Technical Glossary

This glossary covers technical terms and expressions used in the project, spanning theoretical PBR rendering aspects, geometric optimizations, and low-level graphics API concepts.

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🎨 Rendering & Physics (PBR / IBL)

Term	Software / Theoretical Definition
PBR	Physically Based Rendering. A rendering model grounded in the laws of physics to simulate how light realistically interacts with materials.
IBL	Image Based Lighting. Using an image (HDR cubemap) to simulate complex global illumination.
BRDF	Bidirectional Reflective Distribution Function. A function defining how a material reflects light (Cook-Torrance model).
NDF (GGX)	Normal Distribution Function. The component of PBR describing the micro-geometry of surfaces (microfacet distribution).
Split-Sum	A mathematical approximation (Epic Games) enabling real-time IBL specular computation via pre-integration (Prefiltered Map + BRDF LUT).
Irradiance / Radiance	Irradiance is the total incident luminous flux (diffuse); Radiance is the flux in a specific direction (specular).
Normal Mapping / TBN	Detail simulation via a texture. The TBN matrix (Tangent, Bitangent, Normal) transforms vectors from Tangent Space to World Space.

📐 Projection Optimizations (Spheres / Billboards)

Term	Software Definition
Impostors	A technique simulating complex 3D geometry (sphere) on a 2D quad via ray-casting in the shader.
Analytic AA	Mathematical anti-aliasing on the sphere edge, computed from the discriminant derivative (fwidth), yielding perfect contours.
Tangent Planes	A geometric method computing the perfect screen-space bounding box (AABB) of a sphere via tangent planes passing through the camera.
Conservative Depth	Positioning the quad at the sphere's closest point to guarantee a correct Z-test before writing gl_FragDepth.
Discriminant	The ray-sphere equation value (\(b^2 - ac\)). Determines whether a pixel is inside (\(>0\)) or outside (\(<0\)) the sphere.
Perspective Distortion	Elliptical deformation of a sphere when it moves away from screen center, handled here by exact tangent projection.

⚙️ Graphics API & Data Flow (GPU)

Term	Software Definition
PBO (Zero-Copy)	Pixel Buffer Object. Using GL_MAP_UNSYNCHRONIZED_BIT to upload data without stalling the CPU.
Fence Sync	A glFenceSync object used to check GPU task completion without forcing a full pipeline flush (stall).
Flat Interpolation	The flat qualifier preventing interpolation between vertices, critical for numerical stability of silhouette calculations on spheres.
Provoking Vertex	The vertex whose value is used for the entire primitive during flat interpolation.
Pipeline Stall	A critical latency where the CPU waits for the GPU (caused by synchronous reads or glFinish).

🚀 Architecture & System

Term	Software Definition
Time Slicing	Splitting heavy operations (IBL) into small slices spread across multiple frames to maintain a constant FPS.
Double Buffering (Pending)	Preparing a new state (e.g., environment) in the background while the old one is still being displayed.
SIMD (AVX)	Using wide processor instructions to process multiple floats simultaneously (used for sphere sorting).
PAL	Platform Abstraction Layer. A layer isolating business logic from system-specific details (Linux/Windows).
MkDocs / Doxygen	Documentation generation tools (Narrative vs. API Reference).
Tracy	A hybrid profiler (CPU/GPU) used to analyze performance in real time.