Upgrade \sqrt zoom and width (#890)

* Fix \sqrt zoom in Safari

This PR evades a Safari bug which causes nested SVGs to zoom improperly. `\sqrt` and single-ended arrow SVGs have been modified.

These have been converted from nested SVGs to single level. Their long tails are now sliced off using CSS `overflow: hidden`.

Safari will still improperly zoom any double-ended stretchy arrows and horizontal braces.

* Fix \sqrt{}

Even if the function argument is empty, still render an SVG whose width equals the surd glyph.

* Fix tall \sqrt when scaled

* update screenshots affected by sqrt fixes

* more screenshots after changes to fix sqrt

* Pick up review comments

src/buildHTML.js

@@ -1115,6 +1115,10 @@ groupTypes.sqrt = function(group, options) {
     // First, we do the same steps as in overline to build the inner group
     // and line
     let inner = buildGroup(group.value.body, options.havingCrampedStyle());
+    if (inner.height === 0) {
+        // Render a small surd.
+        inner.height = options.fontMetrics().xHeight;
+    }
 
     // Some groups can return document fragments.  Handle those by wrapping
     // them in a span.
@@ -1159,26 +1163,16 @@ groupTypes.sqrt = function(group, options) {
     // Shift the sqrt image
     const imgShift = img.height - inner.height - lineClearance - ruleWidth;
 
-    // We add a special case here, because even when `inner` is empty, we
-    // still get a line. So, we use a simple heuristic to decide if we
-    // should omit the body entirely. (note this doesn't work for something
-    // like `\sqrt{\rlap{x}}`, but if someone is doing that they deserve for
-    // it not to work.
-    let body;
-    if (inner.height === 0 && inner.depth === 0) {
-        body = makeSpan();
-    } else {
-        inner.style.paddingLeft = img.surdWidth + "em";
+    inner.style.paddingLeft = img.advanceWidth + "em";
 
-        // Overlay the image and the argument.
-        body = buildCommon.makeVList([
-            {type: "elem", elem: inner},
-            {type: "kern", size: -(inner.height + imgShift)},
-            {type: "elem", elem: img},
-            {type: "kern", size: ruleWidth},
-        ], "firstBaseline", null, options);
-        body.children[0].children[0].classes.push("svg-align");
-    }
+    // Overlay the image and the argument.
+    const body = buildCommon.makeVList([
+        {type: "elem", elem: inner},
+        {type: "kern", size: -(inner.height + imgShift)},
+        {type: "elem", elem: img},
+        {type: "kern", size: ruleWidth},
+    ], "firstBaseline", null, options);
+    body.children[0].children[0].classes.push("svg-align");
 
     if (!group.value.index) {
         return makeSpan(["mord", "sqrt"], [body], options);

src/delimiter.js

@@ -329,14 +329,13 @@ const sqrtSvg = function(sqrtName, height, viewBoxHeight, options) {
     }
     const pathNode = new domTree.pathNode(sqrtName, alternate);
 
-    let attributes = [["width", "100%"], ["height", height + "em"]];
+    // Note: 1000:1 ratio of viewBox to document em width.
+    const attributes = [["width", "400em"], ["height", height + "em"]];
     attributes.push(["viewBox", "0 0 400000 " + viewBoxHeight]);
     attributes.push(["preserveAspectRatio", "xMinYMin slice"]);
-    const innerSVG =  new domTree.svgNode([pathNode], attributes);
+    const svg =  new domTree.svgNode([pathNode], attributes);
 
-    attributes = [["width", "100%"], ["height", height + "em"]];
-    const svg = new domTree.svgNode([innerSVG], attributes);
-    return buildCommon.makeSpan([], [svg], options);
+    return buildCommon.makeSpan(["hide-tail"], [svg], options);
 };
 
 const sqrtSpan = function(height, delim, options) {
@@ -353,22 +352,25 @@ const sqrtSpan = function(height, delim, options) {
         sizeMultiplier = newOptions.sizeMultiplier / options.sizeMultiplier;
         spanHeight = 1 * sizeMultiplier;
         span = sqrtSvg("sqrtMain", spanHeight, viewBoxHeight, options);
-        span.surdWidth = 0.833 * sizeMultiplier;   // from the font.
+        span.style.minWidth = "0.853em";
+        span.advanceWidth = 0.833 * sizeMultiplier;   // from the font.
 
