Fix: allow single-arg atan() outside strands; add unit test

src/webgl/ShaderGenerator.js

@@ -1615,8 +1615,10 @@ function shadergenerator(p5, fn) {
     'asin': { args: ['genType'], returnType: 'genType', isp5Function: true },
     'asinh': { args: ['genType'], returnType: 'genType', isp5Function: false },
     'atan': [
-      { args: ['genType'], returnType: 'genType', isp5Function: false },
-      { args: ['genType', 'genType'], returnType: 'genType', isp5Function: false }
+      // Single-argument atan is a normal p5 function and should work outside strands
+      { args: ['genType'], returnType: 'genType', isp5Function: true},
+      // Two-argument atan(y, x) is GLSL-only and remains strands-only
+      { args: ['genType', 'genType'], returnType: 'genType', isp5Function: false},
     ],
     'atanh': { args: ['genType'], returnType: 'genType', isp5Function: false },
     'cos': { args: ['genType'], returnType: 'genType', isp5Function: true },

test/unit/math/atan.js

@@ -0,0 +1,33 @@
+import trigonometry from '../../../src/math/trigonometry.js';
+import { assert } from 'chai';
+
+suite('atan', function() {
+  const mockP5 = {
+    RADIANS: 'radians',
+    DEGREES: 'degrees',
+    _validateParameters: () => {}
+  };
+  const mockP5Prototype = {};
+
+  beforeEach(function() {
+    mockP5Prototype._angleMode = mockP5.RADIANS;
+    mockP5Prototype.angleMode = function(mode) {
+      this._angleMode = mode;
+    };
+    trigonometry(mockP5, mockP5Prototype);
+  });
+
+  test('should return the correct value for atan(0.5) in radians', function() {
+    mockP5Prototype.angleMode(mockP5.RADIANS);
+    const expected = 0.4636476090008061; // pre-calculated value
+    const actual = mockP5Prototype.atan(0.5);
+    assert.closeTo(actual, expected, 1e-10);
+  });
+
+  test('should return the correct value for atan(0.5) in degrees', function() {
+    mockP5Prototype.angleMode(mockP5.DEGREES);
+    const expected = 26.56505117707799; // pre-calculated value
+    const actual = mockP5Prototype.atan(0.5);
+    assert.closeTo(actual, expected, 1e-10);
+  });
+});

test/unit/spec.js

@@ -55,7 +55,7 @@ var spec = {
     // to omit some for speed if they should only be run manually.
     'webgl',
     'typography',
-    'shape_modes'
+    'shape_modes',
   ]
 };
 document.write(