[Git][freetype/freetype][undefined_scale] [base] Undefined scale means n

Alexei Podtelezhnikov pushed to branch undefined_scale at FreeType / FreeType

Commits:

3d9c3045

by Alexei Podtelezhnikov at 2022-01-19T14:53:12-05:00

[base] Undefined scale means no scale.

It might be surprising that FreeType does not have default ppem and
the size has to be set explicitly or face undefined behavior with
undefined variables and errors. This offers an alternative to
missing or zero scale by simply setting FT_LOAD_NO_SCALE.

This is alternative to !132 and discussed in
  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=43708

* src/base/ftobjs.c (FT_Load_Glyph): Deal with zero scale.
* include/freetype/freetype.h: Document it.

2 changed files:

include/freetype/freetype.h
src/base/ftobjs.c

Changes:

include/freetype/freetype.h


    *   size.
    *
    * @note:
-   *   An @FT_Face has one _active_ @FT_Size object that is used by functions
+   *   An @FT_Face has one _active_ FT_Size object that is used by functions
    *   like @FT_Load_Glyph to determine the scaling transformation that in
    *   turn is used to load and hint glyphs and metrics.
    *
    *   You can use @FT_Set_Char_Size, @FT_Set_Pixel_Sizes, @FT_Request_Size
    *   or even @FT_Select_Size to change the content (i.e., the scaling
-   *   values) of the active @FT_Size.
+   *   values) of the active FT_Size.
    *
    *   You can use @FT_New_Size to create additional size objects for a given
    *   @FT_Face, but they won't be used by other functions until you activate

    *
    *   load_flags ::
    *     A flag indicating what to load for this glyph.  The @FT_LOAD_XXX
-   *     constants can be used to control the glyph loading process (e.g.,
+   *     flags can be used to control the glyph loading process (e.g.,
    *     whether the outline should be scaled, whether to load bitmaps or
    *     not, whether to hint the outline, etc).
    *

    *   FreeType error code.  0~means success.
    *
    * @note:
+   *   For proper scaling and hinting, the active @FT_Size object owned by
+   *   the face has to be meaningfully non-trivially initialized by
+   *   calling @FT_Set_Char_Size before this function, for example.
    *   The loaded glyph may be transformed.  See @FT_Set_Transform for the
    *   details.
    *

    *
    *   FT_LOAD_NO_SCALE ::
    *     Don't scale the loaded outline glyph but keep it in font units.
+   *     This flag is also assumed if @FT_Size owned by the face was not
+   *     properly initialized.
    *
    *     This flag implies @FT_LOAD_NO_HINTING and @FT_LOAD_NO_BITMAP, and
    *     unsets @FT_LOAD_RENDER.

src/base/ftobjs.c

@@ -858,6 +858,11 @@
      library = driver->root.library;
      hinter  = library->auto_hinter;
 +    /* undefined scale means no scale */
 +    if ( face->size->metrics.x_ppem == 0 ||
 +         face->size->metrics.y_ppem == 0 )
 +      load_flags |= FT_LOAD_NO_SCALE;
++
      /* resolve load flags dependencies */
      if ( load_flags & FT_LOAD_NO_RECURSE )

From:	Alexei Podtelezhnikov (@apodtele)
Subject:	[Git][freetype/freetype][undefined_scale] [base] Undefined scale means no scale.
Date:	Wed, 19 Jan 2022 19:55:33 +0000

...	...	@@ -522,13 +522,13 @@ FT_BEGIN_HEADER
522	522	* size.
523	523	*
524	524	* @note:
525		- * An @FT_Face has one _active_ @FT_Size object that is used by functions
	525	+ * An @FT_Face has one _active_ FT_Size object that is used by functions
526	526	* like @FT_Load_Glyph to determine the scaling transformation that in
527	527	* turn is used to load and hint glyphs and metrics.
528	528	*
529	529	* You can use @FT_Set_Char_Size, @FT_Set_Pixel_Sizes, @FT_Request_Size
530	530	* or even @FT_Select_Size to change the content (i.e., the scaling
531		- * values) of the active @FT_Size.
	531	+ * values) of the active FT_Size.
532	532	*
533	533	* You can use @FT_New_Size to create additional size objects for a given
534	534	* @FT_Face, but they won't be used by other functions until you activate
...	...	@@ -2819,7 +2819,7 @@ FT_BEGIN_HEADER
2819	2819	*
2820	2820	* load_flags ::
2821	2821	* A flag indicating what to load for this glyph. The @FT_LOAD_XXX
2822		- * constants can be used to control the glyph loading process (e.g.,
	2822	+ * flags can be used to control the glyph loading process (e.g.,
2823	2823	* whether the outline should be scaled, whether to load bitmaps or
2824	2824	* not, whether to hint the outline, etc).
2825	2825	*
...	...	@@ -2827,6 +2827,9 @@ FT_BEGIN_HEADER
2827	2827	* FreeType error code. 0~means success.
2828	2828	*
2829	2829	* @note:
	2830	+ * For proper scaling and hinting, the active @FT_Size object owned by
	2831	+ * the face has to be meaningfully non-trivially initialized by
	2832	+ * calling @FT_Set_Char_Size before this function, for example.
2830	2833	* The loaded glyph may be transformed. See @FT_Set_Transform for the
2831	2834	* details.
2832	2835	*
...	...	@@ -2918,6 +2921,8 @@ FT_BEGIN_HEADER
2918	2921	*
2919	2922	* FT_LOAD_NO_SCALE ::
2920	2923	* Don't scale the loaded outline glyph but keep it in font units.
	2924	+ * This flag is also assumed if @FT_Size owned by the face was not
	2925	+ * properly initialized.
2921	2926	*
2922	2927	* This flag implies @FT_LOAD_NO_HINTING and @FT_LOAD_NO_BITMAP, and
2923	2928	* unsets @FT_LOAD_RENDER.