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This PR requires @minetest/minetest#3677 Farming and plant growth has traditionally in minetest been implemented using ABM's. These ABM's periodically tick and cause plants to grow. The way these ABM's work has several side effects that can be considered harmful. Not to mention a comprehensive list of downsides here, but ABM's are chance-dependent. That results in the chance that some nodes potentially never get processed by the ABM action, and others get processed always. One can easily find this effect by planting a large field of crops, and seeing that some nodes are fully grown really fast, and some just won't make it to fully grown status even after hours or play time. One could solve the problem by making the ABM's slower, and giving them a 100% of action, but this would cause the entire field to grow a step instantly at ABM intervals, and is both ugly, and a large number of node updates that needs to be sent out to each client. Very un-ideal. With NodeTimers though, each node will see a separate node timer event, and they will likely not coalesce. This means that we can stop relying on chance to distribute plant growth, and assign a single timer event to grow the plant to the next phase. Due to the timer implementation, we won't ever miss a growth event, and we can re-scehdule them until the plant has reached full size. Previously, plants would attempt to grow every 9 seconds, with a chance of 1/20. This means typically, a plant would need 9*20 seconds to grow 1 phase, and since there are 8 steps, a typical plant growth would require 9*20*8 ABM node events. (spread out over 9*8 ABM actual underlying events per block, roughly). because plants are likely not growing to full for a very long time due to statistics working against it (5% of the crops take 20x longer than the median to grow to full, we'd be seeing ABMs fire possibly up to 9*20*8*20 with a 95% confidence interval (the actual math is likely off, but the scale should be correct). That's incredibly wasteful. We'd reach those conditions easily with 20 plant nodes. Now, after we convert to NodeTimers, each plant node will see exactly 8 NodeTimer events, and no more. This scales lineairly per plant. I've tuned the growth rate of crops to be mature in just under 3 whole days. That's about 1hr of game time. Previously, about half the crops would grow to full in under 2 days, but many plants would still not be mature by the end of day 3. This is more consistent. An additional problem in the farming mod was that the final fully-grown plant was also included in the ABM, causing infinite more ABM's even after the entire field had grown to completion. Now, we're left with the problem that none of the pre-existing plants have actual node timers started on them, and we do not want a new ABM to fix this issue, since that would be wasteful. Fortunately, there is now an LBM concept, and we can use it to assure that NodeTimers on crop nodes are properly started, and only have to do the actual conversion once per block, ever. We want to provide a fairly similar growth rate after this conversion and as such I've resorted to modelling some statistical data. For this I created a virtual 32x32 crop field with 9 steps (8 transitions) as is the default wheat crop. We then apply a step where 1 in 20 plants in the field grows a step (randomly chosen) and count the number of steps needed to get to 25%, 50, 75% and 95% grown. The resulting data looks as follows: 25% - ~120 steps * 9 sec / abm = 1080s 50% - ~152 steps = 1368s 75% - ~194 steps = 1746s 95% - ~255 steps = 2295s Next, we want to create a model where the chance that a crop grows is 100% every node timer. Since there will only be 8 steps ever, we want the slowest crops to grow in intervals of ~ 2300 / 8 seconds and the fastest 1/4 of crops to grow 1080 / 8 seconds intervals. We can roughly compare this to a normal distribution with a median of 1400 with a stddev of ~350 (thick fingering this one here). The rest is a bit of thick-fingering to get similar growth rates, taking into account that ABM's fire regularly so if they're missed it's fairly painless, but our timers are going to be 1-2 minutes apart at minimum. I calculate the timer should be around 150s median, and experimented with several jitter ranges. Eventually I settled for now on [80,200] with a redo of [40,80], meaning that each growth step at minimum takes (80 to 200) seconds, and if a negative growth condition was found (darkness, soil not wet, etc), then the growth step is retried every (40 to 80) seconds. The end result is a growth period from seed to full in ~ 2.25 minetest days. This is a little bit shorter than the current growth rate but the chances you'll miss timer ticks is a bit larger, so in normal gameplay it should be fairly comparable. A side effect is that fields grow to full yield fairly quickly after crops make it to mature growth, and no crops are mature a very long time before the majority grows to full. The spread and view over a growing field is also fairly even, there's no large updates with plenty of nodes. Just a node here or there every second or so in large fields. Ultimately, we get rid of ABM rollercoasters that cause tens of node updates every 9 seconds. This will help multiplayer servers likely a lot. |
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| .. | ||
| beds | ||
| boats | ||
| bones | ||
| bucket | ||
| creative | ||
| default | ||
| doors | ||
| dye | ||
| farming | ||
| fire | ||
| flowers | ||
| give_initial_stuff | ||
| screwdriver | ||
| sethome | ||
| stairs | ||
| tnt | ||
| vessels | ||
| walls | ||
| wool | ||
| xpanes | ||