DWrite: Don't convert subpixel antialiasing to grayscale

Reuse the win32 font code to create a glyph mask for a dwrite font.
Renamed a function _compute_mask in cairo-win32-font.c to
_cairo_compute_glyph_mask.

3 files changed, 9 insertions, 41 deletions

diff --git a/src/win32/cairo-dwrite-font.cpp b/src/win32/cairo-dwrite-font.cpp
index 994889e21..edd606abe 100644
--- a/src/win32/cairo-dwrite-font.cpp
+++ b/src/win32/cairo-dwrite-font.cpp
@@ -1126,42 +1126,6 @@ _cairo_dwrite_scaled_font_init_glyph_color_surface(cairo_dwrite_scaled_font_t *s
     return CAIRO_INT_STATUS_SUCCESS;
 }
 
-/* Helper function adapted from _compute_mask in cairo-win32-font.c */
-
-/* Compute an alpha-mask from a monochrome RGB24 image
- */
-static cairo_surface_t *
-_compute_a8_mask (cairo_surface_t *surface)
-{
-    cairo_image_surface_t *glyph;
-    cairo_image_surface_t *mask;
-    int i, j;
-
-    glyph = (cairo_image_surface_t *)cairo_surface_map_to_image (surface, NULL);
-    if (unlikely (glyph->base.status))
-        return &glyph->base;
-
-    /* No quality param, just use the non-ClearType path */
-
-    /* Compute an alpha-mask by using the green channel of a (presumed monochrome)
-     * RGB24 image.
-     */
-    mask = (cairo_image_surface_t *)
-        cairo_image_surface_create (CAIRO_FORMAT_A8, glyph->width, glyph->height);
-    if (likely (mask->base.status == CAIRO_STATUS_SUCCESS)) {
-        for (i = 0; i < glyph->height; i++) {
-            uint32_t *p = (uint32_t *) (glyph->data + i * glyph->stride);
-            uint8_t *q = (uint8_t *) (mask->data + i * mask->stride);
-
-            for (j = 0; j < glyph->width; j++)
-                *q++ = 255 - ((*p++ & 0x0000ff00) >> 8);
-        }
-    }
-
-    cairo_surface_unmap_image (surface, &glyph->base);
-    return &mask->base;
-}
-
 static cairo_int_status_t
 _cairo_dwrite_scaled_font_init_glyph_surface(cairo_dwrite_scaled_font_t *scaled_font,
 					     cairo_scaled_glyph_t	*scaled_glyph)
@@ -1240,7 +1204,7 @@ _cairo_dwrite_scaled_font_init_glyph_surface(cairo_dwrite_scaled_font_t *scaled_
 
     GdiFlush();
 
-    image = _compute_a8_mask (&surface->base);
+    image = _cairo_compute_glyph_mask (&surface->base, CLEARTYPE_QUALITY);
     status = (cairo_int_status_t)image->status;
     if (status)
 	goto FAIL;
diff --git a/src/win32/cairo-win32-font.c b/src/win32/cairo-win32-font.c
index 6bc8bef94..fd9461363 100644
--- a/src/win32/cairo-win32-font.c
+++ b/src/win32/cairo-win32-font.c
@@ -1335,9 +1335,9 @@ _cairo_win32_scaled_font_load_type1_data (void	            *abstract_font,
 							 length);
 }
 
-static cairo_surface_t *
-_compute_mask (cairo_surface_t *surface,
-	       int quality)
+cairo_surface_t *
+_cairo_compute_glyph_mask (cairo_surface_t *surface,
+			   int quality)
 {
     cairo_image_surface_t *glyph;
     cairo_image_surface_t *mask;
@@ -1421,7 +1421,7 @@ _cairo_win32_scaled_font_init_glyph_surface (cairo_win32_scaled_font_t *scaled_f
     if (status)
 	goto FAIL;
 
-    image = _compute_mask (surface, scaled_font->quality);
+    image = _cairo_compute_glyph_mask (surface, scaled_font->quality);
     status = image->status;
     if (status)
 	goto FAIL;
diff --git a/src/win32/cairo-win32-private.h b/src/win32/cairo-win32-private.h
index 486b12811..6af09c0e1 100644
--- a/src/win32/cairo-win32-private.h
+++ b/src/win32/cairo-win32-private.h
@@ -214,6 +214,10 @@ cairo_bool_t
 _cairo_win32_surface_get_extents (void			  *abstract_surface,
 				  cairo_rectangle_int_t   *rectangle);
 
+cairo_surface_t *
+_cairo_compute_glyph_mask (cairo_surface_t *surface,
+			   int quality);
+
 uint32_t
 _cairo_win32_flags_for_dc (HDC dc, cairo_format_t format);