From 39e15575baa413b6bba0e3d10ed5fbc5609b4c92 Mon Sep 17 00:00:00 2001
From: Boof2015 <75185879+Boof2015@users.noreply.github.com>
Date: Sat, 28 Mar 2026 03:34:54 -0400
Subject: [PATCH] make gain slider work with native audio

---
 src/renderer/audio/AudioCapture.ts | 25 ++++++++++++++++----
 src/renderer/audio/inputGain.ts    | 21 +++++++++++++++++
 test/renderer-helpers.test.ts      | 37 ++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+), 5 deletions(-)
 create mode 100644 src/renderer/audio/inputGain.ts

diff --git a/src/renderer/audio/AudioCapture.ts b/src/renderer/audio/AudioCapture.ts
index e6d2046..91c8747 100644
--- a/src/renderer/audio/AudioCapture.ts
+++ b/src/renderer/audio/AudioCapture.ts
@@ -5,6 +5,7 @@
  */
 
 import { audioRouter } from './AudioRouter'
+import { applyInputGainToStereoSamples, inputGainDbToLinear } from './inputGain'
 import type {
   CaptureBackendKind,
   CaptureBackendPolicy,
@@ -120,11 +121,11 @@ class ElectronCaptureRuntime {
   private sequence = 0
   private sampleRate = 48000
   private channelCount = 2
+  private inputGainLinear = 1
 
   setInputGain(db: number): void {
-    if (this.gainNode) {
-      this.gainNode.gain.value = Math.pow(10, db / 20)
-    }
+    this.inputGainLinear = inputGainDbToLinear(db)
+    this.syncGainNode()
   }
 
   subscribe(listener: (chunk: CaptureChunk) => void): () => void {
@@ -202,8 +203,8 @@ class ElectronCaptureRuntime {
 
     if (!this.gainNode) {
       this.gainNode = this.audioContext.createGain()
-      this.gainNode.gain.value = 1.0
     }
+    this.syncGainNode()
 
     if (!this.workletNode) {
       this.workletNode = new AudioWorkletNode(this.audioContext, 'capture-processor', {
@@ -266,6 +267,12 @@ class ElectronCaptureRuntime {
     this.currentConfigKey = configKey
   }
 
+  private syncGainNode(): void {
+    if (this.gainNode) {
+      this.gainNode.gain.value = this.inputGainLinear
+    }
+  }
+
   private async requestSystemStream(): Promise<MediaStream> {
     const sources = await window.electronAPI.getDesktopSources()
     if (!sources.length) {
@@ -575,6 +582,8 @@ class AudioCapture {
   private backendPolicy: CaptureBackendPolicy = DEFAULT_BACKEND_POLICY
   private activeBackendReason: string | null = null
   private sessionId: number | null = null
+  private inputGainDb = 0
+  private inputGainLinear = 1
   private statusListeners = new Set<StatusListener>()
 
   constructor() {
@@ -819,6 +828,10 @@ class AudioCapture {
       return
     }
 
+    if (originKind.startsWith('native-') && this.inputGainLinear !== 1) {
+      applyInputGainToStereoSamples(chunk.left, chunk.right, this.inputGainLinear)
+    }
+
     audioRouter.ingestChunk(chunk.left, chunk.right, {
       sessionId: this.sessionId,
       channelCount: chunk.channelCount,
@@ -828,7 +841,9 @@ class AudioCapture {
   }
 
   setInputGain(db: number): void {
-    this.electronRuntime.setInputGain(db)
+    this.inputGainDb = db
+    this.inputGainLinear = inputGainDbToLinear(this.inputGainDb)
+    this.electronRuntime.setInputGain(this.inputGainDb)
   }
 
   private emitStatus(): void {
diff --git a/src/renderer/audio/inputGain.ts b/src/renderer/audio/inputGain.ts
new file mode 100644
index 0000000..40b597d
--- /dev/null
+++ b/src/renderer/audio/inputGain.ts
@@ -0,0 +1,21 @@
+export function inputGainDbToLinear(db: number): number {
+  return Math.pow(10, db / 20)
+}
+
+export function applyInputGainToStereoSamples(
+  left: Float32Array,
+  right: Float32Array,
+  linearGain: number,
+): void {
+  if (linearGain === 1) {
+    return
+  }
+
+  for (let index = 0; index < left.length; index += 1) {
+    left[index] *= linearGain
+  }
+
+  for (let index = 0; index < right.length; index += 1) {
+    right[index] *= linearGain
+  }
+}
diff --git a/test/renderer-helpers.test.ts b/test/renderer-helpers.test.ts
index 52b791a..060312b 100644
--- a/test/renderer-helpers.test.ts
+++ b/test/renderer-helpers.test.ts
@@ -6,6 +6,10 @@ import {
   parseColorToRgb,
   resolveColorToRgb,
 } from '../src/renderer/utils/color'
+import {
+  applyInputGainToStereoSamples,
+  inputGainDbToLinear,
+} from '../src/renderer/audio/inputGain'
 import { moveDockedScopeOrder } from '../src/renderer/stores/settingsStore'
 import { SCOPE_KINDS, type ScopeKind } from '../src/types/scope'
 import type { ScopePopoutStateMap } from '../src/types/popout'
@@ -116,6 +120,39 @@ test('color helpers fall back predictably for invalid values', () => {
   assert.deepEqual(resolveColorToRgb('rgb(4, 5, 6)'), { r: 4, g: 5, b: 6 })
 })
 
+test('inputGainDbToLinear converts dB offsets to expected linear gain values', () => {
+  assert.equal(inputGainDbToLinear(0), 1)
+  assertAlmostEqual(inputGainDbToLinear(6), 1.9952623149688795, 1e-12, '+6 dB gain')
+  assertAlmostEqual(inputGainDbToLinear(-6), 0.5011872336272722, 1e-12, '-6 dB gain')
+})
+
+test('applyInputGainToStereoSamples scales both channels in place', () => {
+  const { left, right } = createFilledStereoChunk(0.25, -0.5, 3)
+  const linearGain = inputGainDbToLinear(6)
+
+  applyInputGainToStereoSamples(left, right, linearGain)
+
+  for (const sample of left) {
+    assertAlmostEqual(sample, 0.25 * linearGain, 1e-6, 'left channel scaled')
+  }
+
+  for (const sample of right) {
+    assertAlmostEqual(sample, -0.5 * linearGain, 1e-6, 'right channel scaled')
+  }
+})
+
+test('applyInputGainToStereoSamples is a no-op for unity gain', () => {
+  const left = new Float32Array([0.1, -0.2, 0.3])
+  const right = new Float32Array([-0.4, 0.5, -0.6])
+  const initialLeft = Array.from(left)
+  const initialRight = Array.from(right)
+
+  applyInputGainToStereoSamples(left, right, 1)
+
+  assert.deepEqual(Array.from(left), initialLeft)
+  assert.deepEqual(Array.from(right), initialRight)
+})
+
 test('VisualizerFrameLoop renders one invalidated frame while idle', () => {
   const raf = installFakeAnimationFrame()