Function DemoUpdateTargetIPD

cube/cube.c:1038–1152

}

void DemoUpdateTargetIPD(struct demo *demo) {
    // Look at what happened to previous presents, and make appropriate
    // adjustments in timing:
    VkResult U_ASSERT_ONLY err;
    VkPastPresentationTimingGOOGLE *past = NULL;
    uint32_t count = 0;

    err = vkGetPastPresentationTimingGOOGLE(demo->device, demo->swapchain, &count, NULL);
    assert(!err);
    if (count) {
        past = (VkPastPresentationTimingGOOGLE *)malloc(sizeof(VkPastPresentationTimingGOOGLE) * count);
        assert(past);
        err = vkGetPastPresentationTimingGOOGLE(demo->device, demo->swapchain, &count, past);
        assert(!err);

        bool early = false;
        bool late = false;
        bool calibrate_next = false;
        for (uint32_t i = 0; i < count; i++) {
            if (!demo->syncd_with_actual_presents) {
                // This is the first time that we've received an
                // actualPresentTime for this swapchain.  In order to not
                // perceive these early frames as "late", we need to sync-up
                // our future desiredPresentTime's with the
                // actualPresentTime(s) that we're receiving now.
                calibrate_next = true;

                // So that we don't suspect any pending presents as late,
                // record them all as suspected-late presents:
                demo->last_late_id = demo->next_present_id - 1;
                demo->last_early_id = 0;
                demo->syncd_with_actual_presents = true;
                break;
            } else if (CanPresentEarlier(past[i].earliestPresentTime, past[i].actualPresentTime, past[i].presentMargin,
                                         demo->refresh_duration)) {
                // This image could have been presented earlier.  We don't want
                // to decrease the target_IPD until we've seen early presents
                // for at least two seconds.
                if (demo->last_early_id == past[i].presentID) {
                    // We've now seen two seconds worth of early presents.
                    // Flag it as such, and reset the counter:
                    early = true;
                    demo->last_early_id = 0;
                } else if (demo->last_early_id == 0) {
                    // This is the first early present we've seen.
                    // Calculate the presentID for two seconds from now.
                    uint64_t lastEarlyTime = past[i].actualPresentTime + (2 * BILLION);
                    uint32_t howManyPresents = (uint32_t)((lastEarlyTime - past[i].actualPresentTime) / demo->target_IPD);
                    demo->last_early_id = past[i].presentID + howManyPresents;
                } else {
                    // We are in the midst of a set of early images,
                    // and so we won't do anything.
                }
                late = false;
                demo->last_late_id = 0;
            } else if (ActualTimeLate(past[i].desiredPresentTime, past[i].actualPresentTime, demo->refresh_duration)) {
                // This image was presented after its desired time.  Since
                // there's a delay between calling vkQueuePresentKHR and when