Round brush coordinates to 14 digits. Fixes #1634

srcjs/output_binding_image.js

@@ -1119,6 +1119,9 @@ imageutils.createBrush = function($el, opts, coordmap, expandPixels) {
     // For reversed scales, the min and max can be reversed, so use findBox
     // to ensure correct order.
     state.boundsData = coordmap.findBox(minData, maxData);
+    // Round to 14 significant digits to avoid spurious changes in FP values
+    // (#1634).
+    state.boundsData = mapValues(state.boundsData, val => roundPrecision(val, 14));
 
     // We also need to attach the data bounds and panel as data attributes, so
     // that if the image is re-sent, we can grab the data bounds to create a new

srcjs/utils.js

@@ -56,6 +56,22 @@ function padZeros(n, digits) {
   return str;
 }
 
+// Round to a specified number of digits after the decimal. 0 means round to
+// integer value. Negative values mean round to digits before decimal.
+function roundDigits(x, digits = 0) {
+  const n = Math.pow(10, digits);
+  return Math.round(x * n) / n;
+}
+
+// Round to a specified number of significant digits.
+function roundPrecision(x, digits = 1) {
+  if (digits < 1)
+    throw "Significant digits must be 1 or greater";
+
+  const scaleFactor = Math.pow(10, Math.floor(Math.log10(Math.abs(x))) + 1);
+  return roundDigits(x / scaleFactor, digits) * scaleFactor;
+}
+
 // Take a string with format "YYYY-MM-DD" and return a Date object.
 // IE8 and QTWebKit don't support YYYY-MM-DD, but they support YYYY/MM/DD
 function parseDate(dateString) {