Use SHM events for synchronisation when possible

1 files changed, 104 insertions, 6 deletions

diff --git a/xlib.c b/xlib.c
index 6ca665d..b98735b 100644
--- a/xlib.c
+++ b/xlib.c
@@ -5,6 +5,12 @@
 #include <stdlib.h>
 
 #include <X11/Xutil.h>
+#include <X11/Xlibint.h>
+#include <X11/Xproto.h>
+#include <X11/extensions/XShm.h>
+#include <X11/extensions/shmproto.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
 
 struct xlib_device {
     struct device base;
@@ -16,8 +22,85 @@ struct xlib_device {
     Window drawable;
     Pixmap pixmap[2];
     GC gc;
+
+    struct {
+	    XShmSegmentInfo shm;
+	    Pixmap pixmap;
+	    int opcode, event;
+    } shm_sync;
 };
 
+static void shm_sync_event (struct xlib_device *device)
+{
+	XShmCompletionEvent ev;
+
+	ev.type = device->shm_sync.event;
+	ev.send_event = 1; /* XXX or lie? */
+	ev.serial = NextRequest (device->display);
+	ev.drawable = device->drawable;
+	ev.major_code = device->shm_sync.opcode;
+	ev.minor_code = X_ShmPutImage;
+	ev.shmseg = device->shm_sync.shm.shmid;
+	ev.offset = device->q;
+
+	XSendEvent (device->display, ev.drawable, False, 0, (XEvent *)&ev);
+	XFlush (device->display);
+}
+
+static void shm_sync_init (struct xlib_device *device)
+{
+    Display *dpy = device->display;
+    int major, minor, has_pixmap;
+    XExtCodes *codes;
+
+    XShmQueryVersion (dpy, &major, &minor, &has_pixmap);
+    if (!has_pixmap)
+	return;
+
+    codes = XInitExtension (dpy, SHMNAME);
+    if (codes == NULL)
+	return;
+
+    device->shm_sync.shm.shmid = shmget(IPC_PRIVATE, 4096, IPC_CREAT | 0777);
+    device->shm_sync.shm.shmaddr = (char *) shmat (device->shm_sync.shm.shmid, NULL, 0);
+    device->shm_sync.shm.readOnly = False;
+
+    if (!XShmAttach (dpy, &device->shm_sync.shm))
+	abort ();
+
+    device->shm_sync.opcode = codes ->major_opcode;
+    device->shm_sync.event = codes->first_event;
+
+    device->shm_sync.pixmap = XShmCreatePixmap (dpy,
+						device->drawable,
+						device->shm_sync.shm.shmaddr,
+						&device->shm_sync.shm,
+						1, 1, 24);
+
+    shm_sync_event (device);
+}
+
+static void shm_sync (struct xlib_device *device)
+{
+    if (!device->shm_sync.pixmap)
+	return;
+
+    do {
+	XEvent ev;
+	XShmCompletionEvent *shm;
+
+	XNextEvent (device->display, &ev);
+	if (ev.type != device->shm_sync.event)
+	    continue;
+
+	shm = (XShmCompletionEvent *)&ev;
+	if (shm->shmseg != device->shm_sync.shm.shmid)
+	    continue;
+
+	return;
+    } while (1);
+}
+
 static void
 destroy (struct framebuffer *fb)
 {
@@ -37,7 +120,9 @@ show (struct framebuffer *fb)
 	      0, 0,
 	      device->base.width, device->base.height,
 	      0, 0);
-    XFlush(device->display);
+
+    XFlush (device->display);
+    shm_sync(device);
 }
 
 static struct framebuffer *
@@ -45,12 +130,23 @@ get_fb (struct device *abstract_device)
 {
     struct xlib_device *device = (struct xlib_device *) abstract_device;
     int q = ++device->q & 1;
-    XImage *image = XGetImage(device->display,
-			      device->pixmap[q],
-			      0, 0, 1, 1,
-			      AllPlanes, ZPixmap);
-    if (image)
+    if (device->shm_sync.pixmap) {
+	XCopyArea(device->display,
+		  device->pixmap[q],
+		  device->shm_sync.pixmap,
+		  device->gc,
+		  0, 0,
+		  1, 1,
+		  0, 0);
+	shm_sync_event (device);
+    } else {
+	XImage *image = XGetImage(device->display,
+				  device->pixmap[q],
+				  0, 0, 1, 1,
+				  AllPlanes, ZPixmap);
+	if (image)
 	    XDestroyImage(image);
+    }
     return &device->fb[q];
 }
 
@@ -155,5 +251,7 @@ xlib_open (int argc, char **argv)
 				   GCGraphicsExposures, &gcv);
     }
 
+    shm_sync_init (device);
+
     return &device->base;
 }