Add custom screen object to render effects on top of the stream

[levs42]

Description & motivation

• Feature: add dedicated video effects screen object

This PR introduces a new screen object that allows to render effects on top of the other screen objects. By default IOVideoMixer uses videoTrackScreenObject to render effects. As result, multicam covers the effects during the rendering. Having custom object allows to add it as a screen child and display extra elements on top of the stream.

Type of change

• New feature (non-breaking change which adds functionality)

Screenshots:

Spoiler

[shogo4405]

From a maintenance perspective, I want to avoid increasing the number of ScreenObjects optimized for specific needs.

If place it on the HaishinKit side, I would like to make it more general so that other users can also utilize it easily. It can be accepted with the following changes:

1. Allow ImageScreenObject to be set from the CIImage library side since there is currently no CIImage-based ImageScreenObject.
2. Rename it to CIImageScreenObject.

public class CIImageScreenObject: ScreenObject {
    public var image: CIImage?
}

[levs42]

I've updated the PR, please take a look. I also added an extra check to ScreenRendererByCPU to avoid the situation where screen object was rendered for some time, than it became invisible, but the rendered still has an image in the images array and renders this cached image.

[shogo4405]

I believe this is a class that should be placed in the app layer as a unique extension on the app side. There is no benefit in placing it on the HK side, so please position it in the app layer.

[levs42]

Sounds good. How about ScreenRendererByCPU cached image issue, is the extra check something that can be merged?

[shogo4405]

I cannot make a decision because there is no material (such as tests or reproducible code) to judge from. Let’s close this as a PR. When you have time, please provide reproducible code and create an issue. I will take care of the fix on my end.

From a design perspective, that check should be on the ScreenObjectContainer side, not on the ScreenRenderer side. https://github.com/shogo4405/HaishinKit.swift/blob/4adecd1a89ecde9bf873fe28911c17a0c93aa4ec/Sources/Screen/ScreenObjectContainer.swift#L60-L7

If I place it on the ScreenRenderer side, it could potentially cause other issues, or it might not. That’s why I’m being cautious.