About code in de2_tv on kit de2

Hi! I am beginer and i want to use demo DE2_TV in cd rom from Kit de2 of Terasic.

Who can explain for me about codes in DE2_TV.v ?

assign m1VGA_Read = VGA_Y[0] ? 1'b0 : VGA_Read ;

assign m2VGA_Read = VGA_Y[0] ? VGA_Read : 1'b0 ;

assign mYCbCr_d = !VGA_Y[0] ? m1YCbCr :

m2YCbCr ;

assign mYCbCr = m5YCbCr;

wire mDVAL;

// Line buffer, delay one line

Line_Buffer u10 ( .clken(VGA_Read),

.clock(OSC_27),

.shiftin(mYCbCr_d),

.shiftout(m3YCbCr));

Line_Buffer u11 ( .clken(VGA_Read),

.clock(OSC_27),

.shiftin(m3YCbCr),

.shiftout(m4YCbCr));

wire [15:0] m4YCbCr;

wire [15:0] m5YCbCr;

wire [8:0] Tmp1,Tmp2;

wire [7:0] Tmp3,Tmp4;

assign Tmp1 = m4YCbCr[7:0]+mYCbCr_d[7:0];

assign Tmp2 = m4YCbCr[15:8]+mYCbCr_d[15:8];

assign Tmp3 = Tmp1[8:2]+m3YCbCr[7:1];

assign Tmp4 = Tmp2[8:2]+m3YCbCr[15:9];

assign m5YCbCr = {Tmp4,Tmp3};

I don't understand function of 2 line buffer and why need use Temp1,2,3,4 with adder ? The first i guess it use for deinterlace ,but then i think it is not correct ?

Thank for your help !