Show pageOld revisionsBacklinksFold/unfold allBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ====== Screen Space ====== ===== 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**. → 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 ==== → color = texture(screenX, screenY) 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/screenspace.txt Last modified: 2026/04/16 19:19by mh