From a399795772e532064a5500884a236cc513a8e50a Mon Sep 17 00:00:00 2001
From: root <root@stein2>
Date: Sun, 13 Sep 2026 18:29:04 +0200
Subject: [PATCH] Shader graph: Pow node, base held at 0, exponent broadcast
 for colours (#80)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 README.md                  |  2 +-
 src/core/shader/nodes.ts   | 17 +++++++++++++++++
 tests/core/shaders.test.ts | 19 +++++++++++++++++++
 tools/e2e/28-shader.mjs    | 33 +++++++++++++++++++++++++++++++++
 4 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 1e0b9cad..58ca89f0 100644
--- a/README.md
+++ b/README.md
@@ -37,7 +37,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 760 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 762 checks (GM_STEPS=20 for one step)
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs
 node tools/seed-actor.mjs && node tools/smoke-actor.mjs
diff --git a/src/core/shader/nodes.ts b/src/core/shader/nodes.ts
index f4988f49..377b5ec6 100644
--- a/src/core/shader/nodes.ts
+++ b/src/core/shader/nodes.ts
@@ -355,6 +355,22 @@ export const ShaderStep: ShaderNodeDef = {
   }),
 };
 
+/** GLSL leaves `pow` undefined below 0, so the base is held at 0 there. */
+export const ShaderPow: ShaderNodeDef = {
+  type: 'ShaderPow',
+  label: 'Pow',
+  category: 'shader',
+  description:
+    'value to the power of exponent: 2 squares it, 0.5 is the square root. Below 0 the value counts as 0. Per channel for colours.',
+  inputs: [anyIn('value', 0), floatIn('exponent', 2)],
+  outputs: [anyOut('result')],
+  params: [],
+  emit: ({ value, exponent }) => {
+    const power = value!.type === 'vec3' ? `vec3(${exponent!.code})` : exponent!.code;
+    return { result: { code: `pow(max(${value!.code}, 0.0), ${power})`, type: value!.type } };
+  },
+};
+
 /** Every node a shader graph offers. Registered by `graph/nodes`, offered by no behavior palette. */
 export const SHADER_NODES: readonly ShaderNodeDef[] = [
   ShaderTextureColor,
@@ -377,6 +393,7 @@ export const SHADER_NODES: readonly ShaderNodeDef[] = [
   ShaderFloor,
   ShaderFract,
   ShaderStep,
+  ShaderPow,
 ];
 
 /** A GLSL float literal: always with a decimal point, so `1` does not become an int. */
diff --git a/tests/core/shaders.test.ts b/tests/core/shaders.test.ts
index 7ab58654..9b2c327a 100644
--- a/tests/core/shaders.test.ts
+++ b/tests/core/shaders.test.ts
@@ -451,6 +451,25 @@ describe('compileShader', () => {
     expect(fragment).toMatch(/vec3 n\d+_result = floor\(n\d+_color\);/);
     expect(fragment).toMatch(/float alpha = clamp\(n\d+_result, 0\.0, 1\.0\);/);
   });
+
+  it('writes Pow as the GLSL call with the base held at 0, the exponent broadcast for a colour', () => {
+    const f = makeProject();
+    const s = shaderEditor(f, 'Gamma');
+    const uv = s.add(SHADER_UV);
+    const eased = s.add('ShaderPow', { exponent: 2 });
+    const tint = s.add('ShaderColor', { value: 0xff8000 });
+    const gamma = s.add('ShaderPow', { exponent: 2.2 });
+    const output = s.add(SHADER_OUTPUT);
+    s.link(uv, 'u', eased, 'value');
+    s.link(eased, 'result', output, 'alpha');
+    s.link(tint, 'color', gamma, 'value');
+    s.link(gamma, 'result', output, 'color');
+    const build = compileShader(s.asset().graph);
+    expect(build.problems).toEqual({});
+    const { fragment } = build.compiled!;
+    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\(2\.2\)\);/);
+  });
 });
 
 describe('a sprite wearing a shader', () => {
diff --git a/tools/e2e/28-shader.mjs b/tools/e2e/28-shader.mjs
index 0ad01587..1c52edbf 100644
--- a/tools/e2e/28-shader.mjs
+++ b/tools/e2e/28-shader.mjs
@@ -470,6 +470,39 @@ export async function shader(t) {
     { vTop, vBottom },
   );
 
+  // 28k-ii. Pow bends the cut: u squared crosses 0.5 at u = 0.707, its square root at u = 0.25.
+  const cutAfterPow = (exponent) =>
+    redOrBlue(
+      [
+        node('uv', 'ShaderUV'),
+        node('pow', 'ShaderPow', { exponent }, 260, 0),
+        node('cut', 'ShaderStep', { edge: 0.5 }, 260, 120),
+      ],
+      [
+        edge('uv', 'u', 'pow', 'value'),
+        edge('pow', 'result', 'cut', 'value'),
+        edge('cut', 'result', 'mix', 't'),
+      ],
+    );
+  await cutAfterPow(2);
+  await sleep(400);
+  const squaredNear = await pixel(0.1, -0.3);
+  const squaredFar = await pixel(0.3, -0.3);
+  check(
+    'Pow 2 moves the cut to u = 0.707: still red at u = 0.6, blue at 0.8',
+    colourDistance(squaredNear, '#ff0000') < 6 && colourDistance(squaredFar, '#0000ff') < 6,
+    { squaredNear, squaredFar },
+  );
+  await cutAfterPow(0.5);
+  await sleep(400);
+  const rootNear = await pixel(-0.3, -0.3);
+  const rootFar = await pixel(-0.15, -0.3);
+  check(
+    'Pow 0.5 pulls it to u = 0.25: red at u = 0.2, blue at 0.35',
+    colourDistance(rootNear, '#ff0000') < 6 && colourDistance(rootFar, '#0000ff') < 6,
+    { rootNear, rootFar },
+  );
+
   // 28l. Sample texture reads the picture where the graph says. On a pasted two-colour picture:
   // flipped u swaps the halves; u + 0.5 past the border shows the Output's Edge – Repeat continues
   // with the far half, Mirror with the near one.