From da3df75a8ce43890bd1b42f69314fff9ca9ffccb Mon Sep 17 00:00:00 2001
From: Yuxuan Shui <yshuiv7@gmail.com>
Date: Sat, 8 Dec 2018 18:15:19 +0000
Subject: [PATCH] Make sure the vsync methods are really available

libglvnd seems to return a pointer to a function that does NOTHING
for things the backing driver doesn't support.

So we check if the extension is actually advertised before using it.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
---
 src/compton.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/compton.c b/src/compton.c
index 0379ba1..f1dd016 100644
--- a/src/compton.c
+++ b/src/compton.c
@@ -4485,6 +4485,11 @@ vsync_opengl_init(session_t *ps) {
   if (!ensure_glx_context(ps))
     return false;
 
+  if (!glx_hasglxext(ps, "GLX_SGI_video_sync")) {
+    printf_errf("(): Your driver doesn't support SGI_video_sync, giving up.");
+    return false;
+  }
+
   // Get video sync functions
   if (!ps->psglx->glXGetVideoSyncSGI)
     ps->psglx->glXGetVideoSyncSGI = (f_GetVideoSync)
@@ -4510,6 +4515,11 @@ vsync_opengl_oml_init(session_t *ps) {
   if (!ensure_glx_context(ps))
     return false;
 
+  if (!glx_hasglxext(ps, "GLX_OML_sync_control")) {
+    printf_errf("(): Your driver doesn't support OML_sync_control, giving up.");
+    return false;
+  }
+
   // Get video sync functions
   if (!ps->psglx->glXGetSyncValuesOML)
     ps->psglx->glXGetSyncValuesOML = (f_GetSyncValuesOML)
@@ -4535,6 +4545,11 @@ vsync_opengl_swc_init(session_t *ps) {
   if (!ensure_glx_context(ps))
     return false;
 
+  if (!glx_hasglxext(ps, "GLX_SGI_swap_control")) {
+    printf_errf("(): Your driver doesn't support SGI_swap_control, giving up.");
+    return false;
+  }
+
   if (!bkend_use_glx(ps)) {
     printf_errf("(): I'm afraid glXSwapIntervalSGI wouldn't help if you are "
         "not using GLX backend. You could try, nonetheless.");
@@ -4563,6 +4578,11 @@ vsync_opengl_mswc_init(session_t *ps) {
   if (!ensure_glx_context(ps))
     return false;
 
+  if (!glx_hasglxext(ps, "GLX_MESA_swap_control")) {
+    printf_errf("(): Your driver doesn't support MESA_swap_control, giving up.");
+    return false;
+  }
+
   if (!bkend_use_glx(ps)) {
     printf_errf("(): I'm afraid glXSwapIntervalMESA wouldn't help if you are "
         "not using GLX backend. You could try, nonetheless.");