LibWeb: Implement BaseAudioContext.createGain

Tests/LibWeb/Text/expected/WebAudio/GainNode.txt

@@ -0,0 +1,5 @@
+GainNode
+AudioNode
+EventTarget
+Object
+[object AudioParam] current: 1, default: 1, min: -3.4028234663852886e+38, max: 3.4028234663852886e+38, rate: a-rate

Tests/LibWeb/Text/input/WebAudio/GainNode.html

@@ -0,0 +1,23 @@
+<script src="../include.js"></script>
+<script>
+    function dumpAudioParam(param) {
+        println(`${param} current: ${param.value}, default: ${param.defaultValue}, min: ${param.minValue}, max: ${param.maxValue}, rate: ${param.automationRate}`);
+    }
+
+    test(() => {
+        const audioContext = new OfflineAudioContext(1, 5000, 44100);
+
+        const node = audioContext.createGain();
+
+        // Check prototype
+        let prototype = Object.getPrototypeOf(node);
+
+        while (prototype) {
+            println(prototype.constructor.name);
+            prototype = Object.getPrototypeOf(prototype);
+        }
+
+        // Audio Params
+        dumpAudioParam(node.gain);
+    });
+</script>

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.cpp

@@ -11,6 +11,7 @@
 #include <LibWeb/WebAudio/AudioBuffer.h>
 #include <LibWeb/WebAudio/BaseAudioContext.h>
 #include <LibWeb/WebAudio/DynamicsCompressorNode.h>
+#include <LibWeb/WebAudio/GainNode.h>
 #include <LibWeb/WebAudio/OscillatorNode.h>
 
 namespace Web::WebAudio {
@@ -61,6 +62,13 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<DynamicsCompressorNode>> BaseAudioContext::
     return DynamicsCompressorNode::create(realm(), *this);
 }
 
+// https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-creategain
+JS::NonnullGCPtr<GainNode> BaseAudioContext::create_gain()
+{
+    // Factory method for GainNode.
+    return GainNode::create(realm(), *this);
+}
+
 // https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createbuffer
 WebIDL::ExceptionOr<void> BaseAudioContext::verify_audio_options_inside_nominal_range(JS::Realm& realm, WebIDL::UnsignedLong number_of_channels, WebIDL::UnsignedLong length, float sample_rate)
 {

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.h

@@ -50,6 +50,7 @@ public:
     WebIDL::ExceptionOr<JS::NonnullGCPtr<AudioBuffer>> create_buffer(WebIDL::UnsignedLong number_of_channels, WebIDL::UnsignedLong length, float sample_rate);
     WebIDL::ExceptionOr<JS::NonnullGCPtr<OscillatorNode>> create_oscillator();
     WebIDL::ExceptionOr<JS::NonnullGCPtr<DynamicsCompressorNode>> create_dynamics_compressor();
+    JS::NonnullGCPtr<GainNode> create_gain();
 
 protected:
     explicit BaseAudioContext(JS::Realm&, float m_sample_rate = 0);

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.idl

@@ -2,6 +2,7 @@
 #import <DOM/EventHandler.idl>
 #import <WebAudio/AudioBuffer.idl>
 #import <WebAudio/DynamicsCompressorNode.idl>
+#import <WebAudio/GainNode.idl>
 #import <WebAudio/OscillatorNode.idl>
 
 // https://www.w3.org/TR/webaudio/#enumdef-audiocontextstate
@@ -33,7 +34,7 @@ interface BaseAudioContext : EventTarget {
     [FIXME] ConvolverNode createConvolver ();
     [FIXME] DelayNode createDelay (optional double maxDelayTime = 1.0);
     DynamicsCompressorNode createDynamicsCompressor();
-    [FIXME] GainNode createGain ();
+    GainNode createGain();
     [FIXME] IIRFilterNode createIIRFilter (sequence<double> feedforward, sequence<double> feedback);
     OscillatorNode createOscillator();
     [FIXME] PannerNode createPanner ();