66 lines
1.8 KiB
C
66 lines
1.8 KiB
C
#include <stdint.h>
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#include <string.h>
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#include "config.h"
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#include "interp.c"
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struct stfu_envelope stfu_pump_envelope(struct stfu_envelope envelope);
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float stfu_get_envelope_duration(struct stfu_envelope envelope);
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struct stfu_envelope stfu_trigger_envelope(struct stfu_envelope envelope);
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/* Basic linear envelope generator with up to 16 points max.
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* First virtual point is always max volume (1.0f).
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*
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* todo: Sustain?
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*/
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struct stfu_envelope {
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/* Initial volume is assumed from previous point */
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struct stfu_envelope_point {
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float dur, vol;
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} pnts[16];
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uint8_t n_pnts;
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float p, v;
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} stfu_init_envelope(struct stfu_envelope_point *points, uint8_t n_points) {
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struct stfu_envelope r = {0};
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memcpy(&r.pnts, points, sizeof(struct stfu_envelope_point) * n_points);
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r.n_pnts = n_points;
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r = stfu_trigger_envelope(r);
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return r;
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}
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struct stfu_envelope stfu_pump_envelope(struct stfu_envelope envelope) {
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envelope.p += 1.0f / STFU_AUDIO_FRAME_RATE;
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float d = stfu_get_envelope_duration(envelope);
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if (envelope.p >= d)
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/* Needs retriggering after that point */
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return envelope;
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float p = 0.0f;
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for (uint8_t i = 0;; ++i) {
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float ends = p + envelope.pnts[i].dur;
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if (envelope.p < ends) {
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float pv = i == 0 ? 1.0f : envelope.pnts[i - 1].vol;
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envelope.v = stfu_linear_interpolate(p, pv, ends, envelope.pnts[i].vol,
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envelope.p);
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break;
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}
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p += envelope.pnts[i].dur;
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}
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return envelope;
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}
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float stfu_get_envelope_duration(struct stfu_envelope envelope) {
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float r = 0.0f;
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for (uint8_t i = 0; i < envelope.n_pnts; ++i) {
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r += envelope.pnts[i].dur;
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}
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return r;
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}
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struct stfu_envelope stfu_trigger_envelope(struct stfu_envelope envelope) {
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envelope.p = 0.0f;
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envelope.v = 1.0f;
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return envelope;
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}
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