realtime:start

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realtime:start [2026/04/16 18:53] – created mhrealtime:start [2026/04/16 18:54] (current) – mh
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 ====== Real-Time Environments ====== ====== Real-Time Environments ======
  
-====== Screen Space ====== +  * **[[realtime:screenspace|Screen Space Techniques]]**
- +
-===== Core Concept ===== +
- +
-Screen Space techniques operate directly in the final image space (the screen), rather than in object or world space. +
- +
-Instead of computing how light interacts with geometry, they reuse what the camera has already rendered and manipulate it to produce the desired visual result. +
- +
-→ If it is not visible on the screen, it does not exist. +
- +
- +
-===== Mental Model ===== +
- +
-Three main spaces to think in: +
- +
-  * World Space → physical simulation, lighting, PBR +
-  * View Space → camera-relative tricks (Matcap, etc.) +
-  * Screen Space → pixel-perfect control of final image +
- +
-Screen Space sits at the top of the stack: +
- +
-→ Not simulation   +
-→ Not approximation   +
-→ Final perception control +
- +
- +
-===== Origin ===== +
- +
-Screen Space techniques emerged in real-time rendering (mid 2000s → early 2010s) as a response to performance limitations. +
- +
-Full physical simulation (ray tracing, global illumination) was too expensive for real-time systems. +
- +
-Solution: +
- +
-→ Only compute what the camera already sees   +
-→ Reuse existing rendered data   +
-→ Fake the rest +
- +
-This led to the rise of: +
- +
-  * SSAO (Ambient Occlusion) +
-  * SSR (Reflections) +
-  * Screen Space shadows and refraction +
- +
- +
-===== Core Principle ===== +
- +
-All Screen Space techniques share the same law: +
- +
-<code> +
-Use the rendered image as the primary data source +
-→ operate in screen coordinates +
-→ trade physical accuracy for performance and control +
-</code> +
- +
-Strength: +
-  * extremely fast +
-  * visually convincing +
- +
-Weakness: +
-  * blind to anything off-screen +
-  * can break at edges or occlusions +
- +
- +
-===== Screen Space Materials ===== +
- +
-A Screen Space material ignores object-based shading and instead displays content aligned with the camera view. +
- +
-Think of it as: +
- +
-→ geometry becomes a canvas   +
-→ the screen becomes the reference +
- +
-Properties: +
- +
-  * Not affected by lighting +
-  * Not affected by environment maps +
-  * Stable regardless of object orientation +
-  * Perfect alignment with output +
- +
-Typical usage: +
- +
-  * projection mapping (exact output match) +
-  * overlays / UI in 3D space +
-  * compositing layers +
-  * debug / data visualization +
- +
- +
-===== Key Consequence ===== +
- +
-<code> +
-color = texture(screen_x, screen_y) +
-</code> +
- +
-The material is evaluated per pixel on screen, not per surface in space. +
- +
-→ UVs become secondary   +
-→ normals become irrelevant   +
-→ lighting is bypassed +
- +
- +
-===== Screen Space Reflections (SSR) ===== +
- +
-SSR uses screen space to approximate reflections. +
- +
-Instead of tracing rays in 3D: +
- +
-→ sample the already rendered image   +
-→ reuse visible pixels as reflection data +
- +
-Limitations: +
- +
-  * cannot reflect off-screen objects +
-  * breaks at screen edges +
-  * unstable in fast motion +
- +
-Relation to Screen Space materials: +
- +
-  * same coordinate system (screen space) +
-  * same dependency on visible data +
-  * different purpose (effect vs display) +
- +
- +
-===== Other Screen Space Techniques ===== +
- +
-Common siblings: +
- +
-  * SSAO → fake contact shadows using depth +
-  * Screen Space Refraction → distort background using screen data +
-  * SSGI → approximate bounced light +
-  * Screen Space Shadows → cheap shadow approximation +
-  * Screen Space Decals → project textures after rendering +
- +
-All share: +
- +
-→ operate on the final image   +
-→ avoid expensive world simulation +
- +
- +
-===== Real-Time Philosophy ===== +
- +
-Screen Space is part of a larger doctrine: +
- +
-<code> +
-Reality → Simulation → Approximation → Screen Space → Perception +
-</code> +
- +
-In real-time systems: +
- +
-→ simulation is expensive   +
-→ approximation is common   +
-→ screen space is strategic control +
- +
- +
-===== Practical Use (Immersive / Media Servers) ===== +
- +
-In immersive environments, Screen Space shifts from optimization to precision. +
- +
-Used for: +
- +
-  * projection-aligned rendering +
-  * predictable visual output +
-  * compositing in 3D pipelines +
-  * stable overlays and UI elements +
- +
-Key advantage: +
- +
-→ What you see = what you output +
- +
- +
-===== Limitations ===== +
- +
-  * breaks physical realism +
-  * flat appearance if misused +
-  * dependent on camera view +
-  * no depth awareness beyond visible data +
- +
-Use when: +
- +
-→ control > realism +
- +
- +
-===== Final Rune ===== +
- +
-Screen Space techniques do not simulate the world. +
- +
-They control what the audience perceives, using only what is already visible. +
- +
-→ Geometry becomes support   +
-→ The screen becomes truth+
  • realtime/start.txt
  • Last modified: 2026/04/16 18:54
  • by mh