From d01eb6cc45ed26fd296fefd8eeea68062dc0f6df Mon Sep 17 00:00:00 2001
From: Andrew Alderwick <andrew@alderwick.co.uk>
Date: Sun, 25 Apr 2021 21:52:39 +0100
Subject: [PATCH] Added currently playing volume readout

---
 projects/demos/musictracker.usm | 11 +++++++++++
 src/apu.c                       | 17 +++++++++++++++++
 src/apu.h                       |  4 +++-
 src/emulator.c                  |  5 ++++-
 4 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/projects/demos/musictracker.usm b/projects/demos/musictracker.usm
index 3b958c2..3ded08e 100644
--- a/projects/demos/musictracker.usm
+++ b/projects/demos/musictracker.usm
@@ -72,6 +72,7 @@ BRK
 @on-screen ( -> )
 	
 	;move-head JSR2
+	;draw-vu JSR2
 	.head/pos PEK #08 MOD #00 NEQ ,&skip JNZ
 		;bang JSR2
 	&skip
@@ -421,6 +422,16 @@ RTN
 
 RTN
 
+@draw-vu ( -- )
+	.ctlframe/x1 PEK2 #0088 ADD2 .ctlframe/y1 PEK2 #0010 ADD2
+		.Audio/volume DEI DUP STH #04 SFT
+	;draw-knob/force JSR2
+	.ctlframe/x1 PEK2 #0098 ADD2 .ctlframe/y1 PEK2 #0010 ADD2
+		STHr #0f AND
+	;draw-knob/force JSR2
+
+RTN
+
 @draw-channels
 	
 	.chnframe/x1 PEK2 .chnframe/y1 PEK2 .chnframe/x2 PEK2 .chnframe/y2 PEK2 #01 ;line-rect JSR2
diff --git a/src/apu.c b/src/apu.c
index c53d616..cceabb6 100644
--- a/src/apu.c
+++ b/src/apu.c
@@ -79,3 +79,20 @@ apu_start(Apu *c, Uint16 adsr, Uint8 pitch)
 	else /* sample repeat mode */
 		c->period = NOTE_PERIOD;
 }
+
+Uint8
+apu_get_vu(Apu *c, Apu *end)
+{
+	size_t i;
+	Sint32 sum[2] = {0, 0};
+	for(; c < end; ++c) {
+		if(!c->advance) continue;
+		sum[0] += envelope(c, c->age) * c->volume_l;
+		sum[1] += envelope(c, c->age) * c->volume_r;
+	}
+	for(i = 0; i < 2; ++i) {
+		sum[i] /= 0x800;
+		if(sum[i] > 0xf) sum[i] = 0xf;
+	}
+	return (sum[0] << 4) | sum[1];
+}
diff --git a/src/apu.h b/src/apu.h
index 383901b..9a4757b 100644
--- a/src/apu.h
+++ b/src/apu.h
@@ -20,8 +20,10 @@ typedef struct {
 	Uint8 *addr;
 	Uint32 count, advance, period, age, a, d, s, r;
 	Uint16 i, len;
-	Uint8 volume_l, volume_r, pitch, repeat;
+	Sint8 volume_l, volume_r;
+	Uint8 pitch, repeat;
 } Apu;
 
 void apu_render(Apu *c, Sint16 *sample, Sint16 *end);
 void apu_start(Apu *c, Uint16 adsr, Uint8 pitch);
+Uint8 apu_get_vu(Apu *c, Apu *end);
diff --git a/src/emulator.c b/src/emulator.c
index 7603280..dcda3c1 100644
--- a/src/emulator.c
+++ b/src/emulator.c
@@ -248,7 +248,10 @@ static void
 audio_talk(Device *d, Uint8 b0, Uint8 w)
 {
 	Apu *c;
-	if(!w) return;
+	if(!w) {
+		if(b0 == 0xe) d->dat[0xe] = apu_get_vu(apu, apu + POLYPHONY);
+		return;
+	}
 	c = &apu[d->dat[0x7] % POLYPHONY];
 	SDL_LockAudioDevice(audio_id);
 	if(b0 == 0x1) c->period -= (Sint16)mempeek16(d->dat, 0x0);