Overcoming Unintended Rotation: A Guide For Game Developers

Understanding Unintended Rotation in Games

Unintended rotation refers to when game objects rotate or spin incorrectly, in ways the developer did not intend. This causes objects to behave erratically, clipping through surfaces, stretching oddly, or otherwise breaking immersion.

Defining the problem more specifically, unintended rotation happens when game entities – such as the player character, NPCs, enemies, props, particles, or even the camera itself – turn, pitch, yaw, roll, or spin on their axes at times or in ways they should not.

Common Causes

Unintended rotation bugs most frequently stem from issues with:

Physics engines: Incorrect mass, friction, velocity, torque, or other physics parameters can make objects unstable and prone to spinning out of control.
Animation state graphs: Transitions between animation states failing to properly reset rotations can accumulate errors over time.
Game code: Bugs in transform update logic, rotation functions, coroutine routines, and other scripts can unintentionally modify rotation.

Impact on Gameplay and User Experience

When players experience unintended rotation, the immersion and coherence of the game world suffers. Strange spinning, clipping, and erratic motions look glitchy and unprofessional while playing.

At best, unintended rotation merely causesvisual artifacts that harm suspension of disbelief. But at worst, they can break gameplay by stopping progress, trapping the player, or allowing sequence breaks.

Overall, unintended rotation harms users’ enjoyment, sense of polish, and can even trigger headaches or motion sickness.

Fixing Rotation Issues

Diagnosing unintended rotation takes careful retracing of steps to identify the root cause. A structured investigation helps find whether the issue lies in physics, animation, game code, or some combination.

Checking Physics Settings

Inspect all rigidbodies, colliders, joints, wheel colliders, forces, and other simulation elements that might influence object rotation. Pay particular attention to mass distribution, drag settings, collision responses, constraints, and torque values.

For example, an uneven center of mass could cause a lopsided spin. Try tweaking the object’s moments of inertia first to stabilize its physics.

Reviewing Animation Graphes

Check animation controller state graphs for problems with transitions failing to reset rotations, thus accumulating unwanted spins over time.

Print out the runtime animation state history while rotating the game object. Determine exactly which transitions and parameter settings contribute to accumulating the unintended rotation.

Then, revise transition conditions and add reset nodes before transitions to prevent rotation accumulating during state changes.

Debugging Game Code

Use debug statements, breakpoints, and step-through debugging to isolate code that unintentionally modifies rotations each frame.

Scrutinize update loops, coroutine routines, callbacks, events, and any custom rotation functions. Pinpoint the exact lines contributing to unintended spins.

Additionally, temporarily freeze other potential factors like physics and animations to confirm code is directly at fault.

Preventing Future Rotation Problems

Once specific issues get addressed, take further steps to guard against unintended rotation recurrin

Conservative Physics Tuning

Tweak mass, drag, angular drag, constraints, and torque limits conservatively to ensure physics stability.

Bias simulations towards underrotation rather than risking overrotation. Freeze axes of rotation if spinning persists.

Clean State Graphs

Reconstruct messy state graphs to use well-defined states, strict transition conditions, and rotation resets to prevent accumulation.

Enforce discipline in graph structure for robustness against state machine problems down the line.

Comment Code Thoroughly

Document scripts clearly on each frame’s intended rotations and changes over time.

Call out potentially problematic areas needing future inspection if anomalies occur.

Add Validation Checks

Detect unintended rotations at runtime with debug assertions, logs, warnings, exceptions, and utilizing error callbacks.

For example, throw errors if rotation speed, acceleration, or momentum exceed normal thresholds.

Example Rotation Constraints

Here is example code for preventing unintended rotation on game objects dynamically at runtime:

Freeze Rotation Axes

  void FreezeXRotation() {
    transform.eulerAngles = new Vector3(0, transform.eulerAngles.y, transform.eulerAngles.z); 
  }

Call above function from animation events, triggers, collision callbacks, etc. Works for Y and Z axes too.

Reset Rotation on Trigger

  void OnCollisionEnter() {
    if (collision.transform.name == "Rotater") {
      transform.rotation = Quaternion.identity;
    }
  }

Resets rotation to zero when colliding with “Rotater” object. Useful for keeping objects upright.

Detect Erratic Rotation via Raycast

  bool CheckForRotationAnomaly() {
    RaycastHit hit;
    if (Physics.Raycast(transform.position, Vector3.down, out hit)) {
      if (Vector3.Angle(transform.up, hit.normal) > maxAngle) {
        return true; 
      } else {
        return false;
      }
    }
  }

Raycast downwards, compare surface normal to transform’s up axis. If angle difference exceeds threshold, rotation is erratic.

Testing Thoroughly for Rotation Issues

Robust testing at all stages is key for noticing and resolving unintended rotation:

Early Playtesting

Test gameplay frequently from the very start, not just before release. The earlier issues get noticed, the easier they are to fix.

Automated Testing

Write unit tests that automatically run game scenes and scan logs for warnings related to odd rotations exceeding set limits.

Player Feedback

Actively gather user feedback on control and simulation. Follow up on complaints about physics glitches or motion sickness for clues.

Fixing unintended rotation ultimately relies both on solid technical practices, and gathering player perspectives to understand the real experience.