panda3d/panda/src/display/graphicsEngine.cxx

// Filename: graphicsEngine.cxx
// Created by:  drose (24Feb02)
//
////////////////////////////////////////////////////////////////////
//
// PANDA 3D SOFTWARE
// Copyright (c) 2001 - 2004, Disney Enterprises, Inc.  All rights reserved
//
// All use of this software is subject to the terms of the Panda 3d
// Software license.  You should have received a copy of this license
// along with this source code; you will also find a current copy of
// the license at http://etc.cmu.edu/panda3d/docs/license/ .
//
// To contact the maintainers of this program write to
// panda3d-general@lists.sourceforge.net .
//
////////////////////////////////////////////////////////////////////

#include "graphicsEngine.h"
#include "graphicsPipe.h"
#include "parasiteBuffer.h"
#include "config_display.h"
#include "pipeline.h"
#include "drawCullHandler.h"
#include "binCullHandler.h"
#include "cullResult.h"
#include "cullTraverser.h"
#include "clockObject.h"
#include "pStatTimer.h"
#include "pStatClient.h"
#include "pStatCollector.h"
#include "mutexHolder.h"
#include "string_utils.h"

#if defined(WIN32)
  #define WINDOWS_LEAN_AND_MEAN
  #include <wtypes.h>
  #undef WINDOWS_LEAN_AND_MEAN  
#else
  #include <sys/time.h>
#endif

PStatCollector GraphicsEngine::_app_pcollector("App");
PStatCollector GraphicsEngine::_yield_pcollector("App:Yield");
PStatCollector GraphicsEngine::_cull_pcollector("Cull");
PStatCollector GraphicsEngine::_draw_pcollector("Draw");
PStatCollector GraphicsEngine::_sync_pcollector("Draw:Sync");
PStatCollector GraphicsEngine::_flip_pcollector("Draw:Flip");
PStatCollector GraphicsEngine::_flip_begin_pcollector("Draw:Flip:Begin");
PStatCollector GraphicsEngine::_flip_end_pcollector("Draw:Flip:End");
PStatCollector GraphicsEngine::_transform_states_pcollector("TransformStates");
PStatCollector GraphicsEngine::_transform_states_unused_pcollector("TransformStates:Unused");
PStatCollector GraphicsEngine::_render_states_pcollector("RenderStates");
PStatCollector GraphicsEngine::_render_states_unused_pcollector("RenderStates:Unused");

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::Constructor
//       Access: Published
//  Description: Creates a new GraphicsEngine object.  The Pipeline is
//               normally left to default to NULL, which indicates the
//               global render pipeline, but it may be any Pipeline
//               you choose.
////////////////////////////////////////////////////////////////////
GraphicsEngine::
GraphicsEngine(Pipeline *pipeline) :
  _pipeline(pipeline)
{
  if (_pipeline == (Pipeline *)NULL) {
    _pipeline = Pipeline::get_render_pipeline();
  }

  _windows_sorted = true;

  // Default frame buffer properties.
  _frame_buffer_properties.set_depth_bits(1);
  _frame_buffer_properties.set_color_bits(1);
  _frame_buffer_properties.set_frame_buffer_mode
    (FrameBufferProperties::FM_rgba | 
     FrameBufferProperties::FM_double_buffer | 
     FrameBufferProperties::FM_depth);

  set_threading_model(GraphicsThreadingModel(threading_model));
  if (!_threading_model.is_default()) {
    display_cat.info()
      << "Using threading model " << _threading_model << "\n";
  }
  _auto_flip = auto_flip;
  _portal_enabled = false;
  _flip_state = FS_flip;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::Destructor
//       Access: Published
//  Description: Gracefully cleans up the graphics engine and its
//               related threads and windows.
////////////////////////////////////////////////////////////////////
GraphicsEngine::
~GraphicsEngine() {
#ifdef DO_PSTATS
  if (_app_pcollector.is_started()) {
    _app_pcollector.stop();
  }
#endif

  remove_all_windows();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::set_frame_buffer_properties
//       Access: Published
//  Description: Specifies the default frame buffer properties for
//               future gsg's created using the one-parameter
//               make_gsg() method.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
set_frame_buffer_properties(const FrameBufferProperties &properties) {
  MutexHolder holder(_lock);
  _frame_buffer_properties = properties;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::get_frame_buffer_properties
//       Access: Published
//  Description: Returns the frame buffer properties for future gsg's.
//               See set_frame_buffer_properties().
////////////////////////////////////////////////////////////////////
FrameBufferProperties GraphicsEngine::
get_frame_buffer_properties() const {
  FrameBufferProperties result;
  {
    MutexHolder holder(_lock);
    result = _frame_buffer_properties;
  }
  return result;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::set_threading_model
//       Access: Published
//  Description: Specifies how future objects created via make_gsg(),
//               make_buffer(), and make_window() will be threaded.
//               This does not affect any already-created objects.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
set_threading_model(const GraphicsThreadingModel &threading_model) {
  if (!threading_model.is_single_threaded() && 
      !Thread::is_threading_supported()) {
    display_cat.warning()
      << "Threading model " << threading_model
      << " requested but threading not supported.\n";
    return;
  }
  MutexHolder holder(_lock);
  _threading_model = threading_model;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::get_threading_model
//       Access: Published
//  Description: Returns the threading model that will be applied to
//               future objects.  See set_threading_model().
////////////////////////////////////////////////////////////////////
GraphicsThreadingModel GraphicsEngine::
get_threading_model() const {
  GraphicsThreadingModel result;
  {
    MutexHolder holder(_lock);
    result = _threading_model;
  }
  return result;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::make_gsg
//       Access: Published
//  Description: Creates a new gsg using the indicated GraphicsPipe
//               and returns it.  The GraphicsEngine does not
//               officially own the pointer to the gsg; but if any
//               windows are created using this GSG, the
//               GraphicsEngine will own the pointers to these
//               windows, which in turn will own the pointer to the
//               GSG.
//
//               There is no explicit way to release a GSG, but it
//               will be destructed when all windows that reference it
//               are destructed, and the draw thread that owns the GSG
//               runs one more time.
////////////////////////////////////////////////////////////////////
PT(GraphicsStateGuardian) GraphicsEngine::
make_gsg(GraphicsPipe *pipe, const FrameBufferProperties &properties,
         GraphicsStateGuardian *share_with) {
  // TODO: ask the draw thread to make the GSG.
  PT(GraphicsStateGuardian) gsg = pipe->make_gsg(properties, share_with);
  if (gsg != (GraphicsStateGuardian *)NULL) {
    gsg->_threading_model = get_threading_model();
    gsg->_pipe = pipe;
    gsg->_engine = this;
  }

