ref: f6d97317c22b5d2e703844728a3f41b6bc3a74a4
dir: /h/line.h/
typedef struct {
SPFLOAT a, dur, b;
SPFLOAT val, incr;
uint32_t sdur, stime;
int init;
} sp_line;
int sp_line_create(sp_line **p);
int sp_line_destroy(sp_line **p);
int sp_line_init(sp_data *sp, sp_line *p);
int sp_line_compute(sp_data *sp, sp_line *p, SPFLOAT *in, SPFLOAT *out);