fltk/src/drivers/WinAPI/Fl_WinAPI_Window_Driver.cxx

//
// "$Id$"
//
// Definition of Apple Cocoa window driver.
//
// Copyright 1998-2016 by Bill Spitzak and others.
//
// This library is free software. Distribution and use rights are outlined in
// the file "COPYING" which should have been included with this file.  If this
// file is missing or damaged, see the license at:
//
//     http://www.fltk.org/COPYING.php
//
// Please report all bugs and problems on the following page:
//
//     http://www.fltk.org/str.php
//


#include "../../config_lib.h"
#include <FL/fl_draw.H>
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Image.H>
#include <FL/Fl_Bitmap.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Overlay_Window.H>
#include <FL/x.H>
#include "Fl_WinAPI_Window_Driver.H"
#include <windows.h>

#if USE_COLORMAP
extern HPALETTE fl_select_palette(void); // in fl_color_win32.cxx
#endif


Fl_Window_Driver *Fl_Window_Driver::newWindowDriver(Fl_Window *w)
{
  return new Fl_WinAPI_Window_Driver(w);
}


Fl_WinAPI_Window_Driver::Fl_WinAPI_Window_Driver(Fl_Window *win)
: Fl_Window_Driver(win)
{
  icon_ = new icon_data;
  memset(icon_, 0, sizeof(icon_data));
}


Fl_WinAPI_Window_Driver::~Fl_WinAPI_Window_Driver()
{
  if (shape_data_) {
    delete shape_data_->todelete_;
    delete shape_data_;
  }
  delete icon_;
}


// --- private

RECT Fl_WinAPI_Window_Driver::border_width_title_bar_height(int &bx, int &by, int &bt)
{
  Fl_Window *win = pWindow;
  RECT r = {0,0,0,0};
  bx = by = bt = 0;
  if (win->shown() && !win->parent() && win->border() && win->visible()) {
    static HMODULE dwmapi_dll = LoadLibrary("dwmapi.dll");
    typedef HRESULT (WINAPI* DwmGetWindowAttribute_type)(HWND hwnd, DWORD dwAttribute, PVOID pvAttribute, DWORD cbAttribute);
    static DwmGetWindowAttribute_type DwmGetWindowAttribute = dwmapi_dll ?
    (DwmGetWindowAttribute_type)GetProcAddress(dwmapi_dll, "DwmGetWindowAttribute") : NULL;
    int need_r = 1;
    if (DwmGetWindowAttribute) {
      const DWORD DWMWA_EXTENDED_FRAME_BOUNDS = 9;
      if ( DwmGetWindowAttribute(fl_xid(win), DWMWA_EXTENDED_FRAME_BOUNDS, &r, sizeof(RECT)) == S_OK ) {
        need_r = 0;
      }
    }
    if (need_r) {
      GetWindowRect(fl_xid(win), &r);
    }
    bx = (r.right - r.left - win->w())/2;
    by = bx;
    bt = r.bottom - r.top - win->h() - 2*by;
  }
  return RECT(r);
}


// --- window data

int Fl_WinAPI_Window_Driver::decorated_w()
{
  int bt, bx, by;
  border_width_title_bar_height(bx, by, bt);
  return w() + 2 * bx;
}

int Fl_WinAPI_Window_Driver::decorated_h()
{
  int bt, bx, by;
  border_width_title_bar_height(bx, by, bt);
  return h() + bt + 2 * by;
}


// --- window management



void Fl_WinAPI_Window_Driver::shape_bitmap_(Fl_Image* b) {
  shape_data_->shape_ = b;
}

void Fl_WinAPI_Window_Driver::shape_alpha_(Fl_Image* img, int offset) {
  int i, j, d = img->d(), w = img->w(), h = img->h(), bytesperrow = (w+7)/8;
  unsigned u;
  uchar byte, onebit;
  // build an Fl_Bitmap covering the non-fully transparent/black part of the image
  const uchar* bits = new uchar[h*bytesperrow]; // to store the bitmap
  const uchar* alpha = (const uchar*)*img->data() + offset; // points to alpha value of rgba pixels
  for (i = 0; i < h; i++) {
    uchar *p = (uchar*)bits + i * bytesperrow;
    byte = 0;
    onebit = 1;
    for (j = 0; j < w; j++) {
      if (d == 3) {
        u = *alpha;
        u += *(alpha+1);
        u += *(alpha+2);
      }
      else u = *alpha;
      if (u > 0) { // if the pixel is not fully transparent/black
        byte |= onebit; // turn on the corresponding bit of the bitmap
      }
      onebit = onebit << 1; // move the single set bit one position to the left
      if (onebit == 0 || j == w-1) {
        onebit = 1;
        *p++ = byte; // store in bitmap one pack of bits
        byte = 0;
      }
      alpha += d; // point to alpha value of next pixel
    }
  }
  Fl_Bitmap* bitmap = new Fl_Bitmap(bits, w, h);
  bitmap->alloc_array = 1;
  shape_bitmap_(bitmap);
  shape_data_->todelete_ = bitmap;
}

