Implement double buffering on MS Windows

* etc/NEWS: Announce changes.
* src/w32fns.c (w32_set_inhibit_double_buffering): New function.
(w32_wnd_proc):
(Fx_create_frame):
(w32_create_tip_frame): Set `inhibit-double-buffering' parameter.
(w32_frame_parm_handlers): Add new handler.

* src/w32term.c (w32_show_back_buffer):
(w32_release_paint_buffer): New functions.
(w32_frame_up_to_date): Show back buffer if applicable.
(w32_buffer_flipping_unblocked_hook): New hook.
(w32_scroll_run): Use BitBlt to scroll instead of window
scrolling functions.
(w32_scroll_bar_clear): Don't clear scroll bars when double
buffered.
(w32_read_socket): Flip buffers after reading input events in
some cases.
(w32_free_frame_resources): Free back buffer.
(w32_create_terminal): Add new hook.

* src/w32term.h (struct w32_output): New fields for handling
back buffers.
* src/w32xfns.c (select_palette): Fix indentation.
(get_frame_dc, release_frame_dc): Return back buffer when
appropriate and set dirty flag.

1 files changed, 66 insertions, 10 deletions

diff --git a/src/w32xfns.c b/src/w32xfns.c
index d5974b906e8..139985c5bdb 100644
--- a/src/w32xfns.c
+++ b/src/w32xfns.c
@@ -136,13 +136,13 @@ select_palette (struct frame *f, HDC hdc)
     f->output_data.w32->old_palette = NULL;
 
   if (RealizePalette (hdc) != GDI_ERROR)
-  {
-    Lisp_Object frame, framelist;
-    FOR_EACH_FRAME (framelist, frame)
     {
-      SET_FRAME_GARBAGED (XFRAME (frame));
+      Lisp_Object frame, framelist;
+      FOR_EACH_FRAME (framelist, frame)
+	{
+	  SET_FRAME_GARBAGED (XFRAME (frame));
+	}
     }
-  }
 }
 
 void
@@ -157,19 +157,68 @@ deselect_palette (struct frame *f, HDC hdc)
 HDC
 get_frame_dc (struct frame *f)
 {
-  HDC hdc;
+  HDC hdc, paint_dc;
+  HBITMAP back_buffer;
+  HGDIOBJ obj;
+  struct w32_output *output;
 
   if (f->output_method != output_w32)
     emacs_abort ();
 
   enter_crit ();
+  output = FRAME_OUTPUT_DATA (f);
+
+  if (output->paint_dc)
+    {
+      if (output->paint_buffer_width != FRAME_PIXEL_WIDTH (f)
+	  || output->paint_buffer_height != FRAME_PIXEL_HEIGHT (f))
+	w32_release_paint_buffer (f);
+      else
+	{
+	  output->paint_buffer_dirty = 1;
+	  return output->paint_dc;
+	}
+    }
 
-  hdc = GetDC (f->output_data.w32->window_desc);
+  hdc = GetDC (output->window_desc);
 
   /* If this gets called during startup before the frame is valid,
      there is a chance of corrupting random data or crashing. */
   if (hdc)
-    select_palette (f, hdc);
+    {
+      select_palette (f, hdc);
+
+      if (FRAME_OUTPUT_DATA (f)->want_paint_buffer)
+	{
+	  back_buffer
+	    = CreateCompatibleBitmap (hdc, FRAME_PIXEL_WIDTH (f),
+				      FRAME_PIXEL_HEIGHT (f));
+
+	  if (back_buffer)
+	    {
+	      paint_dc = CreateCompatibleDC (hdc);
+
+	      if (!paint_dc)
+		DeleteObject (back_buffer);
+	      else
+		{
+		  obj = SelectObject (paint_dc, back_buffer);
+
+		  output->paint_dc_object = obj;
+		  output->paint_dc = paint_dc;
+		  output->paint_buffer_handle = hdc;
+		  output->paint_buffer = back_buffer;
+		  output->paint_buffer_width = FRAME_PIXEL_WIDTH (f);
+		  output->paint_buffer_height = FRAME_PIXEL_HEIGHT (f);
+		  output->paint_buffer_dirty = 1;
+
+		  SET_FRAME_GARBAGED (f);
+
+		  return paint_dc;
+		}
+	    }
+	}
+    }
 
   return hdc;
 }
@@ -179,8 +228,15 @@ release_frame_dc (struct frame *f, HDC hdc)
 {
   int ret;
 
-  deselect_palette (f, hdc);
-  ret = ReleaseDC (f->output_data.w32->window_desc, hdc);
+  /* Avoid releasing the double-buffered DC here, since it'll be
+     released upon the next buffer flip instead.  */
+  if (hdc != FRAME_OUTPUT_DATA (f)->paint_dc)
+    {
+      deselect_palette (f, hdc);
+      ret = ReleaseDC (f->output_data.w32->window_desc, hdc);
+    }
+  else
+    ret = 0;
 
   leave_crit ();