// Filename: wglGraphicsStateGuardian.cxx
// Created by:  drose (27Jan03)
//
////////////////////////////////////////////////////////////////////
//
// 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 "wglGraphicsStateGuardian.h"
#include "wglGraphicsBuffer.h"
#include "string_utils.h"

TypeHandle wglGraphicsStateGuardian::_type_handle;

const char * const wglGraphicsStateGuardian::_twindow_class_name = "wglGraphicsStateGuardian";
bool wglGraphicsStateGuardian::_twindow_class_registered = false;

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::Constructor
//       Access: Public
//  Description:
////////////////////////////////////////////////////////////////////
wglGraphicsStateGuardian::
wglGraphicsStateGuardian(GraphicsPipe *pipe,
                         wglGraphicsStateGuardian *share_with) : 
  GLGraphicsStateGuardian(pipe),
  _share_with(share_with)
{
  _made_context = false;
  _context = (HGLRC)NULL;

  _twindow = (HWND)0;
  _twindow_dc = (HDC)0;

  _pfnum = -1;
  _pfnum_supports_pbuffer = false;
  _pfnum_properties.clear();
  
  _supports_pbuffer = false;
  _supports_pixel_format = false;
  _supports_wgl_multisample = false;
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::Destructor
//       Access: Public
//  Description:
////////////////////////////////////////////////////////////////////
wglGraphicsStateGuardian::
~wglGraphicsStateGuardian() {
  release_twindow();
  if (_context != (HGLRC)NULL) {
    wglDeleteContext(_context);
    _context = (HGLRC)NULL;
  }
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::get_properties
//       Access: Private
//  Description: Gets the FrameBufferProperties to match the
//               indicated pixel format descriptor.
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
get_properties(FrameBufferProperties &properties, HDC hdc, int pfnum) {
  
  PIXELFORMATDESCRIPTOR pfd;
  ZeroMemory(&pfd,sizeof(PIXELFORMATDESCRIPTOR));
  pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
  pfd.nVersion = 1;

  DescribePixelFormat(hdc, pfnum, sizeof(PIXELFORMATDESCRIPTOR), &pfd);

  properties.clear();
  properties.set_all_specified();
  
  if (((pfd.dwFlags & PFD_SUPPORT_OPENGL) == 0)||
      ((pfd.dwFlags & PFD_DRAW_TO_WINDOW) == 0)) {
    // Return without setting either RGB or Indexed Color.
    // This indicates a window that can't do anything at all.
    return;
  }

  if (pfd.iPixelType == PFD_TYPE_COLORINDEX) {
    properties.set_indexed_color(1);
  } else {
    properties.set_rgb_color(1);
  }

  int mode = 0;
  if (pfd.dwFlags & PFD_DOUBLEBUFFER) {
    properties.set_back_buffers(1);
  }
  if (pfd.dwFlags & PFD_STEREO) {
    properties.set_stereo(1);
  }
  if (pfd.dwFlags & PFD_GENERIC_FORMAT) {
    properties.set_force_software(1);
  } else {
    properties.set_force_hardware(1);
  }
  
  if (pfd.cColorBits != 0) {
    properties.set_color_bits(pfd.cColorBits);
  }
  if (pfd.cAlphaBits != 0) {
    properties.set_alpha_bits(pfd.cAlphaBits);
  }
  if (pfd.cDepthBits != 0) {
    properties.set_depth_bits(pfd.cDepthBits);
  }
  if (pfd.cStencilBits != 0) {
    properties.set_stencil_bits(pfd.cStencilBits);
  }

  // The basic API doesn't do accum or multisample.
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::get_properties_advanced
//       Access: Private
//  Description: Gets the FrameBufferProperties to match the
//               indicated pixel format descriptor, using the WGL
//               extensions.
////////////////////////////////////////////////////////////////////
bool wglGraphicsStateGuardian::
get_properties_advanced(FrameBufferProperties &properties, 
                        HDC window_dc, int pfnum) {
  
  static const int max_attrib_list = 32;
  int iattrib_list[max_attrib_list];
  int ivalue_list[max_attrib_list];
  int ni = 0;
  
