Fullscreen Video Gesture Overlay

Fullscreen video gesture overlay

A fullscreen video screen is three siblings in one box, in this order:

// adapted
Box {
    VideoSurface(Modifier.fillMaxSize(), isInPipMode = isInPipMode)   // always on
    if (!isInPipMode) {
        Row(Modifier.fillMaxSize()) {          // gesture layer: two seek zones
            SeekZone(Modifier.weight(1f), seekBack() })
            SeekZone(Modifier.weight(1f), seekForward() })
        }
        Crossfade(chromeVisible) { if (it) Chrome(...) }               // chrome, on top
    }
}

Two equal-weight zones fill the whole surface — no dead strip down the middle, so every tap lands in a zone and the toggle is never lost. The chrome composes nothing while hidden, so hit testing falls straight through to the zones; while shown, its buttons are on top and take their own taps.

Traps

Every zone needs the single-tap toggle, not just the double-tap. The tap detector is written once per zone, so the toggle is duplicated by construction, and a zone that grew an onDoubleTap and never got an onTap swallows single taps on its half of the screen — the controls appear when you tap the left of the video and do nothing on the right. Same two-entry-point shape as guard-on-every-trigger-path.

A tap detector gives no press feedback — wire the ripple by hand. clickable would supply one, but it also claims the pointer and offers no double-tap, so the zone drives the indication itself:

// adapted
Box(
    Modifier
        .fillMaxHeight()
        .weight(1f)
        .clip(RoundedCornerShape(topEndPercent = 10, bottomEndPercent = 10))
        .indication(interactionSource = interactionSource, indication = ripple())
        .pointerInput(Unit) {
            detectTapGestures(
                chromeVisible = !chromeVisible },
                offset ->
                    scope.launch {
                        val press = PressInteraction.Press(offset)
                        interactionSource.emit(press)
                        onSeek()
                        interactionSource.emit(PressInteraction.Release(press))
                    }
                },
            )
        },
)

Three things that are easy to get wrong here: the release must carry the same press instance that was emitted, or the indication never clears and the zone stays lit; emit suspends, so it needs a scope, not the gesture callback's own frame; and the ripple is bounded by the modifier chain's clip, so clipping the zone's inner corners is what makes it read as a rounded half of the screen instead of a rectangle meeting its twin at a hard seam.

The auto-hide timer is a LaunchedEffect whose keys are the postponement list.

// adapted
LaunchedEffect(key1 = chromeVisible, key2 = isSliding) {
    if (chromeVisible && !isSliding) {
        delay(AUTO_HIDE_MS)
        chromeVisible = false
    }
}

Keying on the visibility flag is what restarts the countdown on each toggle — a LaunchedEffect(Unit) looping over a delay keeps its own clock and hides the chrome moments after the user opened it. Keying on the scrub flag is what pauses it: the effect is cancelled when the drag begins and relaunched when it ends, so the user gets a full window afterwards rather than the remainder of one. Every future interaction that must hold the chrome open is another key, never another branch inside the body — a branch runs once, on the keys you already had.

The scrub value must stop following the player while the thumb is down, same flag again:

// adapted
LaunchedEffect(key1 = timelineState, key2 = isSliding) {
    if (!isSliding) sliderValue = fractionOf(timelineState)
}

Without the guard, each incoming position update overwrites the value the drag is producing and the thumb snaps back under the finger. Set the flag in onValueChange and clear it in onValueChangeFinished, dispatching the seek there — one seek per gesture, not one per frame.

Both the gesture and the button must dispatch the same seek command, and it should be the engine's own relative seek. Sending "current position ± N" from the UI puts a second copy of the increment in the screen; the engine's seek-back / seek-forward command keeps one. The label you draw next to the arrows is then a claim about the engine's configured increment — change the increment without the label and the UI lies in the one place the user is watching.

Gate the gesture layer on picture-in-picture (PiP) too, not just the chrome. In a thumbnail-sized floating window the transport controls belong to the system, and a stray double-tap seek there is worse than no gesture at all. The flag is platform-observed state — a subscription to the mode-change callback where the concept exists, a constant false where it does not — so it must be read as state the composition recomposes on, never sampled once into a plain variable. The video surface itself stays outside the guard, or the window goes black as it shrinks.

A dispose block that restores a value twice restores the second one. Entering fullscreen typically locks orientation, hides the system bars and holds the screen awake; leaving must undo all three. Capture the original orientation before forcing landscape — after, you save your own value and "restore" is a no-op. Then check it is written once: computing the saved orientation into a when and following it with an unconditional "unspecified" makes the whole when dead, and the bug hides because simply unlocking the orientation also looks plausible.

Verifying it

1. grep -rn --include="*.kt" "onDoubleTap" . — expect one per seek zone. Any other hit must live somewhere that cannot sit over the video (a window title bar, for instance); one handler on a screen that has two zones is the bug.
2. grep -rn --include="*.kt" -B 8 "delay(" . | grep "LaunchedEffect" — one per timer, each a LaunchedEffect(...) header with keys inline. Keep the window wide — a hide-timer's delay sits in an else branch below its header, so -B 3 drops exactly those (9 of 11 here; the misses include a volume popup whose keys are its postponement list). A timer whose chrome holds a scrub control and whose keys are only the visibility flag is this bug.
3. grep -rn --include="*.kt" "PressInteraction.Press(" . — each hit must be bound to a local and released with that same value a few lines below.
4. grep -rn --include="*.kt" "rememberIsInPipMode\|isInPictureInPictureMode" . — one declaration, one implementation per platform, one read per screen that draws chrome over video.
5. By hand, in this order: tap the right half (controls appear); double-tap each half (seek, plus a ripple centred on the finger that fades); start a scrub and hold still past the auto-hide window (controls stay), then release (they stay a full window longer); shrink to a floating window (no chrome, no gesture) and restore it. Leave the screen last and confirm the device orientation and system bars are as they were before you entered.