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Fix: Scrollable vertical legend for long lists #12136

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Fix: Scrollable vertical legend for long lists #12136

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200 changes: 141 additions & 59 deletions src/plugins/plugin.legend.js
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,9 @@ import {
import {_alignStartEnd, _textX, _toLeftRightCenter} from '../helpers/helpers.extras.js';
import {toTRBLCorners} from '../helpers/helpers.options.js';




/**
* @typedef { import('../types/index.js').ChartEvent } ChartEvent
*/
Expand Down Expand Up @@ -119,40 +122,74 @@ export class Legend extends Element {

this.legendItems = legendItems;
}
fit() {
const { options, ctx } = this;
if (!options.display) {
this.width = this.height = 0;
return;
}

fit() {
const {options, ctx} = this;

// The legend may not be displayed for a variety of reasons including
// the fact that the defaults got set to `false`.
// When the legend is not displayed, there are no guarantees that the options
// are correctly formatted so we need to bail out as early as possible.
if (!options.display) {
this.width = this.height = 0;
return;
}
const labelOpts = options.labels;
const labelFont = toFont(labelOpts.font);
const fontSize = labelFont.size;
const titleHeight = this._computeTitleHeight();
const { boxWidth, itemHeight } = getBoxSize(labelOpts, fontSize);

let width, height;
ctx.font = labelFont.string;

if (this.isHorizontal()) {
width = this.maxWidth;
height = this._fitRows(titleHeight, fontSize, boxWidth, itemHeight) + 10;
} else {
height = this.maxHeight;
width = this._fitCols(titleHeight, labelFont, boxWidth, itemHeight) + 10;
}

const labelOpts = options.labels;
const labelFont = toFont(labelOpts.font);
const fontSize = labelFont.size;
const titleHeight = this._computeTitleHeight();
const {boxWidth, itemHeight} = getBoxSize(labelOpts, fontSize);
// --- handle scroll height limit ---
const scrollOpts = options.scroll || {};
if (scrollOpts.enabled && scrollOpts.maxItems) {
const singleItemHeight = itemHeight + labelOpts.padding;
const visibleHeight = singleItemHeight * scrollOpts.maxItems + titleHeight + labelOpts.padding * 2;
this.height = Math.min(this.height, visibleHeight);

let width, height;
// wrap legend in scroll container
this._wrapLegendScroll(visibleHeight);
}

ctx.font = labelFont.string;
this.width = Math.min(width, options.maxWidth || this.maxWidth);
this.height = Math.min(height, options.maxHeight || this.maxHeight);
}

if (this.isHorizontal()) {
width = this.maxWidth; // fill all the width
height = this._fitRows(titleHeight, fontSize, boxWidth, itemHeight) + 10;
} else {
height = this.maxHeight; // fill all the height
width = this._fitCols(titleHeight, labelFont, boxWidth, itemHeight) + 10;
}
/**
* Private helper to wrap the <ul> legend in a scrollable container
*/
_wrapLegendScroll(visibleHeight) {
const canvasContainer = this.chart.canvas.parentNode;
if (!canvasContainer) return;

const legendUL = canvasContainer.querySelector('ul.chartjs-legend');
if (!legendUL) return;

// Skip if already wrapped
if (canvasContainer.querySelector('.legend-scroll-wrapper')) return;

const legendWrapper = document.createElement('div');
legendWrapper.className = 'legend-scroll-wrapper';
legendWrapper.style.overflowY = 'auto';
legendWrapper.style.maxHeight = `${visibleHeight}px`;
legendWrapper.style.display = 'inline-block';

// Force single-column layout
legendUL.style.display = 'flex';
legendUL.style.flexDirection = 'column';
legendUL.style.margin = '0';
legendUL.style.padding = '0';

legendUL.parentNode.insertBefore(legendWrapper, legendUL);
legendWrapper.appendChild(legendUL);
}

this.width = Math.min(width, options.maxWidth || this.maxWidth);
this.height = Math.min(height, options.maxHeight || this.maxHeight);
}

/**
* @private
Expand Down Expand Up @@ -188,45 +225,62 @@ export class Legend extends Element {
return totalHeight;
}

_fitCols(titleHeight, labelFont, boxWidth, _itemHeight) {
const {ctx, maxHeight, options: {labels: {padding}}} = this;
const hitboxes = this.legendHitBoxes = [];
const columnSizes = this.columnSizes = [];
const heightLimit = maxHeight - titleHeight;
_fitCols(titleHeight, labelFont, boxWidth, _itemHeight) {
const {ctx, maxHeight, options: {labels: {padding}}} = this;
const scrollOpts = this.options.scroll || {};
const hitboxes = this.legendHitBoxes = [];
const columnSizes = this.columnSizes = [];

let totalWidth = padding;
let currentColWidth = 0;
let currentColHeight = 0;
const heightLimit = maxHeight - titleHeight;

let left = 0;
let col = 0;
// --- SCROLL ENABLED: force single column ---
if (scrollOpts.enabled && scrollOpts.maxItems) {
let totalWidth = 0;
let top = 0;
let maxItemWidth = 0;

this.legendItems.forEach((legendItem, i) => {
const {itemWidth, itemHeight} = calculateItemSize(boxWidth, labelFont, ctx, legendItem, _itemHeight);