  return gsg;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::make_window
//       Access: Published
//  Description: Creates a new window using the indicated
//               GraphicsStateGuardian and returns it.  The
//               GraphicsEngine becomes the owner of the window; it
//               will persist at least until remove_window() is called
//               later.
////////////////////////////////////////////////////////////////////
GraphicsWindow *GraphicsEngine::
make_window(GraphicsStateGuardian *gsg, const string &name, int sort) {
  GraphicsThreadingModel threading_model = get_threading_model();

  nassertr(gsg != (GraphicsStateGuardian *)NULL, NULL);
  nassertr(this == gsg->get_engine(), NULL);
  nassertr(threading_model.get_draw_name() ==
           gsg->get_threading_model().get_draw_name(), NULL);

  // TODO: ask the window thread to make the window.
  PT(GraphicsWindow) window = gsg->get_pipe()->make_window(gsg, name);
  if (window != (GraphicsWindow *)NULL) {
    window->_sort = sort;
    do_add_window(window, gsg, threading_model);
  }
  return window;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::make_buffer
//       Access: Published
//  Description: Creates a new offscreen buffer using the indicated
//               GraphicsStateGuardian and returns it.  The
//               GraphicsEngine becomes the owner of the buffer; it
//               will persist at least until remove_window() is called
//               later.
//
//               This usually returns a GraphicsBuffer object, but it
//               may actually return a GraphicsWindow if show-buffers
//               is configured true.
////////////////////////////////////////////////////////////////////
GraphicsOutput *GraphicsEngine::
make_buffer(GraphicsStateGuardian *gsg, const string &name, 
            int sort, int x_size, int y_size, bool want_texture) {
  if (show_buffers) {
    GraphicsWindow *window = make_window(gsg, name, sort);
    if (window != (GraphicsWindow *)NULL) {
      WindowProperties props;
      props.set_size(x_size, y_size);
      props.set_fixed_size(true);
      props.set_title(name);
      window->request_properties(props);

      if (want_texture) {
        window->setup_copy_texture(name);
      }

      return window;
    }
  }

  GraphicsThreadingModel threading_model = get_threading_model();
  nassertr(gsg != (GraphicsStateGuardian *)NULL, NULL);
  nassertr(this == gsg->get_engine(), NULL);
  nassertr(threading_model.get_draw_name() ==
           gsg->get_threading_model().get_draw_name(), NULL);

  // TODO: ask the window thread to make the buffer.
  PT(GraphicsBuffer) buffer = 
    gsg->get_pipe()->make_buffer(gsg, name, x_size, y_size, want_texture);
  if (buffer != (GraphicsBuffer *)NULL) {
    buffer->_sort = sort;
    do_add_window(buffer, gsg, threading_model);
  }
  return buffer;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::make_parasite
//       Access: Published
//  Description: Creates a new offscreen parasite buffer based on the
//               indicated host.  See parasiteBuffer.h.  The
//               GraphicsEngine becomes the owner of the buffer; it
//               will persist at least until remove_window() is called
//               later.
//
//               This usually returns a ParasiteBuffer object, but it
//               may actually return a GraphicsWindow if show-buffers
//               is configured true.
////////////////////////////////////////////////////////////////////
GraphicsOutput *GraphicsEngine::
make_parasite(GraphicsOutput *host, const string &name, 
              int sort, int x_size, int y_size) {
  GraphicsStateGuardian *gsg = host->get_gsg();

  if (show_buffers) {
    GraphicsWindow *window = make_window(gsg, name, sort);
    if (window != (GraphicsWindow *)NULL) {
      WindowProperties props;
      props.set_size(x_size, y_size);
      props.set_fixed_size(true);
      props.set_title(name);
      window->request_properties(props);
      window->setup_copy_texture(name);

      return window;
    }
  }

  GraphicsThreadingModel threading_model = get_threading_model();
  nassertr(gsg != (GraphicsStateGuardian *)NULL, NULL);
  nassertr(this == gsg->get_engine(), NULL);
  nassertr(threading_model.get_draw_name() ==
           gsg->get_threading_model().get_draw_name(), NULL);

  ParasiteBuffer *buffer = new ParasiteBuffer(host, name, x_size, y_size);
  buffer->_sort = sort;
  do_add_window(buffer, gsg, threading_model);

  return buffer;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::remove_window
//       Access: Published
//  Description: Removes the indicated window or offscreen buffer from
//               the set of windows that will be processed when
//               render_frame() is called.  This also closes the
//               window if it is open, and removes the window from its
//               GraphicsPipe, allowing the window to be destructed if
//               there are no other references to it.  (However, the
//               window may not be actually closed until next frame,
//               if it is controlled by a sub-thread.)
//
//               The return value is true if the window was removed,
//               false if it was not found.
//
//               Unlike remove_all_windows(), this function does not
//               terminate any of the threads that may have been
//               started to service this window; they are left running
//               (since you might open a new window later on these
//               threads).  If your intention is to clean up before
//               shutting down, it is better to call
//               remove_all_windows() then to call remove_window() one
//               at a time.
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::
remove_window(GraphicsOutput *window) {
  // First, make sure we know what this window is.
  PT(GraphicsOutput) ptwin = window;
  size_t count;
  {
    MutexHolder holder(_lock);
    if (!_windows_sorted) {
      do_resort_windows();
    }
    count = _windows.erase(ptwin);
  }
  if (count == 0) {
    // Never heard of this window.  Do nothing.
    return false;
  }

  do_remove_window(window);

  nassertr(count == 1, true);
  return true;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::remove_all_windows
//       Access: Published
//  Description: Removes and closes all windows from the engine.  This
//               also cleans up and terminates any threads that have
//               been started to service those windows.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
remove_all_windows() {
  Windows::iterator wi;
  for (wi = _windows.begin(); wi != _windows.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    do_remove_window(win);
  }
  