void Fl_WinAPI_Window_Driver::shape(const Fl_Image* img) {
  if (shape_data_) {
    if (shape_data_->todelete_) { delete shape_data_->todelete_; }
  }
  else {
    shape_data_ = new shape_data_type;
  }
  memset(shape_data_, 0, sizeof(shape_data_type));
  pWindow->border(false);
  int d = img->d();
  if (d && img->count() >= 2) shape_pixmap_((Fl_Image*)img);
  else if (d == 0) shape_bitmap_((Fl_Image*)img);
  else if (d == 2 || d == 4) shape_alpha_((Fl_Image*)img, d - 1);
  else if ((d == 1 || d == 3) && img->count() == 1) shape_alpha_((Fl_Image*)img, 0);
}


static inline BYTE bit(int x) { return (BYTE)(1 << (x%8)); }

static HRGN bitmap2region(Fl_Image* image) {
  HRGN hRgn = 0;
  /* Does this need to be dynamically determined, perhaps? */
  const int ALLOC_UNIT = 100;
  DWORD maxRects = ALLOC_UNIT;
  
  RGNDATA* pData = (RGNDATA*)malloc(sizeof(RGNDATAHEADER)+(sizeof(RECT)*maxRects));
  pData->rdh.dwSize = sizeof(RGNDATAHEADER);
  pData->rdh.iType = RDH_RECTANGLES;
  pData->rdh.nCount = pData->rdh.nRgnSize = 0;
  SetRect(&pData->rdh.rcBound, MAXLONG, MAXLONG, 0, 0);
  
  const int bytesPerLine = (image->w() + 7)/8;
  BYTE* p, *data = (BYTE*)*image->data();
  for (int y = 0; y < image->h(); y++) {
    // each row, left to right
    for (int x = 0; x < image->w(); x++) {
      int x0 = x;
      while (x < image->w()) {
        p = data + x / 8;
        if (!((*p) & bit(x))) break; // transparent pixel
        x++;
      }
      if (x > x0) {
        RECT *pr;
        /* Add the pixels (x0, y) to (x, y+1) as a new rectangle
         * in the region
         */
        if (pData->rdh.nCount >= maxRects) {
          maxRects += ALLOC_UNIT;
          pData = (RGNDATA*)realloc(pData, sizeof(RGNDATAHEADER)
                                    + (sizeof(RECT)*maxRects));
        }
        pr = (RECT*)&pData->Buffer;
        SetRect(&pr[pData->rdh.nCount], x0, y, x, y+1);
        if (x0 < pData->rdh.rcBound.left)
          pData->rdh.rcBound.left = x0;
        if (y < pData->rdh.rcBound.top)
          pData->rdh.rcBound.top = y;
        if (x > pData->rdh.rcBound.right)
          pData->rdh.rcBound.right = x;
        if (y+1 > pData->rdh.rcBound.bottom)
          pData->rdh.rcBound.bottom = y+1;
        pData->rdh.nCount++;
        /* On Windows98, ExtCreateRegion() may fail if the
         * number of rectangles is too large (ie: >
         * 4000). Therefore, we have to create the region by
         * multiple steps.
         */
        if (pData->rdh.nCount == 2000) {
          HRGN h = ExtCreateRegion(NULL, sizeof(RGNDATAHEADER)
                                   + (sizeof(RECT)*maxRects), pData);
          if (hRgn) {
            CombineRgn(hRgn, hRgn, h, RGN_OR);
            DeleteObject(h);
          } else
            hRgn = h;
          pData->rdh.nCount = 0;
          SetRect(&pData->rdh.rcBound, MAXLONG, MAXLONG, 0, 0);
        }
      }
    }
    /* Go to next row */
    data += bytesPerLine;
  }
  /* Create or extend the region with the remaining rectangles*/
  HRGN h = ExtCreateRegion(NULL, sizeof(RGNDATAHEADER)
                           + (sizeof(RECT)*maxRects), pData);
  if (hRgn) {
    CombineRgn(hRgn, hRgn, h, RGN_OR);
    DeleteObject(h);
  } else hRgn = h;
  free(pData); // I've created the region so I can free this now, right?
  return hRgn;
}


