Preallocate buffers for use with LightingComposite.BlenderContext

[kwvanderlinde]

Identify the Bug or Feature request

Implements #4072

Description of the Change

Avoids allocating buffers in LightingComposite.BlenderContext.compose() as that method is called potentially many thousands of times per frame, especially with overlapping lights. The buffer size was chosen to hold 4096 pixels (16 KiB) in order to avoid chunked blending in most cases.

Another improvement was reducing the number of buffers from 3 to 2 since we don't need a separate output buffer.

From a performance perspective, the same situation as in #4042 and #4054 went from typically looking like this

Timer ZoneRenderer.renderZone (66 elements)
    0.      63 ms  paintComponent
   36.      48 ms  lights
   38.      48 ms  renderLights:renderLightOverlay
   41.      39 ms  renderLightOverlay:drawLights
   42.      39 ms  renderLightOverlay:fillLight

to

Timer ZoneRenderer.renderZone (66 elements)
    0.      45 ms  paintComponent
   36.      31 ms  lights
   38.      31 ms  renderLights:renderLightOverlay
   41.      23 ms  renderLightOverlay:drawLights
   42.      23 ms  renderLightOverlay:fillLight

So roughly 30% shaved off lights rendering as a result.

Possible Drawbacks

32 KiB of unreclaimable memory, and a guilty conscience ...

Documentation Notes

N/A

Release Notes

• Improved lighting performance and memory usage.

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This change is 

[Scubba]

Thanks, @kwvanderlinde great to see this!