmanx_display_close(display);
        return -1;
    }

    vc_dispmanx_rect_set(&rect1, 0, 0, vinfo.xres, vinfo.yres);

    // Initialise callback
    vc_dispmanx_vsync_callback(display, (DISPMANX_CALLBACK_FUNC_T)copy_screen, NULL);

    // Do nothing
    pause();

    // Cleanup on kill signal
    munmap(fbp, finfo.smem_len);
    close(fbfd);
    vc_dispmanx_resource_delete(screen_resource);
    vc_dispmanx_vsync_callback(display, NULL, NULL);
    vc_dispmanx_display_close(display);

    return;
}