stable_fluid.py里用了staggered网格吗？

综合讨论区
#1 
_velocities = ti.Vector.field(2, float, shape=(res, res))
_new_velocities = ti.Vector.field(2, float, shape=(res, res))
velocity_divs = ti.field(float, shape=(res, res))
velocity_curls = ti.field(float, shape=(res, res))
_pressures = ti.field(float, shape=(res, res))
_new_pressures = ti.field(float, shape=(res, res))
_dye_buffer = ti.Vector.field(3, float, shape=(res, res))
_new_dye_buffer = ti.Vector.field(3, float, shape=(res, res))

速度和压力的矩阵维度都是(res, res)，交错网格的话不应该u是(res+1, res)，v是(res, res+1)吗？

@ti.kernel
def advect(vf: ti.template(), qf: ti.template(), new_qf: ti.template()):
    for i, j in vf:
        p = ti.Vector([i, j]) + 0.5
        p = backtrace(vf, p, dt)
        new_qf[i, j] = bilerp(qf, p) * dye_decay

advect函数里对要backtrace的坐标加0.5又是什么意思呢？