void Fl_WinAPI_Window_Driver::draw_begin()
{
  if (shape_data_) {
    if ((shape_data_->lw_ != w() || shape_data_->lh_ != h()) && shape_data_->shape_) {
      // size of window has changed since last time
      shape_data_->lw_ = w();
      shape_data_->lh_ = h();
      Fl_Image* temp = shape_data_->shape_->copy(shape_data_->lw_, shape_data_->lh_);
      HRGN region = bitmap2region(temp);
      SetWindowRgn(fl_xid(pWindow), region, TRUE); // the system deletes the region when it's no longer needed
      delete temp;
    }
  }
}


void Fl_WinAPI_Window_Driver::flush_double()
{
  if (!shown()) return;
  pWindow->make_current(); // make sure fl_gc is non-zero
  Fl_X *i = Fl_X::i(pWindow);
  if (!i) return; // window not yet created

  if (!i->other_xid) {
    i->other_xid = fl_create_offscreen(w(), h());
    pWindow->clear_damage(FL_DAMAGE_ALL);
  }
  if (pWindow->damage() & ~FL_DAMAGE_EXPOSE) {
    fl_clip_region(i->region); i->region = 0;
    fl_begin_offscreen(i->other_xid);
    fl_graphics_driver->clip_region( 0 );
    draw();
    fl_end_offscreen();
  }

  int X,Y,W,H; fl_clip_box(0,0,w(),h(),X,Y,W,H);
  if (i->other_xid) fl_copy_offscreen(X, Y, W, H, i->other_xid, X, Y);
}


void Fl_WinAPI_Window_Driver::flush_overlay()
{
  Fl_Overlay_Window *oWindow = pWindow->as_overlay_window();

  if (!shown()) return;
  pWindow->make_current(); // make sure fl_gc is non-zero
  Fl_X *i = Fl_X::i(pWindow);
  if (!i) return; // window not yet created

  int eraseoverlay = (pWindow->damage()&FL_DAMAGE_OVERLAY);
  pWindow->clear_damage((uchar)(pWindow->damage()&~FL_DAMAGE_OVERLAY));

  if (!i->other_xid) {
    i->other_xid = fl_create_offscreen(w(), h());
    pWindow->clear_damage(FL_DAMAGE_ALL);
  }
  if (pWindow->damage() & ~FL_DAMAGE_EXPOSE) {
    fl_clip_region(i->region); i->region = 0;
    fl_begin_offscreen(i->other_xid);
    fl_graphics_driver->clip_region(0);
    draw();
    fl_end_offscreen();
  }

  if (eraseoverlay) fl_clip_region(0);
  int X, Y, W, H; fl_clip_box(0, 0, w(), h(), X, Y, W, H);
  if (i->other_xid) fl_copy_offscreen(X, Y, W, H, i->other_xid, X, Y);

  if (overlay() == oWindow) oWindow->draw_overlay();
}


void Fl_WinAPI_Window_Driver::icons(const Fl_RGB_Image *icons[], int count) {
  free_icons();
  
  if (count > 0) {
    icon_->icons = new Fl_RGB_Image*[count];
    icon_->count = count;
    // FIXME: Fl_RGB_Image lacks const modifiers on methods
    for (int i = 0;i < count;i++)
      icon_->icons[i] = (Fl_RGB_Image*)((Fl_RGB_Image*)icons[i])->copy();
  }
  
  if (Fl_X::i(pWindow))
    Fl_X::i(pWindow)->set_icons();
}

const void *Fl_WinAPI_Window_Driver::icon() const {
  return icon_->legacy_icon;
}

void Fl_WinAPI_Window_Driver::icon(const void * ic) {
  free_icons();
  icon_->legacy_icon = ic;
}

void Fl_WinAPI_Window_Driver::free_icons() {
  int i;
  icon_->legacy_icon = 0L;
  if (icon_->icons) {
    for (i = 0;i < icon_->count;i++)
      delete icon_->icons[i];
    delete [] icon_->icons;
    icon_->icons = 0L;
  }
  icon_->count = 0;
  if (icon_->big_icon)
    DestroyIcon(icon_->big_icon);
  if (icon_->small_icon)
    DestroyIcon(icon_->small_icon);
  icon_->big_icon = NULL;
  icon_->small_icon = NULL;
}


/** Sets the window icons using Windows' native HICON icon handles.
 
