Add initial version of the code

.clang-format

@@ -0,0 +1,7 @@
+BasedOnStyle: LLVM
+---
+Language: Cpp
+DerivePointerAlignment: false
+PointerAlignment: Right
+AlwaysBreakTemplateDeclarations: true
+ColumnLimit: 100

.gitignore

@@ -50,3 +50,6 @@ modules.order
 Module.symvers
 Mkfile.old
 dkms.conf
+
+# Our executable
+i3bgwin

Makefile

@@ -0,0 +1,9 @@
+CC=gcc
+CFLAGS=-std=c99 -Wall -Wextra
+LDFLAGS=-s
+LDLIBS=-lX11 -lXext
+
+all: i3bgwin
+
+i3bgwin: i3bgwin.o
+	$(CC) $(LDFLAGS) $^ -o $@ $(LDLIBS)

i3bgwin.c

@@ -0,0 +1,115 @@
+#define _DEFAULT_SOURCE
+
+#include <X11/Xatom.h>
+#include <X11/Xlib.h>
+#include <X11/extensions/shape.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[]) {
+  Display *display = XOpenDisplay(NULL);
+  if (display == NULL) {
+    fprintf(stderr, "Cannot open display\n");
+    exit(1);
+  }
+
+  int ignored;
+  if (!XShapeQueryExtension(display, &ignored, &ignored)) {
+    fprintf(stderr, "No SHAPE extension\n");
+    exit(1);
+  }
+
+  int screen = DefaultScreen(display);
+  XVisualInfo vinfo;
+  XMatchVisualInfo(display, screen, 32, TrueColor, &vinfo);
+
+  XSetWindowAttributes attrs = {};
+  attrs.event_mask =
+      SubstructureRedirectMask | SubstructureNotifyMask | StructureNotifyMask | ExposureMask;
+  attrs.do_not_propagate_mask = 0;
+  attrs.colormap = XCreateColormap(display, RootWindow(display, screen), vinfo.visual, AllocNone);
+  attrs.border_pixel = 0;
+  attrs.background_pixel = 0;
+  attrs.override_redirect = True;
+
+  Window window = XCreateWindow(
+      display, RootWindow(display, screen), 0, 0, DisplayWidth(display, screen),
+      DisplayHeight(display, screen), 0, vinfo.depth, InputOutput, vinfo.visual,
+      CWEventMask | CWColormap | CWBorderPixel | NoEventMask | CWBackPixel | CWOverrideRedirect,
+      &attrs);
+
+  Atom wmDeleteMessage = XInternAtom(display, "WM_DELETE_WINDOW", False);
+  XSetWMProtocols(display, window, &wmDeleteMessage, 1);
+
+  Atom netWmWindowType = XInternAtom(display, "_NET_WM_WINDOW_TYPE", False);
+  Atom netWmWindowTypeDesktop = XInternAtom(display, "_NET_WM_WINDOW_TYPE_DESKTOP", False);
+  XChangeProperty(display, window, netWmWindowType, XA_ATOM, 32, PropModeReplace,
+                  (unsigned char *)&netWmWindowTypeDesktop, 1);
+
+  XLowerWindow(display, window);
+
+  Region region = XCreateRegion();
+  XShapeCombineRegion(display, window, ShapeInput, 0, 0, region, ShapeSet);
+  XDestroyRegion(region);
+
+  XMapWindow(display, window);
+
+  pid_t pid = fork();
+  if (pid == -1) {
+    perror("Failed to fork");
+    exit(1);
+  } else if (pid == 0) {
+    char window_id[64];
+    sprintf(window_id, "%lu", window);
+
+    char **child_argv = calloc(argc, sizeof(char *));
+    for (int i = 0; i < argc; ++i) {
+      if (argv[i + 1] && strcmp(argv[i + 1], "{windowid}") == 0) {
+        child_argv[i] = window_id;
+      } else {
+        child_argv[i] = argv[i + 1];
+      }
+    }
+
+    execvp(child_argv[0], child_argv);
+
+    perror("Can't execute child process!");
+    _exit(1);
+  }
+
+  Display *child_display = NULL;
+  Window child_window = 0;
+
+  while (1) {
+    XEvent event;
+    XNextEvent(display, &event);
+
+    if (event.type == MapRequest) {
+      XMapWindow(event.xmaprequest.display, event.xmaprequest.window);
+      child_display = event.xmaprequest.display;
+      child_window = event.xmaprequest.window;
+    } else if (event.type == ConfigureNotify || event.type == MapRequest) {
+      if (child_window) {
+        XWindowAttributes attrs;
+        XGetWindowAttributes(display, window, &attrs);
+        XMoveResizeWindow(child_display, child_window, 0, 0, attrs.width, attrs.height);
+      }
+    } else if (event.type == Expose) {
+      XClearWindow(display, window);
+    } else if (event.type == DestroyNotify) {
+      break;
+    } else if (event.type == ClientMessage && event.xclient.data.l[0] == (long)wmDeleteMessage) {
+      break;
+    }
+  }
+
+  kill(pid, SIGTERM);
+  wait(0);
+
+  XCloseDisplay(display);
+  return 0;
+}