Line drawing routine

I'm using the SDL for graphics. and i am trying to write a function for drawing a line,
this is what i came up with
When angles are extreem it doesnt draw quite right. i helped with problem by drawing calculattes x.00 -> x1 x.00 to garner more y coordinates too use, still didnt help to much
any ideas on a better way to code this?

Code:

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void Artist::drawLine(int f, int p, int u , int t, Uint8 r, Uint8 g, Uint8 b)
        {
                float rise =  (p * 1.0) - (t * 1.0);
                float run  =  (f * 1.0) - (u * 1.0);
                float slope = rise / run;

                float y,x, d;
                d =    (slope * f ) - p ;
               
                for ( f = f * 100, u = u * 100; f <= u; f ++)
                        {
                                drawPixel(surface, f / 100 , ( (f*slope) + d ) / 100, r,g,b);
                        }


        }

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Code:

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void Line(Video *Device,int x,int y,int x2,int y2,DWORD color)
{
  int eterm=0;
  int length=0;
  int diffx=x2-x;
  int diffy=y2-y;

 
  int stepx=1;
  int stepy=Device->GetBufferPitch();

  DWORD offset=(y*stepy)+x;

  if (diffx<0)
  {
    stepx=-stepx;
    diffx=-diffx;
  }

  if (diffy<0)
  {
    stepy=-stepy;
    diffy=-diffy;
  }

  if (diffx>diffy)
  {
    length=diffx+1;
    for (int i=0;i<length;i++)
    {
      Video->Buffer[offset]=color;
      offset+=stepx;
      eterm+=diffy;
      if (eterm>diffx)
      {
        eterm-=diffx;
        offset+=stepy;
      }
    }
  }
  else
  {
    length=diffy+1;
    for (int i=0;i<length;i++)
    {
      Video->Buffer[offset]=color;
      offset+=stepy;
      eterm+=diffx;
      if (eterm>0)
      {
        eterm-=diffx;
        offset+=stepy;
      }
    }
  }
}

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There are other variations of this algorithm known as Bresehnam's algorithm.

and another...

Code:

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/* Draw line from x1, y1 to x2, y2 using Bresenham's Algorithm */
void bresenhamLine(const int x1, const int y1, const int x2, const int y2) {

  int dx = (x1 <= x2) ? x2 - x1 : x1 - x2;
  int dy = (y1 <= y2) ? y2 - y1 : y1 - y2;
  int x  = x1;
  int y  = y1;
  int e  = 0;

  int xInc = (x1 <= x2) ? 1 : -1;
  if(x1 == x2)
    xInc = 0;

  int yInc = (y1 <= y2) ? 1 : -1;
  if(y1 == y2)
    yInc = 0;


  if(dy <= dx) {
    /* x iterative loop */
    for( ; (xInc*x <= xInc*x2) && (yInc*y <= yInc*y2); x += xInc ) {
      setPixel(x,y);
      e += dy;
      if( yInc && (2*e + yInc*dy) >= xInc*dx ) {
        y += yInc;
        e -= dx;
      }
    }
  }
  else {
    /* y iterative loop */
    for( ; (yInc*y <= yInc*y2) && (xInc*x <= xInc*x2); y += yInc ) {
      setPixel(x,y);
      e += dx;
      if( xInc && (2*e + xInc*dx) >= yInc*dy ) {
        x += xInc;
        e -= dy;
      }
    }
  }
}

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