The mesh primitives: each particle draws a whole 3D mesh, chosen by mMesh and placed,
turned and scaled by the particle.
Transform. The mesh takes the particle's full world transform: its position, its
rotation about all three axes (BirthRotation0, the rotation rates and Rotation0), the
turn from BirthOrbitalVelocity, and the emitter's and the system's transforms. Scale is
per axis, scale.x, scale.y and scale.z on the mesh's X, Y and Z, unless the emitter
sets IsUniformScale, which applies scale.x to all three. When the emitter sets
IsDirectionOriented, the mesh's local +Z points along the particle's direction of
travel.
Cost. Meshes are not batched. Every particle is drawn on its own, once for each submesh
it shows, and a skinned mesh also uploads its whole skeleton pose for every particle.
Camera alignment
AlignYawToCamera and AlignPitchToCamera replace part of the particle's orientation
with a rotation that faces the camera. With either set, every frame the particle is aimed
from its own position toward an aim point built per axis:
The camera's up vector is the up axis of the result, and the particle's position is kept.
- Yaw alone turns the mesh about the vertical to face the camera and keeps it upright.
- Pitch alone aims the mesh within the vertical plane through the particle, keeping
the particle's X. It works as a tilt toward the camera only when the camera has about
the same X as the particle.
- Both point the mesh at the camera's position.
Which side of the mesh ends up facing the camera depends on the mesh type. A skinned mesh
(.skn) points its local +Z at the camera. A static mesh (.scb, .gmesh) is turned a
half turn about the up axis from that, so its local -Z faces the camera.
Whether the particle's own rotation survives the alignment is set by 0x6aec9e7a.
