private float moveUp(float riseAmount, CharacterCollider collider, Vector3f position) {
   Vector3f to =
       new Vector3f(position.x, position.y + riseAmount + VERTICAL_PENETRATION_LEEWAY, position.z);
   if (collider != null) {
     SweepCallback callback = collider.sweep(position, to, VERTICAL_PENETRATION_LEEWAY, -1f);
     if (callback.hasHit()) {
       float actualDist =
           Math.max(
               0,
               ((riseAmount + VERTICAL_PENETRATION_LEEWAY) * callback.getClosestHitFraction())
                   - VERTICAL_PENETRATION_LEEWAY);
       position.y += actualDist;
       return actualDist;
     }
   }
   position.y += riseAmount;
   return riseAmount;
 }
  /**
   * Checks of the player will step up to an object. In a single movement step the player can only
   * step up a single item.
   *
   * @param collider
   * @param position
   * @param direction
   * @param callback
   * @param slopeFactor
   * @param stepHeight
   * @return
   */
  private boolean checkStep(
      CharacterCollider collider,
      Vector3f position,
      Vector3f direction,
      SweepCallback callback,
      float slopeFactor,
      float stepHeight) {
    if (!stepped) {
      stepped = true;

      boolean moveUpStep =
          callback.checkForStep(direction, stepHeight, slopeFactor, CHECK_FORWARD_DIST);

      if (moveUpStep) {
        steppedUpDist = moveUp(stepHeight, collider, position);
        return true;
      }
    }
    return false;
  }
  private boolean moveHorizontal(
      Vector3f horizMove,
      CharacterCollider collider,
      Vector3f position,
      float slopeFactor,
      float stepHeight) {
    float remainingFraction = 1.0f;
    float dist = horizMove.length();
    if (dist < physics.getEpsilon()) {
      return false;
    }
    boolean horizontalHit = false;
    Vector3f normalizedDir = Vector3fUtil.safeNormalize(horizMove, new Vector3f());

    if (collider == null) {
      // ignore collision
      normalizedDir.scale(dist);
      position.add(normalizedDir);
      return false;
    }

    Vector3f targetPos = new Vector3f(normalizedDir);
    targetPos.scale(dist + HORIZONTAL_PENETRATION_LEEWAY);
    targetPos.add(position);
    int iteration = 0;
    Vector3f lastHitNormal = new Vector3f(0, 1, 0);
    while (remainingFraction >= 0.01f && iteration++ < 10) {
      SweepCallback callback =
          collider.sweep(position, targetPos, HORIZONTAL_PENETRATION, slopeFactor);

      /* Note: this isn't quite correct (after the first iteration the closestHitFraction is only for part of the moment)
      but probably close enough */
      float actualDist =
          Math.max(
              0,
              (dist + HORIZONTAL_PENETRATION_LEEWAY) * callback.getClosestHitFraction()
                  - HORIZONTAL_PENETRATION_LEEWAY);
      if (actualDist != 0) {
        remainingFraction -= actualDist / dist;
      }
      if (callback.hasHit()) {
        if (actualDist > physics.getEpsilon()) {
          Vector3f actualMove = new Vector3f(normalizedDir);
          actualMove.scale(actualDist);
          position.add(actualMove);
        }
        dist -= actualDist;
        Vector3f newDir = new Vector3f(normalizedDir);
        newDir.scale(dist);
        float slope = callback.getHitNormalWorld().dot(new Vector3f(0, 1, 0));

