Tool Mouse Behaviour : Sensitivity adjustments + bug fixes

[themissingcow]

Summary

Extend the hold <shift> for precision mode to more tools and mouse interactions, to include the scroll wheel and camera movements.

User Story

What

As a user I'd like to be able to make finer adjustments when using the mouse to interact with the scene. Either using the various Viewer tools, or using the mouse wheel to interact with the Node Graph and other editors.

Why

• As a lighter, when looking through a light and repositioning using the mouse, it is often too sensitive and hard to make fine adjustments.

• As a general user, when navigating large node graphs it can be difficult to zoom to a suitable level using the mouse wheel. It is either too big or too small.

Feature Proposal

• Add support for precise mode to mouse-wheel movements and the camera tool.
• Constrain GraphEditor zoom to useful zoom levels (prevent loosing the graph).
• When engaging precise mode, preserve the existing offset caused by any earlier movement rather than snapping back as if precise mode was held the whole time. If exiting precise mode with the mouse button still down, adjust the handle as if precise mode had not been enabled (ie: return the handle to the mouse). This prevents long-term object disconnection buildups.

[themissingcow]

During user testing, concerns were raised by the "snap back to cursor on shift key-up" behaviour. This can be very disorienting with camera motion, and has the risk of mis-timed key .vs. button releases causing positional jumps for object manipulations.

A behaviour of "don't worry about the disconnect" was prototyped. This works very well for camera movements, but is problematic handles in the generic sense. The issue is that the mouse position relative to the handle is often meaningful to its function, despite it not being directly coupled. Eg: for rotations, we intersect an imaginary circle to work out the rotation angle. Disconnects in the perceived .vs. actual mouse position then result in totally bogus angles being calculated.

If all handles were simply offset accumulations, then it would work. Having different behaviours per-tool is confusing. So the following compromise seems the only sustainable one:

• Allow disconnection for camera movements.
• All other tools snap-back to the cursor when the shift key is released.