ref: 2e86b938c226edc0d8bd6c3855baf3bec02b5179
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);