Better 2D label quality in saved images

[goddard@…]

The following bug report has been submitted:
Platform:        Darwin-19.4.0-x86_64-i386-64bit
ChimeraX Version: 0.94 (2020-04-16)
Description
2D labels have poor appearance when saved in high resolution images.

Log:
UCSF ChimeraX version: 0.94.dev202004160103 (2020-04-16)  
© 2016-2020 Regents of the University of California. All rights reserved.  
How to cite UCSF ChimeraX  

> 2dlabels text Hello

> save test2.png width 2000




OpenGL version: 4.1 ATI-3.8.24
OpenGL renderer: AMD Radeon Pro Vega 20 OpenGL Engine
OpenGL vendor: ATI Technologies Inc.

[Tom Goddard]

The same label texture is used when saving an image as when rendering on screen. That texture is chosen to be 1 texture pixel per screen pixel. So an image 3 times larger has texture pixels that are 3 times as large as image pixels. Also no texture size increase is made fro retina displays and the texture size is currently based on logical pixels instead of render pixels, so on retina displays the texture is half the size it should be for best quality.

[Tom Goddard]

Fixed.

2d labels now adjust texture size for image saving and also for retina displays to make 1 texture pixel per rendered pixel.

Arrows should get the same fixes to have good quality in images.

[Tom Goddard]

Also made 2dlabel arrows render with higher quality when saving high resolution images.