examples: add bytebeat melody using sokol.audio

examples/sokol/sounds/melody.v

@@ -0,0 +1,35 @@
+import os
+import sokol.audio
+
+struct AContext {
+mut:
+	frame_0 int
+}
+
+fn my_audio_stream_callback(buffer &f32, num_frames, num_channels int, mut acontext AContext) {
+	mut soundbuffer := buffer
+	for frame := 0; frame < num_frames; frame++ {
+		t := int(f32(acontext.frame_0 + frame) * 0.245)
+		// Credits for the formula below: https://www.youtube.com/watch?v=V4GfkFbDojc
+		// "Techno" by Gabriel Miceli
+		y := (t * (((t / 10 | 0) ^ ((t / 10 | 0) -
+			1280)) % 11) / 2 & 127) +
+			(t * (((t / 640 | 0) ^ ((t / 640 | 0) - 2)) % 13) / 2 & 127)
+		for ch := 0; ch < num_channels; ch++ {
+			idx := frame * num_channels + ch
+			unsafe {
+				soundbuffer[idx] = f32(byte(y) - 127) / 255.0
+			}
+		}
+	}
+	acontext.frame_0 += num_frames
+}
+
+fn main() {
+	audio.setup({
+		stream_userdata_cb: my_audio_stream_callback
+		user_data: &AContext{}
+	})
+	os.input('Press Enter to exit')
+	audio.shutdown()
+}