Posted 15 February 2018 - 07:05 AM
The results for most rendering should be the same between the two. The same rendering engine is drawing the pixels.
A noticeable difference should be brought up as a possible bug. There are some effects that only work in Multi-pass.
The dig difference between regular and multipass is how the anti-aliasing is done.
Multi-pass subdivides each pixel (16 passes would be a 4 x 4 subdivision) and does a full render for each sub pixel then averages the sub pixels together.
However, a pixel that is among other pixels of similar color (like in a blue sky) needs no anti-aliasing and won't benefit from it. Multipass rendering wastes time subdividing it.
Regular render does "adaptive anti-aliasing." Every pixel is rendered, then the contrast between pairs of pixels is compared. If the contrast is above some threshold the pixels are subdivided and re-rendered on a 2x2 grid. The sub pixels are again compared for contrast and if any pairs are above the threshold they are subdivided again and rendered.
The result is that regular rendering has anti-aliasing detail equivalent to 16-pass rendering, but usually in far less time.
It is possible for an extremely detailed scene to take longer in regular rendering and I have noticed that objects with thin lines look better with multipass.
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