GCMC source code: Draw and label a decade of logarithmic ticks

## Circular Slide Rule Scales.gcmc
//----
// Define tick layout for scales
//  Numeric value for scale, corresponding tick length

TickScaleNarrow = {
  [1.0,TickMajor],
  [1.1,TickMinor],[1.2,TickMinor],[1.3,TickMinor],[1.4,TickMinor],
  [1.5,TickMid],
  [1.6,TickMinor],[1.7,TickMinor],[1.8,TickMinor],[1.9,TickMinor],
  [2.0,TickMajor],
  [2.2,TickMinor],[2.4,TickMinor],[2.6,TickMinor],[2.8,TickMinor],
  [3.0,TickMajor],
  [3.2,TickMinor],[3.4,TickMinor],[3.6,TickMinor],[3.8,TickMinor],
  [4.0,TickMajor],
  [4.5,TickMinor],
  [5.0,TickMajor],
  [5.5,TickMinor],
  [6.0,TickMajor],
  [6.5,TickMinor],
  [7.0,TickMajor],
  [7.5,TickMinor],
  [8.0,TickMajor],
  [8.5,TickMinor],
  [9.0,TickMajor],
  [9.5,TickMinor]
};

TickScaleWide = {
  [1.0,TickMajor],
  [1.1,TickMinor],[1.2,TickMinor],[1.3,TickMinor],[1.4,TickMinor],
  [1.5,TickMid],
  [1.6,TickMinor],[1.7,TickMinor],[1.8,TickMinor],[1.9,TickMinor],
  [2.0,TickMajor],
  [2.1,TickMinor],[2.2,TickMinor],[2.3,TickMinor],[2.4,TickMinor],
  [2.5,TickMid],
  [2.6,TickMinor],[2.7,TickMinor],[2.8,TickMinor],[2.9,TickMinor],
  [3.0,TickMajor],
  [3.2,TickMinor],[3.4,TickMinor],[3.6,TickMinor],[3.8,TickMinor],
  [4.0,TickMajor],
  [4.2,TickMinor],[4.4,TickMinor],[4.6,TickMinor],[4.8,TickMinor],
  [5.0,TickMajor],
  [5.5,TickMinor],
  [6.0,TickMajor],
  [6.5,TickMinor],
  [7.0,TickMajor],
  [7.5,TickMinor],
  [8.0,TickMajor],
  [8.5,TickMinor],
  [9.0,TickMajor],
  [9.5,TickMinor]
};

TickLabels = [1,2,5];                     // labels only these ticks, must be integers


/-----
// Draw a decade of ticks & labels
// ArcLength > 0 = CCW, < 0 = CW
// UnitOnly forces just the unit tick, so as to allow creating the last tick of the scale

function DrawTicks(Radius,TickMarks,TickOrient,UnitAngle,ArcLength,Decade,LabelOrient,UnitOnly) {

  feedrate(ScaleSpeed);

  local a,r0,r1,p0,p1;

  if (Decade == 1 || UnitOnly) {                    // draw unit marker
    a = UnitAngle;
    r0 = Radius + TickOrient * (TickMajor + 2*TickGap + ScaleTextSize.y);
    p0 = r0 * [cos(a),sin(a)];
    r1 = Radius + TickOrient * (ScaleSpace - 2*TickGap);
    p1 = r1 * [cos(a),sin(a)];

    goto(p0);
    move([-,-,EngraveZ]);
    move(p1);
    goto([-,-,TravelZ]);
  }

  local ticklist = UnitOnly ? {TickMarks[0]} : TickMarks;

  local tick;
  foreach(ticklist; tick) {
    a = UnitAngle + ArcLength * log10(tick[0]);
    p0 = Radius * [cos(a), sin(a)];
    p1 = (Radius + TickOrient*tick[1]) * [cos(a), sin(a)];

    goto(p0);
    move([-,-,EngraveZ]);
    move(p1);
    goto([-,-,TravelZ]);
  }

  feedrate(TextSpeed);                              // draw scale values

  local lrad = Radius + TickOrient * (TickMajor + TickGap);

  if (TickOrient == INWARD) {
    if (LabelOrient == INWARD) {
      lrad -= ScaleTextSize.y;        // inward ticks + inward labels = offset inward
    }
  }
  else {
    if (LabelOrient == OUTWARD) {
      lrad += ScaleTextSize.y;        // outward ticks + outward labels = offset outward
    }
  }

  ticklist = UnitOnly ? [TickLabels[0]] : TickLabels;

  local ltext,lpath,tpa;
  foreach(ticklist; tick) {
    ltext = to_string(Decade * to_int(tick));
    lpath = scale(typeset(ltext,TextFont),ScaleTextSize);
    a = UnitAngle + ArcLength * log10(tick);
    tpa = ArcText(lpath,[0mm,0mm],lrad,a,TEXT_CENTERED,LabelOrient);
    engrave(tpa,TravelZ,EngraveZ);
  }

}