Man pages matching name xcb_glx_get_pixel_mapfv in section 3:

xcb_glx_get_pixel_mapfv.3.en	debian 10 / libxcb-doc
xcb_glx_get_pixel_mapfv.3.en	debian 11 / libxcb-doc
xcb_glx_get_pixel_mapfv.3.en	debian 12 / libxcb-doc