With the default priorities, all VDC2 sprites should appear behind the VDC1 background, and it looks like you'd just set the VDC1 sprites to low-priority to put them behind the VDC1 background too
Yes, until today I thought that too,but when i set VDC1 sprite to low priority my sprite is in low priority as expected but filled with a black shape.
May be i missed something .
EDIT1:Aaaarg, in fact my routine who's changing sprites attributes which has a bug
EDIT2:not my routine but my brain lol, i set priority low/high with a define like that:
PRIORITY_LOW .equ $7F
PRIORITY_HIGH .equ $80
ldx #( SZ_32x64 | NO_FLIP ) & ( FLIP_MAS | SIZE_MAS )
ldy #( 1 | PRIORITY_HIGH )
jsr _spr_set_attribs_vdc1
And for low priority
ldx #( SZ_32x64 | NO_FLIP ) & ( FLIP_MAS | SIZE_MAS )
ldy #( 1 | PRIORITY_LOW )
jsr _spr_set_attribs_vdc1
i did | rather than &