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LibDSP: Add Envelope abstraction

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For the upcoming synthesizer, having an abstracted ADSR envelope concept
is highly desirable. Additionally, Envelope is mostly constexpr and
therefore super fast :^)
This commit is contained in:
kleines Filmröllchen 2021-09-28 17:58:21 +02:00 • committed by Andreas Kling
parent a1093abe26
commit cc9aab7462
2 changed files with 103 additions and 0 deletions
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33
Userland/Libraries/LibDSP/Music.h
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@ -11,6 +11,7 @@
#include <AK/Variant.h>
#include <AK/Vector.h>
#include <LibAudio/Buffer.h>
#include <LibDSP/Envelope.h>
namespace LibDSP {
@ -26,6 +27,38 @@ struct RollNote {
u32 off_sample;
u8 pitch;
i8 velocity;
Envelope to_envelope(u32 time, u32 attack_samples, u32 decay_samples, u32 release_samples)
{
i64 time_since_end = static_cast<i64>(time) - static_cast<i64>(off_sample);
// We're before the end of this note.
if (time_since_end < 0) {
i64 time_since_start = static_cast<i64>(time) - static_cast<i64>(on_sample);
if (time_since_start < 0)
return {};
if (time_since_start < attack_samples) {
if (attack_samples == 0)
return Envelope::from_attack(0);
return Envelope::from_attack(static_cast<double>(time_since_start) / static_cast<double>(attack_samples));
}
if (time_since_start < attack_samples + decay_samples) {
if (decay_samples == 0)
return Envelope::from_decay(0);
return Envelope::from_decay(static_cast<double>(time_since_start - attack_samples) / static_cast<double>(decay_samples));
}
// This is a note-dependent value!
u32 sustain_samples = length() - attack_samples - decay_samples;
return Envelope::from_sustain(static_cast<double>(time_since_start - attack_samples - decay_samples) / static_cast<double>(sustain_samples));
}
// Overshot the release time
if (time_since_end > release_samples)
return {};
return Envelope::from_release(static_cast<double>(time_since_end) / static_cast<double>(release_samples));
}
constexpr bool is_playing(u32 time) { return on_sample <= time && time <= off_sample; }
};
enum class SignalType : u8 {