Re: Question about display engine

[Eli Zaretskii]

> Date: Sun, 13 Oct 2019 21:38:36 +0200
> From: Ergus <address@hidden>
> Cc: address@hidden, address@hidden
> 
> (gdb) p it->sp
> $1 = 0
> (gdb) p it->method
> $2 = GET_FROM_C_STRING

If we are producing glyphs from a C string, then faces should not be
used at all, because C strings cannot have faces.

So you should to condition the call to face_at_pos on something like

  it->s == NULL

because there can not be any face on any position of a C string.

> (gdb) pgrowx it->glyph_row                                                    
>         
> TEXT: 85 glyphs
>   0    0: CHAR[-] str=0x4fab1a8f[0] blev=0,btyp=L w=1 a+d=0+0 face=1
>   1    1: CHAR[U] str=0x4fab18f0[1] blev=0,btyp=L w=1 a+d=0+0 face=1
>   2    2: CHAR[U] str=0x4fab18f0[1] blev=0,btyp=L w=1 a+d=0+0 face=1
>   3    3: CHAR[U] str=0x4fab18f0[1] blev=0,btyp=L w=1 a+d=0+0 face=1
>   4    4: CHAR[:] str=0xf2787f0[0] blev=0,btyp=L w=1 a+d=0+0 face=1
>   5    5: CHAR[%] str=0x4faaee54[1] blev=0,btyp=L w=1 a+d=0+0 face=1
>   6    6: CHAR[%] str=0x4faaede4[1] blev=0,btyp=L w=1 a+d=0+0 face=1
>   7    7: CHAR[-] str=0x4fab1721[1] blev=0,btyp=L w=1 a+d=0+0 face=1
>   8    8: CHAR[-] str=0x4fa9d9a8[0] blev=0,btyp=L w=1 a+d=0+0 face=1
>   9    9: CHAR[F] str=0x4fa9d9a8[2] blev=0,btyp=L w=1 a+d=0+0 face=1
>  10   10: CHAR[1] str=0x4fa9d9a8[2] blev=0,btyp=L w=1 a+d=0+0 face=1

This is a mode line, so it figures out: extend_face_to_end_of_line was
called when the iterator was processing the final blanks of the mode
line, see display_mode_line.