MacOS下Brush Script MT字体调用FT_Load_Glyph返回140错误排查

开发的程序使用FreeType库在屏幕绘制字形，在MacOS系统加载Brush Script MT字体文件时，FT_Load_Glyph返回错误码140，该错误在FreeType文档中描述为“too many function definitions”（函数定义过多）。此问题仅出现在MacOS，Windows系统无异常，且目前未发现其他字体触发该错误。

受此影响，Brush Script MT字体的所有字符均无法在屏幕上渲染，目前临时解决方案是使用占位字体Lucida Grande作为替代。

最小复现代码 #

以下是使用Xojo编写的最小复现示例（语法与Visual Basic类似），在MacOS上调试时FT_Load_Glyph会返回140错误：

// INITIALIZE FREETYPE LIBRARY

dim freetype_library_ptr as ptr

soft declare function FT_Init_FreeType lib freetype (byRef alibrary as ptr) as int32
dim err as int32 = FT_Init_FreeType(freetype_library_ptr)

// CREATE BRUSH SCRIPT MT FACE

dim face_index as integer = 0
dim p as ptr

dim brush_script_file as new folderitem("/System/Library/Fonts/Supplemental/Brush Script.ttf")
dim path as string = brush_script_file.shellpath
#if targetMacOS
  path=replaceall(path,"\","")
#endif

soft declare function FT_New_Face lib freetype (library as ptr,filepathname as cstring,face_index as int32,byref aface as ptr) as int32
err=FT_New_Face(freetype_library_ptr,path,face_index,p)

// SET CHARACTER SIZE FOR GLYPH

dim char_width as int32 = 0
dim char_height as int32 = 262144
dim horz_resolution as uint32 = 72
dim vert_resolution as uint32 = 72

soft declare function FT_Set_Char_Size lib freetype (face as ptr,char_width as int32,char_height as int32,horz_resolution as uint32,vert_resolution as uint32) as int32
err=FT_Set_Char_Size(p,char_width,char_height,horz_resolution,vert_resolution)

// RETRIEVE A GLYPH FROM THE FACE

dim glyph_index as integer = 75 // Index for K character
dim load_flags as integer = 0

soft declare function FT_Load_Glyph lib freetype (face as ptr,glyph_index as uint32,load_flags as int32) as int32
err=FT_Load_Glyph(p,glyph_index,load_flags) // ERROR 140 on MacOS: too many function definitions

// FINISHED USING  BRUSH SCRIPT MT FACE

soft declare function FT_Done_Face lib freetype (face as ptr) as int32
err=FT_Done_Face(p)

// FINISHED USING FREETYPE LIBRARY

soft declare function FT_Done_FreeType lib freetype (library as ptr) as int32
err=FT_Done_FreeType(freetype_library_ptr)

关键信息 #

• 使用FreeType 2.4.2版本
• 运行平台：MacOS Monterey（12.6.5版本）

调试发现 #

以调试模式重新编译FreeType库后，观察加载Brush Script MT字体字形时的日志：调用FT_Load_Glyph时，日志会打印一次“NPUSHB”和11次“FDEF”。

在依赖文件ttinterp.c中找到如下代码，确认是numFDefs超过maxFDefs的限制触发了错误，但不清楚Brush Script MT字体会出现这种情况的原因：

if ( CUR.numFDefs >= CUR.maxFDefs )
{
    CUR.error = TT_Err_Too_Many_Function_Defs;
    return;
}
CUR.numFDefs++;

字体特殊点 #

Brush Script MT并非MacOS默认系统字体，随Microsoft Word安装而来，且该字体家族仅包含斜体样式。

内容的提问来源于stack exchange，提问作者Shem S