ref: a8e4563c3418ed74d39019a6c5e2122d12c8f56f
parent: 1949a7ec3a71572c24fe00e879b2a9b2b54f773d
author: Werner Lemberg <[email protected]>
date: Sat Mar 19 19:54:31 EDT 2022
Add `FT_FACE_FLAG_SBIX_OVERLAY` and `FT_HAS_SBIX_OVERLAY`. * include/freetype/freetype.h (FT_FACE_FLAG_SBIX_OVERLAY, FT_HAS_SBIX_OVERLAY): New macro. * src/sfnt/ttsbit.c (tt_face_load_sbit): Handle `FT_FACE_FLAG_SBIX_OVERLAY`. Remove obsolete tracing message.
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -155,6 +155,7 @@
* FT_FACE_FLAG_HINTER
* FT_FACE_FLAG_SVG
* FT_FACE_FLAG_SBIX
+ * FT_FACE_FLAG_SBIX_OVERLAY
*
* FT_HAS_HORIZONTAL
* FT_HAS_VERTICAL
@@ -165,6 +166,7 @@
* FT_HAS_MULTIPLE_MASTERS
* FT_HAS_SVG
* FT_HAS_SBIX
+ * FT_HAS_SBIX_OVERLAY
*
* FT_IS_SFNT
* FT_IS_SCALABLE
@@ -1244,6 +1246,10 @@
* For such fonts, @FT_FACE_FLAG_SCALABLE is not set by default to
* retain backward compatibility.
*
+ * FT_FACE_FLAG_SBIX_OVERLAY ::
+ * [Since 2.12] The face has an 'sbix' OpenType table where outlines
+ * should be drawn on top of bitmap strikes.
+ *
*/
#define FT_FACE_FLAG_SCALABLE ( 1L << 0 )
#define FT_FACE_FLAG_FIXED_SIZES ( 1L << 1 )
@@ -1263,6 +1269,7 @@
#define FT_FACE_FLAG_VARIATION ( 1L << 15 )
#define FT_FACE_FLAG_SVG ( 1L << 16 )
#define FT_FACE_FLAG_SBIX ( 1L << 17 )
+#define FT_FACE_FLAG_SBIX_OVERLAY ( 1L << 18 )
/**************************************************************************
@@ -1528,11 +1535,96 @@
* A macro that returns true whenever a face object contains an 'sbix'
* OpenType table *and* outline glyphs.
*
+ * Currently, FreeType only supports bitmap glyphs in PNG format for this
+ * table (i.e., JPEG and TIFF formats are unsupported, as are
+ * Apple-specific formats not part of the OpenType specification).
+ *
+ * @note:
+ * For backward compatibility, a font with an 'sbix' table is treated as
+ * a bitmap-only face. Using @FT_Open_Face with @FT_PARAM_TAG_NO_SBIX,
+ * an application can switch off 'sbix' handling so that the face is
+ * treated as an ordinary outline font with scalable outlines.
+ *
+ * Here is some pseudo code that roughly illustrates how to implement
+ * 'sbix' handling according to the OpenType specification.
+ *
+ * ```
+ * if ( FT_HAS_SBIX( face ) )
+ * {+ * // open font as a scalable one without sbix handling
+ * FT_Face face2;
+ * FT_Parameter param = { FT_PARAM_TAG_IGNORE_SBIX, NULL };+ * FT_Open_Args args = { FT_OPEN_PARAMS | ...,+ * ...,
+ * 1, ¶m };
+ *
+ *
+ * FT_Open_Face( library, &args, 0, &face2 );
+ *
+ * <sort `face->available_size` as necessary into
+ * `preferred_sizes`[*]>
+ *
+ * for ( i = 0; i < face->num_fixed_sizes; i++ )
+ * {+ * size = preferred_sizes[i].size;
+ *
+ * error = FT_Set_Pixel_Sizes( face, size, size );
+ * <error handling omitted>
+ *
+ * // check whether we have a glyph in a bitmap strike
+ * error = FT_Load_Glyph( face,
+ * glyph_index,
+ * FT_LOAD_SBITS_ONLY |
+ * FT_LOAD_BITMAP_METRICS_ONLY );
+ * if ( error == FT_Err_Invalid_Argument )
+ * continue;
+ * else if ( error )
+ * <other error handling omitted>
+ * else
+ * break;
+ * }
+ *
+ * if ( i != face->num_fixed_sizes )
+ * <load embedded bitmap with `FT_Load_Glyph`,
+ * scale it, display it, etc.>
+ *
+ * if ( i == face->num_fixed_sizes ||
+ * FT_HAS_SBIX_OVERLAY( face ) )
+ * <use `face2` to load outline glyph with `FT_Load_Glyph`,
+ * scale it, display it on top of the bitmap, etc.>
+ * }
+ * ```
+ *
+ * [*] Assuming a target value of 400dpi and available strike sizes 100,
+ * 200, 300, and 400dpi, a possible order might be [400, 200, 300, 100]:
+ * scaling 200dpi to 400dpi usually gives better results than scaling
+ * 300dpi to 400dpi; it is also much faster. However, scaling 100dpi to
+ * 400dpi can yield a too pixelated result, thus the preference might be
+ * 300dpi over 100dpi.
+ *
* @since:
* 2.12
*/
#define FT_HAS_SBIX( face ) \
( !!( (face)->face_flags & FT_FACE_FLAG_SBIX ) )
+
+
+ /**************************************************************************
+ *
+ * @macro:
+ * FT_HAS_SBIX_OVERLAY
+ *
+ * @description:
+ * A macro that returns true whenever a face object contains an 'sbix'
+ * OpenType table with bit~1 in its `flags` field set, instructing the
+ * application to overlay the bitmap strike with the corresponding
+ * outline glyph. See @FT_HAS_SBIX for pseudo code how to use it.
+ *
+ * @since:
+ * 2.12
+ */
+#define FT_HAS_SBIX_OVERLAY( face ) \
+ ( !!( (face)->face_flags & FT_FACE_FLAG_SBIX_OVERLAY ) )
/**************************************************************************
--- a/src/sfnt/ttsbit.c
+++ b/src/sfnt/ttsbit.c
@@ -172,17 +172,8 @@
goto Exit;
}
-#ifdef FT_DEBUG_LEVEL_TRACE
- /* we currently don't support bit 1; however, it is better to */
- /* draw at least something... */
if ( flags == 3 )
- {- FT_TRACE1(( "tt_face_load_sbit_strikes:"
- " sbix overlay not supported yet\n" ));
- FT_TRACE1(( " "
- " expect bad rendering results\n" ));
- }
-#endif
+ face->root.face_flags |= FT_FACE_FLAG_SBIX_OVERLAY;
/*
* Count the number of strikes available in the table. We are a bit