- var scale, low_val, high_val, nTicks;
- for (var i = -10; i < 50; i++) {
- if (kmg2) {
- var base_scale = Math.pow(16, i);
- } else {
- var base_scale = Math.pow(10, i);
- }
- for (var j = 0; j < mults.length; j++) {
- scale = base_scale * mults[j];
- low_val = Math.floor(a / scale) * scale;
- high_val = Math.ceil(b / scale) * scale;
- nTicks = Math.abs(high_val - low_val) / scale;
- var spacing = pixels / nTicks;
- // wish I could break out of both loops at once...
- if (spacing > pixels_per_tick) break;
- }
+
+ // Get the maximum number of permitted ticks based on the
+ // graph's pixel size and pixels_per_tick setting.
+ var max_ticks = Math.ceil(pixels / pixels_per_tick);
+
+ // Now calculate the data unit equivalent of this tick spacing.
+ // Use abs() since graphs may have a reversed Y axis.
+ var units_per_tick = Math.abs(b - a) / max_ticks;
+
+ // Based on this, get a starting scale which is the largest
+ // integer power of the chosen base (10 or 16) that still remains
+ // below the requested pixels_per_tick spacing.
+ var base_power = Math.floor(Math.log(units_per_tick) / Math.log(base));
+ var base_scale = Math.pow(base, base_power);
+
+ // Now try multiples of the starting scale until we find one
+ // that results in tick marks spaced sufficiently far apart.
+ // The "mults" array should cover the range 1 .. base^2 to
+ // adjust for rounding and edge effects.
+ var scale, low_val, high_val, spacing;
+ for (j = 0; j < mults.length; j++) {
+ scale = base_scale * mults[j];
+ low_val = Math.floor(a / scale) * scale;
+ high_val = Math.ceil(b / scale) * scale;
+ nTicks = Math.abs(high_val - low_val) / scale;
+ spacing = pixels / nTicks;