What really happens when node is rotated??

[thatdudeoverthere]

My question is when you tell a scene node to rotate on an axis(y for example) what really happens is that Irrlicht is taking the mesh's vertices and rotating them around the axis to simulate the effect of a rotation on its axis based on a quaternion. is this correct?? I'm just asking to better understand how irrlicht works and to stasify my curosity and if not then can someone explain what's happening. Thanks in advance!

[vitek]

For the most part, Irrlicht doesn't move vertices at all. There are a few functions that do, but those are part of the IMeshManipulator interface.

Every scene node has an affine transformation matrix, called the world matrix, that defines the relative position, rotation and scale of the vertex data relative to some other point in 3d space. These matrices can be multiplied together to accumulate position, rotation and scale. This allows objects defined by multiple vertices to move relative to some other moving object (imagine the moon orbiting around the earth, which orbits around the sun).

Changing the position, rotation or scale of a scene node just updates one of these matrices. The matrix is later passed along to the video driver (Direct3D, OpenGL, ...) which uses the world matrix (along with the view and projection matrices) to transform the vertex data into screen space.

Irrlicht doesn't use quaternions for rotations internally. It could definitely do it, but the video drivers all expect matrices, so Irrlicht would need to convert quaternions into matrices all the time.

Travis

[thatdudeoverthere]

Ok so the video drivers are the ones doing the rotations based on matrices and irrlicht just passes the vertices data along.. Thanks Vitek!! that cleared some things up