Add TriangleWaveGenerator

app/src/main/java/com/github/nisrulz/samplezentone/MainActivity.kt

@@ -23,7 +23,7 @@ import androidx.appcompat.app.AppCompatActivity
 import com.github.nisrulz.samplezentone.databinding.ActivityMainBinding
 import com.github.nisrulz.zentone.MIN_FREQUENCY
 import com.github.nisrulz.zentone.ZenTone
-import com.github.nisrulz.zentone.wave_generators.SineWaveGenerator
+import com.github.nisrulz.zentone.wave_generators.TriangleWaveGenerator
 
 class MainActivity : AppCompatActivity() {
 
@@ -117,7 +117,7 @@ class MainActivity : AppCompatActivity() {
                     zenTone.play(
                         frequency = freq,
                         volume = volume,
-                        waveByteArrayGenerator = SineWaveGenerator
+                        waveByteArrayGenerator = TriangleWaveGenerator
                     )
                     myFAB.setImageResource(R.drawable.stop)
                 }

zentone/src/main/java/com/github/nisrulz/zentone/wave_generators/TriangleWaveGenerator.kt

@@ -0,0 +1,22 @@
+package com.github.nisrulz.zentone.wave_generators
+
+import kotlin.math.asin
+import kotlin.math.sin
+
+/**
+ * Triangle wave generator
+ *
+ * Triangle Wave: Defined as the arc sine function of a sinusoid
+ *
+ * @see <a
+ *     href="https://en.wikipedia.org/wiki/Triangle_wave">Wikipedia</a>
+ */
+object TriangleWaveGenerator : WaveByteArrayGenerator {
+
+    override fun calculateData(index: Int, samplingInterval: Float, amplitude: Int): Byte {
+        val angle: Double = (Math.PI * index) / samplingInterval
+        return (amplitude * waveFunction(angle) * Byte.MAX_VALUE).toInt().toByte()
+    }
+
+    private fun waveFunction(angle: Double): Double = asin(sin(angle))
+}