  int acceleration_i, pixel_type_i, double_buffer_i, stereo_i,
    color_bits_i, alpha_bits_i, accum_bits_i, depth_bits_i, 
    stencil_bits_i, multisamples_i;
  
  iattrib_list[acceleration_i = ni++] = WGL_ACCELERATION_ARB;
  iattrib_list[pixel_type_i = ni++] = WGL_PIXEL_TYPE_ARB;
  iattrib_list[double_buffer_i = ni++] = WGL_DOUBLE_BUFFER_ARB;
  iattrib_list[stereo_i = ni++] = WGL_STEREO_ARB;
  iattrib_list[color_bits_i = ni++] = WGL_COLOR_BITS_ARB;
  iattrib_list[alpha_bits_i = ni++] = WGL_ALPHA_BITS_ARB;
  iattrib_list[accum_bits_i = ni++] = WGL_ACCUM_BITS_ARB;
  iattrib_list[depth_bits_i = ni++] = WGL_DEPTH_BITS_ARB;
  iattrib_list[stencil_bits_i = ni++] = WGL_STENCIL_BITS_ARB;
  
  if (_supports_wgl_multisample) {
    iattrib_list[multisamples_i = ni++] = WGL_SAMPLES_ARB;
  }
  
  // Terminate the list.
  nassertr(ni <= max_attrib_list, false);
  
  if (!_wglGetPixelFormatAttribivARB(window_dc, pfnum, 0,
                                     ni, iattrib_list, ivalue_list)) {
    return false;
  }
  
  properties.clear();
  properties.set_all_specified();

  int frame_buffer_mode = 0;
  if (ivalue_list[acceleration_i] == WGL_NO_ACCELERATION_ARB) {
    properties.set_force_software(1);
  } else {
    properties.set_force_hardware(1);
  }
  
  if (ivalue_list[pixel_type_i] == WGL_TYPE_COLORINDEX_ARB) {
    properties.set_indexed_color(1);
  } else {
    properties.set_rgb_color(1);
  }

  if (ivalue_list[double_buffer_i]) {
    properties.set_back_buffers(1);
  }
  
  if (ivalue_list[stereo_i]) {
    properties.set_stereo(1);
  }
  
  if (ivalue_list[alpha_bits_i] != 0) {
    properties.set_alpha_bits(ivalue_list[alpha_bits_i]);
  }

  if (ivalue_list[accum_bits_i] != 0) {
    properties.set_accum_bits(ivalue_list[accum_bits_i]);
  }
  
  if (ivalue_list[depth_bits_i] != 0) {
    properties.set_depth_bits(ivalue_list[depth_bits_i]);
  }

  if (ivalue_list[stencil_bits_i] != 0) {
    properties.set_stencil_bits(ivalue_list[stencil_bits_i]);
  }

  if (_supports_wgl_multisample) {
    if (ivalue_list[multisamples_i] != 0) {
      properties.set_multisamples(ivalue_list[multisamples_i]);
    }
  }
  
  properties.set_color_bits(ivalue_list[color_bits_i]);
  
  return true;
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::choose_pixel_format
//       Access: Private
//  Description: Selects a pixel format for all the windows and
//               buffers that use this gsg.
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
choose_pixel_format(const FrameBufferProperties &properties,
                    bool need_pbuffer) {

  //// Choose best format available using DescribePixelFormat.
  //
  // In the process, we need a DC to examine the available
  // pixel formats.  We'll use the screen DC.

  if (gl_force_pixfmt.has_value()) {
    wgldisplay_cat.info()
      << "overriding pixfmt choice with gl-force-pixfmt(" 
      << gl_force_pixfmt << ")\n";
    _pfnum = gl_force_pixfmt;
    _pfnum_properties = properties;
    _pfnum_supports_pbuffer = true;
    return;
  }
  
  int  best_pfnum = 0;
  int  best_quality = 0;
  FrameBufferProperties best_prop;
  
  HDC hdc = GetDC(NULL);

  int max_pfnum = DescribePixelFormat(hdc, 1, 0, NULL);
  
  for (int pfnum = 0; pfnum<max_pfnum; ++pfnum) {
    FrameBufferProperties pfprop;
    get_properties(pfprop, hdc, pfnum);
    int quality = pfprop.get_quality(properties);
    if (quality > best_quality) {
      best_pfnum = pfnum;
      best_quality = quality;
      best_prop = pfprop;
    }
  }
  
