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Zoom in use smaller tip size and increase brush spacing and install a faster CPU all thing are not done with you nvidia GPU. Sampling and mixing million of pixels is quite a job and is essentially a sequential process I would think not much threading can be done to speed up the processing to reduce the execution time. To improve performance you need to reduce the work being done work on smaller areas and not mix with 1% spacing the fasted machine can easily be overloaded using a large tip brush, 1% spacing, zoomed out where each brush stroke will be processing and changing millions of pixels. Photoshop works on you documents actual pixels not the scaled image being displayed. Photoshop can not just work on the scale image being displayed it has to work on your actual image. Nine woman can not produce a single baby in one month however in nine months they may produce more the nine babies.
My machine is so slow zoomed all the way in to 100% this 300 pixel complex tipped mixer brush stroke at 1% spacing took 10 seconds to render on my 16Bit document.
At 2% spacing it took like 3 second the stroke looks much different
At 10% spacing the stroke looks much different but the lag in acceptable.
Sized 15Px at 2% spacing the bush would be useable on my machine zoomed in to 100%
zoomed out took 3 second to stroke across the full image view. Reducing toe 8bit color the stroke still took 2seconds
My other camera image image have twice the number of pixels.........
I created a 16bit RGB document 30,000px x 30,000px It took CC 2018 6 seconds to fill that canvas with a gradient and the 300px 1% spaced mixer brush stroke took 3.2 minutes to render across that gradient. My machine has two slow 6 core 2GHZ xeon processors, 40GB of ECC RAM, a small 256GB SSD, a Nvidia quadro 4000, a 500GB Hard disk and a 4TB external usb3 disk an old slow cheap workstation its all I need. I do not do Video or play games on my workstatiom....
thanks for your reply, I do understand the spacing and how the various settings hit on the hardware and its limits,
my issue is more related to the fact that the performance of the same brush, with the same size and settings at one zoom level is acceptable, but it gradually declines until I zoom out and back in again. it then goes back to being sorta smooth.
seems more like a bug than a hardware limit, since in certain conditions the brush works well.
here's some steps to repro the conditions of my tests if you want to try:
1 in a document that's at least say 3000px wide create a layer and fill with 50% gray,
2 go to filter, add noise
3 duplicate noise layer a few times, say 4 times
4 set all noise layers to overlay
5 now at say 50% zoom in a layer underneath all the noise layers, use the mixer brush, (personally I use a custom brush with a texture on but you should be able to reproduce with most brushes), make sure its set to sample all layers,(autoload and autoclean disabled) some wetness, (say 30%) 100%load, 0% mix, 100%flow
do some strokes with it, sample again, etc try to simulate a little painting..while doing this it appears to me that the performance of the stroke goes down,regardless of the brush size (reducing the brush size doesn't seem to improve the performance for example)
then zoom in to say 100%, now do another stroke and in my machine it just becomes so much faster.
alternatively try zooming out and then back in, again massive performance increase.
then if I keep working at this zoom level for a while I notice a gradual loss of performance, until I zoom out/ in again.
is anyone able to reproduce this conditions? I'm pretty sure I've noticed it on different machines
It seem like what your seeing is normal. If you keep stroking each stroke take some amount of time to perform. You get way ahead of Photoshop processing of the strokes. The stroke are done in sequence and are queued up for rendering. The brush stroke that took 3 minuets to render on my machine had I done 10 strokes in a few seconds would still take a half hour for Photoshop to render all the strokes. It may even be possible for one to get so far ahead of Photoshop that the system may not be able to queue up additional strokes because a system resources was exhausted..
no sorry, I don't queue strokes and wait for PS to finish them all..
I always wait for one stroke to finish before doing the next, the performance change I mention is in relation of start to finish of the actual, current, stroke.