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vonpietro
04-21-2018, 12:02 AM
hi,

think i found a bug - i rendered robbie the robot with different tile sizes
his dome faceplate is a dielectric.
i started with 128 up to 1024
every render gave a different result to the glass dielectric
from being clear
to being tinted (which is what i think it was supposed to be)
to being clear and tinted but in sections

all with just changing the tile size.


also, i had different render times with different tile sizes.

also, i'm finding my cpu is not rendering at full ghz either - with the larger tiles sizes i'm not getting turbo boost mode anymore. weird.

anyone else try rendering dielectric glass and futz with tilesizes - see if you get different results.

DogBoy
04-21-2018, 02:58 AM
can you get this into a format you can submit?

rustythe1
04-24-2018, 12:06 PM
hi,

think i found a bug - i rendered robbie the robot with different tile sizes
his dome faceplate is a dielectric.
i started with 128 up to 1024
every render gave a different result to the glass dielectric
from being clear
to being tinted (which is what i think it was supposed to be)
to being clear and tinted but in sections

all with just changing the tile size.


also, i had different render times with different tile sizes.

also, i'm finding my cpu is not rendering at full ghz either - with the larger tiles sizes i'm not getting turbo boost mode anymore. weird.

anyone else try rendering dielectric glass and futz with tilesizes - see if you get different results.

regarding the tile size, that's not a bug, it will take more or less time depending on tile size, don't know where the thread is, but you have to do a little maths between the render size, tile size, and how many threads you have as tiles work with the hardware, if you don't get the correct size some of the time you can have threads running idle as they are waiting for other threads to finish and catch up before going on, (or as far as i know that's how it works, don't know the exact reason, i think it may be briefly mentioned in the docs too but not in any detail)

jwiede
04-24-2018, 03:56 PM
regarding the tile size, that's not a bug

The differences in appearance (esp. w.r.t. coloration, and how much is colored) of the material when only tile size is adjusted definitely sounds like a BUG.

Kryslin
04-24-2018, 08:43 PM
Re: Tile Size

What I've found is a good starting point is to take your render size, and divide each by the tile size, and round down. Take those numbers, and multiply them. If this result is equal to or greater than the number of threads you have, you're good.

Example:
My render size is 800 x 600. Since a 256 x 256 tile (800 / 256 = 3, 600 / 256 = 2, 3 x 2 = 6, I have an i7 960, 8 threads) yields a result less than my total number of threads, I drop it back down to 128 x 128. This way all threads of execution are working whike rendering.

In testing, I've noticed that either size works well, and keeps all threads saturated pretty well. Of course after the first pass, the renderer can assign multiple cores to tiles as the image nears completion.

Note that this is what works for me; it doesn't provide for optimum rendertimes, but a more efficient CPU load. A single 1K x 1K tile will still render an 800 x 600 frame faster than any smaller tile size.