struct ADSRTableEntry
{
s32 ticks;
s32 step;
};
enum : u32
{
NUM_ADSR_TABLE_ENTRIES = 128,
NUM_ADSR_DIRECTIONS = 2 // increasing, decreasing
};
using ADSRTableEntries = std::array<std::array<ADSRTableEntry, NUM_ADSR_TABLE_ENTRIES>, NUM_ADSR_DIRECTIONS>;
static constexpr ADSRTableEntries ComputeADSRTableEntries()
{
ADSRTableEntries entries = {};
for (u32 decreasing = 0; decreasing < 2; decreasing++)
{
for (u32 rate = 0; rate < NUM_ADSR_TABLE_ENTRIES; rate++)
{
if (rate < 48)
{
entries[decreasing][rate].ticks = 1;
if (decreasing != 0)
entries[decreasing][rate].step =
static_cast<s32>(static_cast<u32>(-8 + static_cast<s32>(rate & 3)) << (11 - (rate >> 2)));
else
entries[decreasing][rate].step = (7 - static_cast<s32>(rate & 3)) << (11 - (rate >> 2));
}
else
{
entries[decreasing][rate].ticks = 1 << (static_cast<s32>(rate >> 2) - 11);
if (decreasing != 0)
entries[decreasing][rate].step = (-8 + static_cast<s32>(rate & 3));
else
entries[decreasing][rate].step = (7 - static_cast<s32>(rate & 3));
}
}
}
return entries;
}
static constexpr ADSRTableEntries s_adsr_table = ComputeADSRTableEntries();
void SPU::VolumeEnvelope::Reset(u8 rate_, bool decreasing_, bool exponential_)
{
rate = rate_;
decreasing = decreasing_;
exponential = exponential_;
const ADSRTableEntry& table_entry = s_adsr_table[BoolToUInt8(decreasing)][rate];
counter = table_entry.ticks;
}
s16 SPU::VolumeEnvelope::Tick(s16 current_level)
{
counter--;
if (counter > 0)
return current_level;
const ADSRTableEntry& table_entry = s_adsr_table[BoolToUInt8(decreasing)][rate];
s32 this_step = table_entry.step;
counter = table_entry.ticks;
if (exponential)
{
if (decreasing)
{
this_step = (this_step * current_level) >> 15;
}
else
{
if (current_level >= 0x6000)
{
if (rate < 40)
{
this_step >>= 2;
}
else if (rate >= 44)
{
counter >>= 2;
}
else
{
this_step >>= 1;
counter >>= 1;
}
}
}
}
return static_cast<s16>(
std::clamp<s32>(static_cast<s32>(current_level) + this_step, ENVELOPE_MIN_VOLUME, ENVELOPE_MAX_VOLUME));
}
void SPU::Voice::UpdateADSREnvelope()
{
switch (adsr_phase)
{
case ADSRPhase::Off:
adsr_target = 0;
adsr_envelope.Reset(0, false, false);
return;
case ADSRPhase::Attack:
adsr_target = 32767; // 0 -> max
adsr_envelope.Reset(regs.adsr.attack_rate, false, regs.adsr.attack_exponential);
break;
case ADSRPhase::Decay:
adsr_target = static_cast<s16>(std::min<s32>((u32(regs.adsr.sustain_level.GetValue()) + 1) * 0x800,
ENVELOPE_MAX_VOLUME)); // max -> sustain level
adsr_envelope.Reset(regs.adsr.decay_rate_shr2 << 2, true, true);
break;
case ADSRPhase::Sustain:
adsr_target = 0;
adsr_envelope.Reset(regs.adsr.sustain_rate, regs.adsr.sustain_direction_decrease, regs.adsr.sustain_exponential);
break;
case ADSRPhase::Release:
adsr_target = 0;
adsr_envelope.Reset(regs.adsr.release_rate_shr2 << 2, true, regs.adsr.release_exponential);
break;
default:
break;
}
}
void SPU::Voice::TickADSR()
{
regs.adsr_volume = adsr_envelope.Tick(regs.adsr_volume);
if (adsr_phase != ADSRPhase::Sustain)
{
const bool reached_target =
adsr_envelope.decreasing ? (regs.adsr_volume <= adsr_target) : (regs.adsr_volume >= adsr_target);
if (reached_target)
{
adsr_phase = GetNextADSRPhase(adsr_phase);
UpdateADSREnvelope();
}
}
}