[no bug] Perspective Projection Field of View

[drewbacca]

Starting with the important bit:

Is it a bug that the projection matrix built by buildProjectionMatrixPerspectiveFovLH in matrix4.h is very close, but doesn't match the matrix used by directX?
http://msdn.microsoft.com/en-us/library ... 85%29.aspx
It is only different in 1 element, so wouldn't this cause irrlicht's projection matrix to not produce the correct aspect ratio?

More info:
I need to create a camera that matches specific FOV parameters. The ICameraSceneNode documentation for setFOV doesn't state what dimension's FOV is set (horizontal, vertical, diagonal) with the function, though the parameter is called fovy which led me to believe that it is the vertical field of view. However, setting up a scene with objects laid out didn't render as expected given my camera's aspect ratio & fov. It looks like this is just a typo due to pulling the aspectRatio mult out of the trig function when setting up the matrix. Changing the projection matrix to directx's creates the view I expect. If this is not a typo, what is setting the camera FOV setting?

[drewbacca]

To make things easier to review: here is the irrlicht code:

Code: Select all

 
const f64 h = reciprocal(tan(fieldOfViewRadians*0.5));
_IRR_DEBUG_BREAK_IF(aspectRatio==0.f); //divide by zero
const T w = (T)(h / aspectRatio);
 
_IRR_DEBUG_BREAK_IF(zNear==zFar); //divide by zero
M[0] = w;
M[1] = 0;
M[2] = 0;
M[3] = 0;
 
M[4] = 0;
M[5] = (T)h;
M[6] = 0;
M[7] = 0;
 
M[8] = 0;
M[9] = 0;
M[10] = (T)(zFar/(zFar-zNear));
M[11] = 1;
 
M[12] = 0;
M[13] = 0;
M[14] = (T)(-zNear*zFar/(zFar-zNear));
M[15] = 0;
 

and changing the w calc to the code below fixed the field of view for me

Code: Select all

const f64 w = reciprocal(tan((fieldOfViewRadians*aspectRatio)*0.5));

[mongoose7]

It depends what you mean by "aspect ratio". You think it is the ratio of the horizontal angle to the vertical angle. The code you quote thinks it is the ratio of the width to the height of the viewport. The latter is normal for the consumer, but you seem to have deeper knowledge.

[drewbacca]

Ahh... you are right, except for the part about me having a deeper knowledge. I was incorrectly applying the aspect ratio to the field of view. With further looking, the matrix follows exactly what is in msdn after all:
http://msdn.microsoft.com/en-us/library ... 85%29.aspx

[mongoose7]

Wow! It *is* confusing to change your units in the middle of a parameter block! The engineer who designed that should be ashamed but I don't think MS engineers feel shame!