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/spec.js

@@ -55,7 +55,8 @@ var spec = {
     // to omit some for speed if they should only be run manually.
     'webgl',
     'typography',
-    'shape_modes'
+    'shape_modes',
+    'math'
   ]
 };
 document.write(

test/unit/visual/cases/math.js

@@ -0,0 +1,17 @@
+import { visualTest, visualSuite } from '../../visual/visualTest.js';
+
+visualSuite('math', () => {
+  visualTest('atan_outside_strands', async (p5, screenshot) => {
+    // Ensure no WebGL/strands context is used; call atan directly and draw text
+    p5.createCanvas(120, 60);
+    p5.background(255);
+    p5.fill(0);
+    const v = p5.atan(0.5);
+    // Draw the numeric value so visual regression will catch undefined/NaN
+    p5.textSize(14);
+    p5.textFont('monospace');
+    p5.textAlign(p5.LEFT, p5.TOP);
+    p5.text(`atan(0.5)=${p5.nf(v, 1, 3)}`, 5, 5);
+    screenshot();
+  });
+});