Visualization: Improve latency and buffering appearance

Adjust the buffering so if latency is too low, we fill the rest of
the output with silence instead of peeking at the oldest part
of the buffer. Also increase latency by half a buffer size so
that the requested sample is in the center of the buffer, which
improves the 4096 sample situation with the current low
latency output.

Signed-off-by: Christopher Snowhill <kode54@gmail.com>

Audio/Visualization/VisualizationController.swift

@@ -98,15 +98,26 @@ class VisualizationController : NSObject {
 		var outPCMCopy = Array<Float>(repeating: 0.0, count: 4096)
 
 		serialQueue.sync {
-			let latencySamples = (Int)(self.latency * self.sampleRate)
+			// Offset latency so the target sample is in the center of the window
+			let latencySamples = (Int)((self.latency + latencyOffset) * self.sampleRate) + 2048
+			var samplesToDo = 4096;
+			if(latencySamples < 4096) {
+				// Latency can sometimes dip below this threshold
+				samplesToDo = latencySamples;
+			}
 			var j = self.visAudioCursor - latencySamples
 			let k = self.visAudioSize
 			if j < 0 { j += k }
-			for i in 0...4095 {
+			for i in 0..<samplesToDo {
 				let x = self.visAudio[j]
 				outPCMCopy[i] = x
 				j += 1; if j >= k { j = 0 }
 			}
+			if(samplesToDo < 4096) {
+				for i in samplesToDo...4095 {
+					outPCMCopy[i] = 0
+				}
+			}
 		}
 
 		if(outPCM != nil) {