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core.scale.js
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core.scale.js
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import Element from './core.element';
import {_alignPixel, _measureText, renderText, clipArea, unclipArea} from '../helpers/helpers.canvas';
import {callback as call, each, finiteOrDefault, isArray, isFinite, isNullOrUndef, isObject, valueOrDefault} from '../helpers/helpers.core';
import {toDegrees, toRadians, _int16Range, _limitValue, HALF_PI} from '../helpers/helpers.math';
import {_alignStartEnd, _toLeftRightCenter} from '../helpers/helpers.extras';
import {createContext, toFont, toPadding, _addGrace} from '../helpers/helpers.options';
import {autoSkip} from './core.scale.autoskip';
const reverseAlign = (align) => align === 'left' ? 'right' : align === 'right' ? 'left' : align;
const offsetFromEdge = (scale, edge, offset) => edge === 'top' || edge === 'left' ? scale[edge] + offset : scale[edge] - offset;
/**
* @typedef { import("./core.controller").default } Chart
* @typedef {{value:number | string, label?:string, major?:boolean, $context?:any}} Tick
*/
/**
* Returns a new array containing numItems from arr
* @param {any[]} arr
* @param {number} numItems
*/
function sample(arr, numItems) {
const result = [];
const increment = arr.length / numItems;
const len = arr.length;
let i = 0;
for (; i < len; i += increment) {
result.push(arr[Math.floor(i)]);
}
return result;
}
/**
* @param {Scale} scale
* @param {number} index
* @param {boolean} offsetGridLines
*/
function getPixelForGridLine(scale, index, offsetGridLines) {
const length = scale.ticks.length;
const validIndex = Math.min(index, length - 1);
const start = scale._startPixel;
const end = scale._endPixel;
const epsilon = 1e-6; // 1e-6 is margin in pixels for accumulated error.
let lineValue = scale.getPixelForTick(validIndex);
let offset;
if (offsetGridLines) {
if (length === 1) {
offset = Math.max(lineValue - start, end - lineValue);
} else if (index === 0) {
offset = (scale.getPixelForTick(1) - lineValue) / 2;
} else {
offset = (lineValue - scale.getPixelForTick(validIndex - 1)) / 2;
}
lineValue += validIndex < index ? offset : -offset;
// Return undefined if the pixel is out of the range
if (lineValue < start - epsilon || lineValue > end + epsilon) {
return;
}
}
return lineValue;
}
/**
* @param {object} caches
* @param {number} length
*/
function garbageCollect(caches, length) {
each(caches, (cache) => {
const gc = cache.gc;
const gcLen = gc.length / 2;
let i;
if (gcLen > length) {
for (i = 0; i < gcLen; ++i) {
delete cache.data[gc[i]];
}
gc.splice(0, gcLen);
}
});
}
/**
* @param {object} options
*/
function getTickMarkLength(options) {
return options.drawTicks ? options.tickLength : 0;
}
/**
* @param {object} options
*/
function getTitleHeight(options, fallback) {
if (!options.display) {
return 0;
}
const font = toFont(options.font, fallback);
const padding = toPadding(options.padding);
const lines = isArray(options.text) ? options.text.length : 1;
return (lines * font.lineHeight) + padding.height;
}
function createScaleContext(parent, scale) {
return createContext(parent, {
scale,
type: 'scale'
});
}
function createTickContext(parent, index, tick) {
return createContext(parent, {
tick,
index,
type: 'tick'
});
}
function titleAlign(align, position, reverse) {
let ret = _toLeftRightCenter(align);
if ((reverse && position !== 'right') || (!reverse && position === 'right')) {
ret = reverseAlign(ret);
}
return ret;
}
