hexagram/src/anim.c

#include <stdlib.h>
#include <string.h>

#include <hexagram/anim.h>

void hexagram_anim_init(hexagram_anim *anim) {
    anim->current = 0;

    gettimeofday(&anim->start, NULL);
}

static inline double tv_seconds(struct timeval *tv) {
    return (double)tv->tv_sec + (double)tv->tv_usec / 1000000.0;
}

static inline double stop_offset(hexagram_anim *anim, size_t index) {
    double offset = 0.0;
    size_t i;

    for (i=0; i<index; i++) {
        offset += anim->stops[i].duration;
    }

    return offset;
}

static inline size_t stop_index(hexagram_anim *anim, double offset) {
    return 0;
}

int hexagram_anim_step(hexagram_anim *anim, cairo_t *bg, cairo_t *fg) {
    struct timeval tv;
    double offset = 0.0, interval, progress;
    size_t i;

    gettimeofday(&anim->now, NULL);

    timersub(&anim->now, &anim->start, &tv);

    /* Determine the interval between initialisation and now */
    interval = tv_seconds(&tv);

    /* Determine current animation stop index and time offset */
    for (i=0; i<anim->count; i++) {
        double duration = anim->stops[i].duration;

        if (duration <= 0) {
            continue;
        }

        if (interval < offset + duration) {
            break;
        }

        offset += duration;
    }

    if (i == anim->count) {
        /* We are apparently at the end. */
        return 0;
    }

    /* Determine current progress through current stop */
    progress = (interval - offset) / anim->stops[i].duration;

    return 1;
}