  _windows.clear();

  _app.do_release(this);
  _app.do_close(this);
  terminate_threads();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::reset_all_windows
//       Access: Published
//  Description: Resets the framebuffer of the current window.  This
//               is currently used by DirectX 8 only. It calls a
//               reset_window function on each active window to 
//               release/create old/new framebuffer
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
reset_all_windows(bool swapchain) {
  Windows::iterator wi;
  for (wi = _windows.begin(); wi != _windows.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    //    if (win->is_active())
    win->reset_window(swapchain);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::is_empty
//       Access: Published
//  Description: Returns true if there are no windows managed by the
//               engine, false if there is at least one.
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::
is_empty() const {
  return _windows.empty();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::render_frame
//       Access: Published
//  Description: Renders the next frame in all the registered windows,
//               and flips all of the frame buffers.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
render_frame() {
  // Anything that happens outside of GraphicsEngine::render_frame()
  // is deemed to be App.
#ifdef DO_PSTATS
  if (_app_pcollector.is_started()) {
    _app_pcollector.stop();
  }
#endif

  // We hold the GraphicsEngine mutex while we wait for all of the
  // threads.  Doing this puts us at risk for deadlock if any of the
  // threads tries to call any methods on the GraphicsEngine.  So
  // don't do that.
  MutexHolder holder(_lock);

  if (!_windows_sorted) {
    do_resort_windows();
  }

  if (_flip_state != FS_flip) {
    do_flip_frame();
  }

  // Are any of the windows ready to be deleted?
  Windows new_windows;
  new_windows.reserve(_windows.size());
  Windows::iterator wi;
  for (wi = _windows.begin(); wi != _windows.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    if (win->get_delete_flag()) {
      do_remove_window(win);

    } else {
      new_windows.push_back(win);
    }
  }
  new_windows.swap(_windows);
  
  // Grab each thread's mutex again after all windows have flipped.
  Threads::const_iterator ti;
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->_cv_mutex.lock();
  }

  // Now cycle the pipeline and officially begin the next frame.
  _pipeline->cycle();
  ClockObject::get_global_clock()->tick();
  PStatClient::main_tick();

  // Reset our pcollectors that track data across the frame.
  CullTraverser::_nodes_pcollector.clear_level();
  CullTraverser::_geom_nodes_pcollector.clear_level();
  
  _transform_states_pcollector.set_level(TransformState::get_num_states());
  _render_states_pcollector.set_level(RenderState::get_num_states());
  if (pstats_unused_states) {
    _transform_states_unused_pcollector.set_level(TransformState::get_num_unused_states());
    _render_states_unused_pcollector.set_level(RenderState::get_num_unused_states());
  }

  // Now signal all of our threads to begin their next frame.
  _app.do_frame(this);
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    if (thread->_thread_state == TS_wait) {
      thread->_thread_state = TS_do_frame;
      thread->_cv.signal();
    }
    thread->_cv_mutex.release();
  }

  // Some threads may still be drawing, so indicate that we have to
  // wait for those threads before we can flip.
  _flip_state = _auto_flip ? FS_flip : FS_draw;

  if (yield_timeslice) { 
    // Nap for a moment to yield the timeslice, to be polite to other
    // running applications.
    PStatTimer timer(_yield_pcollector);
    struct timeval tv;
    tv.tv_sec = 0;
    tv.tv_usec = 0;
    select(0, NULL, NULL, NULL, &tv);
  }

  // Anything that happens outside of GraphicsEngine::render_frame()
  // is deemed to be App.
  _app_pcollector.start();
}


////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::open_windows
//       Access: Published
//  Description: Fully opens (or closes) any windows that have
//               recently been requested open or closed, without
//               rendering any frames.  It is not necessary to call
//               this explicitly, since windows will be automatically
//               opened or closed when the next frame is rendered, but
//               you may call this if you want your windows now
//               without seeing a frame go by.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
open_windows() {
  MutexHolder holder(_lock);

  if (!_windows_sorted) {
    do_resort_windows();
  }

  _app.do_windows(this);

  Threads::const_iterator ti;
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    if (thread->_thread_state == TS_wait) {
      thread->_thread_state = TS_do_windows;
      thread->_cv.signal();
    }
    thread->_cv_mutex.release();
  }

  // We do it twice, to allow both cull and draw to process the
  // window.
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    if (thread->_thread_state == TS_wait) {
      thread->_thread_state = TS_do_windows;
      thread->_cv.signal();
    }
    thread->_cv_mutex.release();
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::sync_frame
//       Access: Published
//  Description: Waits for all the threads that started drawing their
//               last frame to finish drawing.  The windows are not
//               yet flipped when this returns; see also flip_frame().
//               It is not usually necessary to call this explicitly,
//               unless you need to see the previous frame right away.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
sync_frame() {
  MutexHolder holder(_lock);

  if (_flip_state == FS_draw) {
    do_sync_frame();
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::flip_frame
//       Access: Published
//  Description: Waits for all the threads that started drawing their
//               last frame to finish drawing, and then flips all the
//               windows.  It is not usually necessary to call this
//               explicitly, unless you need to see the previous frame
//               right away.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
flip_frame() {
  MutexHolder holder(_lock);

