ocioview: Cube Inspector

[michdolan]

This PR adds a cube inspector to ocioview, which is a 3D viewport that plots a color cube or image as a point cloud, with the current viewer's processor applied.

Individual points can be clicked to sample them, displaying RGB output values and a swatch, similar to the image viewer. I had originally implemented sampling on hover, but depending on the image density, this can get slow, so I removed it for now.

Other options provide control of cube size, image sample density, sample decimal precision, whether to clamp samples to the source cube, and whether to display source cube edges. Left click pans around the cube and the scroll wheel zooms towards or away from its center.

ocioview with Cube Inspector

33x33x33 cube

9x9x9 cube

image point cloud:

image point cloud, clamped

image point cloud, clamped, cube edges hidden

[michdolan]

I'm going to close this for now, and will open a new PR once we settle on a graphics framework for this and other ocioview 3D inspectors.