 The given icons are copied. You can free the icons immediately after
 this call.
 
 \param[in] big_icon large window icon
 \param[in] small_icon  small window icon
 */
void Fl_Window::icons(HICON big_icon, HICON small_icon)
{
  free_icons();
  
  if (big_icon != NULL)
    ((Fl_WinAPI_Window_Driver*)pWindowDriver)->icon_->big_icon = CopyIcon(big_icon);
  if (small_icon != NULL)
    ((Fl_WinAPI_Window_Driver*)pWindowDriver)->icon_->small_icon = CopyIcon(small_icon);
  
  if (Fl_X::i(this))
    Fl_X::i(this)->set_icons();
}


/** Sets the default window icons.
 
 Convenience function to set the default icons using Windows'
 native HICON icon handles.
 
 The given icons are copied. You can free the icons immediately after
 this call.
 
 \param[in] big_icon default large icon for all windows
 subsequently created
 \param[in] small_icon default small icon for all windows
 subsequently created
 
 \see Fl_Window::default_icon(const Fl_RGB_Image *)
 \see Fl_Window::default_icons(const Fl_RGB_Image *[], int)
 \see Fl_Window::icon(const Fl_RGB_Image *)
 \see Fl_Window::icons(const Fl_RGB_Image *[], int)
 \see Fl_Window::icons(HICON, HICON)
 */
void Fl_Window::default_icons(HICON big_icon, HICON small_icon) {
  Fl_X::set_default_icons(big_icon, small_icon);
}


void Fl_WinAPI_Window_Driver::wait_for_expose() {
  if (!shown()) return;
  Fl_X *i = Fl_X::i(pWindow);
  while (!i || i->wait_for_expose) {
    Fl::wait();
  }
}


void Fl_WinAPI_Window_Driver::make_current() {
  fl_GetDC(fl_xid(pWindow));
  
#if USE_COLORMAP
  // Windows maintains a hardware and software color palette; the
  // SelectPalette() call updates the current soft->hard mapping
  // for all drawing calls, so we must select it here before any
  // code does any drawing...
  fl_select_palette();
#endif // USE_COLORMAP
  
  fl_graphics_driver->clip_region(0);
}

void Fl_WinAPI_Window_Driver::label(const char *name,const char *iname) {
  if (shown() && !parent()) {
    if (!name) name = "";
    size_t l = strlen(name);
    //  WCHAR *lab = (WCHAR*) malloc((l + 1) * sizeof(short));
    //  l = fl_utf2unicode((unsigned char*)name, l, (wchar_t*)lab);
    unsigned wlen = fl_utf8toUtf16(name, (unsigned) l, NULL, 0); // Pass NULL to query length
    wlen++;
    unsigned short * lab = (unsigned short*)malloc(sizeof(unsigned short)*wlen);
    wlen = fl_utf8toUtf16(name, (unsigned) l, lab, wlen);
    lab[wlen] = 0;
    SetWindowTextW(fl_xid(pWindow), (WCHAR *)lab);
    free(lab);
  }
}


extern void fl_clipboard_notify_retarget(HWND wnd);
extern void fl_update_clipboard(void);

void Fl_WinAPI_Window_Driver::hide() {
  Fl_X* ip = Fl_X::i(pWindow);
  // STR#3079: if there remains a window and a non-modal window, and the window is deleted,
  // the app remains running without any apparent window.
  // Bug mechanism: hiding an owner window unmaps the owned (non-modal) window(s)
  // but does not delete it(them) in FLTK.
  // Fix for it:
  // when hiding a window, build list of windows it owns, and do hide/show on them.
  int count = 0;
  Fl_Window *win, **doit = NULL;
  for (win = Fl::first_window(); win && ip; win = Fl::next_window(win)) {
    if (win->non_modal() && GetWindow(fl_xid(win), GW_OWNER) == ip->xid) {
      count++;
    }
  }
  if (count) {
    doit = new Fl_Window*[count];
    count = 0;
    for (win = Fl::first_window(); win && ip; win = Fl::next_window(win)) {
      if (win->non_modal() && GetWindow(fl_xid(win), GW_OWNER) == ip->xid) {
        doit[count++] = win;
      }
    }
  }

  if (hide_common()) return;
  
