The cpdf_set_text_rendering() function determines how text is rendered. 如果成功则返回 TRUE，失败则返回 FALSE。
The possible values for rendermode are 0=fill text, 1=stroke text, 2=fill and stroke text, 3=invisible, 4=fill text and add it to clipping path, 5=stroke text and add it to clipping path, 6=fill and stroke text and add it to clipping path, 7=add it to clipping path.