diff --git a/main.c b/main.c
index 934a591..bbe839d 100644
--- a/main.c
+++ b/main.c
@@ -8,6 +8,179 @@
 
 #include <bcm_host.h>
 
+#define INTERLACE_NUM 2
+
+int process_interlaced() {
+    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;
+
+    uint16_t *screenbuf[3];
+    uint8_t bufNum = 0;
+
+    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;
+    }
+
+    // Allocate 3 screen buffers (current, prior, delta)
+    screenbuf[0] = (uint16_t *)malloc(vinfo.xres * vinfo.yres * 2 * 3);
+    if(!screenbuf[0]) {
+        printf("malloc fail");
+        return -1;
+    }
+    memset(screenbuf[0], 0, vinfo.xres * vinfo.yres * 2 * 2);
+    screenbuf[1] = &screenbuf[0][vinfo.xres * vinfo.yres];
+    screenbuf[2] = &screenbuf[1][vinfo.xres * vinfo.yres];
+
+    fbp = (char*) mmap(0, finfo.smem_len, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
+    if (fbp <= 0) {
+        syslog(LOG_ERR, "Unable to create mamory 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);
+
+    int row_offset = 0;
+
+    while (1) {
+        ret = vc_dispmanx_snapshot(display, screen_resource, 0);
+
+        // Transfer snamshot to screenbuf
+        vc_dispmanx_resource_read_data(screen_resource, &rect1,
+          (char *)screenbuf[bufNum], vinfo.xres * vinfo.bits_per_pixel / 8);
+
+        // Calculate XOR between two screenbufs
+        uint32_t *p0 = (uint32_t *)screenbuf[0], // 32-bit ops
+                 *p1 = (uint32_t *)screenbuf[1],
+                 *p2 = (uint32_t *)screenbuf[2];
+
+        //Only xor the rows we need
+        for(int i=row_offset; i< vinfo.xres * vinfo.yres / 2; i += INTERLACE_NUM) {
+          p2[i] = p0[i] ^ p1[i];
+        }
+
+        //not yet sure if needed, but zero out the rest
+        for(int i= (row_offset + 1 % INTERLACE_NUM); i< vinfo.xres * vinfo.yres / 2; i += INTERLACE_NUM) {
+          p2[i] = 0;
+        }
+
+        // Find bounding rect of nonzero pixels
+        uint32_t first;
+        uint32_t last;
+
+        // Find first nonzero lword
+        for(first=0; (first < (vinfo.xres * vinfo.yres / 2)) && !p2[first];
+          first++);
+
+        if(first < (vinfo.xres * vinfo.yres / 2)) { // ANY change?
+          // Find last nonzero lword
+          for(last=(vinfo.xres * vinfo.yres / 2) - 1; (last > first) &&
+            !p2[last]; last--);
+
+          int firstRow = first / (vinfo.xres / 2);
+          int lastRow  = last  / (vinfo.xres / 2);
+
+#if 0
+          // Let's try a full-width copy (single memcpy operation)
+          memcpy(
+            (uint16_t *)&fbp[firstRow * vinfo.xres * 2],
+            &screenbuf[bufNum][firstRow * vinfo.xres],
+            vinfo.xres * (lastRow - firstRow + 1) * 2);
+#else
+          // Find actual rect bounds and use memcpy-per-row
+          int firstCol = vinfo.xres - 1, lastCol = 0;
+
+          for(int row= firstRow; row <= lastRow; row += INTERLACE_NUM) {
+            uint16_t *s = (uint16_t *)&p2[row * vinfo.xres / 2];
+
+            for(int col=0; col<vinfo.xres; col++) {
+              if(s[col]) {
+                if(col < firstCol) firstCol = col;
+                if(col > lastCol)  lastCol  = col;
+              }
+            }
+          }
+
+          // printf("(%d,%d) (%d,%d)\n", firstCol, firstRow, lastCol, lastRow);
+
+          int bytes = (lastCol - firstCol + 1) * 2;
+          uint16_t *src = &screenbuf[bufNum][firstRow * vinfo.xres + firstCol];
+          uint16_t *dst = (uint16_t *)&fbp[(firstRow * vinfo.xres + firstCol) * 2];
+
+          for(int row = firstRow; row <= lastRow; row += INTERLACE_NUM) {
+            memcpy(dst, src, bytes);
+            src += vinfo.xres;
+            dst += vinfo.xres;
+          }
+
+//          memcpy(fbp, screenbuf[2], vinfo.xres * vinfo.yres * 2);
+#endif
+          bufNum = 1 - bufNum;
+        }
+        
+        usleep(1000000 / 30); // 30 fps max
+
+        row_offset += 1;
+
+        if (row_offset >= INTERLACE_NUM) {
+          row_offset = 0;
+        }
+    }
+
+    munmap(fbp, finfo.smem_len);
+    close(fbfd);
+    ret = vc_dispmanx_resource_delete(screen_resource);
+    vc_dispmanx_display_close(display);
+}
+
+
 int process() {
     DISPMANX_DISPLAY_HANDLE_T display;
     DISPMANX_MODEINFO_T display_info;
@@ -160,7 +333,7 @@ int main(int argc, char **argv) {
     setlogmask(LOG_UPTO(LOG_DEBUG));
     openlog("fbcp", LOG_NDELAY | LOG_PID, LOG_USER);
 
-    return process();
+    return process_interlaced();
 }