  // make sure any custom icons get freed
  icons(NULL, 0);
  // this little trick keeps the current clipboard alive, even if we are about
  // to destroy the window that owns the selection.
  if (GetClipboardOwner()==ip->xid)
    fl_update_clipboard();
  // Make sure we unlink this window from the clipboard chain
  fl_clipboard_notify_retarget(ip->xid);
  // Send a message to myself so that I'll get out of the event loop...
  PostMessage(ip->xid, WM_APP, 0, 0);
  if (ip->private_dc) fl_release_dc(ip->xid, ip->private_dc);
  if (ip->xid == fl_window && fl_graphics_driver->gc()) {
    fl_release_dc(fl_window, (HDC)fl_graphics_driver->gc());
    fl_window = (HWND)-1;
    fl_graphics_driver->gc(0);
# ifdef FLTK_USE_CAIRO
    if (Fl::cairo_autolink_context()) Fl::cairo_make_current((Fl_Window*) 0);
# endif
  }
  
  if (ip->region) Fl_Graphics_Driver::XDestroyRegion(ip->region);
  
  // this little trickery seems to avoid the popup window stacking problem
  HWND p = GetForegroundWindow();
  if (p==GetParent(ip->xid)) {
    ShowWindow(ip->xid, SW_HIDE);
    ShowWindow(p, SW_SHOWNA);
  }
  DestroyWindow(ip->xid);
  // end of fix for STR#3079
  if (count) {
    int ii;
    for (ii = 0; ii < count; ii++)  doit[ii]->hide();
    for (ii = 0; ii < count; ii++)  {
      if (ii != 0) doit[0]->show(); // Fix for STR#3165
      doit[ii]->show();
    }
    delete[] doit;
  }
  // Try to stop the annoying "raise another program" behavior
  if (pWindow->non_modal() && Fl::first_window() && Fl::first_window()->shown())
    Fl::first_window()->show();
  delete ip;
}


void Fl_WinAPI_Window_Driver::map() {
  ShowWindow(fl_xid(pWindow), SW_RESTORE); // extra map calls are harmless
}


void Fl_WinAPI_Window_Driver::unmap() {
  ShowWindow(fl_xid(pWindow), SW_HIDE);
}


void Fl_X::make_fullscreen(int X, int Y, int W, int H) {
  int top, bottom, left, right;
  int sx, sy, sw, sh;
  
  top = w->fullscreen_screen_top;
  bottom = w->fullscreen_screen_bottom;
  left = w->fullscreen_screen_left;
  right = w->fullscreen_screen_right;
  
  if ((top < 0) || (bottom < 0) || (left < 0) || (right < 0)) {
    top = Fl::screen_num(X, Y, W, H);
    bottom = top;
    left = top;
    right = top;
  }
  
  Fl::screen_xywh(sx, sy, sw, sh, top);
  Y = sy;
  Fl::screen_xywh(sx, sy, sw, sh, bottom);
  H = sy + sh - Y;
  Fl::screen_xywh(sx, sy, sw, sh, left);
  X = sx;
  Fl::screen_xywh(sx, sy, sw, sh, right);
  W = sx + sw - X;
  
  DWORD flags = GetWindowLong(xid, GWL_STYLE);
  flags = flags & ~(WS_THICKFRAME|WS_CAPTION);
  SetWindowLong(xid, GWL_STYLE, flags);
  
  // SWP_NOSENDCHANGING is so that we can override size limits
  SetWindowPos(xid, HWND_TOP, X, Y, W, H, SWP_NOSENDCHANGING | SWP_FRAMECHANGED);
}


void Fl_WinAPI_Window_Driver::fullscreen_on() {
  pWindow->_set_fullscreen();
  Fl_X::i(pWindow)->make_fullscreen(x(), y(), w(), h());
  Fl::handle(FL_FULLSCREEN, pWindow);
}


