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#include <assert.h>
#include <math.h>
#include <pthread.h>
#include "sig.h"
typedef struct ops_sin_ctxt_t {
sig_sig_t *hz;
float theta;
unsigned last_ticks_ms;
pthread_mutex_t mutex;
} ops_sin_ctxt_t;
static size_t ops_sin_size(va_list ap)
{
return sizeof(ops_sin_ctxt_t);
}
static void ops_sin_init(void *context, va_list ap)
{
ops_sin_ctxt_t *ctxt = context;
assert(ctxt);
ctxt->hz = va_arg(ap, sig_sig_t *);
pthread_mutex_init(&ctxt->mutex, NULL);
}
static void ops_sin_destroy(void *context)
{
ops_sin_ctxt_t *ctxt = context;
assert(ctxt);
sig_free(ctxt->hz);
pthread_mutex_destroy(&ctxt->mutex);
}
static float output_sin(float rads)
{
return sinf(rads) * .5f + .5f;
}
static float output_sqr(float rads)
{
if (sinf(rads) < 0.f)
return 0.f;
return 1.f;
}
static float output_tri(float rads)
{
/* This approximation comes from:
* https://calculushowto.com/triangle-wave-function/
*/
return M_2_PI * asinf(fabsf(sinf(M_PI * rads)));
}
static float output(void *context, unsigned ticks_ms, float (*output_fn)(float rads))
{
ops_sin_ctxt_t *ctxt = context;
float rads_per_ms, theta, hz;
int delta_ticks;
assert(ctxt);
assert(ctxt->hz);
hz = sig_output(ctxt->hz, ticks_ms);
if (hz < .001f)
return 0.f;
pthread_mutex_lock(&ctxt->mutex);
/* TODO: ^^^ eliminate the need for this mutex!
*
* This became necessary when ops_sin became stateful with the
* addition of {last_ticks,theta}. The experimental signals
* module exercising this code performs parallel rendering of
* signals, some of which share sig contexts via sig_ref().
*
* Prior to {last_ticks,theta}, all the sigs stuff was
* stateless and this shared contexts w/parallel output
* situation Just Worked. So why can't we just keep things
* stateless like before, why have {last_ticks,theta}, what
* was wrong?
*
* The old ops_sin would simply multiply the incoming ticks_ms
* by rads_per_ms to calculate theta for the sin function.
* This approach produces potential discontinuities in the
* output when hz varies, by applying the hz to *all* of
* ticks_ms, and not just the delta since the last sample. By
* making theta stateful, and keeping track of the last
* sample's ticks_ms, the current hz only gets applied to the
* time difference, and applied relative to the last theta,
* resulting in better continuity in the face of a varying hz.
*
* I'm sure this all needs more work in general...
*/
{
int ticks, last_ticks;
unsigned base;
base = ticks_ms < ctxt->last_ticks_ms ? ticks_ms : ctxt->last_ticks_ms;
ticks = ticks_ms - base;
last_ticks = ctxt->last_ticks_ms - base;
delta_ticks = ticks - last_ticks;
}
theta = ctxt->theta;
rads_per_ms = (M_PI * 2.f) * hz * .001f;
theta += delta_ticks * rads_per_ms;
theta = fmodf(theta, M_PI * 2.f);
ctxt->theta = theta;
ctxt->last_ticks_ms = ticks_ms;
pthread_mutex_unlock(&ctxt->mutex);
return output_fn(theta);
}
static float ops_sin_output(void *context, unsigned ticks_ms)
{
return output(context, ticks_ms, output_sin);
}
static float ops_sqr_output(void *context, unsigned ticks_ms)
{
return output(context, ticks_ms, output_sqr);
}
static float ops_tri_output(void *context, unsigned ticks_ms)
{
return output(context, ticks_ms, output_tri);
}
sig_ops_t sig_ops_sin = {
.size = ops_sin_size,
.init = ops_sin_init,
.destroy = ops_sin_destroy,
.output = ops_sin_output,
};
sig_ops_t sig_ops_sqr = {
.size = ops_sin_size,
.init = ops_sin_init,
.destroy = ops_sin_destroy,
.output = ops_sqr_output,
};
sig_ops_t sig_ops_tri = {
.size = ops_sin_size,
.init = ops_sin_init,
.destroy = ops_sin_destroy,
.output = ops_tri_output,
};
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