What exactly is a "mesh island" ?

well technically in the FM you got shards and mesh islands: Shards are the result of fracturing, while mesh islands manage the "look" of the simulation mesh. But here I used the term "mesh island" synonymously for each separate shard or piece of geometry the FM creates. So a mesh island = a piece of geometry whose vertices are moved as an unit according to motion data of the appropriate rigid body it belongs to.

If I do the adjustments as under 1) and 2) and also 3) ...so make the wall Triggered and the Wrecking Ball the Trigger and I also set the angle to zero it does not work. Only when I keep angle = 1 degree. It this correct ?

yup, angle zero means to ignore the breaking angle and rely only on breaking thresholds. the default threshold of 10 is way too strong for the default mass of 1 (where each shard gets assigned a fraction according to the fraction of the shards volume to the total volume (roughly)). So the special breaking conditions like angle, percentage or distance are there to let things break "easier".

I thought it as meant that when you make the wall triggered and the wrecking ball the trigger that the constraints are not of importance any more ?

should I lower the breaking treshold ?

constraints are there to glue the shards together in general. you can use triggering with or without them. But in simple cases of triggering, to achieve certain effects, you might as well omit the constraints, yes. But there are use cases to have constraints too (easily breakable ones together with clusters for example, to let for example collapse simulated geometry easier when it is hit (e.g. a building)

hi

thanks

hey, maybe its better we chat here instead of filling the response log :)

is it ok that I ask you some simple questions ?

well the breaking threshold was the first setting i implemented, before the angle and stuff, the angle /percentage / distance setting is there for easier control

yup, you can ask :)

starting with the "threshold" ... what is this exactly ...how does it the wall prevent from breaking or not

how should I look to the amount of threshold ?

well its just a value which needs to be exceeded by a force affecting both constraint partners, this is handled in bullet internally. if the force is stronger than the threshold, the constraint will break. The forces will become higher if the constraint partners have more mass, more speed (fall from higher height for example)

well, try for example 0.1 or 0.01 with those default settings of mass, or crank up the mass to 10 or 100 or so

you need to experiment a bit if using thresholds and masses only, until the result comes close to that what you wanna achieve, a bit hard to give good general advice here

so the threshold is related to the mass of the "trigger" and the "triggered" object

yes I understand

then angle, percentage and distance ?

well, trigger and triggered are there to activate shards on impact, technically animated rigidbodys (before they are triggered) have a mass of 0, means they dont participate in simulation (internally)

yup, angle is in degrees, means if the angle between 2 constraint partners exceeds x degrees, it will break... distance... if a distance in blenderunits is exceeded (like 0.01 or so) it will break... and percentage... if say 50 % of all constraints this islands participates with are broken, break all others of this island too

constraints partners are in my case the wall and the wrecking ball ?

you can adjust the values of angle say to 5 degrees, it will break later than with 1 degree, and 0 means always ignore the settings

no, constraint partners are the shards of the wall, per constraint we have a pair of shards, and each shard can be in multiple constraint partner pairs

so mostly between each shard and its surrounding neighbors we have constraints

ok ...so the constraints relate to the relationships between shards

shard x and neighbor 1, shard x and neighbor 2, and so on.. and shard x participates in constraint pairs with neighbor 1 and 2

ok

yes @ relationship between shards, a constraint just says shard x and shard y are connected

what exactly is this search radius

well each shard "looks" with this distance around its centroid whether there are neighbor centroids, and connects with those found neighbors. The higher the radius, the farther away "neighbors" are taken into account too (means more constraints, object becomes more stable, but simulation becomes slower too due to more constraints are needed to be processed

distance is blender units ?

so if you have a default cube with size 2, and say 100 shards, each shard is likely to be rather small, so it might be enough to have a search radius of 0.5 to connect all... if you have a cube with size 5 and 10 shards or so, you might need radius 2 or more... and yes its plain blender units

atleast i didnt take special care to take units into account there, in the code

but what does the modifier with the shards within search radius ?

what do you mean with the "connect all"

if constraints are enabled, then each shard will build constraints with each other found shard in this radius

connect all means the object doesnt fall apart initially, only after it hits something or so, it should stay together

ah ok ... so when constraints enables the search radius tells the distance within those constraints are working

the radius is applied sequentially to each shard centroid, say you have 10 shards, each of those 10 will look for neighbors around it

ok ... now this Triggered and Trigger .... if the wall is Triggered and the Wrecking Ball is the Trigger .... are the constraints still of importance ( I Thought the constraints did not matter anymore)

I thought the angle did not matter anymore in this situation

you also may switch from Constraint Target "Centroid" to "Vertex"... then you need to take care to reduce the radius to 0.01 or so, because then each vertex(!) searches for nearby vertices of other shards, this means you mostly get only adjacent neighbors.... and... yes the constraints are still useful... but in case of a static object being hit with a trigger you "may" also omit the constraints, it might look similar

you can use constraints and triggers together or not, depending on your desired result

but I thought when using triggers (and not constraints) then the shards should break when hit by the trigger

In my blend file that does not happen

again its a bit hard to give good general advice here... well i guess you still have the angle to 0 and constraint checkbox enabled or ?

to disable constraints, disable the checkbox too

hmmm you mean the wall does not break without constraints ?

you are right .... I have to uncheck the checkbox

stupid me

else the threshold takes precedence if the checkbox is still enabled

so the constraints are working when you check the checkbox

yes, this is a global switch

ahhhhhhh

so when checked the treshold rules

unless you specify angle and stuff, yes

and when unchecked simply trigger and triggered rule

then the angle and perc. / distance if set take precedence

ok

trigger starts the simulation of hit objects basically

before that, they are kinda "asleep"

yes but when that happens and constraints are unchecked they dont interfere with the simulation

but when constraints are checked they can influence the "triggered" simulation ... is it like that ?

well they just influence the "stability" of the object, no matter whether triggered or not... in your case you had a high constraint search radius and limit, means you connected a lot of islands with even farther neighbors, which makes the object more "stable"

i only added triggered / trigger so that the entire wall doesnt start participating in the sim from the start

but only the hit shards after being hit

when triggered only the shards that are hit participate ?

yup, only the ones hit by the trigger (there are more options too, but thats for more advanced usage)

the others remain animated / kinematic, means they only "respond" to animation

so, my lunch break is over in about 5 minutes... then i need to continue my work :)

haha

thanks a lot .... I now can go further

youre welcome :)

this really helped

cool :)

thank you for your time !!!!

and thanks for using the FM :)

yes, the possibilities are fascinating

I want also try to do some PR

I like it that you made it part of the Physics

bye for now

yes, the modifier stack panel would be rather full with all the settings

hi .... just giving your lecture another read :)

I was thinking .... is maybe Constraint Radius not more self-explanatory than Search Radius ?