diff --git a/unix/kasmxproxy/kasmxproxy.c b/unix/kasmxproxy/kasmxproxy.c
index cea6c4d..f74371f 100644
--- a/unix/kasmxproxy/kasmxproxy.c
+++ b/unix/kasmxproxy/kasmxproxy.c
@@ -21,8 +21,14 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
 #include <unistd.h>
 #include <X11/Xlib.h>
+#include <X11/Xutil.h>
+#include <X11/extensions/XShm.h>
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
 
 static void help(const char name[]) {
 	printf("Usage: %s [opts]\n\n"
@@ -80,5 +86,96 @@ int main(int argc, char **argv) {
 		}
 	}
 
+	Display *appdisp = XOpenDisplay(appstr);
+	if (!appdisp) {
+		printf("Cannot open display %s\n", appstr);
+		return 1;
+	}
+	if (!XShmQueryExtension(appdisp)) {
+		printf("Display %s lacks SHM extension\n", appstr);
+		return 1;
+	}
+
+	Display *vncdisp = XOpenDisplay(vncstr);
+	if (!vncdisp) {
+		printf("Cannot open display %s\n", vncstr);
+		return 1;
+	}
+	if (!XShmQueryExtension(vncdisp)) {
+		printf("Display %s lacks SHM extension\n", vncstr);
+		return 1;
+	}
+
+	const int appscreen = DefaultScreen(appdisp);
+	const int vncscreen = DefaultScreen(vncdisp);
+	Visual *appvis = DefaultVisual(appdisp, appscreen);
+	Visual *vncvis = DefaultVisual(vncdisp, vncscreen);
+	const int appdepth = DefaultDepth(appdisp, appscreen);
+	const int vncdepth = DefaultDepth(vncdisp, vncscreen);
+	if (appdepth != vncdepth) {
+		printf("Depths don't match, app %u vnc %u\n", appdepth, vncdepth);
+		return 1;
+	}
+
+	Window approot = DefaultRootWindow(appdisp);
+	Window vncroot = DefaultRootWindow(vncdisp);
+	XWindowAttributes appattr, vncattr;
+
+	XGCValues gcval;
+	gcval.plane_mask = AllPlanes;
+	gcval.function = GXcopy;
+	GC gc = XCreateGC(vncdisp, vncroot, GCFunction | GCPlaneMask, &gcval);
+
+	XImage *img = NULL;
+	XShmSegmentInfo shminfo;
+	unsigned imgw = 0, imgh = 0;
+
+	const unsigned sleeptime = 1000 * 1000 / fps;
+
+	while (1) {
+		if (!XGetWindowAttributes(appdisp, approot, &appattr))
+			break;
+		if (!XGetWindowAttributes(vncdisp, vncroot, &vncattr))
+			break;
+		if (resize && (appattr.width != vncattr.width ||
+				appattr.height != vncattr.height)) {
+			// TODO resize app display to VNC display size
+		}
+
+		const unsigned w = min(appattr.width, vncattr.width);
+		const unsigned h = min(appattr.height, vncattr.height);
+
+		if (w != imgw || h != imgh) {
+			if (img) {
+				XShmDetach(appdisp, &shminfo);
+				XDestroyImage(img);
+				shmdt(shminfo.shmaddr);
+				shmctl(shminfo.shmid, IPC_RMID, NULL);
+			}
+			img = XShmCreateImage(appdisp, appvis, appdepth, ZPixmap,
+						NULL, &shminfo, w, h);
+			if (!img)
+				break;
+
+			shminfo.shmid = shmget(IPC_PRIVATE,
+						img->bytes_per_line * img->height,
+						IPC_CREAT | 0666);
+			if (shminfo.shmid == -1)
+				break;
+			shminfo.shmaddr = img->data = shmat(shminfo.shmid, 0, 0);
+			shminfo.readOnly = False;
+			if (!XShmAttach(appdisp, &shminfo))
+				break;
+
+			imgw = w;
+			imgh = h;
+		}
+
+		XShmGetImage(appdisp, approot, img, 0, 0, 0xffffffff);
+		XPutImage(vncdisp, vncroot, gc, img, 0, 0, 0, 0, w, h);
+
+		usleep(sleeptime);
+	}
+
 	return 0;
 }