diff options
| -rw-r--r-- | plugins/eg03-metro.lv2/metro.c | 83 |
1 files changed, 39 insertions, 44 deletions
diff --git a/plugins/eg03-metro.lv2/metro.c b/plugins/eg03-metro.lv2/metro.c index d2ac982..9048e21 100644 --- a/plugins/eg03-metro.lv2/metro.c +++ b/plugins/eg03-metro.lv2/metro.c @@ -63,7 +63,17 @@ typedef enum { STATE_OFF // Silent } State; -/** The plugin instance structure: */ +/** + This plugin must keep track of more state than previous examples to be able + to render audio. The basic idea is to generate a single cycle of a sine + wave which is conceptually played continuously. The 'tick' is generated by + enveloping the amplitude so there is a short attack/decay peak around a + tick, and silence the rest of the time. + + This example uses a simple AD envelope with fixed parameters. A more + sophisticated implementation might use a more advanced envelope and allow + the user to modify these parameters, the frequency of the wave, and so on. + */ typedef struct { LV2_URID_Map* map; // URID map feature MetroURIs uris; // Cache of mapped URIDs @@ -74,33 +84,20 @@ typedef struct { float* output; } ports; - /** The rate, bpm, and speed are the basic information sent by the host. */ - double rate; - float bpm; - float speed; + // Variables to keep track of the tempo information sent by the host + double rate; // Sample rate + float bpm; // Beats per minute (tempo) + float speed; // Transport speed (usually 0=stop, 1=play) - /** To keep track of when to play the next click, we need to keep track of - a few pieces of information: */ + uint32_t elapsed_len; // Frames since the start of the last click + uint32_t wave_offset; // Current play offset in the wave + State state; // Current play state - /** - The frames since the start of the last click is stored */ - uint32_t elapsed_len; - - /** - The current play offset in the wave */ - uint32_t wave_offset; - - /** - The current play state (attack, decay, or off) */ - State state; - - /** The wave to play is a simple sine wave generated at instantiation time - based on the sample rate. The length in frames is stored in order to - continuously play the wave in a cycle to avoid discontinuity clicks. */ + // One cycle of a sine wave float* wave; uint32_t wave_len; - /** The continuously playing sine wave is enveloped to provide an actual - metronome tick. This plugin uses a simple AD envelope with fixed - parameters. A more sophisticated implementation might use a more - advanced envelope and allow the user to modify these parameters. */ + // Envelope parameters uint32_t attack_len; uint32_t decay_len; } Metro; @@ -148,7 +145,7 @@ instantiate(const LV2_Descriptor* descriptor, return NULL; } - /** Scan host features for URID map */ + // Scan host features for URID map LV2_URID_Map* map = NULL; for (int i = 0; features[i]; ++i) { if (!strcmp(features[i]->URI, LV2_URID_URI "#map")) { @@ -161,7 +158,7 @@ instantiate(const LV2_Descriptor* descriptor, return NULL; } - /** Map URIS */ + // Map URIS MetroURIs* const uris = &self->uris; self->map = map; uris->atom_Blank = map->map(map->handle, LV2_ATOM__Blank); @@ -174,14 +171,14 @@ instantiate(const LV2_Descriptor* descriptor, uris->time_beatsPerMinute = map->map(map->handle, LV2_TIME__beatsPerMinute); uris->time_speed = map->map(map->handle, LV2_TIME__speed); - /** Initialise fields */ + // Initialise instance fields self->rate = rate; self->bpm = 120.0f; self->attack_len = attack_s * rate; self->decay_len = decay_s * rate; self->state = STATE_OFF; - /** Generate one cycle of a sine wave at the desired frequency. */ + // Generate one cycle of a sine wave at the desired frequency const double freq = 440.0 * 2.0; const double amp = 0.5; self->wave_len = rate / freq; @@ -213,7 +210,7 @@ play(Metro* self, uint32_t begin, uint32_t end) for (uint32_t i = begin; i < end; ++i) { switch (self->state) { case STATE_ATTACK: - /** Amplitude increases from 0..1 until attack_len */ + // Amplitude increases from 0..1 until attack_len output[i] = self->wave[self->wave_offset] * self->elapsed_len / (float)self->attack_len; if (self->elapsed_len >= self->attack_len) { @@ -221,7 +218,7 @@ play(Metro* self, uint32_t begin, uint32_t end) } break; case STATE_DECAY: - /** Amplitude decreases from 1..0 until attack_len + decay_len */ + // Amplitude decreases from 1..0 until attack_len + decay_len output[i] = 0.0f; output[i] = self->wave[self->wave_offset] * (1 - ((self->elapsed_len - self->attack_len) / @@ -234,10 +231,10 @@ play(Metro* self, uint32_t begin, uint32_t end) output[i] = 0.0f; } - /** We continuously play the sine wave regardless of envelope */ + // We continuously play the sine wave regardless of envelope self->wave_offset = (self->wave_offset + 1) % self->wave_len; - /** Update elapsed time and start attack if necessary */ + // Update elapsed time and start attack if necessary if (++self->elapsed_len == frames_per_beat) { self->state = STATE_ATTACK; self->elapsed_len = 0; @@ -250,7 +247,7 @@ update_position(Metro* self, const LV2_Atom_Object* obj) { const MetroURIs* uris = &self->uris; - /** Received new transport position/speed */ + // Received new transport position/speed LV2_Atom *beat = NULL, *bpm = NULL, *speed = NULL; lv2_atom_object_get(obj, uris->time_barBeat, &beat, @@ -258,18 +255,16 @@ update_position(Metro* self, const LV2_Atom_Object* obj) uris->time_speed, &speed, NULL); if (bpm && bpm->type == uris->atom_Float) { - /** Tempo changed, update BPM */ + // Tempo changed, update BPM self->bpm = ((LV2_Atom_Float*)bpm)->body; } if (speed && speed->type == uris->atom_Float) { - /** Speed changed, e.g. 0 (stop) to 1 (play) */ + // Speed changed, e.g. 0 (stop) to 1 (play) self->speed = ((LV2_Atom_Float*)speed)->body; } if (beat && beat->type == uris->atom_Float) { - /** Received a beat position, synchronise. - This is a simple hard sync that may cause clicks. - A real plugin would do something more graceful. - */ + // Received a beat position, synchronise + // This hard sync may cause clicks, a real plugin would be more graceful const float frames_per_beat = 60.0f / self->bpm * self->rate; const float bar_beats = ((LV2_Atom_Float*)beat)->body; const float beat_beats = bar_beats - floorf(bar_beats); @@ -290,35 +285,35 @@ run(LV2_Handle instance, uint32_t sample_count) Metro* self = (Metro*)instance; const MetroURIs* uris = &self->uris; - /** Empty notify output for now */ + // Empty notify output for now LV2_Atom_Sequence* notify = self->ports.notify; notify->atom.type = self->uris.atom_Sequence; notify->atom.size = sizeof(LV2_Atom_Sequence_Body); notify->body.unit = notify->body.pad = 0; - /** Work forwards in time frame by frame, handling events as we go */ + // Work forwards in time frame by frame, handling events as we go const LV2_Atom_Sequence* in = self->ports.control; uint32_t last_t = 0; for (LV2_Atom_Event* ev = lv2_atom_sequence_begin(&in->body); !lv2_atom_sequence_is_end(&in->body, in->atom.size, ev); ev = lv2_atom_sequence_next(ev)) { - /** Play the click for the time slice from last_t until now */ + // Play the click for the time slice from last_t until now play(self, last_t, ev->time.frames); if (ev->body.type == uris->atom_Blank) { const LV2_Atom_Object* obj = (LV2_Atom_Object*)&ev->body; if (obj->body.otype == uris->time_Position) { - /** Received position information, update */ + // Received position information, update update_position(self, obj); } } - /** Update time for next iteration and move to next event*/ + // Update time for next iteration and move to next event last_t = ev->time.frames; } - /** Play for remainder of cycle */ + // Play for remainder of cycle play(self, last_t, sample_count); } |