Use the XComposite extension when present.

Should fix some issues with semi-transparent notification windows.

Makefile.am

@@ -30,6 +30,9 @@ xsecurelock_CPPFLAGS = \
 if HAVE_SCRNSAVER
 xsecurelock_CPPFLAGS += -DHAVE_SCRNSAVER
 endif
+if HAVE_COMPOSITE
+xsecurelock_CPPFLAGS += -DHAVE_COMPOSITE
+endif
 if HAVE_XF86MISC
 xsecurelock_CPPFLAGS += -DHAVE_XF86MISC
 endif

configure.ac

@@ -25,6 +25,10 @@ AC_SEARCH_LIBS(XScreenSaverQueryExtension, Xss,
  [have_scrnsaver=true], [have_scrnsaver=false])
 AM_CONDITIONAL([HAVE_SCRNSAVER], [test x$have_scrnsaver = xtrue])
 
+AC_SEARCH_LIBS(XCompositeQueryExtension, Xcomposite,
+ [have_composite=true], [have_composite=false])
+AM_CONDITIONAL([HAVE_COMPOSITE], [test x$have_composite = xtrue])
+
 AC_SEARCH_LIBS(XF86MiscSetGrabKeysState, Xxf86misc,
  [have_xf86misc=true], [have_xf86misc=false])
 AM_CONDITIONAL([HAVE_XF86MISC], [test x$have_xf86misc = xtrue])

main.c

@@ -37,6 +37,9 @@ limitations under the License.
 #ifdef HAVE_SCRNSAVER
 #include <X11/extensions/scrnsaver.h>
 #endif
+#ifdef HAVE_COMPOSITE
+#include <X11/extensions/Xcomposite.h>
+#endif
 #ifdef HAVE_XF86MISC
 #include <X11/extensions/xf86misc.h>
 #endif
@@ -348,13 +351,35 @@ int main(int argc, char **argv) {
  coverattrs.cursor =
  XCreatePixmapCursor(display, bg, bg, &Black, &Black, 0, 0);
 
+ Window parent_window = root_window;
+
+#ifdef HAVE_COMPOSITE
+ int composite_event_base, composite_error_base,
+ composite_major_version = 0, composite_minor_version = 0;
+ int have_composite =
+ XCompositeQueryExtension(display, &composite_event_base,
+ &composite_error_base) &&
+ // Require at least XComposite 0.3.
+ XCompositeQueryVersion(display, &composite_major_version,
+ &composite_minor_version) &&
+ (composite_major_version >= 1 || composite_minor_version >= 3);
+ Window composite_window;
+ if (have_composite) {
+ composite_window = XCompositeGetOverlayWindow(display, root_window);
+ parent_window = composite_window;
+ fprintf(stderr, "XComposite using parent window 0x%x.\n", parent_window);
+ } else {
+ fprintf(stderr, "XComposite extension not detected.\n");
+ }
+#endif
+
  // Create the two windows.
  // grab_window is the outer window which we grab input on.
  // saver_window is the "visible" window that the savers will draw on.
  // These windows are separated because XScreenSaver's savers might
  // XUngrabKeyboard on their window.
  Window grab_window = XCreateWindow(
- display, root_window, 0, 0, w, h, 0, CopyFromParent, InputOutput,
+ display, parent_window, 0, 0, w, h, 0, CopyFromParent, InputOutput,
  CopyFromParent, CWOverrideRedirect | CWSaveUnder, &coverattrs);
  Window saver_window = XCreateWindow(
  display, grab_window, 0, 0, w, h, 0, CopyFromParent, InputOutput,
@@ -534,7 +559,7 @@ int main(int argc, char **argv) {
  }
  switch (priv.ev.type) {
  case ConfigureNotify:
- if (priv.ev.xconfigure.window == root_window) {
+ if (priv.ev.xconfigure.window == parent_window) {
  // Root window size changed. Adjust the saver_window window too!
  w = priv.ev.xconfigure.width;
  h = priv.ev.xconfigure.height;
@@ -666,6 +691,11 @@ int main(int argc, char **argv) {
  // Free our resources, and exit.
  XDestroyWindow(display, saver_window);
  XDestroyWindow(display, grab_window);
+#ifdef HAVE_COMPOSITE
+ if (have_composite) {
+ XCompositeReleaseOverlayWindow(display, composite_window);
+ }
+#endif
  XFreeCursor(display, coverattrs.cursor);
  XFreePixmap(display, bg);