Editing 2916: Machine

{{comic
| number    = 2916
| date      = April 5, 2024
| title     = Machine
| image     = machine_2x.png
| imagesize = 740x740px
| noexpand  = true
| titletext = The Credible Machine
}}
* To experience the interactivity, visit the [https://xkcd.com/2916/ original comic].

==Explanation==
{{incomplete|Created by a WELL OILED ROBOT. Do NOT delete this tag too soon.}}
This is the 14th [[:Category:April fools' comics|April fools' comic]] released by [[Randall]]. The previous April fools' comic was [[2765: Escape Speed]] from 2023, which was released on Wednesday, April 19, 2023.

Once again an April Fool's Day Comic came out late, as Randall did not release this on April 1st, even though April 1st did fall on a Monday, a normal release day. It first came four days later with the Friday release on April 5th. That this is to be considered an April fools' comic, in spite of the later release, was confirmed on the xkcd Facebook page, see the [[#Trivia|trivia section]] below.

This is a spin on the game {{w|The Incredible Machine}}. The title text explicitly references this, albeit in a linguistic reversal.

Upon loading the page, you are presented with marbles being added to a box by geared wheels, with a button to open a “tool panel”. You are encouraged by Cueball to direct the marbles into a little “output” gear, and told that marbles have a lifespan of 30 seconds to reduce clutter. There are large and small boards available for use, as well as some gimmicky stuff like prisms<!-- that sort marbles by color SEEM TO 'RANDOMLY' REFRACT/DEFLECT, IF SORTING IS TRUE THEN EXPLAIN IN NEW/RELOCATED SECTION? --> (which deflect marbles) and fans (which blow marbles around).

The comic starts in a main screen where the user can create a {{w|Rube Goldberg machine}} in a "Cell" where the goal is to route a constant stream of colored balls from an input on the ceiling or a wall to outputs of a matching color on the walls or floor. After the comic is first opened a window pops up over the machine where Cueball in a lab coat tells you to route the balls from the inputs to the outputs. If any balls are left in your cell for more than 30 seconds, they fade away. The first time a ball fades away another popup informs you that the balls are removed for security reasons. When you have built a machine which succeeds in routing enough balls to the output, a popup will prompt you to submit your cell to be added to the public machine.

<gallery heights="200" widths="150">
File:2916_popup_intro.png|Introduction popup
File:2916_popup_time.png|Time limit popup
File:2916_popup_submit.png|Submission popup
</gallery>

The button in the bottom right corner brings you to a page where you can drag around to view all of the machines that have been submitted, with a title for each in the upper left corner. In this view you can see that all of the outputs are also inputs for another cell, except for the top row where the inputs come from off screen and the lowest row which output through a launcher of some kind to a set of four colored-coded containers far below. Any empty cells are marked off by yellow tape with the words "UNDER CONSTRUCTION" as well as "DJIA ↑ 31415" once in each cell. "DJIA" stands for the Dow Jones Industrial Average, with "DJIA ↑ 31415" indicating that it rose to 31415 points, 31415 being the first five digits of pi, without the period.

Under construction cells will feed balls of the appropriate colour into neighbouring cells so long as you are not looking at them. Once you scroll to look at them, the supply of balls stops and subsequent cells in the chain will not receive any; scroll away from them again and the supply will resume.

When you press submit, you will see your creation placed on the grid.  However if you refresh that cell will likely be under construction or replaced with someone else's machine. However, other people's machines are consistently placed, so it appears that there is some moderation process selecting a machine for each cell out of the machines submitted by users.

The grid is 12 cells wide, and grows in height. The largest size observed so far is 12x48, for a total of 576 cells.  The machine's height is determined by the lowest cell; This can be either your submitted cell, or a cell created by another user.

Whenever balls reach the bottom of the grid, they are directed towards 4 containers, one of each color. Each ball is accurately sent to their appropriate container. These containers are above a pit, and periodically dump their contents. If no balls are directed towards the containers, the pit will be empty. If one or two streams of balls are making it, Cueball and Megan sit in a small boat named the USS Buoyancy.  More streams of balls are likely to add more changes.

