Geometry Billboards
I built a Houdini Digital Asset that turns full 3D geometry into camera-facing billboards. The difference from traditional square cards: this tool generates silhouette-accurate meshes, which reduces or eliminates the need for alpha transparency.
I used this extensively in Vision Pro environments for large-scale foliage rendering. Entire groves of Joshua Trees, for example. The billboards held up at VR distances while staying within the tight performance budgets of a wearable device.
This tool became a key part of my WWDC25 session on optimizing Vision Pro environments.
The Problems with Standard Billboards
Standard billboards rely on alpha masking, which is expensive for rendering and sorting. Square cards rarely match the actual outline of the source object, wasting overdraw. And billboards generated out of context need complex shaders to shade correctly at each position, and they often look wrong.
I needed a way to simplify large numbers of meshes while keeping believable silhouettes and some depth cues intact.
Main Features
Silhouette-Accurate Billboards
The tool projects all mesh points toward a single origin point to generate a precise silhouette cutout, eliminating the boxy look of standard cards and reducing alpha reliance.
Convex Hull Mode
An option to build convex hulls as a lightweight compromise. Minimal geometry with only partial alpha needed for detail edges.
Context-Aware Generation
Billboards are generated in place, using each object’s actual location and transform. Every result has unique geometry and UVs aligned to its scene context, so lighting and shading stay correct.
Collision-Based Projection
A tube or sphere collision proxy defines the projection radius from each object’s centroid. All mesh points raycast into this proxy to form a 2D projection mesh, then Houdini’s 2D solver produces clean, non-overlapping triangulation.
Texture Integration
Spherical renders project onto the silhouette meshes. The system packs everything into a screen-space-scaled atlas for optimized texture usage.
Results
This tool simplified hundreds of meshes into silhouette-accurate billboards for Vision Pro environments. Parallax and presence held up even with flattened depth, and rendering costs dropped significantly by cutting transparency overhead. I presented the workflow at WWDC25 as part of the Vision Pro optimization pipeline.