  if (_flip_state != FS_flip) {
    do_flip_frame();
  }
}


////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::render_subframe
//       Access: Published
//  Description: Performs a complete cull and draw pass for one
//               particular display region.  This is normally useful
//               only for special effects, like shaders, that require
//               a complete offscreen render pass before they can
//               complete.
//
//               This always executes completely within the calling
//               thread, regardless of the threading model in use.
//               Thus, it must always be called from the draw thread,
//               whichever thread that may be.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
render_subframe(GraphicsStateGuardian *gsg, DisplayRegion *dr,
                bool cull_sorting) {
  if (cull_sorting) {
    cull_bin_draw(gsg, dr);
  } else {
    cull_and_draw_together(gsg, dr);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::add_callback
//       Access: Public
//  Description: Adds the indicated C/C++ function and an arbitrary
//               associated data pointer to the list of functions that
//               will be called in the indicated thread at the
//               indicated point of the frame.
//
//               The thread name may be one of the cull or draw names
//               specified in set_threading_model(), or it may be the
//               empty string to indicated the app or main thread.
//
//               The return value is true if the function and data
//               pointer are successfully added to the appropriate
//               callback list, or false if the same function and data
//               pointer were already there.
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::
add_callback(const string &thread_name, 
             GraphicsEngine::CallbackTime callback_time,
             GraphicsEngine::CallbackFunction *func, void *data) {
  WindowRenderer *wr = get_window_renderer(thread_name);
  return wr->add_callback(callback_time, Callback(func, data));
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::remove_callback
//       Access: Public
//  Description: Removes a callback added by a previous call to
//               add_callback().  All parameters must match the same
//               parameters passed to add_callback().  The return
//               value is true if the callback is successfully
//               removed, or false if it was not on the list (either
//               one or more of the parameters did not match the call
//               to add_callback(), or the callback has already been
//               removed).
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::
remove_callback(const string &thread_name, 
                GraphicsEngine::CallbackTime callback_time,
                GraphicsEngine::CallbackFunction *func, void *data) {
  WindowRenderer *wr = get_window_renderer(thread_name);
  return wr->remove_callback(callback_time, Callback(func, data));
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::set_window_sort
//       Access: Private
//  Description: Changes the sort value of a particular window (or
//               buffer) on the GraphicsEngine.  This requires
//               securing the mutex.
//
//               Users shouldn't call this directly; use
//               GraphicsOutput::set_sort() instead.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
set_window_sort(GraphicsOutput *window, int sort) {
  MutexHolder holder(_lock);
  window->_sort = sort;
  _windows_sorted = false;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::cull_and_draw_together
//       Access: Private
//  Description: This is called in the cull+draw thread by individual
//               RenderThread objects during the frame rendering.  It
//               culls the geometry and immediately draws it, without
//               first collecting it into bins.  This is used when the
//               threading model begins with the "-" character.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
cull_and_draw_together(const GraphicsEngine::Windows &wlist) {
  Windows::const_iterator wi;
  for (wi = wlist.begin(); wi != wlist.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    if (win->is_active() && win->get_gsg()->is_active()) {
      if (win->begin_frame()) {
        win->clear();
      
        int num_display_regions = win->get_num_active_display_regions();
        for (int i = 0; i < num_display_regions; i++) {
          DisplayRegion *dr = win->get_active_display_region(i);
          if (dr != (DisplayRegion *)NULL) {
            cull_and_draw_together(win->get_gsg(), dr);
          }
        }
        win->end_frame();

        if (_auto_flip) {
          if (win->flip_ready()) {
            {
              PStatTimer timer(GraphicsEngine::_flip_begin_pcollector);
              win->begin_flip();
            }
            {
              PStatTimer timer(GraphicsEngine::_flip_end_pcollector);
              win->end_flip();
            }
          }
        }
      }
    }
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::cull_and_draw_together
//       Access: Private
//  Description: This variant of cull_and_draw_together() is called
//               only by render_subframe().
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
cull_and_draw_together(GraphicsStateGuardian *gsg, DisplayRegion *dr) {
  nassertv(gsg != (GraphicsStateGuardian *)NULL);

  PT(SceneSetup) scene_setup = setup_scene(dr->get_camera(), gsg);
  if (setup_gsg(gsg, scene_setup)) {
    DisplayRegionStack old_dr = gsg->push_display_region(dr);
    gsg->prepare_display_region();
    if (dr->is_any_clear_active()) {
      gsg->clear(dr);
    }

    DrawCullHandler cull_handler(gsg);
    if (gsg->begin_scene()) {
      do_cull(&cull_handler, scene_setup, gsg);
      gsg->end_scene();
    }
    
    gsg->pop_display_region(old_dr);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::cull_bin_draw
//       Access: Private
//  Description: This is called in the cull thread by individual
//               RenderThread objects during the frame rendering.  It
//               collects the geometry into bins in preparation for
//               drawing.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
cull_bin_draw(const GraphicsEngine::Windows &wlist) {
  Windows::const_iterator wi;
  for (wi = wlist.begin(); wi != wlist.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    if (win->is_active() && win->get_gsg()->is_active()) {
      // This should be done in the draw thread, not here.
      if (win->begin_frame()) {
        win->clear();
      
        int num_display_regions = win->get_num_active_display_regions();
        for (int i = 0; i < num_display_regions; i++) {
          DisplayRegion *dr = win->get_active_display_region(i);
          if (dr != (DisplayRegion *)NULL) {
            cull_bin_draw(win->get_gsg(), dr);
          }
        }
        win->end_frame();

        if (_auto_flip) {
          if (win->flip_ready()) {
            {
              PStatTimer timer(GraphicsEngine::_flip_begin_pcollector);
              win->begin_flip();
            }
            {
              PStatTimer timer(GraphicsEngine::_flip_end_pcollector);
              win->end_flip();
            }
          }
        }
      }
    }
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::cull_bin_draw
//       Access: Private
//  Description: This variant of cull_bin_draw() is called
//               by render_subframe(), as well as within the
//               implementation of cull_bin_draw(), above.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
cull_bin_draw(GraphicsStateGuardian *gsg, DisplayRegion *dr) {
  nassertv(gsg != (GraphicsStateGuardian *)NULL);

