如何使用freetype2访问单色位图中像素的状态

下面是一段代码片段:

wchar_t wc=L"か";
FT_UInt glyph_index = FT_Get_Char_Index(face, wc);
FT_Load_Glyph(face, glyph_index, FT_LOAD_DEFAULT);
if(face->glyph->format !=ft_glyph_format_bitmap)
{
    FT_Render_Glyph(face->glyph, FT_RENDER_MODE_MONO);
}
FT_GlyphSlot slot = face->glyph;
int rows = slot->bitmap.rows;
int cols = slot->bitmap.width; 
for (int i = 0; i < rows; ++i) 
{
    for (int j = 0; j < cols; ++j) 
    {
        int off  = i * slot->bitmap.pitch + j / 8;
        if (slot->bitmap.buffer[off] & (0xC0 >> (j % 8))) 
        {
              //do something if above condition met
        }
}

off 和条件 slot->bitmap.buffer[off] & (0x80 >> (j % 8))

实际上,类似的情况也可以找到 here . 函数定义如下:

bool glyphBit(const FT_GlyphSlot &glyph, const int x, const int y)
{
    int pitch = abs(glyph->bitmap.pitch);
    unsigned char *row = &glyph->bitmap.buffer[pitch * y];
    char cValue = row[x >> 3];

    return (cValue & (128 >> (x & 7))) != 0;
}

它基本上等同于上面的代码片段,所以我相信存在一个像素索引标准,但即使使用 official document