RDG integration

Prysm’s rendering is integrated directly into Unreal’s frame rendering through the Render Dependency Graph. This integration is achieved through the usage of a Scene View Extension by overriding the ISceneViewExtension::SubscribeToPostProcessingPass. Effectively, each Prysm‘s View in a given Scene will have it’s cohtml::View::Paint called inside a single GraphBuilder-scheduled pass per frame. In addition to greater parallelization and rendering resource memory management, this allows Views to directly sample the current backbuffer state for features such as the Backdrop Filter.

By default, the execution of Prysm‘s rendering is set to ISceneViewExtension::EPostProcessingPass::Tonemap, which means it happens after the Tonemapper. However, in some cases, a different post processing pass may be required, depending on what needs to be achieved, thus we’ve allowed this to be configurable to any ISceneViewExtension::EPostProcessingPass value that is supported by your Unreal Engine version. Also worth mentioning is that since there could be multiple existing Scene View Extensions that are rendering in the same post processing pass, there is also a way to specify the priority of each, so this priority value has been exposed in the Prysm‘s Rendering Options as well:

In certain cases, your pre-existing usage of Prysm may be architecturally not suited to use the newer RDG-coupled rendering flow. For this reason we have also exposed a Use Legacy Paint Schedule option which will essentially move the cohtml::View::Paint to happen inside a ENQUEUE_RENDER_COMMAND:

Caution

Please be aware that using the Use Legacy Paint Schedule option will result in the Backdrop Filter feature to not work correctly (since the backbuffer will not be sampled). The option is meant to ease the transition between your older Prysm version to the newer one that has the RDG integration (in case that is necessary at all), but does not guarantee a zero-issue behavior. We highly encourage moving away from this option as quickly as possible, as it will also be removed in future versions.