fix(effects): run no sharpen pass when its slider is at 0 (#1398)

Disable the sharpen pass when its intensity is zero.

Contribution by @quanticsoul4772.

changelog.d/1398-sharpen-zero-off.md

@@ -0,0 +1,2 @@
+- The Sharpen slider at 0 now turns the sharpen pass off instead of still
+  sharpening at a low amount (quanticsoul4772, #1398).

docs/CURRENT-STATE.md

@@ -1301,6 +1301,8 @@ Stopping the controller revokes animation before asynchronous UI teardown; final
 destruction removes its stages and restores the borrowed bloom configuration.
 Snow's sideways sway stays within a fixed range at any session age; Wind scales
 its amplitude.
+Sharpen runs only when enabled with intensity above 0.001. At slider zero its
+stage is disabled; raising the slider resumes it when sharpen is enabled.
 
 ## Display control ownership
 

src/ui/visualEffects.js

@@ -159,18 +159,30 @@ export class VisualEffects {
     this.requestRender('bloom');
   }
 
+  /**
+   * Sharpen runs only when it is on and its slider is above 0, as the style
+   * stages do: the pass costs the same at any amount (~1.5 ms GPU per frame
+   * on the Arc, 2026-10-24), and `0.1 + value * 2` still sharpened at 0.
+   */
+  syncSharpenEnabled() {
+    if (this.stopped || !this.sharpenStage) return;
+    this.sharpenStage.enabled =
+      this.sharpenEnabled && this.sharpenIntensity > 0.001;
+  }
+
   applySharpenIntensity(value) {
     if (this.stopped) return;
     this.sharpenIntensity = value;
     if (this.sharpenStage)
       this.sharpenStage.uniforms.amount = 0.1 + value * 2.0;
+    this.syncSharpenEnabled();
     this.requestRender('sharpen');
   }
 
   setSharpenEnabled(enabled) {
     if (this.stopped) return;
     this.sharpenEnabled = !!enabled;
-    if (this.sharpenStage) this.sharpenStage.enabled = this.sharpenEnabled;
+    this.syncSharpenEnabled();
     this.requestRender('sharpen');
   }
 

src/ui/visualEffects.test.mjs

@@ -224,6 +224,24 @@ test('sharpen uses the existing uniform scale and keeps values while disabled',
   f.effects.destroy();
 });
 
+test('sharpen at 0 runs no pass, and comes back with the slider', () => {
+  const f = fixture();
+  f.effects.initPostProcess(0.49);
+  f.effects.setSharpenEnabled(true);
+  assert.equal(f.effects.sharpenStage.enabled, true);
+  f.effects.applySharpenIntensity(0);
+  assert.equal(
+    f.effects.sharpenStage.enabled,
+    false,
+    'no residual sharpen at 0',
+  );
+  f.effects.setSharpenEnabled(true);
+  assert.equal(f.effects.sharpenStage.enabled, false, 'on at 0 is still off');
+  f.effects.applySharpenIntensity(0.2);
+  assert.equal(f.effects.sharpenStage.enabled, true);
+  f.effects.destroy();
+});
+
 test('stop revokes pending work immediately but retains stages until final destruction', () => {
   const f = fixture();
   f.effects.initStyles();