Fix Kicker's release stage (LMMS#7226)

When applying its release stage Kicker did not take the frames before the release into account but instead always applied the release to the full buffer. This potentially lead to a jump in the attenuation values instead of a clean linear decay.

See LMMS#7225 for more details.

plugins/Kicker/Kicker.cpp

@@ -188,13 +188,22 @@ void KickerInstrument::playNote( NotePlayHandle * _n,
 
 	if( _n->isReleased() )
 	{
-		const float done = _n->releaseFramesDone();
+		// We need this to check if the release has ended
 		const float desired = desiredReleaseFrames();
-		for( fpp_t f = 0; f < frames; ++f )
+
+		// This can be considered the current release frame in the "global" context of the release.
+		// We need it with the desired number of release frames to compute the linear decay.
+		fpp_t currentReleaseFrame = _n->releaseFramesDone();
+
+		// Start applying the release at the correct frame
+		const float framesBeforeRelease = _n->framesBeforeRelease();
+		for (fpp_t f = framesBeforeRelease; f < frames; ++f, ++currentReleaseFrame)
 		{
-			const float fac = ( done+f < desired ) ? ( 1.0f - ( ( done+f ) / desired ) ) : 0;
-			_working_buffer[f+offset][0] *= fac;
-			_working_buffer[f+offset][1] *= fac;
+			const bool releaseStillActive = currentReleaseFrame < desired;
+			const float attenuation = releaseStillActive ? (1.0f - (currentReleaseFrame / desired)) : 0.f;
+
+			_working_buffer[f + offset][0] *= attenuation;
+			_working_buffer[f + offset][1] *= attenuation;
 		}
 	}
 }