win32: Introduce new flag to mark surfaces that support solid brush drawing

This is part of a patch series to speed up CAIRO_OPERATOR_SOURCE when
used to copy data to an argb32 cairo surface corresponding to a win32 dc
from a "backbuffer" - DibSection-based cairo surface created with
cairo_surface_create_similar().

This initial patch presents only private header changes without changing
any implementation logic.

The big problem with argb32 surfaces and GDI is that GDI is unable to
correctly set the alpha channel when using operations other than BitBlt
and AlphaBlend.

To solve this, a CAIRO_WIN32_SURFACE_CAN_RGB_BRUSH flag is introduced in
this commit to be mark surfaces that correctly handle such brushes
- essentially all surface types except argb32.
The _cairo_win32_flags_for_dc() call receives a new argument that is
used to calculate the flag.

src/win32/cairo-win32-device.c

@@ -153,7 +153,7 @@ _cairo_win32_device_get (void)
 }
 
 unsigned
-_cairo_win32_flags_for_dc (HDC dc)
+_cairo_win32_flags_for_dc (HDC dc, cairo_format_t format)
 {
     uint32_t flags = 0;
     int cap;

src/win32/cairo-win32-display-surface.c

@@ -258,7 +258,7 @@ _create_dc_and_bitmap (cairo_win32_display_surface_t *surface,
 	}
     }
 
-    surface->win32.flags = _cairo_win32_flags_for_dc (surface->win32.dc);
+    surface->win32.flags = _cairo_win32_flags_for_dc (surface->win32.dc, format);
 
     return CAIRO_STATUS_SUCCESS;
 
@@ -1007,7 +1007,7 @@ cairo_win32_surface_create_with_format (HDC hdc, cairo_format_t format)
     surface->is_dib = FALSE;
     surface->saved_dc_bitmap = NULL;
 
-    surface->win32.flags = _cairo_win32_flags_for_dc (surface->win32.dc);
+    surface->win32.flags = _cairo_win32_flags_for_dc (surface->win32.dc, format);
 
     device = _cairo_win32_device_get ();
 

src/win32/cairo-win32-printing-surface.c

@@ -2159,7 +2159,7 @@ cairo_win32_printing_surface_create (HDC hdc)
 	return _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_NO_MEMORY));
     }
 
-    surface->win32.flags = _cairo_win32_flags_for_dc (surface->win32.dc);
+    surface->win32.flags = _cairo_win32_flags_for_dc (surface->win32.dc, CAIRO_FORMAT_RGB24);
     surface->win32.flags |= CAIRO_WIN32_SURFACE_FOR_PRINTING;
 
     _cairo_win32_printing_surface_init_ps_mode (surface);

src/win32/cairo-win32-private.h

@@ -81,6 +81,9 @@ enum {
 
     /* Whether we can use the CHECKPNGFORMAT escape function */
     CAIRO_WIN32_SURFACE_CAN_CHECK_PNG = (1<<8),
+
+    /* Whether we can use gdi drawing with solid rgb brush with this surface */
+    CAIRO_WIN32_SURFACE_CAN_RGB_BRUSH = (1<<9),
 };
 
 typedef struct _cairo_win32_surface {
@@ -204,7 +207,7 @@ _cairo_win32_surface_get_extents (void			  *abstract_surface,
 				  cairo_rectangle_int_t   *rectangle);
 
 uint32_t
-_cairo_win32_flags_for_dc (HDC dc);
+_cairo_win32_flags_for_dc (HDC dc, cairo_format_t format);
 
 cairo_int_status_t
 _cairo_win32_surface_emit_glyphs (cairo_win32_surface_t *dst,