From f0cac767184937b8ddbec2914d5edaa003a91de9 Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Tue, 3 Aug 2021 23:51:24 +0200
Subject: [PATCH] Add expression for Math.abs

---
 src/ol/style/expressions.js                    | 12 ++++++++++++
 test/browser/spec/ol/style/expressions.test.js |  6 ++++++
 2 files changed, 18 insertions(+)

diff --git a/src/ol/style/expressions.js b/src/ol/style/expressions.js
index 8f9aa6bb1d..5c33fb0da9 100644
--- a/src/ol/style/expressions.js
+++ b/src/ol/style/expressions.js
@@ -27,6 +27,7 @@ import {asArray, isStringColor} from '../color.js';
  *   * `['clamp', value, low, high]` clamps `value` between `low` and `high`
  *   * `['%', value1, value2]` returns the result of `value1 % value2` (modulo)
  *   * `['^', value1, value2]` returns the value of `value1` raised to the `value2` power
+ *   * `['abs', value1]` returns the absolute value of `value1`
  *
  * * Transform operators:
  *   * `['case', condition1, output1, ...conditionN, outputN, fallback]` selects the first output whose corresponding
@@ -551,6 +552,17 @@ Operators['^'] = {
   },
 };
 
+Operators['abs'] = {
+  getReturnType: function (args) {
+    return ValueTypes.NUMBER;
+  },
+  toGlsl: function (context, args) {
+    assertArgsCount(args, 1);
+    assertNumbers(args);
+    return `abs(${expressionToGlsl(context, args[0])})`;
+  },
+};
+
 Operators['>'] = {
   getReturnType: function (args) {
     return ValueTypes.BOOLEAN;
diff --git a/test/browser/spec/ol/style/expressions.test.js b/test/browser/spec/ol/style/expressions.test.js
index caabe63156..fcf1f9e004 100644
--- a/test/browser/spec/ol/style/expressions.test.js
+++ b/test/browser/spec/ol/style/expressions.test.js
@@ -235,6 +235,12 @@ describe('ol.style.expressions', function () {
       expect(expressionToGlsl(context, ['^', ['%', ['time'], 10], 2])).to.eql(
         'pow(mod(u_time, 10.0), 2.0)'
       );
+      expect(
+        expressionToGlsl(context, [
+          'abs',
+          ['-', ['get', 'attr3'], ['get', 'attr2']],
+        ])
+      ).to.eql('abs((a_attr3 - a_attr2))');
       expect(expressionToGlsl(context, ['>', 10, ['get', 'attr4']])).to.eql(
         '(10.0 > a_attr4)'
       );