[I am posting this on behalf of NiranV Dean, author of the Black Dragon viewer.]
General purpose improvements to the way the Viewer locally handles and displays mouselook for the user.
Adds an animation that the Viewer uses to modify the avatar's torso rotation to point towards the aiming direction, this in combination with a "holding" animation that objects can trigger normally allows the user to visually see and aim, say a gun around in first person, making the gun follow the aim direction, keeping it on screen, improving overall look and feel of the first person immersion.
Fixes an oversight with animated child prims that causes them to be interpolated while in mouselook, resulting in them lagging behind the root object, for instance when firing a gun that animates parts of it. With the above animation allowing the weapon to stay onscreen this becomes even more of an issue.
Mouselook head position improvements that puts the camera where the eyes of the avatar are, instead of "assuming" where the head is and forcing the body attach to the camera, which often results in the body clipping into the ground or moving around weirdly, this doesn't feel immersive at all and makes it hard if not impossible to line up animations for holding objects.
((Shown in the first video with the test running animation to simulate headbobbing))
Going in tandem with the above are improvements to the way mouselook handles and hides the head of the user while in Mouselook, locally scaling down head bones and including hiding rigged mesh attached to the head slots which were previously missing, this should help eliviate issues with the head clipping into the camera and blocking the view.
((Can be seen in the first video looking down, the shadows show the head being chopped off, something that may or may not be able to be fixed))
[Darksider Alex has provided an additional video to demonstrate the requested feature: https://gyazo.com/6964e720c1b02133d19976d3fa89f60c ]