  ReleaseDC(NULL, hdc);

  _pfnum = best_pfnum;
  _pfnum_supports_pbuffer = false;
  _pfnum_properties = best_prop;
  
  if (best_quality == 0) {
    wgldisplay_cat.error()
      << "Could not find a usable pixel format.\n";
    return;
  }

  if (wgldisplay_cat.is_debug()) {
    wgldisplay_cat.debug()
      << "Preliminary pixfmt #" << _pfnum << " = " 
      << _pfnum_properties << "\n";
  }

  //// See whether or not the wgl extensions are available.
  //
  // This routine is called before "reset".  So the extensions
  // list is empty.  We need to create a twindow, make it current,
  // fetch the extensions temporarily, get the few extensions
  // we need, then clear the extensions list again in preparation
  // for the reset.
  
  HDC twindow_dc = get_twindow_dc();
  if (twindow_dc == 0) {
    return;
  }

  HGLRC twindow_ctx = wglCreateContext(twindow_dc);
  if (twindow_ctx == 0) {
    return;
  }

  wglGraphicsPipe::wgl_make_current(twindow_dc, twindow_ctx, NULL);

  _extensions.clear();
  save_extensions((const char *)GLP(GetString)(GL_EXTENSIONS));
  get_extra_extensions();
  _supports_pixel_format = has_extension("WGL_ARB_pixel_format");
  _supports_wgl_multisample = has_extension("WGL_ARB_multisample");
  _extensions.clear();

  if (!_supports_pixel_format) {
    wglDeleteContext(twindow_ctx);
    return;
  }

  _wglGetPixelFormatAttribivARB =
    (PFNWGLGETPIXELFORMATATTRIBIVARBPROC)wglGetProcAddress("wglGetPixelFormatAttribivARB");
  _wglGetPixelFormatAttribfvARB =
    (PFNWGLGETPIXELFORMATATTRIBFVARBPROC)wglGetProcAddress("wglGetPixelFormatAttribfvARB");
  _wglChoosePixelFormatARB =
    (PFNWGLCHOOSEPIXELFORMATARBPROC)wglGetProcAddress("wglChoosePixelFormatARB");

  if (_wglGetPixelFormatAttribivARB == NULL ||
      _wglGetPixelFormatAttribfvARB == NULL ||
      _wglChoosePixelFormatARB == NULL) {
    wgldisplay_cat.error()
      << "Driver claims to support WGL_ARB_pixel_format extension, but does not define all functions.\n";
    wglDeleteContext(twindow_ctx);
    return;
  }

  //// Use the wgl extensions to find a better format.
  //
  
  static const int max_attrib_list = 64;
  int iattrib_list[max_attrib_list];
  float fattrib_list[max_attrib_list];
  int ni = 0;
  int nf = 0;
  
  iattrib_list[ni++] = WGL_SUPPORT_OPENGL_ARB;
  iattrib_list[ni++] = true;
  iattrib_list[ni++] = WGL_PIXEL_TYPE_ARB;
  iattrib_list[ni++] = WGL_TYPE_RGBA_ARB;

  if (need_pbuffer) {
    iattrib_list[ni++] = WGL_DRAW_TO_PBUFFER_ARB;
    iattrib_list[ni++] = true;
    if (_pfnum_properties.get_alpha_bits()) {
      iattrib_list[ni++] = WGL_BIND_TO_TEXTURE_RGBA_ARB;
      iattrib_list[ni++] = true;
    } else {
      iattrib_list[ni++] = WGL_BIND_TO_TEXTURE_RGB_ARB;
      iattrib_list[ni++] = true;
    }
  }

  nassertv(ni < max_attrib_list && nf < max_attrib_list);
  iattrib_list[ni] = 0;
  fattrib_list[nf] = 0;
  
  static const int max_pformats = 1024;
  int pformat[max_pformats];
  memset(pformat, 0, sizeof(pformat));
  int nformats = 0;
  
  if (!_wglChoosePixelFormatARB(twindow_dc, iattrib_list, fattrib_list,
                                max_pformats, pformat, (unsigned int *)&nformats)) {
    nformats = 0;
  }
  nformats = min(nformats, max_pformats);
  
