#派生軸のタイプ
const config = { type: 'line', data, options: { responsive: true, scales: { x: { display: true, }, y: { display: true, type: 'log2', } } } };
#Log2軸の実装
import {Scale, LinearScale} from 'chart.js';
export default class Log2Axis extends Scale {
constructor(cfg) {
super(cfg);
this._startValue = undefined;
this._valueRange = 0;
}
parse(raw, index) {
const value = LinearScale.prototype.parse.apply(this, [raw, index]);
return isFinite(value) && value > 0 ? value : null;
}
determineDataLimits() {
const {min, max} = this.getMinMax(true);
this.min = isFinite(min) ? Math.max(0, min) : null;
this.max = isFinite(max) ? Math.max(0, max) : null;
}
buildTicks() {
const ticks = [];
let power = Math.floor(Math.log2(this.min || 1));
let maxPower = Math.ceil(Math.log2(this.max || 2));
while (power <= maxPower) {
ticks.push({value: Math.pow(2, power)});
power += 1;
}
this.min = ticks[0].value;
this.max = ticks[ticks.length - 1].value;
return ticks;
}
/**
* @protected
*/
configure() {
const start = this.min;
super.configure();
this._startValue = Math.log2(start);
this._valueRange = Math.log2(this.max) - Math.log2(start);
}
getPixelForValue(value) {
if (value === undefined || value === 0) {
value = this.min;
}
return this.getPixelForDecimal(value === this.min ? 0
: (Math.log2(value) - this._startValue) / this._valueRange);
}
getValueForPixel(pixel) {
const decimal = this.getDecimalForPixel(pixel);
return Math.pow(2, this._startValue + decimal * this._valueRange);
}
}
Log2Axis.id = 'log2';
Log2Axis.defaults = {};
// The derived axis is registered like this:
// Chart.register(Log2Axis);