From e39ed74796041eb6167dec30ebb9135c31531f88 Mon Sep 17 00:00:00 2001
From: Andrew Alderwick <andrew@alderwick.co.uk>
Date: Fri, 2 Apr 2021 19:26:50 +0100
Subject: [PATCH] Implemented ADSR envelopes.

---
 projects/examples/dev.time.usm | 14 +++++---------
 src/emulator.c                 | 24 ++++++++++++++++++++----
 2 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/projects/examples/dev.time.usm b/projects/examples/dev.time.usm
index b127ccb..cb92380 100644
--- a/projects/examples/dev.time.usm
+++ b/projects/examples/dev.time.usm
@@ -11,14 +11,13 @@
 ;needles { hx 2 hy 2 mx 2 my 2 sx 2 sy 2 }
 ;line { x0 2 y0 2 x 2 y 2 sx 2 sy 2 dx 2 dy 2 e1 2 e2 2 }
 ;color { byte 1 }
-;ding { volume 1 }
 
 ( devices )
 
 |0100 ;Console { pad 8 char 1 byte 1 short 2 }
 |0110 ;Screen { width 2 height 2 pad 4 x 2 y 2 color 1 }
 |0120 ;Sprite { pad 8 x 2 y 2 addr 2 color 1 }
-|0170 ;Audio { ch1asdr 2 ch2asdr 2 ch3asdr 2 ch4asdr 2 ch1pitch 1 ch1vol 1 ch2pitch 1 ch2vol 1 ch3pitch 1 ch3vol 1 ch4pitch 1 ch4vol 1 }
+|0170 ;Audio { ch1adsr 2 ch2adsr 2 ch3adsr 2 ch4adsr 2 ch1pitch 1 ch1vol 1 ch2pitch 1 ch2vol 1 ch3pitch 1 ch3vol 1 ch4pitch 1 ch4vol 1 }
 |0190 ;Time { year 2 month 1 day 1 hour 1 minute 1 second 1 dow 1 doy 2 isdst 1 get 1 }
 |01F0 ;System { pad 8 r 2 g 2 b 2 }
 
@@ -38,20 +37,17 @@ BRK
 
 @FRAME
 	
-	~ding.volume
-	DUP #00 EQU ^$keep JNZ
-	DUP #04 SUB =ding.volume
-	$keep
-	=Audio.ch1vol
-
 	#00 =Time.get
 
 	( only draw once per second )
 	~Time.second ~current.second NEQ #01 JNZ BRK
 	~Time.second =current.second
 
+	~Time.second #03 AND ^$no-sound JNZ
+	#ffff =Audio.ch1adsr
 	~Time.second #1d ADD =Audio.ch1pitch
-	#fc =ding.volume
+	#ff =Audio.ch1vol
+	$no-sound
 
 	( clear )
 	#0080 SCALEX #0080 SCALEY ~needles.sx ~needles.sy #00 ,draw-line JSR2
diff --git a/src/emulator.c b/src/emulator.c
index fb474a1..144441d 100644
--- a/src/emulator.c
+++ b/src/emulator.c
@@ -68,8 +68,8 @@ static Uint32 note_periods[12] = { /* middle C (C4) is note 60 */
 
 static struct audio_channel {
 	Uint32 period, count;
-	int value;
-	Sint16 volume;
+	Sint32 age, a, d, s, r;
+	Sint16 volume, value;
 } channels[4];
 
 static SDL_Window *gWindow;
@@ -247,12 +247,23 @@ audio_callback(void* userdata, Uint8* stream, int len) {
 		if (!c->volume) continue;
 		if (c->period < (1 << 20)) continue;
 		for (j = 0; j < len; ++j) {
+			c->age += 1;
 			c->count += 1 << 20;
 			while (c->count > c->period) {
-				c->value = !c->value;
+				int mul = c->value < 0 ? c->volume : -c->volume;
 				c->count -= c->period;
+				if (c->age < c->a)
+					c->value = mul * c->age / c->a;
+				else if (c->age < c->d)
+					c->value = mul * (2 * c->d - c->a - c->age) / 2 / (c->d - c->a);
+				else if (c->age < c->s)
+					c->value = mul / 2;
+				else if (c->age < c->r)
+					c->value = mul * (c->r - c->age) / 2 / (c->r - c->s);
+				else
+					c->volume = c->value = 0;
 			}
-			samples[j] += (c->value * 2 - 1) * c->volume;
+			samples[j] += c->value;
 		}
 	}
 	(void) userdata;
@@ -469,6 +480,11 @@ audio_poke(Uxn *u, Uint16 ptr, Uint8 b0, Uint8 b1)
 		c->period = note_periods[m[channel_addr + 8] % 12] >> (m[channel_addr + 8] / 12);
 		c->count %= c->period;
 		c->volume = m[channel_addr + 9] << 5;
+		c->age = 0;
+		c->a = ((m[channel_addr] >> 4) & 0xf) * (SAMPLE_FREQUENCY >> 4);
+		c->d = c->a + (m[channel_addr] & 0xf) * (SAMPLE_FREQUENCY >> 4);
+		c->s = c->d + ((m[channel_addr + 1] >> 4) & 0xf) * (SAMPLE_FREQUENCY >> 4);
+		c->r = c->s + (m[channel_addr + 1] & 0xf) * (SAMPLE_FREQUENCY >> 4);
 		SDL_UnlockAudioDevice(audio_id);
 	}
 	return b1;