thinkingParticles 7.3

BulletPhysics

 

thinkingParticles ships with multiple physics solvers and there are three  to choose from. Some solvers are better in certain situations than others, thinkingParticles' native solver "Shape Collision" is used on high-end movie productions when quality and accuracy of collisions are more important than simulation times.  On the other hand PhysX is more often used in game productions were simulation accuracy is not that important. BulletPhysics offers the best compromise of both worlds accuracy and speed, even so it is not as accurate as the one found in the "SC" solver.

 

 

Because of the academically challenging nature of the subject matter, it is assumed that you have at least some basic knowledge of computer based physics and dynamic simulations. If not, it is recommended that you get hold of a good book and familiarize yourself with the concepts of computer based physics simulations.

 

Operator Inputs  

ON - (Bool) This input data stream determines whether the operator is considered 'on' or 'off'. You can connect other operators to this input channel such as a Bool Helper to activate/deactivate the whole operator.

Time - (Time) This input data stream is used to define the local time for the operator when the user wants to override the default system time.

Floor Node - (Node) This input data stream is used to specify through a node helper for example a 3D mesh as a floor collision object. A floor object is automatically treated as immovable with an infinite mass.

UI Control Parameters - those input data streams are the equivalent of the UI controls, keep in mind that there is no visual indication that an operator is connected to any of those inputs! It might be needless to adjust a value if it gets overwritten by a connected operator.

Operator Outputs  

Particle - (Particle) This output data stream supplies the current particle information. Use this to modify specific particle properties.

Collided - (Bool) Whenever a collision event occurs, this output data stream will return true as its value. In all other non-colliding situations, the output will report false as the value.

Collision Average Position - (Position) This output data stream provides the current interpolated collision point.

   

Collision Average Normal - (Normal) This output data stream outputs the interpolated normal of the calculated collision point.

Sleeping - (Bool) This output data stream holds the frozen status of the particles, as determined by the parameters set forth in the particle group rollout. When particles are considered "frozen" or "inactive", this value will be true. When particles are actively moving, this value will return false.

Double Star = Secondary Initiator Outputs  

Double Star Output (**) behaves like the Top-Level Initiator outputs, this outputs activate connected nodes for evaluation. It is important to understand that all connected nodes will be evaluated. However, as this is a secondary Initiator output, it can not be combined with the Top Level Output at the same time. The main rule still applies: Never use 2 Initiators on the same node or wiring.

Number of Collisions - (Integer) holds the total number of all collisions that happened for a particle. A collision may happen multiple times, especially with sliding objects (surface - surface). Note, this is a secondary Initiator output that can not be combined with the top level Initiator outputs at the same time. Either the Top-Level will be active or the low level department but not both at the same time.

Coll Index - (Integer) outputs the current index number of the collision. This might be used to get the current progress of the collision evaluation. Collision index can become as big as the Number of Collisions value, if this is reached the collisions are done.

Coll Particle A - (Particle) outputs the particle A of the collision pair. This output is always evaluated before particle B!

Coll Particle B - (Particle) outputs particle B of the collision pair.

Coll Floor - (Bool) when a collision with the floor object happens, this output will be set to True.

Coll Position - (Position) outputs the real world position Collision point.

Coll Normal - (Normal) outputs the normal of the calculated collision point.

Coll Position A - (Position) outputs the collision position of Particle A in local object space.

Coll Position B - (Position) outputs the collision position of Particle B in local object space.

 

Rollout Menu  

The BulletPhysics operator is used to control the physics solver parameters.  The settings you find within this menu are "global" settings those settings would affect the overall simulation.

Particle

  

Group - this drop-down list selects the particle collision partners for the floor or inter-particle collision.

       

Deflector - is used to choose the deflector objects. Important: those objects will be treated as unyielding, all the time, regardless of their local physics settings. One application would be to use recorded particles as deflectors.

IMPORTANT
Deflector Particles will use the physics settings from the Floor controls.

Floor  

Shape - defines the shape of the collision object used for the floor.  There are 10 options to choose from, two was the one that fits closest to the object type used as floor.

Mesh - select this option to define the floor object as a mesh object.
Convex Hull - select this optimized version when the floor object represents a convex mesh.
Box - choose this option to use the highest level of optimization when the floor resembles a box shape
Sphere - select is option when the floor object is also a spherical shape.
Cylinder X,Y,Z - to optimize the floor collision with cylindrical objects choose either X,Y or Z.  
Cone X,Y,Z - for optimum collision detection with cone shaped objects, choose this option.