function titleArgs(scale, offset, position, align) {
const {top, left, bottom, right, chart} = scale;
const {chartArea, scales} = chart;
let rotation = 0;
let maxWidth, titleX, titleY;
const height = bottom - top;
const width = right - left;
if (scale.isHorizontal()) {
titleX = _alignStartEnd(align, left, right);
if (isObject(position)) {
const positionAxisID = Object.keys(position)[0];
const value = position[positionAxisID];
titleY = scales[positionAxisID].getPixelForValue(value) + height - offset;
} else if (position === 'center') {
titleY = (chartArea.bottom + chartArea.top) / 2 + height - offset;
} else {
titleY = offsetFromEdge(scale, position, offset);
}
maxWidth = right - left;
} else {
if (isObject(position)) {
const positionAxisID = Object.keys(position)[0];
const value = position[positionAxisID];
titleX = scales[positionAxisID].getPixelForValue(value) - width + offset;
} else if (position === 'center') {
titleX = (chartArea.left + chartArea.right) / 2 - width + offset;
} else {
titleX = offsetFromEdge(scale, position, offset);
}
titleY = _alignStartEnd(align, bottom, top);
rotation = position === 'left' ? -HALF_PI : HALF_PI;
}
return {titleX, titleY, maxWidth, rotation};
}
export default class Scale extends Element {
// eslint-disable-next-line max-statements
constructor(cfg) {
super();
/** @type {string} */
this.id = cfg.id;
/** @type {string} */
this.type = cfg.type;
/** @type {any} */
this.options = undefined;
/** @type {CanvasRenderingContext2D} */
this.ctx = cfg.ctx;
/** @type {Chart} */
this.chart = cfg.chart;
// implements box
/** @type {number} */
this.top = undefined;
/** @type {number} */
this.bottom = undefined;
/** @type {number} */
this.left = undefined;
/** @type {number} */
this.right = undefined;
/** @type {number} */
this.width = undefined;
/** @type {number} */
this.height = undefined;
this._margins = {
left: 0,
right: 0,
top: 0,
bottom: 0
};
/** @type {number} */
this.maxWidth = undefined;
/** @type {number} */
this.maxHeight = undefined;
/** @type {number} */
this.paddingTop = undefined;
/** @type {number} */
this.paddingBottom = undefined;
/** @type {number} */
this.paddingLeft = undefined;
/** @type {number} */
this.paddingRight = undefined;
// scale-specific properties
/** @type {string=} */
this.axis = undefined;
/** @type {number=} */
this.labelRotation = undefined;
this.min = undefined;
this.max = undefined;
this._range = undefined;
/** @type {Tick[]} */
this.ticks = [];
/** @type {object[]|null} */
this._gridLineItems = null;
/** @type {object[]|null} */
this._labelItems = null;
/** @type {object|null} */
this._labelSizes = null;
this._length = 0;
this._maxLength = 0;
this._longestTextCache = {};
/** @type {number} */
this._startPixel = undefined;
/** @type {number} */
this._endPixel = undefined;
this._reversePixels = false;
this._userMax = undefined;
this._userMin = undefined;
this._suggestedMax = undefined;
this._suggestedMin = undefined;
this._ticksLength = 0;
this._borderValue = 0;
this._cache = {};
this._dataLimitsCached = false;
this.$context = undefined;
}
/**
* @param {any} options
* @since 3.0
*/
init(options) {
this.options = options.setContext(this.getContext());
this.axis = options.axis;
// parse min/max value, so we can properly determine min/max for other scales
this._userMin = this.parse(options.min);
this._userMax = this.parse(options.max);
this._suggestedMin = this.parse(options.suggestedMin);
this._suggestedMax = this.parse(options.suggestedMax);
}
/**
* Parse a supported input value to internal representation.
