From 9678108fd1dcf614ea09e670901b9eb9d583de2e Mon Sep 17 00:00:00 2001
From: qm210 <quantenmace@gmail.com>
Date: Tue, 22 Oct 2024 01:04:39 +0200
Subject: [PATCH] feat: envelopexp ported to go synth

---
 cmd/sointu-play/main.go |  4 ++--
 vm/go_synth.go          | 19 +++++++++++++------
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/cmd/sointu-play/main.go b/cmd/sointu-play/main.go
index aea297a..52359e3 100644
--- a/cmd/sointu-play/main.go
+++ b/cmd/sointu-play/main.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
+	"github.com/vsariola/sointu/cmd"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -14,7 +15,6 @@ import (
 	"github.com/vsariola/sointu"
 	"github.com/vsariola/sointu/oto"
 	"github.com/vsariola/sointu/version"
-	"github.com/vsariola/sointu/vm/compiler/bridge"
 )
 
 func main() {
@@ -93,7 +93,7 @@ func main() {
 				return fmt.Errorf("the song could not be parsed as .json (%v) or .yml (%v)", errJSON, errYaml)
 			}
 		}
-		buffer, err := sointu.Play(bridge.NativeSynther{}, song, nil) // render the song to calculate its length
+		buffer, err := sointu.Play(cmd.MainSynther, song, nil) // render the song to calculate its length
 		if err != nil {
 			return fmt.Errorf("sointu.Play failed: %v", err)
 		}
diff --git a/vm/go_synth.go b/vm/go_synth.go
index ffcbdad..ecc2857 100644
--- a/vm/go_synth.go
+++ b/vm/go_synth.go
@@ -330,25 +330,27 @@ func (s *GoSynth) Render(buffer sointu.AudioBuffer, maxtime int) (samples int, t
 					stack = append(stack, output)
 				}
 			case opEnvelopexp:
-				// TODO @qm210 - for now, this just clones the envelope so everything is wired up, but IT IS NOT IMPLEMENTED YET
-				// is ignoring for now
-				// - params[1] - attack shape parameter (center value should mean "linear")
-				// - params[3] - decay shape parameter (center value should mean "linear")
 				if !voices[0].sustain {
 					unit.state[0] = envStateRelease // set state to release
 				}
 				state := unit.state[0]
 				level := unit.state[1]
+				exponent := float64(1)
+				baseline := float32(0)
 				switch state {
 				case envStateAttack:
+					exponent = scaledEnvelopExponent(params[1])
 					level += nonLinearMap(params[0])
 					if level >= 1 {
 						level = 1
 						state = envStateDecay
 					}
 				case envStateDecay:
+					exponent = scaledEnvelopExponent(params[3])
+					sustain := params[4]
+					baseline = sustain
 					level -= nonLinearMap(params[2])
-					if sustain := params[4]; level <= sustain {
+					if level <= sustain {
 						level = sustain
 					}
 				case envStateRelease:
@@ -359,7 +361,8 @@ func (s *GoSynth) Render(buffer sointu.AudioBuffer, maxtime int) (samples int, t
 				}
 				unit.state[0] = state
 				unit.state[1] = level
-				output := level * params[6]
+				expLevel := float32(math.Pow(float64(level), exponent))
+				output := (baseline + (1-baseline)*expLevel) * params[6]
 				stack = append(stack, output)
 				if stereo {
 					stack = append(stack, output)
@@ -646,6 +649,10 @@ func nonLinearMap(value float32) float32 {
 	return float32(math.Exp2(float64(-24 * value)))
 }
 
+func scaledEnvelopExponent(value float32) float64 {
+	return math.Pow(2, 6*(0.5-float64(value)))
+}
+
 func clip(value float32) float32 {
 	if value < -1 {
 		return -1