fix: Update legend maxheight calculation logic

src/components/legend/attributes.js

@@ -38,11 +38,12 @@ module.exports = {
         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.',
+            'Sets the max height (in px) of the legend, or max height ratio (reference height * ratio) if less than or equal to 1.',
             '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.'
+            'The reference height is the full layout height with the following exception: vertically oriented legends with',
+            'a `yref` of `"paper" located to the side of the plot. In this case, the reference height',
+            'is the plot height.'
         ].join(' ')
     },
     borderwidth: {
@@ -243,7 +244,7 @@ module.exports = {
         values: ['auto', 'top', 'middle', 'bottom'],
         editType: 'legend',
         description: [
-            'Sets the legend\'s vertical position anchor',
+            'Sets the legend\'s vertical position anchor.',
             'This anchor binds the `y` position to the *top*, *middle*',
             'or *bottom* of the legend.',
             'Value *auto* anchors legends at their bottom for `y` values less than or equal to 1/3,',

src/components/legend/defaults.js

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

src/components/legend/draw.js

@@ -769,8 +769,12 @@ function computeLegendDimensions(gd, groups, traces, legendObj) {
     var traceGroupGap = legendObj.tracegroupgap;
     var legendGroupWidths = {};
 
-    var { maxheight, orientation, yref } = legendObj;
-    var heightToBeScaled = orientation === "v" && yref === "paper" ? gs.h : fullLayout.height;
+    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;