// If too tall, go to new column
if (i > 0 && currentColHeight + itemHeight + 2 * padding > heightLimit) {
totalWidth += currentColWidth + padding;
columnSizes.push({width: currentColWidth, height: currentColHeight}); // previous column size
left += currentColWidth + padding;
col++;
currentColWidth = currentColHeight = 0;
}

// Store the hitbox width and height here. Final position will be updated in `draw`
hitboxes[i] = {left, top: currentColHeight, col, width: itemWidth, height: itemHeight};

// Get max width
currentColWidth = Math.max(currentColWidth, itemWidth);
currentColHeight += itemHeight + padding;
hitboxes[i] = {left: 0, top, col: 0, width: itemWidth, height: itemHeight};
top += itemHeight + padding;
maxItemWidth = Math.max(maxItemWidth, itemWidth);
});

totalWidth += currentColWidth;
columnSizes.push({width: currentColWidth, height: currentColHeight}); // previous column size
columnSizes.push({width: maxItemWidth, height: top});
totalWidth = maxItemWidth + 2 * padding;

return totalWidth;
}

// --- SCROLL DISABLED: original multi-column logic ---
let totalWidth = padding;
let currentColWidth = 0;
let currentColHeight = 0;
let left = 0;
let col = 0;

this.legendItems.forEach((legendItem, i) => {
const {itemWidth, itemHeight} = calculateItemSize(boxWidth, labelFont, ctx, legendItem, _itemHeight);

if (i > 0 && currentColHeight + itemHeight + 2 * padding > heightLimit) {
totalWidth += currentColWidth + padding;
columnSizes.push({width: currentColWidth, height: currentColHeight});
left += currentColWidth + padding;
col++;
currentColWidth = currentColHeight = 0;
}

hitboxes[i] = {left, top: currentColHeight, col, width: itemWidth, height: itemHeight};

currentColWidth = Math.max(currentColWidth, itemWidth);
currentColHeight += itemHeight + padding;
});

totalWidth += currentColWidth;
columnSizes.push({width: currentColWidth, height: currentColHeight});

return totalWidth;
}
adjustHitBoxes() {
if (!this.options.display) {
return;
Expand Down Expand Up @@ -391,7 +445,12 @@ export class Legend extends Element {
overrideTextDirection(this.ctx, opts.textDirection);

const lineHeight = itemHeight + padding;
this.legendItems.forEach((legendItem, i) => {
const scrollOpts = this.options.scroll || {};
let legendItems = this.legendItems;
if (scrollOpts.enabled && scrollOpts.maxItems) {
legendItems = legendItems.slice(0, scrollOpts.maxItems);
}
legendItems.forEach((legendItem, i) => {
ctx.strokeStyle = legendItem.fontColor; // for strikethrough effect
ctx.fillStyle = legendItem.fontColor; // render in correct colour

Expand Down Expand Up @@ -552,6 +611,15 @@ export class Legend extends Element {
}
}










function calculateItemSize(boxWidth, labelFont, ctx, legendItem, _itemHeight) {
const itemWidth = calculateItemWidth(legendItem, boxWidth, labelFont, ctx);
const itemHeight = calculateItemHeight(_itemHeight, legendItem, labelFont.lineHeight);
Expand Down Expand Up @@ -624,7 +692,21 @@ export default {
const legend = chart.legend;
legend.buildLabels();
legend.adjustHitBoxes();
},
const scrollOpts = legend.options.scroll || {};
if (scrollOpts.enabled && scrollOpts.maxItems) {
const canvasContainer = chart.canvas.parentNode;
if (canvasContainer) {
const legendUL = canvasContainer.querySelector('ul.chartjs-legend');
if (legendUL && !canvasContainer.querySelector('.legend-scroll-wrapper')) {
const singleItemHeight = legend.legendHitBoxes[0].height + legend.options.labels.padding;
const titleHeight = legend._computeTitleHeight();
const visibleHeight = singleItemHeight * scrollOpts.maxItems + titleHeight + legend.options.labels.padding * 2;
legend._wrapLegendScroll(visibleHeight);
console.log('Legend wrapper created inside afterUpdate!');
}
}
}
},


afterEvent(chart, args) {
Expand Down Expand Up @@ -717,4 +799,4 @@ export default {
_scriptable: (name) => !['generateLabels', 'filter', 'sort'].includes(name),
}
},
};
};