Question Planet Rendering in D3D9Client

[dumbo2007]

Hi,

I am trying to understand how planets are rendered in the D3D9 client code. It seems that all co-ordinates are camera centric.

There is a call to vObject::Update() which seems to get all the distances wrt the global camera position. The distance of the planet from the camera is in cdist:

From http://d3d9client.codeplex.com/SourceControl/latest#trunk/Orbitersdk/D3D9Client/VObject.cpp

	MATRIX3 grot;
	oapiGetRotationMatrix(hObj, &grot);
	oapiGetGlobalPos(hObj, &cpos);
	cpos -= scn->GetCameraGPos();

	// object positions are relative to camera

	cdist = length(cpos);

	// camera distance
	D3DMAT_SetInvRotation(&mWorld, &grot);
	D3DMAT_SetTranslation(&mWorld, &cpos);

Why is D3DMAT_SetInvRotation(&mWorld, &grot) used ? Shouldnt the rotation thats put into the world matrix be wrt the camera as the world matrix itself seems to be based on camera distances ?

Also since the world matrix seems to have all co-ordinates wrt the camera, I am guessing that no multiplication is needed with a view matrix ?

Usually there is a modeling matrix and a view matrix and the object co-ordinates in world space are multiplied with each in that order.

But is there a view matrix needed here ?

 

[jarmonik]

The camera is in the origin and the world moves around the camera, however, the world does not rotate. The camera is rotated. So, there is a view matrix that's passed to the shaders directly.

The code that you have quoted contains a code that builds an object's world matrix relative to the camera. D3DMAT_SetInvRotation() will set object's rotation around it's own local axes not around the camera.