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Planar Reflections in 4.15 not rendering any faster with lower screen percentage

In previous versions of the engine, I would get a huge fps increase by lowering the screen percentage on the planar reflections actor. In 4.15, setting this to 100 percent renders faster than previous versions at 100 percent, but lowering it seems to have no effect on frame time. This has caused scenes with water to take a significant fps hit.

Product Version: UE 4.15
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asked Mar 07 '17 at 03:14 PM in Bug Reports

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3DMoss
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avatar image Ed Burgess ♦♦ STAFF Mar 09 '17 at 09:39 PM

Hey 3dMoss,

I didn't reproduce this behavior on my end so it could be because I have a different testing setup that yourself. Here are the steps I took:

  • Created a blank project (with support global clip plane enabled for planar reflections).

  • Put in several planar reflection actors to ensure a performance hit.

  • Scaled up the floor mesh and applied a reflective metalic material(see screen for how I had it set up)

alt text

  • Enabled Stat FPS in the console

  • Took note of FPS at screen percentage 0, 100, and 50

  • I then did the same test in 4.15

In 4.15 I noticed the FPS increase as the screen percentage lowered.

To ensure we are testing under the same conditioned I would recommend testing in a blank project.

testscreen.jpg (335.1 kB)
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Thanks for checking this Ed. I can confirm the same result as you in a blank project. I tried that previously, but didn't think to duplicate the reflection actor to exaggerate the hit. It seems that planar reflections are now more efficient to render, and the render time difference between 20% and 100% is much less than in 4.12 which my project was upgraded from. After unchecking some unnecessary flags, the frame time is now fine, with much better quality reflections. I don't think 4.12 had flags, and I'm guessing that is why the difference in frame time when lowering the resolution was so much greater. Thanks again.

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answered Mar 10 '17 at 02:44 AM

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3DMoss
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