  PT(CullResult) cull_result = dr->_cull_result;
  if (cull_result != (CullResult *)NULL) {
    cull_result = cull_result->make_next();
  } else {
    cull_result = new CullResult(gsg);
  }

  PT(SceneSetup) scene_setup = setup_scene(dr->get_camera(), gsg);
  if (scene_setup != (SceneSetup *)NULL) {
    BinCullHandler cull_handler(cull_result);
    do_cull(&cull_handler, scene_setup, gsg);
    
    cull_result->finish_cull();
    
    // Save the results for next frame.
    dr->_cull_result = cull_result;
    
    // Now draw.
    // This should get deferred into the next pipeline stage.
    do_draw(cull_result, scene_setup, gsg, dr);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::make_contexts
//       Access: Private
//  Description: Called in the draw thread, this calls make_context()
//               on each window on the list to guarantee its graphics
//               context gets created.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
make_contexts(const GraphicsEngine::Windows &wlist) {
  Windows::const_iterator wi;
  for (wi = wlist.begin(); wi != wlist.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    if (win->needs_context()) {
      win->make_context();
    }
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::process_events
//       Access: Private
//  Description: This is called by the RenderThread object to process
//               all the windows events (resize, etc.) for the given
//               list of windows.  This is run in the window thread.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
process_events(const GraphicsEngine::Windows &wlist) {
  Windows::const_iterator wi;
  for (wi = wlist.begin(); wi != wlist.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    win->process_events();
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::flip_windows
//       Access: Private
//  Description: This is called by the RenderThread object to flip the
//               buffers for all of the non-single-buffered windows in
//               the given list.  This is run in the draw thread.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
flip_windows(const GraphicsEngine::Windows &wlist) {
  Windows::const_iterator wi;
  for (wi = wlist.begin(); wi != wlist.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    if (win->flip_ready()) {
      PStatTimer timer(GraphicsEngine::_flip_begin_pcollector);
      win->begin_flip();
    }
  }
  for (wi = wlist.begin(); wi != wlist.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    if (win->flip_ready()) {
      PStatTimer timer(GraphicsEngine::_flip_end_pcollector);
      win->end_flip();
    }
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::do_sync_frame
//       Access: Private
//  Description: The implementation of sync_frame().  We assume _lock
//               is already held before this method is called.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
do_sync_frame() {
  // Statistics
  PStatTimer timer(_sync_pcollector);

  nassertv(_flip_state == FS_draw);

  // Wait for all the threads to finish their current frame.  Grabbing
  // and releasing the mutex should achieve that.
  Threads::const_iterator ti;
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->_cv_mutex.lock();
    thread->_cv_mutex.release();
  }

  _flip_state = FS_sync;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::do_flip_frame
//       Access: Private
//  Description: The implementation of flip_frame().  We assume _lock
//               is already held before this method is called.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
do_flip_frame() {
  // Statistics
  PStatTimer timer(_flip_pcollector);

  nassertv(_flip_state == FS_draw || _flip_state == FS_sync);

  // First, wait for all the threads to finish their current frame, if
  // necessary.  Grabbing the mutex should achieve that.
  Threads::const_iterator ti;
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->_cv_mutex.lock();
  }
  
  // Now signal all of our threads to flip the windows.
  _app.do_flip(this);
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    if (thread->_thread_state == TS_wait) {
      thread->_thread_state = TS_do_flip;
      thread->_cv.signal();
    }
    thread->_cv_mutex.release();
  }

  _flip_state = FS_flip;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::setup_scene
//       Access: Private
//  Description: Returns a new SceneSetup object appropriate for
//               rendering the scene from the indicated camera, or
//               NULL if the scene should not be rendered for some
//               reason.
////////////////////////////////////////////////////////////////////
PT(SceneSetup) GraphicsEngine::
setup_scene(const NodePath &camera, GraphicsStateGuardian *gsg) {
  if (camera.is_empty()) {
    // No camera, no draw.
    return NULL;
  }

  Camera *camera_node;
  DCAST_INTO_R(camera_node, camera.node(), NULL);

  if (!camera_node->is_active()) {
    // Camera inactive, no draw.
    return NULL;
  }
  camera_node->cleanup_aux_scene_data();

  Lens *lens = camera_node->get_lens();
  if (lens == (Lens *)NULL) {
    // No lens, no draw.
    return NULL;
  }

  NodePath scene_root = camera_node->get_scene();
  if (scene_root.is_empty()) {
    // No scene, no draw.
    return NULL;
  }

  PT(SceneSetup) scene_setup = new SceneSetup;

  // We will need both the camera transform (the net transform to the
  // camera from the scene) and the world transform (the camera
  // transform inverse, or the net transform to the scene from the
  // camera).  These are actually defined from the parent of the
  // scene_root, because the scene_root's own transform is immediately
  // applied to these during rendering.  (Normally, the parent of the
  // scene_root is the empty NodePath, although it need not be.)
  NodePath scene_parent = scene_root.get_parent();
  CPT(TransformState) camera_transform = camera.get_transform(scene_parent);
  CPT(TransformState) world_transform = scene_parent.get_transform(camera);

  // The render transform is the same as the world transform, except
  // it is converted into the GSG's internal coordinate system.  This
  // is the transform that the GSG will apply to all of its vertices.
  CPT(TransformState) cs_transform = TransformState::make_identity();
  CoordinateSystem external_cs = gsg->get_coordinate_system();
  CoordinateSystem internal_cs = gsg->get_internal_coordinate_system();
  if (internal_cs != CS_default && internal_cs != external_cs) {
    cs_transform = 
      TransformState::make_mat(LMatrix4f::convert_mat(external_cs, internal_cs));
  }

  scene_setup->set_scene_root(scene_root);
  scene_setup->set_camera_path(camera);
  scene_setup->set_camera_node(camera_node);
  scene_setup->set_lens(lens);
  scene_setup->set_camera_transform(camera_transform);
  scene_setup->set_world_transform(world_transform);
  scene_setup->set_cs_transform(cs_transform);

  return scene_setup;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::do_cull
//       Access: Private
//  Description: Fires off a cull traversal using the indicated camera.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
do_cull(CullHandler *cull_handler, SceneSetup *scene_setup,
        GraphicsStateGuardian *gsg) {
  // Statistics
  PStatTimer timer(_cull_pcollector);

  CullTraverser trav;
  trav.set_cull_handler(cull_handler);
  trav.set_depth_offset_decals(gsg->depth_offset_decals());
  trav.set_scene(scene_setup);
  trav.set_camera_mask(scene_setup->get_camera_node()->get_camera_mask());
  
  if (view_frustum_cull) {
    // If we're to be performing view-frustum culling, determine the
    // bounding volume associated with the current viewing frustum.

