 	static const float zThreshold = 0.05f;
 	static const float nThreshold = 0.98f;
 
+	aten::vec4 centerPrevPos;
+
 	for (int y = -1; y <= 1; y++) {
 		for (int x = -1; x <= 1; x++) {
 			int xx = clamp(ix + x, 0, width - 1);

				&prevPos,
				mtxs);

			// [0, 1]͈͓̔ɓĂ邩.
			bool isInsideX = (0.0 <= prevPos.x) && (prevPos.x <= 1.0);
			bool isInsideY = (0.0 <= prevPos.y) && (prevPos.y <= 1.0);

			width, height,
			&prevPos,
			mtxs);
#else
		aten::vec4 prevPos = centerPrevPos;
#endif

		// [0, 1]͈͓̔ɓĂ邩.
		bool isInsideX = (0.0 <= prevPos.x) && (prevPos.x <= 1.0);