* @param {*} raw
* @param {number} [index]
* @since 3.0
*/
parse(raw, index) { // eslint-disable-line no-unused-vars
return raw;
}
/**
* @return {{min: number, max: number, minDefined: boolean, maxDefined: boolean}}
* @protected
* @since 3.0
*/
getUserBounds() {
let {_userMin, _userMax, _suggestedMin, _suggestedMax} = this;
_userMin = finiteOrDefault(_userMin, Number.POSITIVE_INFINITY);
_userMax = finiteOrDefault(_userMax, Number.NEGATIVE_INFINITY);
_suggestedMin = finiteOrDefault(_suggestedMin, Number.POSITIVE_INFINITY);
_suggestedMax = finiteOrDefault(_suggestedMax, Number.NEGATIVE_INFINITY);
return {
min: finiteOrDefault(_userMin, _suggestedMin),
max: finiteOrDefault(_userMax, _suggestedMax),
minDefined: isFinite(_userMin),
maxDefined: isFinite(_userMax)
};
}
/**
* @param {boolean} canStack
* @return {{min: number, max: number}}
* @protected
* @since 3.0
*/
getMinMax(canStack) {
// eslint-disable-next-line prefer-const
let {min, max, minDefined, maxDefined} = this.getUserBounds();
let range;
if (minDefined && maxDefined) {
return {min, max};
}
const metas = this.getMatchingVisibleMetas();
for (let i = 0, ilen = metas.length; i < ilen; ++i) {
range = metas[i].controller.getMinMax(this, canStack);
if (!minDefined) {
min = Math.min(min, range.min);
}
if (!maxDefined) {
max = Math.max(max, range.max);
}
}
// Make sure min <= max when only min or max is defined by user and the data is outside that range
min = maxDefined && min > max ? max : min;
max = minDefined && min > max ? min : max;
return {
min: finiteOrDefault(min, finiteOrDefault(max, min)),
max: finiteOrDefault(max, finiteOrDefault(min, max))
};
}
/**
* Get the padding needed for the scale
* @return {{top: number, left: number, bottom: number, right: number}} the necessary padding
* @private
*/
getPadding() {
return {
left: this.paddingLeft || 0,
top: this.paddingTop || 0,
right: this.paddingRight || 0,
bottom: this.paddingBottom || 0
};
}
/**
* Returns the scale tick objects
* @return {Tick[]}
* @since 2.7
*/
getTicks() {
return this.ticks;
}
/**
* @return {string[]}
*/
getLabels() {
const data = this.chart.data;
return this.options.labels || (this.isHorizontal() ? data.xLabels : data.yLabels) || data.labels || [];
}
/**
* @return {LabelItem[]}
*/
getLabelItems(chartArea = this.chart.chartArea) {
const items = this._labelItems || (this._labelItems = this._computeLabelItems(chartArea));
return items;
}
// When a new layout is created, reset the data limits cache
beforeLayout() {
this._cache = {};
this._dataLimitsCached = false;
}
// These methods are ordered by lifecycle. Utilities then follow.
// Any function defined here is inherited by all scale types.
// Any function can be extended by the scale type
beforeUpdate() {
call(this.options.beforeUpdate, [this]);
}
/**
* @param {number} maxWidth - the max width in pixels
* @param {number} maxHeight - the max height in pixels
* @param {{top: number, left: number, bottom: number, right: number}} margins - the space between the edge of the other scales and edge of the chart
* This space comes from two sources:
* - padding - space that's required to show the labels at the edges of the scale
* - thickness of scales or legends in another orientation
*/
update(maxWidth, maxHeight, margins) {
const {beginAtZero, grace, ticks: tickOpts} = this.options;
const sampleSize = tickOpts.sampleSize;
// Update Lifecycle - Probably don't want to ever extend or overwrite this function ;)
this.beforeUpdate();
// Absorb the master measurements
this.maxWidth = maxWidth;
this.maxHeight = maxHeight;
this._margins = margins = Object.assign({
left: 0,
right: 0,
top: 0,
bottom: 0
}, margins);
this.ticks = null;
this._labelSizes = null;
this._gridLineItems = null;
this._labelItems = null;
// Dimensions
this.beforeSetDimensions();
this.setDimensions();
this.afterSetDimensions();
this._maxLength = this.isHorizontal()
? this.width + margins.left + margins.right
: this.height + margins.top + margins.bottom;
// Data min/max
if (!this._dataLimitsCached) {
this.beforeDataLimits();
this.determineDataLimits();
this.afterDataLimits();
this._range = _addGrace(this, grace, beginAtZero);
this._dataLimitsCached = true;
}
this.beforeBuildTicks();
this.ticks = this.buildTicks() || [];
// Allow modification of ticks in callback.
this.afterBuildTicks();
// Compute tick rotation and fit using a sampled subset of labels
// We generally don't need to compute the size of every single label for determining scale size
const samplingEnabled = sampleSize < this.ticks.length;
this._convertTicksToLabels(samplingEnabled ? sample(this.ticks, sampleSize) : this.ticks);
// configure is called twice, once here, once from core.controller.updateLayout.
