Function computeLegendDimensions

src/components/legend/draw.js:861–1087

(gd, groups, traces, legendObj, scrollBox)

 *  - _maxWidth (for orientation:h only): maximum width before starting new row
 */
function computeLegendDimensions(gd, groups, traces, legendObj, scrollBox) {
    var fullLayout = gd._fullLayout;
    var legendId = helpers.getId(legendObj);
    if(!legendObj) {
        legendObj = fullLayout[legendId];
    }
    var gs = fullLayout._size;

    var isVertical = helpers.isVertical(legendObj);
    var isGrouped = helpers.isGrouped(legendObj);
    var isFraction = legendObj.entrywidthmode === 'fraction';

    var bw = legendObj.borderwidth;
    var bw2 = 2 * bw;
    var itemGap = constants.itemGap;
    var textGap = legendObj.indentation + legendObj.itemwidth + itemGap * 2;
    var endPad = 2 * (bw + itemGap);

    var yanchor = getYanchor(legendObj);
    var isBelowPlotArea = legendObj.y < 0 || (legendObj.y === 0 && yanchor === 'top');
    var isAbovePlotArea = legendObj.y > 1 || (legendObj.y === 1 && yanchor === 'bottom');

    var traceGroupGap = legendObj.tracegroupgap;
    var legendGroupWidths = {};

    const { orientation, yref } = legendObj;
    let { maxheight } = legendObj;
    const useFullLayoutHeight = isBelowPlotArea || isAbovePlotArea || orientation !== "v" || yref !== "paper"
    // Set default maxheight here since it depends on values passed in by user
    maxheight ||= useFullLayoutHeight ? 0.5 : 1;
    const heightToBeScaled = useFullLayoutHeight ? fullLayout.height : gs.h;
    legendObj._maxHeight = Math.max(maxheight > 1 ? maxheight : maxheight * heightToBeScaled, 30);

    var toggleRectWidth = 0;
    legendObj._width = 0;
    legendObj._height = 0;
    var titleSize = getTitleSize(legendObj);

    if(isVertical) {
        traces.each(function(d) {
            var h = d[0].height;
            Drawing.setTranslate(this,
                bw + titleSize[0],
                bw + titleSize[1] + legendObj._height + h / 2 + itemGap
            );
            legendObj._height += h;
            legendObj._width = Math.max(legendObj._width, d[0].width);
        });

        toggleRectWidth = textGap + legendObj._width;
        legendObj._width += itemGap + textGap + bw2;
        legendObj._height += endPad;

        if(isGrouped) {
            groups.each(function(d, i) {
                Drawing.setTranslate(this, 0, i * legendObj.tracegroupgap);
            });
            legendObj._height += (legendObj._lgroupsLength - 1) * legendObj.tracegroupgap;