SergeyAxiomatic · Oct 20, 2026 · Oct 21, 2026 · Oct 21, 2026
diff --git a/draftlogs/8138_fix.md b/draftlogs/8138_fix.md
@@ -0,0 +1,2 @@
+- Fix hover labels that are a single tex expression being truncated by `hoverlabel.namelength` [[#8138](https://github.com/plotly/plotly.js/pull/8138)]
+- Fix tex in hover labels being misplaced when labels are rotated in `hovermode: 'y'` [[#8138](https://github.com/plotly/plotly.js/pull/8138)]
diff --git a/src/components/fx/hover.js b/src/components/fx/hover.js
@@ -2650,8 +2650,10 @@ function spikesChanged(gd, oldspikepoints) {
 }
 
 function plainText(s, len) {
-    return svgTextUtils.plainText(s || '', {
-        len: len,
+    s = s || '';
+    return svgTextUtils.plainText(s, {
+        // truncating a tex expression drops its closing $, so it would no longer be typeset
+        len: svgTextUtils.isPureTex(s) ? undefined : len,
         allowedTags: ['br', 'sub', 'sup', 'b', 'i', 'em', 's', 'u']
     });
 }

diff --git a/src/lib/svg_text_utils.js b/src/lib/svg_text_utils.js
@@ -37,6 +37,30 @@ const isPureTex = (str) => {
 };
 exports.isPureTex = isPureTex;
 
+/**
+ * Size of the typeset glyphs in their own coordinate system when an ancestor
+ * is rotated (e.g. a hover label in hovermode 'y'), where getBoundingClientRect
+ * would report the larger screen-space box of the rotated shape.
+ *
+ * @param {d3 selection} newSvg: the typeset <svg>
+ * @param {d3 selection} g: the <g> inside newSvg that holds the glyphs
+ * @return {?{width: number, height: number}} null if no ancestor is rotated
+ */
+function getUnrotatedSize(newSvg, g) {
+    var svgNode = newSvg.node();
+    var ctm = svgNode.getScreenCTM();
+    if(!ctm || (Math.abs(ctm.b) < 1e-6 && Math.abs(ctm.c) < 1e-6)) return null;
+
+    var bbox = g.node().getBBox();
+    var viewBox = svgNode.viewBox.baseVal;
+    // the glyphs are letterboxed, so they scale by the smaller of the two ratios
+    var scale = Math.min(
+        svgNode.width.baseVal.value / viewBox.width,
+        svgNode.height.baseVal.value / viewBox.height
+    );
+    return {width: bbox.width * scale, height: bbox.height * scale};
+}
+
 /**
  * Positions a MathJax-typeset group against its source <text> node's x/y
  * and text-anchor.
@@ -50,10 +74,13 @@ exports.isPureTex = isPureTex;
  * @param {number} [width0]: the SVG's own reported width, to detect the
  *   Firefox v82+ overflow bug (see link below); omit to skip that check
  * @param {number} [height0]: same, for height
+ * @param {boolean} [unrotated]: measure in the group's own coordinates when an
+ *   ancestor is rotated. Off by default so convertToTspans' other callers keep
+ *   the screen-space measurement they were laid out with
  */
-function positionMathGroup(_context, svgClass, mathjaxGroup, newSvg, textAnchor, fontSize, width0, height0) {
+function positionMathGroup(_context, svgClass, mathjaxGroup, newSvg, textAnchor, fontSize, width0, height0, unrotated) {
     var g = newSvg.select('g');
-    var bb = g.node().getBoundingClientRect();
+    var bb = (unrotated && getUnrotatedSize(newSvg, g)) || g.node().getBoundingClientRect();
     var w = bb.width;
     var h = bb.height;
     var w0 = width0 === undefined ? w : width0;
@@ -260,7 +287,7 @@ exports.repositionMathGroup = function(_context) {
 
     var textAnchor = _context.attr('text-anchor');
     var fontSize = parseInt(_context.node().style.fontSize, 10);
-    positionMathGroup(_context, svgClass, mathjaxGroup, newSvg, textAnchor, fontSize);
+    positionMathGroup(_context, svgClass, mathjaxGroup, newSvg, textAnchor, fontSize, undefined, undefined, true);
 };
 
 /**

diff --git a/test/jasmine/bundle_tests/mathjax_test.js b/test/jasmine/bundle_tests/mathjax_test.js
@@ -593,6 +593,147 @@ describe('Test MathJax v' + mathjaxVersion + ':', function() {
             .then(done, done.fail);
         });
 
