# OpenGL - Calculating camera view matrix

Problem

I am calculating the model, view and projection matrices independently to be used in my shader as follows:

gl_Position = projection * view * model * vec4(in_Position, 1.0);


When I try to calculate my camera's view matrix the Z axis is flipped and my camera seems like it is looking backwards.

My program is written in C# using the OpenTK library.

Translation (Working)

I've created a test scene as follows:  From my understanding of the OpenGL coordinate system they are positioned correctly.

The model matrix is created using:

Matrix4 translation = Matrix4.CreateTranslation(modelPosition);
Matrix4 model = translation;


The view matrix is created using:

Matrix4 translation = Matrix4.CreateTranslation(-cameraPosition);
Matrix4 view = translation;


Rotation (Not-Working)

I now want to create the camera's rotation matrix. To do this I use the camera's right, up and forward vectors:

// Hard coded example orientation:
// Normally calculated from up and forward
// Similar to look-at camera.
Vector3 r = Vector.UnitX;
Vector3 u = Vector3.UnitY;
Vector3 f = -Vector3.UnitZ;

Matrix4 rot = new Matrix4(
r.X, r.Y, r.Z, 0,
u.X, u.Y, u.Z, 0,
f.X, f.Y, f.Z, 0,
0.0f, 0.0f, 0.0f, 1.0f);


This results in the following matrix being created: I know that multiplying by the identity matrix would produce no rotation. This is clearly not the identity matrix and therefore will apply some rotation.

I thought that because this is aligned with the OpenGL coordinate system is should produce no rotation. Is this the wrong way to calculate the rotation matrix?

I then create my view matrix as:

// OpenTK is row-major so the order of operations is reversed:
Matrix4 view = translation * rot;


Rotation almost works now but the -Z/+Z axis has been flipped, with the green cube now appearing closer to the camera. It seems like the camera is looking backwards, especially if I move it around.

My goal is to store the position and orientation of all objects (including the camera) as:

Vector3 position;
Vector3 up;
Vector3 forward;


Apologies for writing such a long question and thank you in advance. I've tried following tutorials/guides from many sites but I keep ending up with something wrong.

Edit: Projection Matrix Set-up

Matrix4 projection = Matrix4.CreatePerspectiveFieldOfView(
(float)(0.5 * Math.PI),
(float)display.Width / display.Height,
0.1f,
1000.0f);

• There is a part of this process that you are currently ignoring. OpenGL does not mandate anything about any of the axes in coordinate spaces prior to clip-space in the programmable pipeline. Clip-space is left-handed, and the only way to achieve this is if your projection matrix flips the Z-axis, given your current view-space setup. Can you show the setup of your projection matrix? – Andon M. Coleman May 27 '14 at 0:29
• I've added the projection matrix set-up to the original post, thanks. – Karle May 27 '14 at 0:40
• Considering that OpenTK is row-major and the function you are calling shares its name with a D3D function... I would not be surprised if that produces a projection matrix that expects left-handed view-space coordinates (D3D convention). If you call Matrix4.Perspective (...) instead, does anything change? – Andon M. Coleman May 27 '14 at 0:51
• I tried calling Matrix4.Perspective(...) with the same arguments and it produced the same matrix (ignoring very small rounding errors). The documentation marks the method as deprecated. – Karle May 27 '14 at 0:56