    // First, we have to get the current viewing frustum, which comes
    // from the lens.
    PT(BoundingVolume) bv = scene_setup->get_lens()->make_bounds();

    if (bv != (BoundingVolume *)NULL &&
        bv->is_of_type(GeometricBoundingVolume::get_class_type())) {
      // Transform it into the appropriate coordinate space.
      PT(GeometricBoundingVolume) local_frustum;
      local_frustum = DCAST(GeometricBoundingVolume, bv->make_copy());

      NodePath scene_parent = scene_setup->get_scene_root().get_parent();
      CPT(TransformState) cull_center_transform = 
        scene_setup->get_cull_center().get_transform(scene_parent);
      local_frustum->xform(cull_center_transform->get_mat());

      trav.set_view_frustum(local_frustum);
    }
  }
  
  trav.traverse(scene_setup->get_scene_root(), get_portal_cull());
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::do_draw
//       Access: Private
//  Description: Draws the previously-culled scene.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
do_draw(CullResult *cull_result, SceneSetup *scene_setup,
        GraphicsStateGuardian *gsg, DisplayRegion *dr) {
  // Statistics
  PStatTimer timer(_draw_pcollector);

  if (setup_gsg(gsg, scene_setup)) {
    DisplayRegionStack old_dr = gsg->push_display_region(dr);
    gsg->prepare_display_region();
    if (dr->is_any_clear_active()) {
      gsg->clear(dr);
    }
    if (gsg->begin_scene()) {
      cull_result->draw();
      gsg->end_scene();
    }
    gsg->pop_display_region(old_dr);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::setup_gsg
//       Access: Private
//  Description: Sets up the GSG to draw the indicated scene.  Returns
//               true if the scene (and its lens) is acceptable, false
//               otherwise.
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::
setup_gsg(GraphicsStateGuardian *gsg, SceneSetup *scene_setup) {
  if (scene_setup == (SceneSetup *)NULL) {
    // No scene, no draw.
    return false;
  }

  const Lens *lens = scene_setup->get_lens();
  if (lens == (const Lens *)NULL) {
    // No lens, no draw.
    return false;
  }

  if (!gsg->set_lens(lens)) {
    // The lens is inappropriate somehow.
    display_cat.error()
      << gsg->get_type() << " cannot render with " << lens->get_type()
      << "\n";
    return false;
  }

  gsg->set_scene(scene_setup);

  return true;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::do_add_window
//       Access: Private
//  Description: An internal function called by make_window() and
//               make_buffer() and similar functions to add the
//               newly-created GraphicsOutput object to the engine's
//               tables.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
do_add_window(GraphicsOutput *window, GraphicsStateGuardian *gsg,
              const GraphicsThreadingModel &threading_model) {
  MutexHolder holder(_lock);
  _windows_sorted = false;
  _windows.push_back(window);
  
  WindowRenderer *cull = get_window_renderer(threading_model.get_cull_name());
  WindowRenderer *draw = get_window_renderer(threading_model.get_draw_name());
  draw->add_gsg(gsg);
  
  if (threading_model.get_cull_sorting()) {
    cull->add_window(cull->_cull, window);
    draw->add_window(draw->_draw, window);
  } else {
    cull->add_window(cull->_cdraw, window);
  }
  
  // We should ask the pipe which thread it prefers to run its
  // windowing commands in (the "window thread").  This is the
  // thread that handles the commands to open, resize, etc. the
  // window.  X requires this to be done in the app thread, but some
  // pipes might prefer this to be done in draw, for instance.  For
  // now, we assume this is the app thread.
  _app.add_window(_app._window, window);
  
  display_cat.info()
    << "Created " << window->get_type() << "\n";
  
  // By default, try to open each window as it is added.
  window->request_open();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::do_remove_window
//       Access: Private
//  Description: An internal function called by remove_window() and
//               remove_all_windows() to actually remove the indicated
//               window from all relevant structures, except the
//               _windows list itself.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
do_remove_window(GraphicsOutput *window) {
  PT(GraphicsPipe) pipe = window->get_pipe();
  window->_pipe = (GraphicsPipe *)NULL;

  if (!_windows_sorted) {
    do_resort_windows();
  }

  // Now remove the window from all threads that know about it.
  _app.remove_window(window);
  Threads::const_iterator ti;
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->remove_window(window);
  }

  // If the window happened to be controlled by the app thread, we
  // might as well close it now rather than waiting for next frame.
  _app.do_pending(this);
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::do_resort_windows
//       Access: Private
//  Description: Resorts all of the Windows lists.  This may need to
//               be done if one or more of the windows' sort
//               properties has changed.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
do_resort_windows() {
  _windows_sorted = true;

  _app.resort_windows();
  Threads::const_iterator ti;
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->resort_windows();
  }

  _windows.sort();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::terminate_threads
//       Access: Private
//  Description: Signals our child threads to terminate and waits for
//               them to clean up.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::
terminate_threads() {
  MutexHolder holder(_lock);
  
  // First, wait for all the threads to finish their current frame.
  // Grabbing the mutex should achieve that.
  Threads::const_iterator ti;
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->_cv_mutex.lock();
  }

  // Now tell them to release their windows' graphics contexts.
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    if (thread->_thread_state == TS_wait) {
      thread->_thread_state = TS_do_release;
      thread->_cv.signal();
    }
    thread->_cv_mutex.release();
  }