        // We step up if we're hitting a big slope, or if we're grazing
        // the ground, otherwise we move up a shallow slope.
        if (slope < slopeFactor || 1 - slope < physics.getEpsilon()) {
          boolean stepping =
              checkStep(collider, position, newDir, callback, slopeFactor, stepHeight);
          if (!stepping) {
            horizontalHit = true;
            Vector3f newHorizDir = new Vector3f(newDir.x, 0, newDir.z);
            Vector3f horizNormal =
                new Vector3f(callback.getHitNormalWorld().x, 0, callback.getHitNormalWorld().z);
            if (horizNormal.lengthSquared() > physics.getEpsilon()) {
              horizNormal.normalize();
              if (lastHitNormal.dot(horizNormal) > physics.getEpsilon()) {
                break;
              }
              lastHitNormal.set(horizNormal);
              extractResidualMovement(horizNormal, newHorizDir);
            }
            newDir.set(newHorizDir);
          }
        } else {
          // Hitting a shallow slope, move up it
          Vector3f newHorizDir = new Vector3f(newDir.x, 0, newDir.z);
          extractResidualMovement(callback.getHitNormalWorld(), newDir);
          Vector3f modHorizDir = new Vector3f(newDir);
          modHorizDir.y = 0;
          newDir.scale(newHorizDir.length() / modHorizDir.length());
        }
        float sqrDist = newDir.lengthSquared();
        if (sqrDist > physics.getEpsilon()) {
          newDir.normalize();
          if (newDir.dot(normalizedDir) <= 0.0f) {
            break;
          }
        } else {
          break;
        }
        dist = (float) Math.sqrt(sqrDist);
        normalizedDir.set(newDir);
        targetPos.set(normalizedDir);
        targetPos.scale(dist + HORIZONTAL_PENETRATION_LEEWAY);
        targetPos.add(position);
      } else {
        normalizedDir.scale(dist);
        position.add(normalizedDir);
        break;
      }
    }
    return horizontalHit;
  }
  private boolean moveDown(
      float dist, float slopeFactor, CharacterCollider collider, Vector3f position) {
    if (collider == null) {
      position.y += dist;
      return false;
    }

    float remainingDist = -dist;
    Vector3f targetPos = new Vector3f(position);
    targetPos.y -= remainingDist + VERTICAL_PENETRATION_LEEWAY;
    Vector3f normalizedDir = new Vector3f(0, -1, 0);
    boolean hit = false;
    int iteration = 0;
    while (remainingDist > physics.getEpsilon() && iteration++ < 10) {
      SweepCallback callback = collider.sweep(position, targetPos, VERTICAL_PENETRATION, -1.0f);
      float actualDist =
          Math.max(
              0,
              (remainingDist + VERTICAL_PENETRATION_LEEWAY) * callback.getClosestHitFraction()
                  - VERTICAL_PENETRATION_LEEWAY);
      Vector3f expectedMove = new Vector3f(targetPos);
      expectedMove.sub(position);
      if (expectedMove.lengthSquared() > physics.getEpsilon()) {
        expectedMove.normalize();
        expectedMove.scale(actualDist);
        position.add(expectedMove);
      }
      remainingDist -= actualDist;
      if (remainingDist < physics.getEpsilon()) {
        break;
      }
      if (callback.hasHit()) {
        float originalSlope = callback.getHitNormalWorld().dot(new Vector3f(0, 1, 0));
        if (originalSlope < slopeFactor) {
          float slope = callback.calculateAverageSlope(originalSlope, CHECK_FORWARD_DIST);
          if (slope < slopeFactor) {
            remainingDist -= actualDist;
            expectedMove.set(targetPos);
            expectedMove.sub(position);
            extractResidualMovement(callback.getHitNormalWorld(), expectedMove);
            float sqrDist = expectedMove.lengthSquared();
            if (sqrDist > physics.getEpsilon()) {
              expectedMove.normalize();
              if (expectedMove.dot(normalizedDir) <= 0.0f) {
                hit = true;
                break;
              }
            } else {
              hit = true;
              break;
            }
            if (expectedMove.y > -physics.getEpsilon()) {
              hit = true;
              break;
            }
            normalizedDir.set(expectedMove);
            expectedMove.scale(-remainingDist / expectedMove.y + HORIZONTAL_PENETRATION_LEEWAY);
            targetPos.set(position);
            targetPos.add(expectedMove);
          } else {
            hit = true;
            break;
          }
        } else {
          hit = true;
          break;
        }
      } else {
        break;
      }
    }
    if (iteration >= 10) {
      hit = true;
    }
    return hit;
  }