Function CalcRaildirsDrawstyle

src/viewport.cpp:3070–3282

while dragging */

/** while dragging */
static void CalcRaildirsDrawstyle(int x, int y, int method)
{
	HighLightStyle b;

	int dx = _thd.selstart.x - (_thd.selend.x & ~TILE_UNIT_MASK);
	int dy = _thd.selstart.y - (_thd.selend.y & ~TILE_UNIT_MASK);
	uint w = abs(dx) + TILE_SIZE;
	uint h = abs(dy) + TILE_SIZE;

	if (method & ~(VPM_RAILDIRS | VPM_SIGNALDIRS)) {
		/* We 'force' a selection direction; first four rail buttons. */
		method &= ~(VPM_RAILDIRS | VPM_SIGNALDIRS);
		int raw_dx = _thd.selstart.x - _thd.selend.x;
		int raw_dy = _thd.selstart.y - _thd.selend.y;
		switch (method) {
			case VPM_FIX_X:
				b = HT_LINE | HT_DIR_Y;
				x = _thd.selstart.x;
				break;

			case VPM_FIX_Y:
				b = HT_LINE | HT_DIR_X;
				y = _thd.selstart.y;
				break;

			case VPM_FIX_HORIZONTAL:
				if (dx == -dy) {
					/* We are on a straight horizontal line. Determine the 'rail'
					 * to build based the sub tile location. */
					b = (x & TILE_UNIT_MASK) + (y & TILE_UNIT_MASK) >= TILE_SIZE ? HT_LINE | HT_DIR_HL : HT_LINE | HT_DIR_HU;
				} else {
					/* We are not on a straight line. Determine the rail to build
					 * based on whether we are above or below it. */
					b = dx + dy >= (int)TILE_SIZE ? HT_LINE | HT_DIR_HU : HT_LINE | HT_DIR_HL;

					/* Calculate where a horizontal line through the start point and
					 * a vertical line from the selected end point intersect and
					 * use that point as the end point. */
					int offset = (raw_dx - raw_dy) / 2;
					x = _thd.selstart.x - (offset & ~TILE_UNIT_MASK);
					y = _thd.selstart.y + (offset & ~TILE_UNIT_MASK);

					/* 'Build' the last half rail tile if needed */
					if ((offset & TILE_UNIT_MASK) > (TILE_SIZE / 2)) {
						if (dx + dy >= (int)TILE_SIZE) {
							x -= (int)TILE_SIZE;
						} else {
							y += (int)TILE_SIZE;
						}
					}

					/* Make sure we do not overflow the map! */
					CheckUnderflow(x, y, 1);
					CheckUnderflow(y, x, 1);
					CheckOverflow(x, y, (Map::MaxX() - 1) * TILE_SIZE, 1);
					CheckOverflow(y, x, (Map::MaxY() - 1) * TILE_SIZE, 1);
					assert(x >= 0 && y >= 0 && x <= (int)(Map::MaxX() * TILE_SIZE) && y <= (int)(Map::MaxY() * TILE_SIZE));
				}