+        it('should not truncate a pure-tex trace name to hoverlabel.namelength', function(done) {
+            var longTex = '$\\alpha_{1c} = 352 \\pm 11 \\text{ km s}^{-1}$';
+
+            Plotly.newPlot(gd, {
+                data: [{
+                    type: 'scatter',
+                    mode: 'markers',
+                    x: [1, 2, 3],
+                    y: [1, 2, 3],
+                    name: longTex,
+                    hoverinfo: 'x+y+name'
+                }],
+                layout: {
+                    width: 500,
+                    height: 400,
+                    margin: {l: 0, t: 0, r: 0, b: 0},
+                    xaxis: {range: [0, 4]},
+                    yaxis: {range: [0, 4]}
+                }
+            })
+            .then(function() {
+                _hover(125, 300);
+                return delay(30)();
+            })
+            .then(function() {
+                var mathGroup = d3Select(gd).select('g.hovertext .name-math-group');
+
+                expect(mathGroup.size()).toBe(1, 'name math group');
+                expect(mathGroup.attr('data-unformatted')).toBe(longTex, 'full, untruncated tex');
+            })
+            .then(done, done.fail);
+        });
+
+        it('should not truncate a pure-tex hovertemplate <extra> name to hoverlabel.namelength', function(done) {
+            var longTex = '$\\alpha_{1c} = 352 \\pm 11 \\text{ km s}^{-1}$';
+
+            Plotly.newPlot(gd, {
+                data: [{
+                    type: 'scatter',
+                    mode: 'markers',
+                    x: [1, 2, 3],
+                    y: [1, 2, 3],
+                    hovertemplate: 'v<extra>' + longTex + '</extra>'
+                }],
+                layout: {
+                    width: 500,
+                    height: 400,
+                    margin: {l: 0, t: 0, r: 0, b: 0},
+                    xaxis: {range: [0, 4]},
+                    yaxis: {range: [0, 4]}
+                }
+            })
+            .then(function() {
+                _hover(125, 300);
+                return delay(30)();
+            })
+            .then(function() {
+                var mathGroup = d3Select(gd).select('g.hovertext .name-math-group');
+
+                expect(mathGroup.size()).toBe(1, 'name math group');
+                expect(mathGroup.attr('data-unformatted')).toBe(longTex, 'full, untruncated tex');
+            })
+            .then(done, done.fail);
+        });
+
+        it('should still truncate a plain-text trace name to hoverlabel.namelength', function(done) {
+            Plotly.newPlot(gd, {
+                data: [{
+                    type: 'scatter',
+                    mode: 'markers',
+                    x: [1, 2, 3],
+                    y: [1, 2, 3],
+                    name: 'a rather long trace name',
+                    hoverinfo: 'x+y+name'
+                }],
+                layout: {
+                    width: 500,
+                    height: 400,
+                    margin: {l: 0, t: 0, r: 0, b: 0},
+                    xaxis: {range: [0, 4]},
+                    yaxis: {range: [0, 4]}
+                }
+            })
+            .then(function() {
+                _hover(125, 300);
+                return delay(30)();
+            })
+            .then(function() {
+                var nameText = d3Select(gd).select('g.hovertext text.name').text();
+
+                expect(nameText.length).toBeLessThan('a rather long trace name'.length, 'truncated');
+                expect(nameText).toMatch(/\.\.\.$/, 'ellipsis');
+            })
+            .then(done, done.fail);
+        });
+
+        it('should keep the tex name inside its box for rotated labels in hovermode y', function(done) {
+            Plotly.newPlot(gd, {
+                data: [
+                    {type: 'scatter', mode: 'markers', x: [1], y: [1], name: '$\\alpha_{1c} = 352 \\pm 11 \\text{ km s}^{-1}$', hoverinfo: 'x+y+name'},
+                    {type: 'scatter', mode: 'markers', x: [2], y: [1], name: '$\\gamma^2$', hoverinfo: 'x+y+name'}
+                ],
+                layout: {
+                    width: 500,
+                    height: 400,
+                    margin: {l: 0, t: 0, r: 0, b: 0},
+                    xaxis: {range: [0, 4]},
+                    yaxis: {range: [0, 4]},
+                    hoverlabel: {namelength: -1},
+                    hovermode: 'y'
+                }
+            })
+            .then(function() {
+                _hover(125, 300);
+                return delay(30)();
+            })
+            .then(function() {
+                var hoverTexts = d3Select(gd).selectAll('g.hovertext');
+
+                expect(hoverTexts.size()).toBe(2, 'two hover labels');
+                expect(hoverTexts.attr('transform')).toContain('rotate', 'labels are rotated');
+
+                hoverTexts.each(function() {
+                    var g = d3Select(this);
+                    var mathGroup = g.select('.name-math-group');
+                    var box = g.select('rect');
+
+                    expect(mathGroup.size()).toBe(1, 'name math group');
+                    expect(box.size()).toBe(1, 'name box');
+
+                    var m = mathGroup.node().getBoundingClientRect();
+                    var b = box.node().getBoundingClientRect();
+                    var dx = (m.left + m.right) / 2 - (b.left + b.right) / 2;
+                    var dy = (m.top + m.bottom) / 2 - (b.top + b.bottom) / 2;
+
+                    expect(Math.sqrt(dx * dx + dy * dy)).toBeLessThan(4, 'tex centered in its name box');
+                });
+            })
+            .then(done, done.fail);
+        });
+
         it('should hand a pure-tex Fx.loneHover label off to MathJax, sized to its final content', function(done) {
             Plotly.newPlot(gd, {
                 data: [{type: 'scatter', mode: 'markers', x: [1], y: [1]}],
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		- Fix hover labels that are a single tex expression being truncated by `hoverlabel.namelength` [[#8138](https://github.com/plotly/plotly.js/pull/8138)]
		- Fix tex in hover labels being misplaced when labels are rotated in `hovermode: 'y'` [[#8138](https://github.com/plotly/plotly.js/pull/8138)]