  if (wgldisplay_cat.is_debug()) {
    wgldisplay_cat.debug()
      << "Found " << nformats << " advanced formats: [";
    for (int i = 0; i < nformats; i++) {
      wgldisplay_cat.debug(false)
        << " " << pformat[i];
    }
    wgldisplay_cat.debug(false)
      << " ]\n";
  }
  
  if (nformats > 0) {
    if (need_pbuffer) {
      best_quality = 0;
    }

    for (int i = 0; i < nformats; i++) {
      FrameBufferProperties pfprop;
      if (get_properties_advanced(pfprop, twindow_dc, pformat[i])) {
        int quality = pfprop.get_quality(properties);
        if (quality > best_quality) {
          best_pfnum = pformat[i];
          best_quality = quality;
          best_prop = pfprop;
        }
      }
    }
    
    _pfnum = best_pfnum;
    _pfnum_supports_pbuffer = need_pbuffer;
    _pfnum_properties = best_prop;
  }
  
  wglDeleteContext(twindow_ctx);
  release_twindow();
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::reset
//       Access: Public, Virtual
//  Description: Resets all internal state as if the gsg were newly
//               created.
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
reset() {
  GLGraphicsStateGuardian::reset();

  _supports_swap_control = has_extension("WGL_EXT_swap_control");

  if (_supports_swap_control) {
    _wglSwapIntervalEXT = 
      (PFNWGLSWAPINTERVALEXTPROC)wglGetProcAddress("wglSwapIntervalEXT");
    if (_wglSwapIntervalEXT == NULL) {
      wgldisplay_cat.error()
        << "Driver claims to support WGL_EXT_swap_control extension, but does not define all functions.\n";
      _supports_swap_control = false;
    }
  }

  if (_supports_swap_control) {
    // Set the video-sync setting up front, if we have the extension
    // that supports it.
    _wglSwapIntervalEXT(sync_video ? 1 : 0);
  }

  _supports_pbuffer = has_extension("WGL_ARB_pbuffer");

  if (_supports_pbuffer) {
    _wglCreatePbufferARB = 
      (PFNWGLCREATEPBUFFERARBPROC)wglGetProcAddress("wglCreatePbufferARB");
    _wglGetPbufferDCARB = 
      (PFNWGLGETPBUFFERDCARBPROC)wglGetProcAddress("wglGetPbufferDCARB");
    _wglReleasePbufferDCARB = 
      (PFNWGLRELEASEPBUFFERDCARBPROC)wglGetProcAddress("wglReleasePbufferDCARB");
    _wglDestroyPbufferARB = 
      (PFNWGLDESTROYPBUFFERARBPROC)wglGetProcAddress("wglDestroyPbufferARB");
    _wglQueryPbufferARB = 
      (PFNWGLQUERYPBUFFERARBPROC)wglGetProcAddress("wglQueryPbufferARB");
    
    if (_wglCreatePbufferARB == NULL ||
        _wglGetPbufferDCARB == NULL ||
        _wglReleasePbufferDCARB == NULL ||
        _wglDestroyPbufferARB == NULL ||
        _wglQueryPbufferARB == NULL) {
      wgldisplay_cat.error()
        << "Driver claims to support WGL_ARB_pbuffer extension, but does not define all functions.\n";
      _supports_pbuffer = false;
    }
  }

  _supports_pixel_format = has_extension("WGL_ARB_pixel_format");

  if (_supports_pixel_format) {
    _wglGetPixelFormatAttribivARB =
      (PFNWGLGETPIXELFORMATATTRIBIVARBPROC)wglGetProcAddress("wglGetPixelFormatAttribivARB");
    _wglGetPixelFormatAttribfvARB =
      (PFNWGLGETPIXELFORMATATTRIBFVARBPROC)wglGetProcAddress("wglGetPixelFormatAttribfvARB");
    _wglChoosePixelFormatARB =
      (PFNWGLCHOOSEPIXELFORMATARBPROC)wglGetProcAddress("wglChoosePixelFormatARB");

    if (_wglGetPixelFormatAttribivARB == NULL ||
        _wglGetPixelFormatAttribfvARB == NULL ||
        _wglChoosePixelFormatARB == NULL) {
      wgldisplay_cat.error()
        << "Driver claims to support WGL_ARB_pixel_format extension, but does not define all functions.\n";
      _supports_pixel_format = false;
    }
  }

