Updated Sept 26, 2019
For the last 6 years, ProSelect has used your Mac's OpenGL libraries to directly access the graphics hardware on your computer when playing slideshows. OpenGL is used to make slideshows run smoother on slower hardware and also allow ProSelect to use GPU intensive effects like the Ken Burns effect. You can still play simple slideshows in ProSelect without OpenGL support turned on.
Last year, Apple announced that they were depreciating support for OpenGL with the release of Mojave (OSX 10.14). This means that they will no longer fix any issues created by changes that they make to OSX that effect the way OpenGL works. Most recent versions of ProSelect work fine on Mojave though you will get a "Not optimized for this Mac" warning if you are using versions earlier than 2019r1 which is a full 64-bit version on Macs. See this article: ProSelect 64-bit and OSX 32-bit Warning
There were rumors that Apple would completely remove support for OpenGL with the next OSX release (OSX 10.15). However, at the June 2019 WWDC event, Apple announced that they will still be supporting OpenGL in OSX 10.15 ("Catalina") but also stated that "now is the time to move" implying that this may be the last OSX release that will support OpenGL.
To ensure ProSelect will continue to work well on Macs into the future, we have invested in upgrading the slideshow in the ProSelect 2019r2 release (coming in July 2019) to use "Metal" which is Apple's recommended replacement for OpenGL.
Does my computer support Metal?
To use Metal, your computer's GPU must support Metal (see this Apple article: Mac computers that support Metal) and you must be running OSX 10.11 or later on that machine.
If your computer supports Metal and you are using OSX 10.11 to 10.13 then, in ProSelect 2019r2, you can choose to use either Metal or OpenGL in ProSelect's Preferences -> Slideshow -> Slideshow Settings -> Performance. If you are using OSX 10.14 (Mojave) or newer, you can only select and use Metal.
The About ProSelect window shows whether OpenGL and/or Metal is available on your computer and which of these is currently selected for use when playing the Slideshow.
Upgrading to ProSelect 2019r2
As usual, if you are on a lease or your PLUS is current at the time of the 2019r2 release, then this release will be a free upgrade for you.
Blue tint during slideshow transitions
This was reported by a few users running ProSelect 2019r2 on older Mac hardware (most seemed to be using earlier MacBook Pros). This issue was addressed and fixed in the 2019r2.3 update.
KnowledgeBase Article: Metal and OpenGL Support on OSX