===Toolbox items===
{| class="wikitable" style="margin:auto"
|+ List of objects
|-
! Description !! Effect !! Image
|-
| Plank || Static || [[File:2916_plank.png|frameless|upright=0.25]]
|-
| Hammer || Static || [[File:2916_hammer.png|frameless|upright=0.25]]
|-
| Sword || Static || [[File:2916_sword.png|frameless|upright=0.25]]
|-
| Hinged scoop || Rotates around its hinge, tries to stay horizontal with a springy effect || [[File:2916_scoop.png|frameless|upright=0.25]]<br>[[File:2916_scoop_mirrored.png|frameless|upright=0.25]]
|-
| Anvil || Static || [[File:2916_anvil.png|frameless|upright=0.125]]
|-
| Brick || Static || [[File:2916_brick.png|frameless|upright=0.125]]
|-
| Fan || Blows away balls in front of it. Different colors are affected by differing amounts (yellow balls are lightest, and can be levitated above an upward-facing fan).|| [[File:2916_fan.png|frameless|upright=0.125]]
|-
| Pillow || Balls will not bounce if they hit it || [[File:2916_pillow.png|frameless|upright=0.125]]
|-
| Round bumper || Bounces balls away at significantly higher speed || [[File:2916_round_bumper.png|frameless|upright=0.125]]
|-
| Triangle bumper left || Bounces balls away at significantly higher speed || [[File:2916_bumper_left.png|frameless|upright=0.125]]
|-
| Triangle bumper right || Bounces balls away at significantly higher speed || [[File:2916_bumper_right.png|frameless|upright=0.125]]
|-
| Attractor/Black Hole || Pulls balls toward center, can be resized || [[File:2916_attractor.png|frameless|upright=0.125]]
|-
| Repulsor/White hole || Repels balls away from center, can be resized || [[File:2916_repulsor.png|frameless|upright=0.125]]
|-
| Prism || "Refracts" balls as they enter and exit || [[File:2916_prism.png|frameless|upright=0.125]]
|-
| Wheel || Spins depending on arrow keys [right/left] pressed while selected (default:anticlockwise), deflects balls, can jam with enough resistance (e.g. glut of balls or against other elements). || [[File:2916_wheel.png|frameless|upright=0.125]]
|-
| "Good job" trophy || Static || [[File:2916_trophy.png|frameless|upright=0.125]]
|-
| Glass cup || Static || [[File:2916_cup.png|frameless|upright=0.125]]
|-
| Cat || Swats away balls in front of themself (was added later) || [[File:2916_cat_new.png|frameless|upright=0.25]]
|}

{| class="wikitable" style="margin:auto"
|+ Characters
|-
! Description !! Image
|-
| Ponytail with raised arms || [[File:2916_ponytail_arms.png|frameless|upright=0.125]]
|-
| Ponytail standing || [[File:2916_ponytail.png|frameless|upright=0.125]]
|-
| Cueball with raised arms || [[File:2916_cueball_arms.png|frameless|upright=0.125]]
|-
| White Hat || [[File:2916_whitehat.png|frameless|upright=0.125]]
|-
| Knit Cap sliding, resting, or floating? || [[File:2916_knitcap_resting.png|frameless|upright=0.25]]
|-
| Knit Cap || [[File:2916_knitcap.png|frameless|upright=0.125]]
|-
| Helmet? || [[File:2916_helmet.png|frameless|upright=0.125]]
|-
| Probably Deterministic sign || [[File:2916_deterministic.png|frameless|upright=0.25]]
|-
| Squirrel || [[File:2916_squirrel.png|frameless|upright=0.125]]
|-
| [[1682: Bun|Bun]] || [[File:2916_rabbit.png|frameless|upright=0.125]]
|-
| Cat || [[File:2916_cat.png|frameless|upright=0.125]]
|}

