Per-landblock frustum culling for the streaming renderer. Extracts
6 normalized view-frustum planes from a View×Projection matrix using
the standard Gribb-Hartmann method. IsAabbVisible tests the AABB's
most-positive vertex against each plane — conservative (no false
negatives) and zero-allocation.
Key implementation note: System.Numerics.Matrix4x4 uses ROW-VECTOR
convention (clip = worldPos * VP), so Gribb-Hartmann must operate on
the COLUMNS of the matrix (not rows). The spec's row-based pseudocode
assumed column-major (OpenGL) convention; the fix is col4 ± col{1..3}.
7 new tests covering ortho, perspective (front/behind/left/far/
near-straddling), and acdream's actual Z-up camera convention.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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