Restitution - Use this parameter to control the bounce value between the floor<->particle collisions. Higher values will make the particles lose less energy per bounce. Be aware that values greater than 100 will create extra energy and the particles will gain energy with each bounce.

Friction - This spinner defines the friction between particles and the floor when they are in contact (sliding). Higher values will make the particles slide less.

Physics

Iteration - sets the number of sub-steps to be used to estimate the real collision point of colliding objects. The lower this number, the faster the simulation will run. However, lower values would also mean less accurate results. In most situations, you can keep this value between 5-10, while in exceptionally complex scenes, you can try to set a value as high as 30 to get more accuracy.

Linear  Slop - Defines the penetration depth for object collisions. this value is measured in world units. A value of 1 equals to 1 unit penetration depth (overlapping). It is recommended to use the default value of 0.

ERP (Error Reduction Parameter) - use this parameter to adjust possible errors in a joint setup. When a joint attaches two bodies, those bodies are required to have certain positions and orientations relative to each other. However, it is possible for the bodies to be in positions where the joint constraints are not met. This ``joint error'' can happen in two ways:

1. 1. If the user sets the position/orientation of one body without correctly setting the position/orientation of the other body.

   2. During the simulation, errors can creep in that result in the bodies drifting away from their required positions.

Split Impulse -  by default, Bullet solves positional constraints and velocity constraints coupled together. This works well in many cases, but the error reduction of position coupled to velocity introduces extra energy (noticeable as 'bounce'). Instead of coupled positional and velocity constraint solving, the two can be solved separately using the 'split impulse' option. This means that recovering from deep penetrations doesn't add any velocity when this option is checked.
Although this removes most of the extra energy/bounce, it degenerates quality a little bit, in particular for stable stacking. Hence, the setting should be disabled. Also note that the split impulse option is only enabled for contact constraints, and none of the other joints (hinge/ball socket and so on), for quality reasons

Randomize Constraints Order - check this option to enhance "stacking" situations. Bullet solves constraints one constraint row at a time. By randomizing the order of solving the constraint rows, stacking stability can be improved (at the cost of a little bit of performance)

Warmstarting - Bullet uses an iterative algorithm where each iteration is based on the solution of previous iteration. If no warmstarting is used, the initial solution for Bullet is set to zero each frame. When using warmstarting, the first iteration uses the last solution of the previous frame. This improves convergence towards a better solution and hence stacking stability.

Factor - defines how much of the previous impulse is used for the next calculation step. A value of zero will turn off warmstarting a value of 1 will use the original value.

Multithreading - when checked some parts of Bullet will use multi-threaded code to speed up collision.

Size As Mass - Activate this check box to enable an automatic mass calculation that is based on the size of the particle. For example, a particle with a size of 2.0 will be treated as 2 Kg.

Wake up Sleeping Bodies - whenever this option is checked (animated) all sleeping objects (out of any physics simulation) are turned active again.

Soft Body

Air Density - defines how much friction between air and objects  should be considered in the physics simulation process. Higher numbers will create more "tumbling" like behavior on free fall simulations.

 

Recorder  

thinkingParticles allows you to record particle dynamics. It is always a good idea to use this feature whenever a simulation seems to be perfect for the job. Recording the particles as they bounce around will make life easier at a later rendering stage. Playback from hard disk is also usually much faster than calculating the solution each time you play back the particle collisions, especially considering time line scrubbing.

Select Record File - Click this button to bring up a standard Windows Save dialog. Any legal name and path can then be specified to save the recorded particle simulation.

Simulate, Play, Record - These buttons are fairly self-explanatory. The Simulate button turns the recorder into playback mode and will play back the recorded file on hard disk as you scrub the 3ds Max frame slider in the view ports. The Record button will switch the recorder into record mode. With the record button pressed, clicking the Play button on the 3ds Max time line will start the recording and simulation of the particle dynamics. After the last frame has been reached, the recording automatically stops and turns into Play mode to show you the results.

Active Time Segment / Range - This is a standard 3ds Max control that lets you choose whether you want to record the entire particle animation, or just a specified range of frames as defined within the two spinners.

Redraw Views - when checked, the 3ds Max view ports will be updated while simulating. Depending on scene complexity it might be a good idea to turn of View Updates while simulating.

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