Function ClampSmoothScroll

src/viewport.cpp:1960–1981

* Clamp the smooth scroll to a maxmimum speed and distance based on time elapsed. * * Every 30ms, we move 1/4th of the distance, to give a smooth movement experience. * But we never go over the max_scroll speed. * * @param delta_ms Time elapsed since last update. * @param delta_hi The distance to move in highest dimension (can't be zero). * @param delta_lo The distance to move in lowest dim

 * @param[out] delta_lo_clamped The clamped distance to move in lowest dimension.
 */
static void ClampSmoothScroll(uint32_t delta_ms, int64_t delta_hi, int64_t delta_lo, int &delta_hi_clamped, int &delta_lo_clamped)
{
	/** A tile is 64 pixels in width at 1x zoom; viewport coordinates are in 4x zoom. */
	constexpr int PIXELS_PER_TILE = TILE_PIXELS * 2 * ZOOM_BASE;

	assert(delta_hi != 0);

	/* Move at most 75% of the distance every 30ms, for a smooth experience */
	int64_t delta_left = delta_hi * std::pow(0.75, delta_ms / 30.0);
	/* Move never more than 16 tiles per 30ms. */
	int max_scroll = Map::ScaleBySize1D(16 * PIXELS_PER_TILE * delta_ms / 30);

	/* We never go over the max_scroll speed. */
	delta_hi_clamped = Clamp(delta_hi - delta_left, -max_scroll, max_scroll);
	/* The lower delta is in ratio of the higher delta, so we keep going straight at the destination. */
	delta_lo_clamped = delta_lo * delta_hi_clamped / delta_hi;

	/* Ensure we always move (delta_hi can't be zero). */
	if (delta_hi_clamped == 0) {
		delta_hi_clamped = delta_hi > 0 ? 1 : -1;
	}
}

/**
 * Update the viewport position being displayed.