// Here we haven't been positioned yet, but dimensions are correct.
// Variables set in configure are needed for calculateLabelRotation, and
// it's ok that coordinates are not correct there, only dimensions matter.
this.configure();
// Tick Rotation
this.beforeCalculateLabelRotation();
this.calculateLabelRotation(); // Preconditions: number of ticks and sizes of largest labels must be calculated beforehand
this.afterCalculateLabelRotation();
// Auto-skip
if (tickOpts.display && (tickOpts.autoSkip || tickOpts.source === 'auto')) {
this.ticks = autoSkip(this, this.ticks);
this._labelSizes = null;
this.afterAutoSkip();
}
if (samplingEnabled) {
// Generate labels using all non-skipped ticks
this._convertTicksToLabels(this.ticks);
}
this.beforeFit();
this.fit(); // Preconditions: label rotation and label sizes must be calculated beforehand
this.afterFit();
// IMPORTANT: after this point, we consider that `this.ticks` will NEVER change!
this.afterUpdate();
}
/**
* @protected
*/
configure() {
let reversePixels = this.options.reverse;
let startPixel, endPixel;
if (this.isHorizontal()) {
startPixel = this.left;
endPixel = this.right;
} else {
startPixel = this.top;
endPixel = this.bottom;
// by default vertical scales are from bottom to top, so pixels are reversed
reversePixels = !reversePixels;
}
this._startPixel = startPixel;
this._endPixel = endPixel;
this._reversePixels = reversePixels;
this._length = endPixel - startPixel;
this._alignToPixels = this.options.alignToPixels;
}
afterUpdate() {
call(this.options.afterUpdate, [this]);
}
//
beforeSetDimensions() {
call(this.options.beforeSetDimensions, [this]);
}
setDimensions() {
// Set the unconstrained dimension before label rotation
if (this.isHorizontal()) {
// Reset position before calculating rotation
this.width = this.maxWidth;
this.left = 0;
this.right = this.width;
} else {
this.height = this.maxHeight;
// Reset position before calculating rotation
this.top = 0;
this.bottom = this.height;
}
// Reset padding
this.paddingLeft = 0;
this.paddingTop = 0;
this.paddingRight = 0;
this.paddingBottom = 0;
}
afterSetDimensions() {
call(this.options.afterSetDimensions, [this]);
}
_callHooks(name) {
this.chart.notifyPlugins(name, this.getContext());
call(this.options[name], [this]);
}
// Data limits
beforeDataLimits() {
this._callHooks('beforeDataLimits');
}
determineDataLimits() {}
afterDataLimits() {
this._callHooks('afterDataLimits');
}
//
beforeBuildTicks() {
this._callHooks('beforeBuildTicks');
}
/**
* @return {object[]} the ticks
*/
buildTicks() {
return [];
}
afterBuildTicks() {
this._callHooks('afterBuildTicks');
}
beforeTickToLabelConversion() {
call(this.options.beforeTickToLabelConversion, [this]);
}
/**
* Convert ticks to label strings
* @param {Tick[]} ticks
*/
generateTickLabels(ticks) {
const tickOpts = this.options.ticks;
let i, ilen, tick;
for (i = 0, ilen = ticks.length; i < ilen; i++) {
tick = ticks[i];
tick.label = call(tickOpts.callback, [tick.value, i, ticks], this);
}
}
afterTickToLabelConversion() {
call(this.options.afterTickToLabelConversion, [this]);
}
//
beforeCalculateLabelRotation() {
call(this.options.beforeCalculateLabelRotation, [this]);
}
calculateLabelRotation() {
const options = this.options;
const tickOpts = options.ticks;
const numTicks = this.ticks.length;
const minRotation = tickOpts.minRotation || 0;