  // Grab the mutex again to wait for the above to complete.
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->_cv_mutex.lock();
  }

  // Now tell them to close their windows and terminate.
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    MutexHolder cv_holder(thread->_cv_mutex);
    thread->_thread_state = TS_terminate;
    thread->_cv.signal();
    thread->_cv_mutex.release();
  }

  // Finally, wait for them all to finish cleaning up.
  for (ti = _threads.begin(); ti != _threads.end(); ++ti) {
    RenderThread *thread = (*ti).second;
    thread->join();
  }
  
  _threads.clear();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::get_window_renderer
//       Access: Private
//  Description: Returns the WindowRenderer with the given name.
//               Creates a new RenderThread if there is no such thread
//               already.
////////////////////////////////////////////////////////////////////
GraphicsEngine::WindowRenderer *GraphicsEngine::
get_window_renderer(const string &name) {
  if (name.empty()) {
    return &_app;
  }

  MutexHolder holder(_lock);
  Threads::iterator ti = _threads.find(name);
  if (ti != _threads.end()) {
    return (*ti).second.p();
  }

  PT(RenderThread) thread = new RenderThread(name, this);
  thread->start(TP_normal, true, true);
  _threads[name] = thread;

  return thread.p();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::add_gsg
//       Access: Public
//  Description: Adds a new GSG to the _gsg list, if it is not already
//               there.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
add_gsg(GraphicsStateGuardian *gsg) {
  MutexHolder holder(_wl_lock);
  _gsgs.insert(gsg);
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::add_window
//       Access: Public
//  Description: Adds a new window to the indicated list, which should
//               be a member of the WindowRenderer.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
add_window(Windows &wlist, GraphicsOutput *window) {
  MutexHolder holder(_wl_lock);
  wlist.insert(window);
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::remove_window
//       Access: Public
//  Description: Immediately removes the indicated window from all
//               lists.  If the window is currently open and is
//               already on the _window list, moves it to the _pending_close
//               list for later closure.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
remove_window(GraphicsOutput *window) {
  MutexHolder holder(_wl_lock);
  PT(GraphicsOutput) ptwin = window;

  _cull.erase(ptwin);

  Windows::iterator wi;

  wi = _cdraw.find(ptwin);
  if (wi != _cdraw.end()) {
    // The window is on our _cdraw list, meaning its GSG operations are
    // serviced by this thread (cull and draw in the same operation).
    
    // Move it to the pending release thread so we can release the GSG
    // when the thread next runs.  We can't do this immediately,
    // because we might not have been called from the subthread.
    _pending_release.push_back(ptwin);
    _cdraw.erase(wi);
  }

  wi = _draw.find(ptwin);
  if (wi != _draw.end()) {
    // The window is on our _draw list, meaning its GSG operations are
    // serviced by this thread (draw performed on this thread).
    
    // Move it to the pending release thread so we can release the GSG
    // when the thread next runs.  We can't do this immediately,
    // because we might not have been called from the subthread.
    _pending_release.push_back(ptwin);
    _draw.erase(wi);
  }

  wi = _window.find(ptwin);
  if (wi != _window.end()) {
    // The window is on our _window list, meaning its open/close
    // operations (among other window ops) are serviced by this
    // thread.

    // Make sure the window isn't about to request itself open.
    ptwin->request_close();

    // If the window is already open, move it to the _pending_close list so
    // it can be closed later.  We can't close it immediately, because
    // we might not have been called from the subthread.
    if (ptwin->is_valid()) {
      _pending_close.push_back(ptwin);
    }

    _window.erase(wi);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::resort_windows
//       Access: Public
//  Description: Resorts all the lists of windows, assuming they may
//               have become unsorted.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
resort_windows() {
  MutexHolder holder(_wl_lock);

  _cull.sort();
  _cdraw.sort();
  _draw.sort();
  _window.sort();
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::do_frame
//       Access: Public
//  Description: Executes one stage of the pipeline for the current
//               thread: calls cull on all windows that are on the
//               cull list for this thread, draw on all the windows on
//               the draw list, etc.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
do_frame(GraphicsEngine *engine) {
  MutexHolder holder(_wl_lock);

  do_callbacks(CB_pre_frame);

  engine->cull_bin_draw(_cull);
  engine->cull_and_draw_together(_cdraw);
  engine->process_events(_window);

  // If any GSG's on the list have no more outstanding pointers, clean
  // them up.  (We are in the draw thread for all of these GSG's.)
  if (any_done_gsgs()) {
    GSGs new_gsgs;
    GSGs::iterator gi;
    for (gi = _gsgs.begin(); gi != _gsgs.end(); ++gi) {
      GraphicsStateGuardian *gsg = (*gi);
      if (gsg->get_ref_count() == 1) {
        // This one has no outstanding pointers; clean it up.
        GraphicsPipe *pipe = gsg->get_pipe();
        engine->close_gsg(pipe, gsg);
      } else { 
        // This one is ok; preserve it.
        new_gsgs.insert(gsg);
      }
    }

    _gsgs.swap(new_gsgs);
  }

  do_callbacks(CB_post_frame);
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::do_windows
//       Access: Public
//  Description: Attempts to fully open or close any windows or
//               buffers associated with this thread, but does not
//               otherwise perform any rendering.  (Normally, this
//               step is handled during do_frame(); call this method
//               only if you want these things to open immediately.)
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
do_windows(GraphicsEngine *engine) {
  MutexHolder holder(_wl_lock);

  engine->process_events(_window);

  engine->make_contexts(_cdraw);
  engine->make_contexts(_draw);
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::do_flip
//       Access: Public
//  Description: Flips the windows as appropriate for the current
//               thread.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
do_flip(GraphicsEngine *engine) {
  MutexHolder holder(_wl_lock);
  engine->flip_windows(_cdraw);
  engine->flip_windows(_draw);
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::do_release
//       Access: Public
//  Description: Releases the rendering contexts for all windows on
//               the _draw list.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
do_release(GraphicsEngine *) {
  MutexHolder holder(_wl_lock);
  Windows::iterator wi;
  for (wi = _draw.begin(); wi != _draw.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    win->release_gsg();
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::do_close
//       Access: Public
//  Description: Closes all the windows on the _window list.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
do_close(GraphicsEngine *engine) {
  MutexHolder holder(_wl_lock);
  Windows::iterator wi;
  for (wi = _window.begin(); wi != _window.end(); ++wi) {
    GraphicsOutput *win = (*wi);
    win->set_close_now();
  }

