function ChangeSlide(q) {
  switch (q)
  {
  case 1:
    i = 1
    break
  case 2:
    i = i - 1
    if (i < 1) { i = 1 }
    break
  case 3:
    i = i + 1
    if (i > imax) { i = imax }

    for (k=1;k<=6;k++) {
      document.getElementById('next' + k).src = "loading.gif"
    }
    break
  }
  
  document.getElementById('knum').innerHTML = "Slide " + i + " of " + imax
  document.getElementById('main_slide').src = "loading.gif"
  document.getElementById('main_slide').src = slide_file[i]  
  
   /* Get started loading the next files in the background. They will be cached 
      by the browser and ready to view quickly, I hope. */

  for (k=1;k<=6;k++) {
    if (i < (imax+4-k)) { document.getElementById('next' + k).src = slide_file[i+k-3] } else 
                        { document.getElementById('next' + k).src = "transparent.gif" }
  }  
  
  for (j=1;j<=i;j++) {       document.getElementById('slide' + j).src = "red.gif"    }
  for (j=i+1;j<=imax;j++) {  document.getElementById('slide' + j).src = "white.gif"  }

  return true;
}

function show_slide(i1) {
  if (i1 < 0) {i1 = 0}
  if (i1 > imax) {i1 = imax}
  i = i1

  document.getElementById('knum').innerHTML = "Slide " + i + " of " + imax
  document.getElementById('main_slide').src = "loading.gif"
  document.getElementById('main_slide').src = slide_file[i]

  for (j=1;j<=i;j++) {       document.getElementById('slide' + j).src = "red.gif"    }
  for (j=i+1;j<=imax;j++) {  document.getElementById('slide' + j).src = "white.gif"  }
  
  for (k=1;k<=6;k++) {
    if (i < (imax+4-k)) { document.getElementById('next' + k).src = slide_file[i+k-3] } else 
                        { document.getElementById('next' + k).src = "transparent.gif" }
  }
}

function load_tasks() {
  document.getElementById('knum').innerHTML = "Slide 1 of " + imax
  document.getElementById('main_slide').src = slide_file[1]
  for (k=1;k<=6;k++) {
    document.getElementById('next' + k).src = slide_file[k-2]
  }
}

function ClickThumb(j) {
  k = i+j
  if (k < 1)    {k = 1}
  if (k > imax) {k = imax}
  show_slide(k)
}