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Fix: Use correct units for particle properties
Needs ReviewPublic

Authored by Leon Eckardt (Leon95) on Feb 1 2019, 3:32 PM.

Diff Detail

rB Blender
Build Status
Buildable 2841
Build 2841: arc lint + arc unit

Event Timeline

Did test the patch to see if the numbers in the viewport actually describe what is happening? I'm not sure about the percentages and velocities.


Maybe that tooltip should be changed then. Just to "Size of particles in the viewport".

Percentages and Velocities are there, tested. Going to fix the tooltip

Leon Eckardt (Leon95) added a comment.EditedFeb 1 2019, 3:53 PM

Understood it wrong. You mean that 1m/s displayed actually means 1m/s, right?

afaik damping & drag_factor should be PROP_FACTOR and not PROP_PERCENTAGE?

Understood it wrong. You mean that 1m/s displayed actually means 1m/s, right?

Right, and the same for all the other properties.

Did some Research:

  • normal_factor (Speed)
  • tangent_factor (Speed)
  • factor_random (Speed)
  • angular_velocity_factor (Speed - Radians per second) How test it? I don't know how it is meant to work.
  • root_radius and tip_radius makes no sense, since there is a radius_scale. But they are in scale if scale_factor = 1. However only cycles shows the hair thickness.
  • mass (Mass) is strangely off: A Particle with the mass of "1kg" behaves roughly like a rigid body of 0.043kg (Using a = F/m applying a constant force with Force Forcefield) see Blendfile

(No guaranty that i overlooked one damping factor)

  • timestep (Time)
  • display_size (Length)

Dont know how to test:
drag_factor (Percentage)
damping (Percentage)
child_parting_min (Angle)
child_parting_max (Angle)
child_radius (Length)
kink_amplitude (Length)
kink_frequency (Length)

switch scenes for the different Properties:

(Stats: 3 bugs, 3 Crashes of wich one is reproducable, will report later)

The mass property is not immediately clear what unit it is in. According to old documentation, mass is indeed supposed to be in kg, but not sure if that's still the case.

@Sergey Sharybin (sergey) Do you know what unit the particles mass property is in?

@William Reynish (billreynish), i would expect it's in kilograms. Don't think this ever changed, but not sure if all aspects are preferring physics accuracy over correct units.

So, what to do for the Mass property? Should we just go ahead a label it as kg?

  • Added PROP_DISTACE: hair_length, size_random
  • set to PROP_FACTOR: drag_factor, damping
  • set to PROP_NONE: root_radius, tip_radius because of radius_scale

@Sergey Sharybin (sergey): I kept particle mass as kg

Leon Eckardt (Leon95) marked an inline comment as done.Feb 5 2019, 1:14 PM
  • Add object_factor; Rename Child Size to Child Scale

Oups, did not want to include that. arc was adding it. But can be added if the default radius_scale can be set to 1.0 by creation time of particle system. (Startup.blend?)