BIMsmith Winter Wonderland Holiday Revit Family Competition 2024
How I built a custom particle system in Revit to simulate falling snow - complete with wind physics, 2,500 animation frames, and the code to make it happen.
What I Built: A Particle System in Revit
The challenge: Create a realistic falling snow animation using only Revit families and parameters.
The result: A custom snowflake family with wind physics, animated across 2,500 frames on the Snowdon Towers sample project.
Why Take on This Challenge?
Every December, I reserve time for the BIMsmith Winter Wonderland competition. It’s my annual excuse to push Revit’s boundaries and discover what’s actually possible.
This year’s question: Can I build a working particle system in Revit?
While testing my plugins on Paul Aubin’s Revit sample project (thanks Paul!), I decided to make it snow on Snowdon Towers. Not just static snow - animated snowflakes falling and swirling in the wind.
How the Snowflake Family Works
The snowflake family looks simple, but it packs some clever engineering:
- Parametric shape control - Basic formulas adjust the snowflake geometry
- Wind physics - A mathematical formula creates realistic swaying as it falls
- Single-parameter animation - The entire fall is controlled by one value: altitude
- Positive AND negative lengths - Yes, you can do this in Revit (it’s a neat trick)
Design principle: Following the KISS rule, I wanted to animate thousands of snowflakes by changing just one parameter per element.
Performance: Why Optimization Mattered
I’ve built fancy parametric snowflakes before, but this time the goal was different.
Previous approach: Complex, detailed, visually impressive
This year’s approach: Minimal, optimized, animation-ready
The reason? I needed to export nearly 2,500 frames. With thousands of snowflake instances updating per frame, every bit of optimization counted.
Try It Yourself
Happy New Year! I hope you enjoy the animation.
Pro tip: The family structure supports swapping geometries. Replace the snowflake with frogs, leaves, or confetti - the physics still work!
Snowflake Animation Demo
Below you can see the final animation result:
Behind the Scenes
Here’s another look at how the parametric families work together:
The Code
using Autodesk.Revit.DB;
using Autodesk.Revit.UI;
using System.Collections.Generic;
using System.Linq;
namespace W7k.Drafter
{
[Autodesk.Revit.Attributes.Transaction(Autodesk.Revit.Attributes.TransactionMode.Manual)]
internal class TestAnimation : IExternalCommand
{
public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elementSet)
{
// SETUP
Autodesk.Revit.ApplicationServices.Application app = commandData.Application.Application;
Autodesk.Revit.DB.Document doc = commandData.Application.ActiveUIDocument.Document;
UIDocument uidoc = new UIDocument(doc);
//SELECTION
var collectorByBuiltInCategory = new W7k.RevitAPI.CollectorByBuiltInCategory(doc, BuiltInCategory.OST_Site);
List<Element> elements = (from s in collectorByBuiltInCategory.GetElements()
where s is FamilyInstance fI && fI.Symbol.FamilyName == "SnowFlake"
select s).ToList();
TaskDialog.Show("Count", elements.Count.ToString());
double step = 0.05;
/* Code to update the animation after crash
using Transaction t2 = new Transaction(doc, $"Previous animation");
{
t2.Start();
foreach (Element el in elements)
{
Parameter param = el.GetParameters("Altitude").First();
param.Set(param.AsDouble() - step * 1013);
}
t2.Commit();
}
*/
//for (int i = 1013; i < 3000; i++)
for (int i = 0; i < 3000; i++)
{
using Transaction t1 = new Transaction(doc, $"Animate {i}");
{
t1.Start();
foreach (Element el in elements)
{
Parameter param = el.GetParameters("Altitude").First();
param.Set(param.AsDouble() - step);
}
t1.Commit();
}
uidoc.RefreshActiveView();
ImageExportOptions options = new ImageExportOptions
{
FilePath = @"D:\test\" + i + ".png",
ZoomType = ZoomFitType.Zoom,
HLRandWFViewsFileType = ImageFileType.PNG,
ImageResolution = ImageResolution.DPI_300,
ShouldCreateWebSite = false
};
options.ExportRange = ExportRange.CurrentView;
doc.ExportImage(options);
}
return Result.Succeeded;
}
}
}
