class AnimationContext2D {
    U64 signature;
    I64 duration;      // in jiffies
    I64 index;         // current frame
    I64 length;        // length in frames
    I64 timer;         // timer + cnts.jiffies = current ticks
    Context2D** frame; // Context2D*, ...
};

AnimationContext2D* @animation2d_new_from_frames(Context2D** frames, I64 length,
    I64 duration = 250)
{
    if (!frames || !length)
        return NULL;
    AnimationContext2D* actx = CAlloc(sizeof(AnimationContext2D));
    actx->signature = 'animated';
    actx->frame = frames;
    actx->length = length;
    actx->duration = duration;
    return actx;
}

Context2D* @animation2d_frame(AnimationContext2D* actx)
{
    I64 ticks = cnts.jiffies;
    if (!actx)
        return NULL;
    if (!actx->length)
        return NULL;
    if (actx->index > actx->length - 1)
        actx->index = 0;
    if (!actx->index && !actx->timer)
        actx->timer = ticks;
    while (ticks >= actx->timer + actx->duration) {
        actx->timer += actx->duration;
        actx->index++;
        if (actx->index > actx->length - 1)
            actx->index = 0;
    }
    return actx->frame[actx->index];
}

Bool @animation2d_is_animation(AnimationContext2D* actx)
{
    return T(actx->signature == 'animated', TRUE, FALSE);
}

U0 @animation2d_reset(AnimationContext2D* actx) { actx->index = 0; }

class @animation2d
{
    Context2D* (*Frame)(AnimationContext2D* actx);
    U0 (*Reset)(AnimationContext2D* actx);
    Bool (*IsAnimation)(AnimationContext2D* actx);
    AnimationContext2D* (*NewFromFrames)(Context2D** frames, I64 length,
        I64 duration = 250);
};

@animation2d Animation2D;
Animation2D.IsAnimation = &@animation2d_is_animation;
Animation2D.NewFromFrames = &@animation2d_new_from_frames;
Animation2D.Frame = &@animation2d_frame;
Animation2D.Reset = &@animation2d_reset;

"animation2d ";