const maxRotation = tickOpts.maxRotation;
let labelRotation = minRotation;
let tickWidth, maxHeight, maxLabelDiagonal;
if (!this._isVisible() || !tickOpts.display || minRotation >= maxRotation || numTicks <= 1 || !this.isHorizontal()) {
this.labelRotation = minRotation;
return;
}
const labelSizes = this._getLabelSizes();
const maxLabelWidth = labelSizes.widest.width;
const maxLabelHeight = labelSizes.highest.height;
// Estimate the width of each grid based on the canvas width, the maximum
// label width and the number of tick intervals
const maxWidth = _limitValue(this.chart.width - maxLabelWidth, 0, this.maxWidth);
tickWidth = options.offset ? this.maxWidth / numTicks : maxWidth / (numTicks - 1);
// Allow 3 pixels x2 padding either side for label readability
if (maxLabelWidth + 6 > tickWidth) {
tickWidth = maxWidth / (numTicks - (options.offset ? 0.5 : 1));
maxHeight = this.maxHeight - getTickMarkLength(options.grid)
- tickOpts.padding - getTitleHeight(options.title, this.chart.options.font);
maxLabelDiagonal = Math.sqrt(maxLabelWidth * maxLabelWidth + maxLabelHeight * maxLabelHeight);
labelRotation = toDegrees(Math.min(
Math.asin(_limitValue((labelSizes.highest.height + 6) / tickWidth, -1, 1)),
Math.asin(_limitValue(maxHeight / maxLabelDiagonal, -1, 1)) - Math.asin(_limitValue(maxLabelHeight / maxLabelDiagonal, -1, 1))
));
labelRotation = Math.max(minRotation, Math.min(maxRotation, labelRotation));
}
this.labelRotation = labelRotation;
}
afterCalculateLabelRotation() {
call(this.options.afterCalculateLabelRotation, [this]);
}
afterAutoSkip() {}
//
beforeFit() {
call(this.options.beforeFit, [this]);
}
fit() {
// Reset
const minSize = {
width: 0,
height: 0
};
const {chart, options: {ticks: tickOpts, title: titleOpts, grid: gridOpts}} = this;
const display = this._isVisible();
const isHorizontal = this.isHorizontal();
if (display) {
const titleHeight = getTitleHeight(titleOpts, chart.options.font);
if (isHorizontal) {
minSize.width = this.maxWidth;
minSize.height = getTickMarkLength(gridOpts) + titleHeight;
} else {
minSize.height = this.maxHeight; // fill all the height
minSize.width = getTickMarkLength(gridOpts) + titleHeight;
}
// Don't bother fitting the ticks if we are not showing the labels
if (tickOpts.display && this.ticks.length) {
const {first, last, widest, highest} = this._getLabelSizes();
const tickPadding = tickOpts.padding * 2;
const angleRadians = toRadians(this.labelRotation);
const cos = Math.cos(angleRadians);
const sin = Math.sin(angleRadians);
if (isHorizontal) {
// A horizontal axis is more constrained by the height.
const labelHeight = tickOpts.mirror ? 0 : sin * widest.width + cos * highest.height;
minSize.height = Math.min(this.maxHeight, minSize.height + labelHeight + tickPadding);
} else {
// A vertical axis is more constrained by the width. Labels are the
// dominant factor here, so get that length first and account for padding
const labelWidth = tickOpts.mirror ? 0 : cos * widest.width + sin * highest.height;
minSize.width = Math.min(this.maxWidth, minSize.width + labelWidth + tickPadding);
}
this._calculatePadding(first, last, sin, cos);
}
}
this._handleMargins();
if (isHorizontal) {
this.width = this._length = chart.width - this._margins.left - this._margins.right;
this.height = minSize.height;
} else {
this.width = minSize.width;
