Algorithm for drawing any line in graphical LCD Ampire 128x64 with controller KS0108

void DrawLine3(int x1, int y1, int x2, int y2, boolean color)
{
int i, deltax, deltay, numpixels;
int d, dinc1, dinc2;
int x, xinc1, xinc2;
int y, yinc1, yinc2;
//calculate deltaX and deltaY
deltax = abs(x2 - x1);
deltay = abs(y2 - y1);
//initialize
if(deltax >= deltay)
{
//If x is independent variable
numpixels = deltax + 1;
d = (2 * deltay) - deltax;
dinc1 = deltay << 1;
dinc2 = (deltay - deltax) << 1;
xinc1 = 1;
xinc2 = 1;
yinc1 = 0;
yinc2 = 1;
}
else
{
//if y is independent variable
numpixels = deltay + 1;
d = (2 * deltax) - deltay;
dinc1 = deltax << 1;
dinc2 = (deltax - deltay) << 1;
xinc1 = 0;
xinc2 = 1;
yinc1 = 1;
yinc2 = 1;
}
//move the right direction
if(x1 > x2)
{
xinc1 = -xinc1;
xinc2 = -xinc2;
}
if(y1 > y2)
{
yinc1 = -yinc1;
yinc2 = -yinc2;
}
x = x1;
y = y1;
//draw the pixels
for(i = 1; i < numpixels; i++)
{
DrawPixel3(x, y, color);
if(d < 0)
{d = d + dinc1;
x = x + xinc1;
y = y + yinc1;
}
else
{
d = d + dinc2;
x = x + xinc2;
y = y + yinc2;
}
}
}

// Purpose:       Draw a line on a graphic LCD using Bresenham's
//                line drawing algorithm
// Inputs:        (x1, y1) - the start coordinate
//                (x2, y2) - the end coordinate
//                color - ON or OFF
// Dependencies:  glcd_pixel()
void glcd_line(int x1, int y1, int x2, int y2, int1 color)
{
   signed int  x, y, addx, addy, dx, dy;
   signed long P;
   int i;
   dx = abs((signed int)(x2 - x1));
   dy = abs((signed int)(y2 - y1));
   x = x1;
   y = y1;

   if(x1 > x2)
      addx = -1;
   else
      addx = 1;
   if(y1 > y2)
      addy = -1;
   else
      addy = 1;

   if(dx >= dy)
   {
      P = 2*dy - dx;

      for(i=0; i<=dx; ++i)
      {
         glcd_pixel(x, y, color);

         if(P < 0)
         {
            P += 2*dy;
            x += addx;
         }
         else
         {
            P += 2*dy - 2*dx;
            x += addx;
            y += addy;
         }
      }
   }
   else
   {
      P = 2*dx - dy;

      for(i=0; i<=dy; ++i)
      {
         glcd_pixel(x, y, color);

         if(P < 0)
         {
            P += 2*dx;
            y += addy;
         }
         else
         {
            P += 2*dx - 2*dy;
            x += addx;
            y += addy;
         }
      }
   }
}