audio filters moved to its own files

src/net/torvald/terrarum/audio/dsp/Bitcrush.kt

@@ -0,0 +1,17 @@
+package net.torvald.terrarum.audio.dsp
+
+import net.torvald.terrarum.audio.TerrarumAudioMixerTrack
+import net.torvald.terrarum.roundToFloat
+
+class Bitcrush(var steps: Int, var inputGain: Float = 1f): TerrarumAudioFilter() {
+    override fun thru(inbuf: List<FloatArray>, outbuf: List<FloatArray>) {
+        for (ch in outbuf.indices) {
+            for (i in 0 until TerrarumAudioMixerTrack.BUFFER_SIZE / 4) {
+                val inn = ((inbuf[ch][i] * inputGain).coerceIn(-1f, 1f) + 1f) / 2f // 0f..1f
+                val stepped = (inn * (steps - 1)).roundToFloat() / (steps - 1)
+                val out = (stepped * 2f) - 1f // -1f..1f
+                outbuf[ch][i] = out
+            }
+        }
+    }
+}