AUTHORS Venceslas Biri Sylvain Michelin Didier Arques University

AUTHORS Venceslas Biri, Sylvain Michelin, Didier Arques University of Marne-la-Vallée. REAL TIME ANIMATION OF REALISTIC FOG GOALS ØDefining easily the shape of fog ØCreate easily animation of this shape ØDo it in real-time FOG ØOften non uniform ØCovers all the scene ØShape affected by the wind FOG SIMPLIFICATIONS IN PARTICIPATING MEDIA ØNo shadows ØIsotropic ØConstant illumination Lfog ØNo global illumination RENDERING METHODS MAIN IDEA Defining coefficient Kt as a sum of user-defined functions. Function Kt must be : ØDefined all over the scene ØAnalytically integrable ØPositive everywhere GENERIC FUNCTIONS USED Sinusoidal functions ØPeriodic ØEasy phase difference Polynomial functions ðComputation of transmittance for all pixels ðMethods : w Compute a transmittance texture and use it as a transparency texture in a plan placed before the screen w Use Pixel Shaders (? ) ðComputation time depends on texture size ØComputing transmittance vertex by vertex ðComputation of transmittance for each vertex. ðSeveral methods : w Use GL_FOG_COORD w Use Vertex Shaders ðComputation time depends on scene complexity RESULTS ØComputation times : Image Size : 800 x 600 ØEasy integration ØCan be defined precisely RENDERING EQUATION ØSimilar to Open. GL fog ØBlending between fog luminance and current colour VARIATIONS OF COLOUR DEPEND ON TRANSMITTANCE ØComputing transmittance pixel by pixel Texture Size 128 x 128 256 x 256 512 x 512 Fps with fog 30 12. 5 3. 5 Pixel/Pixel Texture Method (fps without fog : 45) Nb. Triangles 31 628 65 450 257 100 Fps with fog 31. 5 6. 5 1. 5 Fps without 77 24 8. 5 Vertex/Vertex GL_Fog_COORD Method ØPixel/Pixel methods : Slow and aliased but precise ØVertex/Vertex methods : Fast, antialiased but less precise between vertex ADDING DETAILS Potential functions ØPotential from virtual objects ØAdd details in fog ØCombined with previous functions ANIMATIONS ØWind effect : ðIntroduced in changing function parameters ØOthers effects : ðAny change in function coefficients induces a change in the fog shape We can design the fog shape ØWithout additional cost in time GOING FURTHER ØUse of pixels shaders : special functions ? Animations ? ØIntroducing single scattering and shadows. ØGlobal Illumination ?