Display Helpers

[colincornaby]

Looking for feedback on this concept. Direct3D is funny in that it directly includes display mode queries as part of its API. For Metal - and OpenGL particularly - things are a bit more interesting. The display mode API is separate from the graphics API.

• Platforms that support multiple renderers may need to share display mode code between the renderers. I.E. Metal and OpenGL on Mac should share the same display mode code for maintainability.
• Some renderers support multiple platforms - and need a maintainable way of abstracting the display mode selection by platform. I.E. OpenGL needs to select display modes on Mac, Windows, and Linux.
• Some platforms have oddities that require deeper interaction with platform native API. I.E. macOS has non rectangular displays, and we need to filter down the available display modes to only that ones that fit on the screen.
• The client itself needs some sort of interaction with this class. It manages the window - and thus knows what display the window is on and when the window changes displays.

This PR adds display helpers as a structure to try to bridge a specific renderer to a platform specific implementation.

I'm not sure how this fits with enumerations - it's possible that this integration needs to happen at a deeper level in the code.

[dpogue]

A few high-level thoughts:

• plPipeline::GetSupportedDisplayModes appears to only be called from the Python code for enumerating the resolution slider options, so we could probably drop the ColorDepth entirely because I don't think that shows up in the options.

• I guess historically this lived in the pipeline stuff because DirectX conflates them, but maybe it should actually be part of plClient instead? It seems a lot more closely related to the platform-specific client and windowing stuff

• There's some stuff about display modes in and around the hsG3DDeviceSelector classes used at pipeline creation time, but maybe we don't actually need any of that there and can leave that focused just on renderer device enumeration?

[colincornaby]

Digging this PR back out - @dpogue I think you are right. One issue is that the client makes a lot of decisions about resolution - but it does it before the pipeline is necessarily available.

One possible issue is the divergent views on if resolution selection is part of the graphics API or the platform API. Apple feels that it's platform API, but Microsoft sees it as a graphics API issue at least under D3D9.

Other pipelines like OpenGL/Vulkan could cause further chaos, especially if you had one accelerator that supported one set of APIs and another adapter that supported a different set.

There are probably Win32 APIs to map a display to resolutions that I'm not aware of. That might be a good solution. But the display helper still includes some graphics API related code to check capabilities.

[colincornaby]

There's also overlap going on between this display helper class and DeviceEnumerator.

[dpogue]

I have mostly avoided thinking about this because (as you mentioned) with OpenGL is becomes a complicated nightmare that can't really be done at the driver level.

I agree with the idea that the display mode stuff should be at the plClient/windowing level rather than the pipeline level, although I see how we might still want to filter that list of modes based on capabilities of the pipeline render device.

The original Direct3D renderer used exclusive fullscreen, which presumably is where it's important to use the driver to enumerate the supported modes. We replaced that with fake-fullscreen though, so it might be less important to use that now vs using standard Win32 APIs to ask for the supported resolutions.

I'm imagining something like plClient::GetAvailableDisplayResolutions() being a per-platform implementation that fills in part of the hsG3DDeviceSelector stuff that gets passed in to the pipeline constructor, and then plPipeline::GetSupportedDisplayModes returning a filtered/constrained list based on the capabilities of the active rendering device. Does that sound like it would work?

[colincornaby]

I'm imagining something like plClient::GetAvailableDisplayResolutions() being a per-platform implementation that fills in part of the hsG3DDeviceSelector stuff that gets passed in to the pipeline constructor, and then plPipeline::GetSupportedDisplayModes returning a filtered/constrained list based on the capabilities of the active rendering device. Does that sound like it would work?

We might need a display handle to go along with that (along with a re-review of where else this concept is already encapsulated in the pipeline.) Resolutions are going to be per display - and it would be good to clean that whole thing up while we're putting in new plumbing.

The client will probably need to vend which display the window is currently on, and broadcast any changes.