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Questions (especially for developers) about EGL, KWIN and QT

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Hi dears, I have read the documentation of the kwin environment variables and have some questions about kwin and QT in relation to EGL.

Premise: I have an Intel Tigerlake iGPU, my main pc is a laptop, I use the X11 session with the Intel driver (configured to use the Mesa Iris driver correctly otherwise it breaks 3D acceleration). I prefer this driver to modesetting because it takes advantage of SNA acceleration.

My questions are related to some environment variables:

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Is there a real advantage for kwin and/or QT in using EGL instead of GLX in terms of performance or battery saving? (for example, I noticed that haruna consumes less CPU, but I think this is related to mpv with vaapi more than to the program. In fact using smplayer I don't notice any difference).
On the other hand, I noticed from eglinfo that EGL does not support several OpenGL extensions (including some Intel-specific ones).

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As I understand it, setting OpenGL ES makes sense on older hardware, does it? Can it result in battery savings on modern hardware?

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I read that the use of INTEL SWAP EVENT was disabled by default, in fact I too noticed little jerky animations, is it my impression or is it a known fact?

Many thanks for the replies.


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