# OpenGL Numerous Issues w/ FPS Camera

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Hello,

I've written a basic FPS-camera class in C# based on GLFrame from the OpenGL Superbible. I'm having a number of issues with it, among them including:
• Yaw (right-left) rotation wraps after 90 degrees in either direction.
• Movement occurs in the wrong directions after having rotated the camera. (For instance, the camera orbits the single sphere when I try to strafe left or right)
• Rotation occurs in the wrong directions after having rotated the camera. (For instance, trying to rotate by pitch (up-down) ends up rotating by roll.
Here's the code to my camera class and also a relevant function from my MathUtilities class:

 using System; using System.Collections.Generic; using System.Linq; using System.Text; using OpenTK; using OpenTK.Input; using SurviveEngine.MathEngine; using SurviveEngine.System; // note: based on GLFrame.h from the GLTools library by Richard S. Wright (OpenGL Superbible author) namespace SurviveEngine.Graphics { public class SurviveFPSCamera { public SurviveFPSCamera() { Position = new Vector3(0, 0, 0); Up = new Vector3(0, 1, 0); Forward = new Vector3(0, 0, 1); keys = KeyboardInput.Instance; LinearSpeed = 1f; AngularSpeed = 1f; } private KeyboardInput keys; public Matrix4 Perspective { get; set; // protected set } public Matrix4 ModelView { get; set; // protected set } public Matrix4 MVP { get; protected set; } public double Speed { get; set; } public Vector3 Forward { get; set; } public Vector3 Up { get; set; } public Vector3 Position { get; set; } /// <summary> /// The speed at which the camera moves. Default is 1.0. /// </summary> public float LinearSpeed { get; set; } /// <summary> /// The speed at which the camera rotates. Default is 1.0. /// </summary> public float AngularSpeed { get; set; } /// <summary> /// A vector of values between 0.01f and 1.0f that defines mouse sensitivity. /// </summary> public Vector2 MouseSensitivity { get; set; } protected float yaw; protected float pitch; public void SetPerspectiveParameters(float width, float height, float fov, float zNear, float zFar) { Perspective = Matrix4.CreatePerspectiveFieldOfView(fov, width / height, zNear, zFar); } public void MoveForward(float delta) { Position += Forward * delta; } public void MoveRight(float delta) { Vector3 right = Vector3.Cross(Up, Forward); Position += right * delta; } public void MoveUp(float delta) { Position += Up * delta; } public void TranslateWorld(Vector3 delta) { Position += delta; } public void TranslateLocal(Vector3 delta) { MoveForward(delta.Z); MoveUp(delta.Y); MoveRight(delta.X); } public void GetMatrix(out Matrix4 result, bool rotationOnly) { result = Matrix4.LookAt(Position, Forward, Up); if (rotationOnly) { result.Row3 = Vector4.UnitW; } } public Matrix4 GetMatrix(bool rotationOnly) { Matrix4 result; GetMatrix(out result, rotationOnly); return result; } public void GetCameraMatrix(out Matrix4 result) { result = Matrix4.LookAt(Position, Forward, Up); } public Matrix4 GetCameraMatrix() { Matrix4 result; GetCameraMatrix(out result); return result; } public void GetRotationMatrix(out Matrix4 result) { Vector3 right = Vector3.Cross(Up, Forward); Matrix4 matrix = new Matrix4(); matrix.Row0 = new Vector4(right.X, Up.X, Forward.X, 0.0f); matrix.Row1 = new Vector4(right.Y, Up.Y, Forward.Y, 0.0f); matrix.Row2 = new Vector4(right.Z, Up.Z, Forward.Z, 0.0f); matrix.Row3 = Vector4.UnitW; result = matrix; } public Matrix4 GetRotationMatrix() { Matrix4 result; GetRotationMatrix(out result); return result; } /// <summary> /// Rotate the camera up or down by <i>angle</i> degrees. /// </summary> /// <param name="angle">The angle, in degrees, to rotate by.</param> public void RotateLocalX(float angle) { Vector3 right = Vector3.Cross(Up, Forward); float angleRadians = angle.ToRadians(); Matrix4 rotationMatrix = Matrix4.CreateFromAxisAngle(right, angleRadians); Up = MathUtilities.RotateVector(Up, rotationMatrix); Forward = MathUtilities.RotateVector(Forward, rotationMatrix); } /// <summary> /// Rotate the camera left or right by <i>angle</i> degrees. /// </summary> /// <param name="angle">The angle, in degrees, to rotate by.