Win32: expose win32 DIB (image) surface creation function, and DC getter

Adds cairo_win32_surface_create_dib() for creating a win32 DIB-backed
surface with a particular format.  Also exposes
cairo_win32_surface_get_dc() to obtain the DC of a win32 surface.
(cherry picked from 0813a1b9b6f35d786fe8cb0d4748771023956cde commit)

src/cairo-win32-font.c

@@ -1159,7 +1159,7 @@ _cairo_win32_scaled_font_show_glyphs (void		       *abstract_font,
 	cairo_surface_pattern_t mask;
 	RECT r;
 
-	tmp_surface = (cairo_win32_surface_t *)_cairo_win32_surface_create_dib (CAIRO_FORMAT_ARGB32, width, height);
+	tmp_surface = (cairo_win32_surface_t *)cairo_win32_surface_create_dib (CAIRO_FORMAT_ARGB32, width, height);
 	if (tmp_surface->base.status)
 	    return CAIRO_STATUS_NO_MEMORY;
 

src/cairo-win32-private.h

@@ -70,11 +70,6 @@ typedef struct _cairo_win32_surface {
 cairo_status_t
 _cairo_win32_print_gdi_error (const char *context);
 
-cairo_surface_t *
-_cairo_win32_surface_create_dib (cairo_format_t format,
-				 int            width,
-				 int            height);
-
 cairo_bool_t
 _cairo_surface_is_win32 (cairo_surface_t *surface);
 

src/cairo-win32-surface.c

@@ -330,9 +330,9 @@ _cairo_win32_surface_create_similar (void	    *abstract_src,
  *   be created (probably because of lack of memory)
  **/
 cairo_surface_t *
-_cairo_win32_surface_create_dib (cairo_format_t format,
-				 int	        width,
-				 int	        height)
+cairo_win32_surface_create_dib (cairo_format_t format,
+				int	       width,
+				int	       height)
 {
     return _cairo_win32_surface_create_for_dc (NULL, format, width, height);
 }
@@ -1007,6 +1007,31 @@ _cairo_surface_is_win32 (cairo_surface_t *surface)
     return surface->backend == &cairo_win32_surface_backend;
 }
 
+/**
+ * cairo_win32_surface_get_dc
+ * @surface: a #cairo_surface_t
+ *
+ * Returns the HDC associated with this surface, or NULL if none.
+ * Also returns NULL if the surface is not a win32 surface.
+ *
+ * Return value: HDC or NULL if no HDC available.
+ **/
+HDC
+cairo_win32_surface_get_dc (cairo_surface_t *surface)
+{
+    cairo_win32_surface_t *winsurf;
+
+    if (surface == NULL)
+	return NULL;
+
+    if (!_cairo_surface_is_win32(surface))
+	return NULL;
+
+    winsurf = (cairo_win32_surface_t *) surface;
+
+    return winsurf->dc;
+}
+
 static const cairo_surface_backend_t cairo_win32_surface_backend = {
     _cairo_win32_surface_create_similar,
     _cairo_win32_surface_finish,

src/cairo-win32.h

@@ -47,6 +47,14 @@ CAIRO_BEGIN_DECLS
 cairo_public cairo_surface_t *
 cairo_win32_surface_create (HDC hdc);
 
+cairo_public cairo_surface_t *
+cairo_win32_surface_create_dib (cairo_format_t format,
+				int width,
+				int height);
+
+cairo_public HDC
+cairo_win32_surface_get_dc (cairo_surface_t *surface);
+
 cairo_public cairo_font_face_t *
 cairo_win32_font_face_create_for_logfontw (LOGFONTW *logfont);