From 544ef137ee927ea51c3ed697578732d965668512 Mon Sep 17 00:00:00 2001
From: rdb <git@rdb.name>
Date: Sat, 24 Nov 2018 22:44:55 +0100
Subject: [PATCH] x11display: fix crash with multithreading and NVIDIA driver

---
 panda/src/x11display/x11GraphicsWindow.cxx | 17 +++++++++++++++++
 panda/src/x11display/x11GraphicsWindow.h   |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/panda/src/x11display/x11GraphicsWindow.cxx b/panda/src/x11display/x11GraphicsWindow.cxx
index 17f6ca0a2a..9a1555c27e 100644
--- a/panda/src/x11display/x11GraphicsWindow.cxx
+++ b/panda/src/x11display/x11GraphicsWindow.cxx
@@ -218,6 +218,23 @@ move_pointer(int device, int x, int y) {
   }
 }
 
+/**
+ * Clears the entire framebuffer before rendering, according to the settings
+ * of get_color_clear_active() and get_depth_clear_active() (inherited from
+ * DrawableRegion).
+ *
+ * This function is called only within the draw thread.
+ */
+void x11GraphicsWindow::
+clear(Thread *current_thread) {
+  if (is_any_clear_active()) {
+    // Evidently the NVIDIA driver may call glXCreateNewContext inside
+    // prepare_display_region, so we need to hold the X11 lock.
+    LightReMutexHolder holder(x11GraphicsPipe::_x_mutex);
+    GraphicsOutput::clear(current_thread);
+  }
+}
+
 /**
  * This function will be called within the draw thread before beginning
  * rendering for a given frame.  It should do whatever setup is required, and
diff --git a/panda/src/x11display/x11GraphicsWindow.h b/panda/src/x11display/x11GraphicsWindow.h
index 078b016262..906a64b623 100644
--- a/panda/src/x11display/x11GraphicsWindow.h
+++ b/panda/src/x11display/x11GraphicsWindow.h
@@ -36,6 +36,8 @@ public:
 
   virtual MouseData get_pointer(int device) const;
   virtual bool move_pointer(int device, int x, int y);
+
+  virtual void clear(Thread *current_thread);
   virtual bool begin_frame(FrameMode mode, Thread *current_thread);
   virtual void end_frame(FrameMode mode, Thread *current_thread);