When changing r.ScreenPercentage the final value used for buffer generation is clamped to the nearest 4 pixels to aid in post processing and other steps. During post processing the same calculation for screen percentage is performed but this quantization does not happen creating up to a 3 pixel discrepancy. This leads to artifacts when buffer sizes and viewports mismatch when working with un-cleared data.

Both calculations should be identical to avoid edge cases which can be particularly apparent on consoles.

Steps to Reproduce

See the example in the UDN, or:
Launch QAGame in -game, set the resolution to 1600x900, set screen percentage to 50%, turn the camera and if correct there should be no black smear at the bottom of the screen.

Community References

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ComponentUE - Rendering
Affects Versions4.84.94.11
Target Fix4.15
Fix Commit3225485
Main Commit3231696
Release Commit3240724
CreatedJul 30, 2015
ResolvedDec 7, 2016
UpdatedJun 23, 2018