=== Color routing ===
The different ball colors have different physical properties. Red balls are more bouncy than other balls, green balls are heavier, and yellow balls are lighter and slightly bouncy. The following values were extracted from the code:
{| class="wikitable sortable"
! Color
! Mass
! Density
! Restitution (bounciness)
! Linear damping (drag)
|-
! data-sort-key="00F" | Blue
| 0.08
| 1
| 0
| 0
|-
! data-sort-key="F00" | Red
| 0.08
| 1
| 0.8
| 0
|-
! data-sort-key="0F0" | Green
| 0.75
| 9.325
| 0
| 0
|-
! data-sort-key="FF0" | Yellow
| 0.024
| 0.3
| 0.6
| 2
|}

For certain combinations of inlet and outlet 'gates', it is necessary to 'cross the streams'. e.g. to direct righthand-entry balls to a lefthand-exit and vice-versa. It is possible to just construct the field to send two (or more!) sets of balls to fly across a common gap, to land on an appropriate reception area that leads to the chosen exit. But, though this is not {{w|Proton pack#Crossing the streams|completely inadvised}}, the timing of the balls cannot be guaranteed to be in sync (or, rather, anti-sync) with each other and collisions ''will'' occur, especially under the variations of delivery that might significantly alter the ballistic path across the gap. Even if the trial machine works, in isolation with a steady stream of all balls entering the field of play, once submitted it will inevitably be fed by a more chaotically-routed preceeding construction.

In order to maintain sufficient correct arrivals at exits<!-- and, I believe, sufficiently few ''wrong'' arrivals... does it enumerate the 'net correct delivery rate' to establish the validity of the output? ...needs more research -->, it may be necessary to add a method of filtering the hues.

This could just mean introducing a 'wrong hue trap' beyond any crossing point(s) that send the occasionally wrong ball back to the cross point (or let them time-out in a dead-end, relying upon few enough failures from the rest of the balls, along with all colliding balls that subsequently missed ''any'' chance of reaching an exit). Alternatively, two (or more) feeds of marbles could be fed through a deliberate 'sorter' that does a sufficiently reasonable job of separating the combined sets out towards their intended target-exits.

The various physical qualities of the balls suggest a number of methods for redirecting separate hues to separate onward journeys. This can be done by isolating a hue from every other hue, then passing on (if necessary) to a setup extracting a different one from the remainder, and perhaps also a third time. It may also be possible to merge 'arrangements' of sorting mechanics to efficiently distribute straight into three ''or even four'' onward tracks towards the desired outputs, but that is left as an exercise to the reader.

<!-- This may not be the most efficient depiction (with just four/less 'core methods', after following "See X/Y"s) but if the Prism or some other item actually adds zignificantly practical pre-"See" differences then the all-vs-all format (with the reversals/same-to-sames still there to be abbreviated/redirected) will come into its own.
If you so wish, redo. e.g. as ";header + :paragraph"s or table of "!Combo(s)!!Methodology"
NB:
  1x ! Row-start Style=                                                 | Row-start 'header'
  4x | *Unwikiparsable key just for editors' benefit* + optional Style= | Contents
...right now, I've mostly added "vertical fan" experiences (which I find useful for all but R/B differentiation), but more about bumpers (including fan-/wheel-collisions), the positive/negative 'force objects' and of course horizontal/angled fans could also be added.
-->
{| class="wikitable"
! style="background-color:black; color:white" | To separate !! style="background-color:lightblue" | Blue !! style="background-color:lightgreen" | Green !! style="background-color:yellow" | Yellow !! style="background-color:red" | Red
|-
! style="background-color:red" | Red
| *R/B* | '''Use 'bounce''''
The sole difference is how much balls will rebound from objects. Well managed and constrained ricochets should allow a sorting action.
| *R/G* | '''Use mass or 'bounce''''
Green balls cannot be levitated by a vertical fan. An incline across any such fan(s) will levitate only non-Greens.<br/>Green, like Blue, rebounds differently to Red. Green balls are also effected by black holes much less than all other balls.
| *R/Y* | ''See Y/B''
| *R/R* style="text-align: center; background-color:black; color:white" | n/a 
|-
! style="background-color:yellow" | Yellow
| *Y/B* | '''All methods'''
Yellow, alone, exhibits high drag against any unforced motion.<br/>It is also unique in all other ways; e.g. can be levitated highest, against all other hues (though most profoundly against Green).
| *Y/G* | ''See Y/B''
| *Y/Y* style="text-align: center; background-color:black; color:white" | n/a
| *Y/R* style="text-align: center; background-color:gray"  | ''See Y/B'' <!-- R/Y->Y/B -->
|-
! style="background-color:lightgreen" | Green
| *G/B* | '''Use mass'''
Green balls cannot be levitated by a vertical fan.<br/>There is also a not so marginal difference in density that might be exploited, such as by using black holes, which only minimally effects green.
| *G/G* style="text-align: center; background-color:black; color:white" | n/a
| *G/Y* style="text-align: center; background-color:gray"  | ''See Y/B'' <!-- Y/G->Y/B -->
| *G/R* style="text-align: center; background-color:gray"  | See R/G
|-
! style="background-color:lightblue" | Blue
| *B/B* style="text-align: center; background-color:black; color:white" | n/a
| *B/G* style="text-align: center; background-color:gray"  | See G/B
| *B/Y* style="text-align: center; background-color:gray"  | See Y/B
| *B/R* style="text-align: center; background-color:gray"  | See R/B
|}