</param> public void RotateLocalY(float angle) { float angleRadians = angle.ToRadians(); Matrix4 rotationMatrix = Matrix4.CreateFromAxisAngle(Up, angleRadians); Forward = MathUtilities.RotateVector(Forward, rotationMatrix); } public void Normalize() { Vector3 right = Vector3.Cross(Up, Forward); Forward = Vector3.Cross(right, Up); Up.Normalize(); Forward.Normalize(); } public void RotateWorld(float angle, Vector3 axis) { Matrix4 rotationMatrix = Matrix4.CreateFromAxisAngle(axis, angle); Vector3 result = MathUtilities.RotateVector(Up, rotationMatrix); Up = result; result = MathUtilities.RotateVector(Forward, rotationMatrix); Forward = result; } public void RotateLocal(float angle, Vector3 axis) { Vector3 worldVector; worldVector = LocalToWorld(axis, true); RotateWorld(angle, worldVector); } /// <summary> /// Convert local coordinates to world coordinates. /// </summary> /// <param name="local">The local coordinates to convert from.</param> /// <param name="world">The result of the conversion.</param> /// <param name="rotationOnly">If true, no translation is done, only rotation.</param> public void LocalToWorld(Vector3 local, out Vector3 world, bool rotationOnly) { Matrix4 rotationMatrix = GetRotationMatrix(); world = MathUtilities.RotateVector(local, rotationMatrix); if (!rotationOnly) { world += Position; } } /// <summary> /// Convert local coordinates to world coordinates. /// </summary> /// <param name="local">The local coordinates to convert from.</param> /// <param name="rotationOnly">If true, no translation is done, only rotation.</param> /// <returns>The result of the conversion.</returns> public Vector3 LocalToWorld(Vector3 local, bool rotationOnly) { Vector3 world; LocalToWorld(local, out world, rotationOnly); return world; } /// <summary> /// Convert world coordinates to local coordinates. /// </summary> /// <param name="world">The world coordinates to convert from.</param> /// <param name="local">The result of the conversion.</param> public void WorldToLocal(Vector3 world, out Vector3 local) { Vector3 newWorld = world - Position; Matrix4 rotationMatrix = GetRotationMatrix(); rotationMatrix.Invert(); local = MathUtilities.RotateVector(newWorld, rotationMatrix); } /// <summary> /// Convert world coordinates to local coordinates. /// </summary> /// <param name="world">The world coordinates to convert from.</param> /// <returns>The result of the conversion.</returns> public Vector3 WorldToLocal(Vector3 world) { Vector3 local; WorldToLocal(world, out local); return local; } public void RotateVector(Vector3 source, out Vector3 destination) { Matrix4 rotationMatrix = GetRotationMatrix(); destination = MathUtilities.RotateVector(source, rotationMatrix); } public void TransformPoint(Vector3 source, out Vector3 destination) { Matrix4 transformMatrix = GetCameraMatrix(); destination = Vector3.Transform(source, transformMatrix); } public void Update(float dt, Vector2 mouseDelta) { Vector3 movement = new Vector3(); if (keys[Key.W]) { movement.Z = LinearSpeed * dt; } else if (keys[Key.S]) { movement.Z = -LinearSpeed * dt; } if (keys[Key.A]) { movement.X = -LinearSpeed * dt; } else if (keys[Key.D]) { movement.X = LinearSpeed * dt; } TranslateLocal(movement); RotateLocalX(mouseDelta.Y * MouseSensitivity.Y * AngularSpeed * dt); RotateLocalY(-mouseDelta.X * MouseSensitivity.X * AngularSpeed * dt); MVP = (ModelView = GetCameraMatrix()) * Perspective; } } } 

Relevant math utility function:

 namespace SurviveEngine.MathEngine { public static class MathUtilities { public static Vector3 RotateVector(Vector3 p, Matrix4 m) { Vector3 vout = new Vector3(); vout.X = m.M11 * p.X + m.M21 * p.Y + m.M31 * p.Z; vout.Y = m.M12 * p.X + m.M22 * p.Y + m.M32 * p.Z; vout.Z = m.M13 * p.X + m.M23 * p.Y + m.M33 * p.Z; return vout; } } } 

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Make sure, that you apply your transformations in the correct order.

This line: "MVP = (ModelView = GetCameraMatrix()) * Perspective;"

suggest you either have the wrong order or you implemented your matrix multiplication wrong (at least unlike what one would expect). Projection is applied after modelview, so it should be Perspective * ModelView.

Also, for FPS style camera, always rotate in the order y,x,z when using Euler Angles and in your case, do NOT use your local up axis. That's exactly what you don't want. Always use (0,1,0). All other rotations will of course use local axes.

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Thanks a lot.

...except that didn't fix anything.

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PS. I base on this tutorial https://learnopengl.com/Getting-started/Textures.

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