GetProjectionMatrix vs _make/convertProjectionMatrix

[Maestro81]

I was wondering, in order to get a proper understanding of Ogre's projection matrix, why the following two code snippets do not return the same projection matrix:

Code: Select all

Ogre::Matrix4 pm1 = m_camera->getProjectionMatrix();

Returns
Matrix4( row0{4.38262 0 0 0 } row1{0 2.41421 0 0 } row2{0 0 -1.0001 -10.0005 } row3{0 0 -1 0 })

Code: Select all

Ogre::Matrix4 temp, pm2; 
Ogre::Root::getSingleton().getRenderSystem()->_makeProjectionMatrix(m_camera->getFOVy(), m_camera->getAspectRatio(), m_camera->getNearClipDistance(), m_camera->getFarClipDistance(), temp);
Ogre::Root::getSingleton().getRenderSystem()->_convertProjectionMatrix( temp, pm2 );

Returns
Matrix4( row0{4.38262 0 -0 0 } row1{0 2.41421 -0 0 } row2{0 0 -1.00003 -2.50012 } row3{0 0 -1 0 })

So, element [2, 3] differs.. From my understanding, this is dependent on the far/near planes... (I'm using the Direct3D RenderSystem)

Anyone any idea why these retrieving the projection matrix does not provide the same result as making a projection matrix with the current camera properties?

[dark_sylinc]

GetProjectionMatrix returns a right hand proj matrix with depth in the range [-1; 1]

_makeProjectionMatrix creates an API-specific proj matrix.
convertProjectionMatrix takes an Ogre proj matrix and converts it to an API matrix.

So convertProjectionMatrix( camera->GetProjectionMatrix() ) should return the same as _makeProjectionMatrix.

Though I wouldn't rely on _makeProjectionMatrix. It seems to be dead code (aka not used anywhere in Ogre).

[Maestro81]

GetProjectionMatrix returns a right hand proj matrix with depth in the range [-1; 1]

_makeProjectionMatrix creates an API-specific proj matrix.
convertProjectionMatrix takes an Ogre proj matrix and converts it to an API matrix.

So convertProjectionMatrix( camera->GetProjectionMatrix() ) should return the same as _makeProjectionMatrix.

Though I wouldn't rely on _makeProjectionMatrix. It seems to be dead code (aka not used anywhere in Ogre).

Tnx