Module rendering/materials/gsplat/material-glsl

GSplat Material for Luxar

Specialized THREE.ShaderMaterial for rendering Gaussian splats using instanced quads. Implements projection-aware volumetric rendering with oriented, anisotropic Gaussian density functions.

Key features:

• Instanced oriented quad geometry (4 vertices per splat)
• Full 3D covariance via Cholesky factors
• Perspective-correct projection of covariance to 2D
• Blending-mode-aware projection (sum ray-integral for emissive additive/luminous, peak for surface max/normal/opaque)
• Shifted Gaussian falloff: scale · max(0, exp(-½ · r²) - C) with C⁰ continuity at truncation
• Per-splat attributes (center, cholesky, amplitude, color)

GPU Optimizations (GLSL ES 3.0 / WebGL2):

• flat interpolation: skips GPU interpolation for per-instance varyings
• Reciprocal precomputation: DIV→MUL in vertex and fragment shaders
• Early discard at truncation radius before expensive exp()
• Higher intensity threshold (1e-4) for fewer blended pixels
• mediump precision for color/amplitude to reduce register pressure

Mathematical basis:

• GSplat density: G(x) = a · scale · max(0, exp(-½ · ‖L⁻¹(x - μ)‖²) - C)
• Sum projection: amplitude boost by σ_ray · c_s (ray integration)
• Max projection: amplitude = a (peak value, no integration)
• 2D covariance: Σ_2D = J · Σ_cam · Jᵀ (perspective Jacobian projection)