Session restore does not show surfaces

[goddard@…]

The following bug report has been submitted:
Platform:        Darwin-19.5.0-x86_64-i386-64bit
ChimeraX Version: 1.1.dev202006250254 (2020-06-25 02:54:05 UTC)
Description
Molecular surfaces on models with nucleotides shown on an undisplayed model saved in a session does not show the surfaces when the session is restore and the model is displayed.

The problem is that cached Drawing._displayed_scene_positions gets set to a length 0 set of places when nucleotides asks for its bounds while the model is undisplayed.  When the structure is displayed it does not reset the cached scene positions so the surfaces are not rendered at any positions.

Log:
UCSF ChimeraX version: 1.1.dev202006250254 (2020-06-25)  
© 2016-2020 Regents of the University of California. All rights reserved.  

> open /Users/goddard/ucsf/chimerax/src/bundles/graphics/test.cxs format
> session

Log from Mon Jun 29 20:38:33 2020UCSF ChimeraX version: 1.1.dev202006250254
(2020-06-25)  
© 2016-2020 Regents of the University of California. All rights reserved.  
How to cite UCSF ChimeraX  

> open 6bna

6bna title:  
Binding of an antitumor drug to DNA. Netropsin and C-G-C-G-A-A-T-T-BRC-G-C-G
[more info...]  
  
Chain information for 6bna #1  
---  
Chain | Description  
A B | DNA (5'-D(*CP*GP*CP*GP*ap*ap*TP*TP*(CBR)P*GP*CP*G)-3')  
  
Non-standard residues in 6bna #1  
---  
NT — netropsin  
  

> surface

> hide #!1 models

> save test.cxs

opened ChimeraX session  

> show #!1 models

> hide #1.2 models

> show #1.2 models




OpenGL version: 4.1 ATI-3.9.15
OpenGL renderer: AMD Radeon Pro Vega 20 OpenGL Engine
OpenGL vendor: ATI Technologies Inc.Hardware:

    Hardware Overview:

      Model Name: MacBook Pro
      Model Identifier: MacBookPro15,3
      Processor Name: 8-Core Intel Core i9
      Processor Speed: 2.4 GHz
      Number of Processors: 1
      Total Number of Cores: 8
      L2 Cache (per Core): 256 KB
      L3 Cache: 16 MB
      Hyper-Threading Technology: Enabled
      Memory: 32 GB
      Boot ROM Version: 1037.120.87.0.0 (iBridge: 17.16.15300.0.0,0)

Software:

    System Software Overview:

      System Version: macOS 10.15.5 (19F101)
      Kernel Version: Darwin 19.5.0
      Time since boot: 1 day 3:41

Graphics/Displays:

    Intel UHD Graphics 630:

      Chipset Model: Intel UHD Graphics 630
      Type: GPU
      Bus: Built-In
      VRAM (Dynamic, Max): 1536 MB
      Vendor: Intel
      Device ID: 0x3e9b
      Revision ID: 0x0002
      Automatic Graphics Switching: Supported
      gMux Version: 5.0.0
      Metal: Supported, feature set macOS GPUFamily2 v1

    Radeon Pro Vega 20:

      Chipset Model: Radeon Pro Vega 20
      Type: GPU
      Bus: PCIe
      PCIe Lane Width: x8
      VRAM (Total): 4 GB
      Vendor: AMD (0x1002)
      Device ID: 0x69af
      Revision ID: 0x00c0
      ROM Revision: 113-D2060I-087
      VBIOS Version: 113-D20601MA0T-016
      Option ROM Version: 113-D20601MA0T-016
      EFI Driver Version: 01.01.087
      Automatic Graphics Switching: Supported
      gMux Version: 5.0.0
      Metal: Supported, feature set macOS GPUFamily2 v1
      Displays:
        Color LCD:
          Display Type: Built-In Retina LCD
          Resolution: 2880 x 1800 Retina
          Framebuffer Depth: 24-Bit Color (ARGB8888)
          Main Display: Yes
          Mirror: Off
          Online: Yes
          Automatically Adjust Brightness: No
          Connection Type: Internal

PyQt version: 5.12.3
Compiled Qt version: 5.12.4
Runtime Qt version: 5.12.8

[Tom Goddard]

Fixed.

Made Drawing reset cached _displayed_scene_positions when any parent changes display state.