Shader graph: Abs node, the distance from 0 per channel

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/core/shaders.test.ts

@@ -470,6 +470,27 @@ describe('compileShader', () => {
     expect(fragment).toMatch(/float n\d+_result = pow\(max\(n\d+_u, 0\.0\), 2\.0\);/);
     expect(fragment).toMatch(/vec3 n\d+_result = pow\(max\(n\d+_color, 0\.0\), vec3\(2\.2\)\);/);
   });
+
+  it('writes Abs as the GLSL call, per channel for a colour', () => {
+    const f = makeProject();
+    const s = shaderEditor(f, 'Fold');
+    const uv = s.add(SHADER_UV);
+    const centred = s.add('ShaderSubtract', { b: 0.5 });
+    const folded = s.add('ShaderAbs');
+    const tint = s.add('ShaderColor', { value: 0xff8000 });
+    const magnitude = s.add('ShaderAbs');
+    const output = s.add(SHADER_OUTPUT);
+    s.link(uv, 'u', centred, 'a');
+    s.link(centred, 'result', folded, 'value');
+    s.link(folded, 'result', output, 'alpha');
+    s.link(tint, 'color', magnitude, 'value');
+    s.link(magnitude, 'result', output, 'color');
+    const build = compileShader(s.asset().graph);
+    expect(build.problems).toEqual({});
+    const { fragment } = build.compiled!;
+    expect(fragment).toMatch(/float n\d+_result = abs\(n\d+_result\);/);
+    expect(fragment).toMatch(/vec3 n\d+_result = abs\(n\d+_color\);/);
+  });
 });
 
 describe('a sprite wearing a shader', () => {