  _supports_wgl_multisample = has_extension("WGL_ARB_multisample");

  _supports_render_texture = has_extension("WGL_ARB_render_texture");

  if (_supports_render_texture) {
    _wglBindTexImageARB = 
      (PFNWGLBINDTEXIMAGEARBPROC)wglGetProcAddress("wglBindTexImageARB");
    _wglReleaseTexImageARB = 
      (PFNWGLRELEASETEXIMAGEARBPROC)wglGetProcAddress("wglReleaseTexImageARB");
    _wglSetPbufferAttribARB = 
      (PFNWGLSETPBUFFERATTRIBARBPROC)wglGetProcAddress("wglSetPbufferAttribARB");
    if (_wglBindTexImageARB == NULL ||
        _wglReleaseTexImageARB == NULL ||
        _wglSetPbufferAttribARB == NULL) {
      wgldisplay_cat.error()
        << "Driver claims to support WGL_ARB_render_texture, but does not define all functions.\n";
      _supports_render_texture = false;
    }
  }
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::get_extra_extensions
//       Access: Protected, Virtual
//  Description: This may be redefined by a derived class (e.g. glx or
//               wgl) to get whatever further extensions strings may
//               be appropriate to that interface, in addition to the
//               GL extension strings return by glGetString().
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
get_extra_extensions() {
  // This is a little bit tricky, since the query function is itself
  // an extension.

  // Look for the ARB flavor first, which wants one parameter, the HDC
  // of the drawing context.
  PFNWGLGETEXTENSIONSSTRINGARBPROC wglGetExtensionsStringARB = 
    (PFNWGLGETEXTENSIONSSTRINGARBPROC)wglGetProcAddress("wglGetExtensionsStringARB");
  if (wglGetExtensionsStringARB != NULL) {
    HDC hdc = wglGetCurrentDC();
    if (hdc != 0) {
      save_extensions((const char *)wglGetExtensionsStringARB(hdc));
      return;
    }
  }

  // If that failed, look for the EXT flavor, which wants no
  // parameters.
  PFNWGLGETEXTENSIONSSTRINGEXTPROC wglGetExtensionsStringEXT = 
    (PFNWGLGETEXTENSIONSSTRINGEXTPROC)wglGetProcAddress("wglGetExtensionsStringEXT");
  if (wglGetExtensionsStringEXT != NULL) {
    save_extensions((const char *)wglGetExtensionsStringEXT());
  }
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::get_extension_func
//       Access: Public, Virtual
//  Description: Returns the pointer to the GL extension function with
//               the indicated name.  It is the responsibility of the
//               caller to ensure that the required extension is
//               defined in the OpenGL runtime prior to calling this;
//               it is an error to call this for a function that is
//               not defined.
////////////////////////////////////////////////////////////////////
void *wglGraphicsStateGuardian::
get_extension_func(const char *prefix, const char *name) {
  string fullname = string(prefix) + string(name);
  return wglGetProcAddress(fullname.c_str());
}


////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::make_context
//       Access: Private
//  Description: Creates a suitable context for rendering into the
//               given window.  This should only be called from the
//               draw thread.
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
make_context(HDC hdc) {
  // We should only call this once for a particular GSG.
  nassertv(!_made_context);

  _made_context = true;

  // Attempt to create a context.
  wglGraphicsPipe::_current_valid = false;
  _context = wglCreateContext(hdc);

  if (_context == NULL) {
    wgldisplay_cat.error()
      << "Could not create GL context.\n";
    return;
  }

  // Now share texture context with the indicated GSG.
  if (_share_with != (wglGraphicsStateGuardian *)NULL) {
    HGLRC share_context = _share_with->get_share_context();
    if (share_context == NULL) {
      // Whoops, the target context hasn't yet made its own context.
      // In that case, it will share context with us.
      _share_with->redirect_share_pool(this);

    } else {
      if (!wglShareLists(share_context, _context)) {
        wgldisplay_cat.error()
          << "Could not share texture contexts between wglGraphicsStateGuardians.\n";
        // Too bad we couldn't detect this error sooner.  Now there's
        // really no way to tell the application it's hosed.