  // Also close all of the GSG's.
  GSGs new_gsgs;
  GSGs::iterator gi;
  for (gi = _gsgs.begin(); gi != _gsgs.end(); ++gi) {
    GraphicsStateGuardian *gsg = (*gi);
    if (gsg->get_ref_count() == 1) {
      // This one has no outstanding pointers; clean it up.
      GraphicsPipe *pipe = gsg->get_pipe();
      engine->close_gsg(pipe, gsg);
    } else { 
      // This one is ok; preserve it.
      new_gsgs.insert(gsg);
    }
  }
  
  _gsgs.swap(new_gsgs);
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::do_pending
//       Access: Public
//  Description: Actually closes any windows that were recently
//               removed from the WindowRenderer.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
do_pending(GraphicsEngine *engine) {
  MutexHolder holder(_wl_lock);

  if (!_pending_release.empty()) {
    // Release any GSG's that were waiting.
    Windows::iterator wi;
    for (wi = _pending_release.begin(); wi != _pending_release.end(); ++wi) {
      GraphicsOutput *win = (*wi);
      win->release_gsg();
    }
    _pending_release.clear();
  }

  if (!_pending_close.empty()) {
    // Close any windows that were pending closure, but only if their
    // associated GSG has already been released.
    Windows new_pending_close;
    Windows::iterator wi;
    for (wi = _pending_close.begin(); wi != _pending_close.end(); ++wi) {
      GraphicsOutput *win = (*wi);
      if (win->get_gsg() == (GraphicsStateGuardian *)NULL) {
        win->set_close_now();
      } else {
        // If the GSG hasn't been released yet, we have to save the
        // close operation for next frame.
        new_pending_close.push_back(win);
      }
    }
    _pending_close.swap(new_pending_close);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::any_done_gsgs
//       Access: Public
//  Description: Returns true if any of the GSG's on this thread's
//               draw list are done (they have no outstanding pointers
//               other than this one), or false if all of them are
//               still good.
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::WindowRenderer::
any_done_gsgs() const {
  GSGs::const_iterator gi;
  for (gi = _gsgs.begin(); gi != _gsgs.end(); ++gi) {
    if ((*gi)->get_ref_count() == 1) {
      return true;
    }
  }

  return false;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::add_callback
//       Access: Public
//  Description: Adds the indicated callback to this renderer's list
//               for the indicated callback time.  Returns true if it
//               is successfully added, false if it was already there.
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::WindowRenderer::
add_callback(GraphicsEngine::CallbackTime callback_time, 
             const GraphicsEngine::Callback &callback) {
  nassertr(callback_time >= 0 && callback_time < CB_len, false);
  MutexHolder holder(_wl_lock);
  return _callbacks[callback_time].insert(callback).second;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::remove_callback
//       Access: Public
//  Description: Removes the indicated callback from this renderer's
//               list for the indicated callback time.  Returns true
//               if it is successfully removed, or false if it was not
//               on the list.
////////////////////////////////////////////////////////////////////
bool GraphicsEngine::WindowRenderer::
remove_callback(GraphicsEngine::CallbackTime callback_time, 
                const GraphicsEngine::Callback &callback) {
  nassertr(callback_time >= 0 && callback_time < CB_len, false);
  MutexHolder holder(_wl_lock);
  Callbacks::iterator cbi = _callbacks[callback_time].find(callback);
  if (cbi != _callbacks[callback_time].end()) {
    _callbacks[callback_time].erase(cbi);
    return true;
  }
  return false;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::WindowRenderer::do_callbacks
//       Access: Private
//  Description: Calls all of the callback functions on the indicated
//               list.  Intended to be called internally when we have
//               reached the indicated point on the frame.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::WindowRenderer::
do_callbacks(GraphicsEngine::CallbackTime callback_time) {
  nassertv(callback_time >= 0 && callback_time < CB_len);
  Callbacks::const_iterator cbi;
  for (cbi = _callbacks[callback_time].begin();
       cbi != _callbacks[callback_time].end();
       ++cbi) {
    (*cbi).do_callback();
  }
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::RenderThread::Constructor
//       Access: Public
//  Description: 
////////////////////////////////////////////////////////////////////
GraphicsEngine::RenderThread::
RenderThread(const string &name, GraphicsEngine *engine) : 
  Thread(name),
  _engine(engine),
  _cv(_cv_mutex)
{
  _thread_state = TS_wait;
}

////////////////////////////////////////////////////////////////////
//     Function: GraphicsEngine::RenderThread::thread_main
//       Access: Public, Virtual
//  Description: The main loop for a particular render thread.  The
//               thread will process whatever cull or draw windows it
//               has assigned to it.
////////////////////////////////////////////////////////////////////
void GraphicsEngine::RenderThread::
thread_main() {
  MutexHolder holder(_cv_mutex);
  while (true) {
    _cv.wait();
    switch (_thread_state) {
    case TS_wait:
      break;

    case TS_do_frame:
      do_pending(_engine);
      do_frame(_engine);
      _thread_state = TS_wait;
      break;

    case TS_do_flip:
      do_flip(_engine);
      _thread_state = TS_wait;
      break;

    case TS_do_release:
      do_pending(_engine);
      do_release(_engine);
      _thread_state = TS_wait;
      break;

    case TS_do_windows:
      do_windows(_engine);
      do_pending(_engine);
      do_release(_engine);
      _thread_state = TS_wait;
      break;

    case TS_terminate:
      do_pending(_engine);
      do_close(_engine);
      return;
    }
  }
}