expand area where data is fully loaded

[clharwood]

For some of the work with the LakeViz project, we would like to expand the area of data that crusta displays at full resolution. So rather than just the area at the cross hairs loading, we would like the whole area of the screen to appear the same. Oliver says that this is possible, but that it is something that has to be changed at a higher level than just merging in a config file. Ideally we'd have this version running on wizard since that's where John and I make the example movies, and then also distribute this version to the LakeViz team.

Oliver's comments are:
Just like LiDAR Viewer, Crusta uses a focus+context LOD model where
areas away from the focus (screen center) are drawn at reduced
resolutions. Unlike LiDAR Viewer, the focus+context drop-off factor
is hardcoded and cannot be changed via the UI.

Ideally, there would be two configurable parameters, not necessarily
via GUI:

• focus area size: area in which tiles are drawn at screen
  resolution. This should be expressed as a multiple of Vrui's
  reported display size.
• focus area weight: scale factor how quickly resolution is reduced
  depending on distance from the focus area. This is usually a number
  =0, with 0 meaning screen resolution everywhere

The focus+context computation is either done in a method preparing
for rendering, such as during an LOD computation traversal of the
node tree, or directly in the display method. I don't know which it
is.