The bug
Starting with Snapshot 13w10a, various small particles will visibly jump to the northwest before following their normal path.
First seen with void particles, has since been observed with the small whitish particles seen in water, the dust particles that rise from mycelium, droplets from the bottom of blocks with either lava or water above them, the larger round bubbles in water, the droplets of rain when they land, and the green particles from using bone meal on a plant.
To view the glitch, simply get to where the particular type of particles would appear and note their movement. Facing either northeast or southwest and either straight down or up (for those particles that appear at the bottom of a block) makes this easier.
Code analysis
Code analysis by @unknown can be found in this comment.
Linked issues
Comments 30
I see that they just go to the northwest no matter what direction you face. Not tested a whole lot though. Cam be seen from a distance, too.
Here you go, Grum.
When I first noticed this problem/glitch, it was the Void Particles near Bedrock. I was accustomed to mining around and seeing particle motion like in this clip from 1.4.7: http://gfycat.com/RealisticAlarmingFly
But then as of the very next update, the particles would appear for one brief frame, and then jump over the course of 2-3 frames @60fps to a new location roughly to their NorthWest before stopping at a new location and then finishing their "journey" for another second or so prior to fading or disappearing. This behavior spans many many versions, but the last version we can still access that shows it fully is 1.7.10: http://gfycat.com/FrenchBouncyDobermanpinscher
By then I was reporting and confirming per version, but I open up 1.8.1-pre3 and see the equivilent of this: (1.8.1): http://gfycat.com/WindingJadedGemsbok
Void particles have been summarily removed. :O
So, I found a new way to confirm that the particle glitch still happens, but now the test is a lot harder and I never encounter the effect in regular gameplay because the void particles were the primary way to see it.
Nonetheless, I can confirm even 15w47c continues the bug.
Steps to reproduce these days: open creative mode, either drink a potion of night vision extended (older versions) or it's going to be cleaner to use an "effect of night vision" command and turn off the obnoxious effect-particles in newer versions. Find water at least 8 blocks deep or so. Dunk down into the bottom. Look down near your feet and press F5 for behind the head view (when you have potion/effect particles spamming your view this helps limit the attention-drawing noise that they generate, but also gives you the best view of the water particles).
Looking down past your head to the ocean floor at a steep angle helps make the particle-glitch a lot easier to notice.
As of 1.4.7, no problem the particles appear, potentially float around by a millimeter or so, and then vanish.
1.4.7: http://gfycat.com/WhoppingGregariousGreendarnerdragonfly
For every newer version, the particles glitch towards the NW prior to settling into their ordinary behavior.
1.5.2: http://gfycat.com/ImprobableOptimisticDobermanpinscher
1.7.10: http://gfycat.com/CautiousOddballKouprey
(Starting with 1.8ish, the noisy potion particles I was too lazy to suppress here stop just wafting upwards and begin to waft out much more aggressively, lol!)
1.8.8: http://gfycat.com/BonyDisfiguredHornet
15w47c: http://gfycat.com/SoreHomelyBasilisk
Here are the save files I made for each of these test scenarios. In both, you should already be in the right place. Underwater, you have night vision active for several more minutes and a bottle of it in you hand to re-quaff at will. Underwater you WILL need to press F5 to set the behind-the-head view, as that is not saved with the world. In Void Particle save, you don't gotta do nothing but sit and observe. xD
http://lightsecond.com/pub/MC-12269%20void%20particles.7z
http://lightsecond.com/pub/MC-12269%20underwater.7z
Reasons to fix this ancient bug:
Making foggy particle systems look professional enough to spend any time looking at. Some time down the road you might want "freezing fog" as a game element, wouldn't that be tits?
Also, this bug most likely tells us that you've got two coordinate systems in the client which have glitched origin points relative to one another. One responsible for spawning each particle and a completely different one responsible for evolving the particles after they leave their spawn points.
I believe I have finally solved this bug, in attempting to fix my own extension of this particle's glitchy movement. Here is the explanation as well as I can give it, using MCP names for the methods involved:
Particle#setSize is bugged in that it sets the BB based on the min coords. so a width/height of 0.2 gives a bb from 0,0,0->0.2,0.2,0.2.
Particle#setPosition moves the BB so that its geometric center is at the particles xyz coords.
There is no problem you call setSize() and then setPosition(). But particles like ParticleDrip call setSize() a second time, which shifts the BB to the NW (negative axes).
Particle#resetPositionToBB is what actually causes the glitched movement.
The bug (imo) is Particle#setSize growing the BB from the min not the center.
After further testing, the particle movement is toward the Northwest, meaning the direction you face will affect the direction the particles move.
Edit: That last part is in relation to screen position. My initial report described the movement as jumping to the right on the screen, but further observations showed the real movement.