freetype2.8 怎么渲染字体背景色？

已经可以使用freetype2.9设置字体的颜色，但是没有找到相关的设置字体背景色的方，有任何帮助感谢！！！下边是绘制带颜色的bitmap字符

for ( S32 n = 0; n < dataLength; n++)
{
    PGlyph pplyph = glyphs+n;
    FT_Vector pen = glyph->pos;
    //error = FT_Glyph_To_Bitmap(&pplyph->glyph, FT_RENDER_MODE_NORMAL, &pen, 0);
    error = FT_Glyph_To_Bitmap(&pplyph->glyph, FT_RENDER_MODE_NORMAL, &pen, 0);
    if ( !error )
    {
        FT_BitmapGlyph bit = (FT_BitmapGlyph)pplyph->glyph;
        start_x = pplyph->drawBox.xMin;
        start_y = height - (pplyph->drawBox.yMin-bbox.yMin+bit->bitmap.rows);
        for (S32 y = 0; y < bit->bitmap.rows; y++)
        {
            for (S32 x = 0; x < bit->bitmap.width; x++)
            {
                unsigned int iy = start_y + y;
                unsigned int ix = start_x + x;
                unsigned int index = (iy*width + ix)*4;
                imageBuffer[index] = ~((dataIndexBuf[n].u32Foreground) & 0xFF);
                imageBuffer[index+1] = ~(((dataIndexBuf[n].u32Foreground) >> 8) &  0xFF);
                imageBuffer[index+2] = ~(((dataIndexBuf[n].u32Foreground) >> 16) &  0xFF);
                imageBuffer[index+3] = bit->bitmap.buffer[y * bit->bitmap.width + x];
            }
        }
        FT_Done_Glyph(pplyph->glyph);
    }
}

https://blog.csdn.net/weixin_40550094/article/details/104071685