     } else if (delim.type === "large") {
         // These SVGs come from fonts: KaTeX_Size1, _Size2, etc.
         viewBoxHeight = 1000 * sizeToMaxHeight[delim.size];
         spanHeight = sizeToMaxHeight[delim.size] / sizeMultiplier;
         span = sqrtSvg("sqrtSize" + delim.size, spanHeight, viewBoxHeight, options);
-        span.surdWidth = 1.0 / sizeMultiplier; // from the font
+        span.style.minWidth = "1.02em";
+        span.advanceWidth = 1.0 / sizeMultiplier; // from the font
 
     } else {
         // Tall sqrt. In TeX, this would be stacked using multiple glyphs.
         // We'll use a single SVG to accomplish the same thing.
         spanHeight = height / sizeMultiplier;
-        viewBoxHeight = Math.floor(1000 * spanHeight);
+        viewBoxHeight = Math.floor(1000 * height);
         span = sqrtSvg("sqrtTall", spanHeight, viewBoxHeight, options);
-        span.surdWidth = 1.056 / sizeMultiplier;
+        span.style.minWidth = "0.742em";
+        span.advanceWidth = 1.056 / sizeMultiplier;
     }
 
     span.height = spanHeight;

src/stretchy.js

@@ -158,6 +158,7 @@ const svgSpan = function(group, options) {
     let path;
     let pathName;
     let svgNode;
+    const classNames = [];
 
     if (utils.contains(["widehat", "widetilde", "undertilde"], label)) {
         // There are four SVG images available for each function.
@@ -208,7 +209,7 @@ const svgSpan = function(group, options) {
             attributes = [];
 
             if (numSvgChildren === 1) {
-                width = "100%";
+                width = "400em";
                 align = alignOne;
             } else if (numSvgChildren === 2) {
                 // small overlap to prevent a 1 pixel gap.
@@ -231,13 +232,22 @@ const svgSpan = function(group, options) {
             attributes.push(["viewBox", `0 0 ${viewBoxWidth} ${vbHeight}`]);
             attributes.push(["preserveAspectRatio", align + " slice"]);
 
-            innerSVGs.push(new domTree.svgNode([path], attributes));
+            if (numSvgChildren > 1) {
+                innerSVGs.push(new domTree.svgNode([path], attributes));
+            } else {
+                // The single svgChild is a child of a hide-tail span, not the
+                // child of another svg.
+                svgNode = new domTree.svgNode([path], attributes);
+                classNames.push("hide-tail");
+            }
+        }
+        if (numSvgChildren > 1) {
+            attributes = [["width", "100%"], ["height", height + "em"]];
+            svgNode = new domTree.svgNode(innerSVGs, attributes);
         }
-        attributes = [["width", "100%"], ["height", height + "em"]];
-        svgNode = new domTree.svgNode(innerSVGs, attributes);
     }
 
-    const span = buildCommon.makeSpan([], [svgNode], options);
+    const span = buildCommon.makeSpan(classNames, [svgNode], options);
     // Note that we are returning span.depth = 0.
     // Any adjustments relative to the baseline must be done in buildHTML.
     span.height = height;

static/katex.less

@@ -575,6 +575,13 @@
         }
     }
 
+    // Hide the long tail of a stretchy SVG.
+    .hide-tail {
+        width: 100%;          // necessary only to get IE to work properly
+        position: relative;   // ditto
+        overflow: hidden;     // This line applies to all browsers.
+    }
+
     // Lengthen the extensible arrows via padding.
     .x-arrow-pad {
         padding: 0 0.5em;