void Fl_WinAPI_Window_Driver::fullscreen_off(int X, int Y, int W, int H) {
  pWindow->_clear_fullscreen();
  DWORD style = GetWindowLong(fl_xid(pWindow), GWL_STYLE);
  // Remove the xid temporarily so that Fl_X::fake_X_wm() behaves like it
  // does in Fl_X::make().
  HWND xid = fl_xid(pWindow);
  Fl_X::i(pWindow)->xid = NULL;
  int wx, wy, bt, bx, by;
  switch (Fl_X::fake_X_wm(pWindow, wx, wy, bt, bx, by)) {
    case 0:
      break;
    case 1:
      style |= WS_CAPTION;
      break;
    case 2:
      if (border()) {
        style |= WS_THICKFRAME | WS_CAPTION;
      }
      break;
  }
  Fl_X::i(pWindow)->xid = xid;
  // Adjust for decorations (but not if that puts the decorations
  // outside the screen)
  if ((X != x()) || (Y != y())) {
    X -= bx;
    Y -= by+bt;
  }
  W += bx*2;
  H += by*2+bt;
  SetWindowLong(fl_xid(pWindow), GWL_STYLE, style);
  SetWindowPos(fl_xid(pWindow), 0, X, Y, W, H,
               SWP_NOACTIVATE | SWP_NOZORDER | SWP_FRAMECHANGED);
  Fl::handle(FL_FULLSCREEN, pWindow);
}


void Fl_WinAPI_Window_Driver::iconize() {
  ShowWindow(fl_xid(pWindow), SW_SHOWMINNOACTIVE);
}


void Fl_WinAPI_Window_Driver::decoration_sizes(int *top, int *left,  int *right, int *bottom) {
  if (size_range_set() && (maxw() != minw() || maxh() != minh())) {
    *left = *right = GetSystemMetrics(SM_CXSIZEFRAME);
    *top = *bottom = GetSystemMetrics(SM_CYSIZEFRAME);
  } else {
    *left = *right = GetSystemMetrics(SM_CXFIXEDFRAME);
    *top = *bottom = GetSystemMetrics(SM_CYFIXEDFRAME);
  }
  *top += GetSystemMetrics(SM_CYCAPTION);
}

int Fl_WinAPI_Window_Driver::scroll(int src_x, int src_y, int src_w, int src_h, int dest_x, int dest_y,
                   void (*draw_area)(void*, int,int,int,int), void* data)
{
  typedef int (WINAPI* fl_GetRandomRgn_func)(HDC, HRGN, INT);
  static fl_GetRandomRgn_func fl_GetRandomRgn = 0L;
  static char first_time = 1;
  // We will have to do some Region magic now, so let's see if the
  // required function is available (and it should be staring w/Win95)
  if (first_time) {
    HMODULE hMod = GetModuleHandle("GDI32.DLL");
    if (hMod) {
      fl_GetRandomRgn = (fl_GetRandomRgn_func)GetProcAddress(hMod, "GetRandomRgn");
    }
    first_time = 0;
  }
  // Now check if the source scrolling area is fully visible.
  // If it is, we will do a quick scroll and just update the
  // newly exposed area. If it is not, we go the safe route and
  // re-render the full area instead.
  // Note 1: we could go and find the areas that are actually
  // obscured and recursively call fl_scroll for the newly found
  // rectangles. However, this practice would rely on the
  // elements of the undocumented Rgn structure.
  // Note 2: although this method should take care of most
  // multi-screen solutions, it will not solve issues scrolling
  // from a different resolution screen onto another.
  // Note 3: this has been tested with image maps, too.
  HDC gc = (HDC)fl_graphics_driver->gc();
  if (fl_GetRandomRgn) {
    // get the DC region minus all overlapping windows
    HRGN sys_rgn = CreateRectRgn(0, 0, 0, 0);
    fl_GetRandomRgn(gc, sys_rgn, 4);
    // now get the source scrolling rectangle
    HRGN src_rgn = CreateRectRgn(src_x, src_y, src_x+src_w, src_y+src_h);
    POINT offset = { 0, 0 };
    if (GetDCOrgEx(gc, &offset)) {
      OffsetRgn(src_rgn, offset.x, offset.y);
    }
    // see if all source pixels are available in the system region
    // Note: we could be a bit more merciful and subtract the
    // scroll destination region as well.
    HRGN dst_rgn = CreateRectRgn(0, 0, 0, 0);
    int r = CombineRgn(dst_rgn, src_rgn, sys_rgn, RGN_DIFF);
    DeleteObject(dst_rgn);
    DeleteObject(src_rgn);
    DeleteObject(sys_rgn);
    if (r != NULLREGION) {
      return 1;
    }
  }
  // Great, we can do an accelerated scroll instead of re-rendering
  BitBlt(gc, dest_x, dest_y, src_w, src_h, gc, src_x, src_y,SRCCOPY);
  return 0;
}

//
// End of "$Id$".
//