12864 (st7920 controller) drawing points and lines subroutine

/*------------------ Draw point subroutine-----------------------------*/
//XY is the expected coordinate system (X:0-127, Y:0-63 in grids), Color 0 is off, 1 is on, 2 is flipped
void DrawPoint(unsigned char X,unsigned char Y,unsigned char Color)
{
    unsigned char Row,Tier,Tier_bit ;
    unsigned char ReadOldH,ReadOldL ;
    wr_comm(0x34); // Select extended instructions and turn off display
    wr_comm(0x36); // Select extended instructions, turn on display
    Tier=X>>4 ; // Shift right 4 bits, that is, divide by 16 and round to the integer, to get the horizontal coordinate DX corresponding to the 12864 to be written
    Tier_bit=X&0x0f ; // Get the number of the x in the DX (0-15), the high 4 bits of 0x0f are all 0,
                       // Bitwise AND eliminates the high 4 bits of X, which is equivalent to X%16, and obtains the number of bits in DX.
    if(Y<32)
    {
        Row=Y ;
    }
    else //y coordinate is greater than 31, to display on the screen, DX also adds 8 accordingly
    {
        Row=Y-32 ;
        Tier+=8 ;
    }
    wr_comm(Row+0x80); //Write (on the LCD) vertical coordinate (page coordinate)
    wr_comm(Tier+0x80); //Write (on the LCD) horizontal coordinate (column coordinate)
    ReadByte(); // Pre-
    readReadOldH=ReadByte(); //Read the data in the GDRAM at this location, the upper 8
    bitsReadOldL=ReadByte(); //low 8
    bitswr_comm(Row+0x80);
    wr_comm(Tier+0x80);
    if(Tier_bit<8) //x is in the lower 8 bits in DX (according to the expected coordinates), but belongs to the upper 8 bits in the LCD internal coordinate system, corresponding to ReadOldH
    {
        switch(Color)
        {
            case 0 : ReadOldH&=(~(0x01<<(7-Tier_bit))); break ; //bit conversion LCD corresponding bit
            case 1 : ReadOldH|=(0x01<<(7-Tier_bit)); break ; //set the specific position to 1 and light up
            case 2 : ReadOldH^=(0x01<<(7-Tier_bit)); break ; //bitwise XOR flip specific bit
            default : break ;
        }
        wr_data(ReadOldH); //write the upper 8 bits first
        wr_data(ReadOldL);
    }
    else
    {
        switch(Color)
        {
            case 0 : ReadOldL&=(~(0x01<<(15-Tier_bit))); break ;
            case 1 : ReadOldL|=(0x01<<(15-Tier_bit)); break ;
            case 2 : ReadOldL^=(0x01<<(15-Tier_bit)); break ;
            default : break ;
        }
        wr_data(ReadOldH);
        wr_data(ReadOldL);
    }
    wr_comm(0x30); //Set the basic instruction set to turn off drawing display
}
//Draw horizontal line:
void DrawLineX( unsigned char X0, unsigned char X1, unsigned char Y, unsigned char Color )
{ unsigned char Temp ;
    if( X0 > X1 )
    {
        Temp = X1 ;
        X1 = X0 ;
        X0 = Temp ;
    }
    for( ; X0 <= X1 ; X0++ )
    DrawPoint( X0, Y, Color ) ;
}
//Draw vertical line:
void DrawLineY( unsigned char X, unsigned char Y0, unsigned char Y1, unsigned char Color )
{
    unsigned char Temp ;
    if( Y0 > Y1 )
    {
        Temp = Y1 ;
        Y1 = Y0 ;
        Y0 = Temp ;
    }
    for(; Y0 <= Y1 ; Y0++)
    DrawPoint( X, Y0, Color) ;
}
//Use Bresenham line drawing algorithm
void DrawLine_any( unsigned char StartX, unsigned char StartY, unsigned char EndX, unsigned char EndY, unsigned char Color )
{
    int t, distance; /*Change variable type according to screen size (such as int type)*/
    int x = 0 , y = 0 , delta_x, delta_y ;
    char incx, incy ;
    delta_x = EndX - StartX ;
    delta_y = EndY - StartY ;
    if( delta_x > 0 )
    {
        incx = 1;
    }
    else if( delta_x == 0 )
    {
        DrawLineY ( StartX, Start delta_x > delta_y ) {     distance = delta_x ; } else     {         distance     = delta_y     ;     }     DrawPoint     (
        StartX         ,     StartY         ,     Color         ) ; /* Draw Line*/     for     (     t     =     0     ;     t     <     =         distance     +     1 ; t++ )     {     DrawPoint( StartX, StartY         , Color ) ;     x     +     =         delta_x ;         y         +         = delta_y ;         if( x > distance )         {             x -= distance ;             StartX += incx ;         }         if( y > distance )         {             y -= distance ;             StartY += incy ;         }     } }