Don't show silhouettes on mesh surfaces

[tic20@…]

The following bug report has been submitted:
Platform:        Darwin-18.7.0-x86_64-i386-64bit
ChimeraX Version: 0.91 (2019-08-30)
Description
Tristan Croll suggests silhouette edges should not be shown for mesh surfaces since it makes them look horrible.

Log:
UCSF ChimeraX version: 0.91 (2019-08-30)  
© 2016-2019 Regents of the University of California. All rights reserved.  
How to cite UCSF ChimeraX  

> open 8624 fromDatabase emdb

Opened emd_8624.map, grid size 210,210,210, pixel 1.03, shown at level 0.0317,
step 1, values float32  

> graphics silhouettes true

> set bgColor white

> graphics silhouettes false




OpenGL version: 4.1 ATI-2.11.20
OpenGL renderer: AMD Radeon Pro Vega 20 OpenGL Engine
OpenGL vendor: ATI Technologies Inc.

[Tom Goddard]

Begin forwarded message:

From: Tristan Croll
Subject: Re: [chimerax-users] silhouette of transparent density
Date: August 30, 2019 at 1:45:43 PM PDT
To: chimerax-users@…

Along the same lines, it might be nice to have the option to turn silhouettes off for wireframe surfaces. Those have a tendency to become very “heavy” looking with silhouettes, particularly when zoomed out - they can end up obscuring everything behind them.

[Tom Goddard]

It would be nice to not have silhouette edges on meshes. The algorithm relies on the depth of the entire scene, it is computed after the whole scene is rendered (or now after opaque and transparent models are rendered) and cannot exclude any models since the same code that computes depth is also drawing the colors. It would take new code that rerenders everything in order to be able to exclude specific models from the silhouette depth calculation. So it is unlikely we can do this — it is too complex. So if meshes are shown I recommend not using silhouettes.

[Elaine Meng]

related to #4420 per-model silhouettes