this.height = this._length = chart.height - this._margins.top - this._margins.bottom;
}
}
_calculatePadding(first, last, sin, cos) {
const {ticks: {align, padding}, position} = this.options;
const isRotated = this.labelRotation !== 0;
const labelsBelowTicks = position !== 'top' && this.axis === 'x';
if (this.isHorizontal()) {
const offsetLeft = this.getPixelForTick(0) - this.left;
const offsetRight = this.right - this.getPixelForTick(this.ticks.length - 1);
let paddingLeft = 0;
let paddingRight = 0;
// Ensure that our ticks are always inside the canvas. When rotated, ticks are right aligned
// which means that the right padding is dominated by the font height
if (isRotated) {
if (labelsBelowTicks) {
paddingLeft = cos * first.width;
paddingRight = sin * last.height;
} else {
paddingLeft = sin * first.height;
paddingRight = cos * last.width;
}
} else if (align === 'start') {
paddingRight = last.width;
} else if (align === 'end') {
paddingLeft = first.width;
} else if (align !== 'inner') {
paddingLeft = first.width / 2;
paddingRight = last.width / 2;
}
// Adjust padding taking into account changes in offsets
this.paddingLeft = Math.max((paddingLeft - offsetLeft + padding) * this.width / (this.width - offsetLeft), 0);
this.paddingRight = Math.max((paddingRight - offsetRight + padding) * this.width / (this.width - offsetRight), 0);
} else {
let paddingTop = last.height / 2;
let paddingBottom = first.height / 2;
if (align === 'start') {
paddingTop = 0;
paddingBottom = first.height;
} else if (align === 'end') {
paddingTop = last.height;
paddingBottom = 0;
}
this.paddingTop = paddingTop + padding;
this.paddingBottom = paddingBottom + padding;
}
}
/**
* Handle margins and padding interactions
* @private
*/
_handleMargins() {
if (this._margins) {
this._margins.left = Math.max(this.paddingLeft, this._margins.left);
this._margins.top = Math.max(this.paddingTop, this._margins.top);
this._margins.right = Math.max(this.paddingRight, this._margins.right);
this._margins.bottom = Math.max(this.paddingBottom, this._margins.bottom);
}
}
afterFit() {
call(this.options.afterFit, [this]);
}
// Shared Methods
/**
* @return {boolean}
*/
isHorizontal() {
const {axis, position} = this.options;
return position === 'top' || position === 'bottom' || axis === 'x';
}
/**
* @return {boolean}
*/
isFullSize() {
return this.options.fullSize;
}
/**
* @param {Tick[]} ticks
* @private
*/
_convertTicksToLabels(ticks) {
this.beforeTickToLabelConversion();
this.generateTickLabels(ticks);
// Ticks should be skipped when callback returns null or undef, so lets remove those.
let i, ilen;
for (i = 0, ilen = ticks.length; i < ilen; i++) {
if (isNullOrUndef(ticks[i].label)) {
ticks.splice(i, 1);
ilen--;
i--;
}
}
this.afterTickToLabelConversion();
}
/**
* @return {{ first: object, last: object, widest: object, highest: object, widths: Array, heights: array }}
* @private
*/
_getLabelSizes() {
let labelSizes = this._labelSizes;
if (!labelSizes) {
const sampleSize = this.options.ticks.sampleSize;
let ticks = this.ticks;
if (sampleSize < ticks.length) {
ticks = sample(ticks, sampleSize);
}
this._labelSizes = labelSizes = this._computeLabelSizes(ticks, ticks.length);
}
return labelSizes;
}
/**
* Returns {width, height, offset} objects for the first, last, widest, highest tick
* labels where offset indicates the anchor point offset from the top in pixels.