Even when not strictly necessary for one's own submission, once submitted into the full playing grid the player's own contribution may find itself working with less 'pure' delivered ball-streams (from an imperfectly separating feed-in contribution). It is possible that this more interactive disruption can make the new setup behave erratically or even entirely incorrectly.

It might be thought good practice (but not ''necessary'') to deliberately combine any or all inputs and do a full job of splitting them again, just in anticipation of possibly having to deal with such cross-contamination and being able to 'clean up' the onward stream(s) for the benefit of others. This would of course be particularly difficult if the isolated building-phase does not provide all four hues to 'test' against, so any speculatively added filtering would have to be added 'blind' (and only on the offchance that any anticipated incorrect balls will actually enter the arena) and without any legitimate exits to which such rejects could be shunted (therefore could accumulate, up until any 'time out' that might apply to any ball once operational as part of the combined grid).

Single-input/single-output designs might not particularly require ''any'' sorting mechanism, in theory, though the unexpected 'contamination' of the system with balls of different masses/etc could perhaps introduce malfunctioning passage from the added chaos it might succumb to.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[The placeholder image shows four balls, colored red, green, yellow and blue, bouncing on top of three white blocks. Text in the center: "[visit xkcd.com to view]"]

:[Cueball with lab coat, intro popup]
:Cueball: Balls falling into your cell should be routed to the outputs at a steady rate.

:[Cueball with lab coat, warning popup]
:Cueball: For security reasons, balls that remain in your device for more than 30 seconds will be removed and destroyed.

:[Cueball with lab coat, submit popup]
:Cueball: Congratulations! Your contraption has passed all tests. Press [submit button] to submit it to be added to the machine!

==Trivia==
*Randall acknowledges the people who helped him create this comic in a [[Header_text#Machine|comic-specific header text]]. 
**With 11 different involved apart from Randall this is by far the comic with most people involved.
*There are some secret key combinations hidden, here are a few of them
**ctrl+alt+b -> follow balls
**ctrl+option+shift+d -> debug overlay
*When Randall posted a [https://www.facebook.com/TheXKCD/posts/pfbid0Cs97awQZi1ZiaEXouAex9tXrwAS3qJV3RmAiuCq5uvZQwqZVMgDmcqJ7JU9LYodYl link to this comic] on his [https://www.facebook.com/TheXKCD Facebook feed], he directly wrote that it was a late April Fools' Day!
**MACHINE
**Happy Belated April Fool's Day!
*This thus ends any discussion of whether this should be seen as an April Fool's comic or not. 
**It just came out 4 days late. This has also happened several times since [[Garden]].
[[File:2916 Machine Facebook April fools' confirmation.png]]


{{comic discussion}}

[[Category:April fools' comics]]
[[Category:Comics with color]]
[[Category:Dynamic comics]]
[[Category:Comics with animation]] 
[[Category:Interactive comics]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Knit Cap]]
[[Category:Characters with hats]]
[[Category:Squirrels]]
[[Category:Buns]]
[[Category:Cats]]