Implementation of DDA Line Algorithm

I have tested all the cases of how a line could be

1. vertically
2. horizontally
3. has a slope that's positive or less than 1

The function works, but I would like it reviewed, such as if there are overflows, etc.

// Draw line using DDA Algorithm
void Graphics::DrawLine( int x1, int y1, int x2, int y2, Color&color )
{

    float xdiff = x1-x2; 
    float ydiff = y1-y2; 
    int slope  = 1; 
    if ( y1  == y2  )
    {
        slope = 0;
    }
    else if (  x1 == x2 )
    {
        slope = 2; // vertical lines have no slopes...
    }
    else
    {
        slope = (int)xdiff/ydiff; 
    }

    if ( slope <= 1 )
    {    
        int startx = 0;
        int endx   = 0;
        if ( x1 > x2 )
        {
            startx = x2;
            endx   = x1;
        }
        else 
        {
            startx = x1;
            endx   = x2;
        }

        float y = y1; // initial value
        for(int x = startx; x <= endx; x++)
        {
            y += slope;
            DrawPixel(x, (int)abs(y), color);
        }
    }

    else if ( slope > 1 )
    {
        float x = x1; // initial value
        for(int y = y1;y <= y2; y++)
        {
            x += 1/slope;
            DrawPixel((int)x, y, color);
        }

    }

}