      } else {
        _prepared_objects = _share_with->get_prepared_objects();
      }
    }

    _share_with = (wglGraphicsStateGuardian *)NULL;
  }
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::get_share_context
//       Access: Private
//  Description: Returns a wgl context handle for the purpose of
//               sharing texture context with this GSG.  This will
//               either be the GSG's own context handle, if it exists
//               yet, or the context handle of some other GSG that
//               this GSG is planning to share with.  If this returns
//               NULL, none of the GSG's in this share pool have yet
//               created their context.
////////////////////////////////////////////////////////////////////
HGLRC wglGraphicsStateGuardian::
get_share_context() const {
  if (_made_context) {
    return _context;
  }
  if (_share_with != (wglGraphicsStateGuardian *)NULL) {
    return _share_with->get_share_context();
  }
  return NULL;
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::redirect_share_pool
//       Access: Private
//  Description: Directs the GSG (along with all GSG's it is planning
//               to share a texture context with) to share texture
//               context with the indicated GSG.
//
//               This assumes that this GSG's context has not yet been
//               created, and neither have any of the GSG's it is
//               planning to share texture context with; but the
//               graphics context for the indicated GSG has already
//               been created.
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
redirect_share_pool(wglGraphicsStateGuardian *share_with) {
  nassertv(!_made_context);
  if (_share_with != (wglGraphicsStateGuardian *)NULL) {
    _share_with->redirect_share_pool(share_with);
  } else {
    _share_with = share_with;
  }
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::make_twindow
//       Access: Private
//  Description: Creates an invisible window to associate with the GL
//               context, even if we are not going to use it.  This is
//               necessary because in the Windows OpenGL API, we have
//               to create window before we can create a GL
//               context--even before we can ask about what GL
//               extensions are available!
////////////////////////////////////////////////////////////////////
bool wglGraphicsStateGuardian::
make_twindow() {
  release_twindow();

  DWORD window_style = 0;

  register_twindow_class();
  HINSTANCE hinstance = GetModuleHandle(NULL);
  _twindow = CreateWindow(_twindow_class_name, "twindow", window_style, 
                          0, 0, 1, 1, NULL, NULL, hinstance, 0);
  
  if (!_twindow) {
    wgldisplay_cat.error()
      << "CreateWindow() failed!" << endl;
    return false;
  }

  ShowWindow(_twindow, SW_HIDE);

  _twindow_dc = GetDC(_twindow);

  PIXELFORMATDESCRIPTOR pixelformat;
  if (!SetPixelFormat(_twindow_dc, _pfnum, &pixelformat)) {
    wgldisplay_cat.error()
      << "SetPixelFormat(" << _pfnum << ") failed after window create\n";
    release_twindow();
    return false;
  }

  return true;
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::release_twindow
//       Access: Private
//  Description: Closes and frees the resources associated with the
//               temporary window created by a previous call to
//               make_twindow().
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
release_twindow() {
  if (_twindow_dc) {
    ReleaseDC(_twindow, _twindow_dc);
    _twindow_dc = 0;
  }
  if (_twindow) {
    DestroyWindow(_twindow);
    _twindow = 0;
  }
}

////////////////////////////////////////////////////////////////////
//     Function: wglGraphicsStateGuardian::register_twindow_class
//       Access: Private, Static
//  Description: Registers a Window class for the twindow created by
//               all wglGraphicsPipes.  This only needs to be done
//               once per session.
////////////////////////////////////////////////////////////////////
void wglGraphicsStateGuardian::
register_twindow_class() {
  if (_twindow_class_registered) {
    return;
  }

  WNDCLASS wc;

  HINSTANCE instance = GetModuleHandle(NULL);

  // Clear before filling in window structure!
  ZeroMemory(&wc, sizeof(WNDCLASS));
  wc.style = CS_OWNDC;
  wc.lpfnWndProc = DefWindowProc;
  wc.hInstance = instance;
  wc.lpszClassName = _twindow_class_name;
  
  if (!RegisterClass(&wc)) {
    wgldisplay_cat.error()
      << "could not register window class!" << endl;
    return;
  }
  _twindow_class_registered = true;
}
