1 files changed, 68 insertions, 4 deletions

diff --git a/progs/xdemos/glxgears.c b/progs/xdemos/glxgears.c
index 8db717f1aa..088f25a357 100644
--- a/progs/xdemos/glxgears.c
+++ b/progs/xdemos/glxgears.c
@@ -23,10 +23,7 @@
  * This is a port of the infamous "gears" demo to straight GLX (i.e. no GLUT)
  * Port by Brian Paul  23 March 2001
  *
- * Command line options:
- *    -info      print GL implementation information
- *    -stereo    use stereo enabled GLX visual
- *
+ * See usage() below for command line options.
  */
 
 
@@ -39,6 +36,11 @@
 #include <GL/gl.h>
 #include <GL/glx.h>
 
+#ifndef GLX_MESA_swap_control
+#define GLX_MESA_swap_control 1
+typedef int (*PFNGLXGETSWAPINTERVALMESAPROC)(void);
+#endif
+
 
 #define BENCHMARK
 
@@ -561,12 +563,73 @@ make_window( Display *dpy, const char *name,
 
 
 /**
+ * Determine whether or not a GLX extension is supported.
+ */
+static int
+is_glx_extension_supported(Display *dpy, const char *query)
+{
+   const int scrnum = DefaultScreen(dpy);
+   const char *glx_extensions = NULL;
+   const size_t len = strlen(query);
+   const char *ptr;
+
+   if (glx_extensions == NULL) {
+      glx_extensions = glXQueryExtensionsString(dpy, scrnum);
+   }
+
+   ptr = strstr(glx_extensions, query);
+   return ((ptr != NULL) && ((ptr[len] == ' ') || (ptr[len] == '\0')));
+}
+
+
+/**
+ * Attempt to determine whether or not the display is synched to vblank.
+ */
+static void
+query_vsync(Display *dpy)
+{
+   int interval = 0;
+
+
+   if (is_glx_extension_supported(dpy, "GLX_MESA_swap_control")) {
+      PFNGLXGETSWAPINTERVALMESAPROC pglXGetSwapIntervalMESA =
+          (PFNGLXGETSWAPINTERVALMESAPROC)
+          glXGetProcAddressARB((const GLubyte *) "glXGetSwapIntervalMESA");
+
+      interval = (*pglXGetSwapIntervalMESA)();
+   } else if (is_glx_extension_supported(dpy, "GLX_SGI_swap_control")) {
+      /* The default swap interval with this extension is 1.  Assume that it
+       * is set to the default.
+       *
+       * Many Mesa-based drivers default to 0, but all of these drivers also
+       * export GLX_MESA_swap_control.  In that case, this branch will never
+       * be taken, and the correct result should be reported.
+       */
+      interval = 1;
+   }
+
+
+   if (interval > 0) {
+      printf("Running synchronized to the vertical refresh.  The framerate should be\n");
+      if (interval == 1) {
+         printf("approximately the same as the monitor refresh rate.\n");
+      } else if (interval > 1) {
+         printf("approximately 1/%d the monitor refresh rate.\n",
+                interval);
+      }
+   }
+}
+
+/**
  * Handle one X event.
  * \return NOP, EXIT or DRAW
  */
 static int
 handle_event(Display *dpy, Window win, XEvent *event)
 {
+   (void) dpy;
+   (void) win;
+
    switch (event->type) {
    case Expose:
       return DRAW;
@@ -686,6 +749,7 @@ main(int argc, char *argv[])
    make_window(dpy, "glxgears", x, y, winWidth, winHeight, &win, &ctx);
    XMapWindow(dpy, win);
    glXMakeCurrent(dpy, win, ctx);
+   query_vsync(dpy);
 
    if (printInfo) {
       printf("GL_RENDERER   = %s\n", (char *) glGetString(GL_RENDERER));