feat: Allow configuration of horizontal legend max height

draftlogs/7359_add.md

@@ -0,0 +1 @@
+ - Allow configuration of horizontal legend max height [[#7359](https://github.com/plotly/plotly.js/pull/7359)]

src/components/legend/attributes.js

@@ -33,6 +33,18 @@ module.exports = {
         editType: 'legend',
         description: 'Sets the color of the border enclosing the legend.'
     },
+    maxheight: {
+        valType: 'number',
+        min: 0,
+        editType: 'legend',
+        description: [
+            'Sets the max height (in px) of the legend, or max height ratio (reference height * ratio) if less than one.',
+            'Default value is: 0.5 for horizontal legends; 1 for vertical legends. The minimum allowed height is 30px.',
+            'For a ratio of 0.5, the legend will take up to 50% of the reference height before displaying a scrollbar.',
+            'The reference height is the full layout height except for vertically oriented legends with',
+            'a `yref` of `"paper"`, where the reference height is the plot height.'
+        ].join(' ')
+    },
     borderwidth: {
         valType: 'number',
         min: 0,

src/components/legend/defaults.js

@@ -188,6 +188,7 @@ function groupDefaults(legendId, layoutIn, layoutOut, fullData) {
 
     coerce('xanchor', defaultXAnchor);
     coerce('yanchor', defaultYAnchor);
+    coerce('maxheight', isHorizontal ? 0.5 : 1);
     coerce('valign');
     Lib.noneOrAll(containerIn, containerOut, ['x', 'y']);
 

src/components/legend/draw.js

@@ -769,12 +769,9 @@ function computeLegendDimensions(gd, groups, traces, legendObj) {
     var traceGroupGap = legendObj.tracegroupgap;
     var legendGroupWidths = {};
 
-    // - if below/above plot area, give it the maximum potential margin-push value
-    // - otherwise, extend the height of the plot area
-    legendObj._maxHeight = Math.max(
-        (isBelowPlotArea || isAbovePlotArea) ? fullLayout.height / 2 : gs.h,
-        30
-    );
+    var { maxheight, orientation, yref } = legendObj;
+    var heightToBeScaled = orientation === "v" && yref === "paper" ? gs.h : fullLayout.height;
+    legendObj._maxHeight = Math.max(maxheight > 1 ? maxheight : maxheight * heightToBeScaled, 30);
 
     var toggleRectWidth = 0;
     legendObj._width = 0;

test/plot-schema.json

@@ -3442,6 +3442,12 @@
      "min": 30,
      "valType": "number"
     },
+    "maxheight": {
+     "description": "Sets the max height (in px) of the legend, or max height ratio (reference height * ratio) if less than one. Default value is: 0.5 for horizontal legends; 1 for vertical legends. The minimum allowed height is 30px. For a ratio of 0.5, the legend will take up to 50% of the reference height before displaying a scrollbar. The reference height is the full layout height except for vertically oriented legends with a `yref` of `\"paper\"`, where the reference height is the plot height.",
+     "editType": "legend",
+     "min": 0,
+     "valType": "number"
+    },
     "orientation": {
      "description": "Sets the orientation of the legend.",
      "dflt": "v",