ld  a, h        ; a=v (integer part)
    add hl, sp      ; v=v+dv : on hlu, compute u=u+du for fractionnal part
    exx             ; swap
    ld  h, a        ; paste integer v on high byte
    ld  e, (hl)     ; fetch texture at $D3VVUU
    ld  a, (de)     ; fetch lighted color
    adc hl, bc      ; u=u+du (integer part)
    exx             ; swap
    ld  (de), a     ; write the pixel to the framebuffer
    inc de          ; advance next pixel