* @return {{ first: object, last: object, widest: object, highest: object, widths: Array, heights: array }}
* @private
*/
_computeLabelSizes(ticks, length) {
const {ctx, _longestTextCache: caches} = this;
const widths = [];
const heights = [];
let widestLabelSize = 0;
let highestLabelSize = 0;
let i, j, jlen, label, tickFont, fontString, cache, lineHeight, width, height, nestedLabel;
for (i = 0; i < length; ++i) {
label = ticks[i].label;
tickFont = this._resolveTickFontOptions(i);
ctx.font = fontString = tickFont.string;
cache = caches[fontString] = caches[fontString] || {data: {}, gc: []};
lineHeight = tickFont.lineHeight;
width = height = 0;
// Undefined labels and arrays should not be measured
if (!isNullOrUndef(label) && !isArray(label)) {
width = _measureText(ctx, cache.data, cache.gc, width, label);
height = lineHeight;
} else if (isArray(label)) {
// if it is an array let's measure each element
for (j = 0, jlen = label.length; j < jlen; ++j) {
nestedLabel = label[j];
// Undefined labels and arrays should not be measured
if (!isNullOrUndef(nestedLabel) && !isArray(nestedLabel)) {
width = _measureText(ctx, cache.data, cache.gc, width, nestedLabel);
height += lineHeight;
}
}
}
widths.push(width);
heights.push(height);
widestLabelSize = Math.max(width, widestLabelSize);
highestLabelSize = Math.max(height, highestLabelSize);
}
garbageCollect(caches, length);
const widest = widths.indexOf(widestLabelSize);
const highest = heights.indexOf(highestLabelSize);
const valueAt = (idx) => ({width: widths[idx] || 0, height: heights[idx] || 0});
return {
first: valueAt(0),
last: valueAt(length - 1),
widest: valueAt(widest),
highest: valueAt(highest),
widths,
heights,
};
}
/**
* Used to get the label to display in the tooltip for the given value
* @param {*} value
* @return {string}
*/
getLabelForValue(value) {
return value;
}
/**
* Returns the location of the given data point. Value can either be an index or a numerical value
* The coordinate (0, 0) is at the upper-left corner of the canvas
* @param {*} value
* @param {number} [index]
* @return {number}
*/
getPixelForValue(value, index) { // eslint-disable-line no-unused-vars
return NaN;
}
/**
* Used to get the data value from a given pixel. This is the inverse of getPixelForValue
* The coordinate (0, 0) is at the upper-left corner of the canvas
* @param {number} pixel
* @return {*}
*/
getValueForPixel(pixel) {} // eslint-disable-line no-unused-vars
/**
* Returns the location of the tick at the given index
* The coordinate (0, 0) is at the upper-left corner of the canvas
* @param {number} index
* @return {number}
*/
getPixelForTick(index) {
const ticks = this.ticks;
if (index < 0 || index > ticks.length - 1) {
return null;
}
return this.getPixelForValue(ticks[index].value);
}
/**
* Utility for getting the pixel location of a percentage of scale
* The coordinate (0, 0) is at the upper-left corner of the canvas
* @param {number} decimal
* @return {number}
*/
getPixelForDecimal(decimal) {
if (this._reversePixels) {
decimal = 1 - decimal;
}
const pixel = this._startPixel + decimal * this._length;
return _int16Range(this._alignToPixels ? _alignPixel(this.chart, pixel, 0) : pixel);
}
/**
* @param {number} pixel
* @return {number}
*/
getDecimalForPixel(pixel) {
const decimal = (pixel - this._startPixel) / this._length;
return this._reversePixels ? 1 - decimal : decimal;
}
/**
* Returns the pixel for the minimum chart value
* The coordinate (0, 0) is at the upper-left corner of the canvas
* @return {number}
*/
getBasePixel() {
return this.getPixelForValue(this.getBaseValue());
}
/**
* @return {number}
*/
getBaseValue() {
const {min, max} = this;
return min < 0 && max < 0 ? max :
min > 0 && max > 0 ? min :
0;
}
/**
* @protected
*/
getContext(index) {
const ticks = this.ticks || [];
if (index >= 0 && index < ticks.length) {
const tick = ticks[index];
return tick.$context ||
(tick.$context = createTickContext(this.getContext(), index, tick));
}
return this.$context ||
(this.$context = createScaleContext(this.chart.getContext(), this));
}
/**
* @return {number}
* @private
*/
_tickSize() {
const optionTicks = this.options.ticks;
// Calculate space needed by label in axis direction.
const rot = toRadians(this.labelRotation);
const cos = Math.abs(Math.cos(rot));
const sin = Math.abs(Math.sin(rot));
const labelSizes = this._getLabelSizes();
const padding = optionTicks.autoSkipPadding || 0;
const w = labelSizes ? labelSizes.widest.width + padding : 0;
const h = labelSizes ? labelSizes.highest.height + padding : 0;
// Calculate space needed for 1 tick in axis direction.
return this.isHorizontal()
? h * cos > w * sin ? w / cos : h / sin
: h * sin < w * cos ? h / cos : w / sin;
}
/**
* @return {boolean}
* @private
*/
_isVisible() {
const display = this.options.display;