Ad Advanced Computer Graphics d C G hi CS 563: Real ‐ Time Ocean Rendering [Real ‐ Time Realistic Ocean Lighting using Seamless [R l Ti R li ti O Li hti i S l Transitions from Geometry to BRDF] Xin Wang March, 20, 2012 , , Computer Science Dept. Worcester Polytechnic Institute (WPI)
B Background k d Photorealistic rendering image Photorealistic rendering image Cannot be used in games, simulators, etc… Realistic animation and rendering
I t Introduction d ti Hierarchical modeling of the ocean Hierarchical modeling of the ocean Illumination reflection using BRDF Lighting effects h ff BRDF model Approximate formula for computing the surfaces f l f h f Rendering
P Pervious Work i W k Physical ocean models Physical ocean models. [CM54,PM64,RD07] Computer graphics ocean models. C t hi d l [Tes01,CC06,HVT*06] Reflectance models. fl d l [CT81,AS00,RDP05] Multi ‐ resolution reflectance models. [Kaj85,HSR07]
O Ocean Model – Phase I M d l Ph I Dynamic scene no pre computations Dynamic scene, no pre ‐ computations physical facts about deep water waves Trochoid Waves. A gerstner wave is defined by p = [ x+hsin(wt − kx), hcos(wt − kx)]T , where w = gk. p [ ( ), ( )] , g
O Ocean Model – Phase II M d l Ph II Ocean surface with sum of n trochoid wave trains Ocean surface with sum of n trochoid wave trains Three sub ‐ models.
O Ocean Model – Phase II M d l Ph II Model hierarchy Average positions Compute inside a grid cell by filtering the trochoids Average normals Compute inside a pixel BRDFs BRDFs Subpixel surface details with statistical properties
O Ocean Model – Result M d l R lt
O Ocean BRDF BRDF A very accurate BRDF model for anisotropic A very accurate BRDF model for anisotropic rough surfaces.
O Ocean BRDF BRDF BRDF model coordinates BRDF model coordinates v and l are unit vectors towards the viewer and the light f is the normal of a microfacet whose x and y light. f is the normal of a microfacet whose x and y
O Ocean Lighting – Sun Lighting Li hti S Li hti Compute the light reflected from the Sun at P by Compute the light reflected from the Sun at P by applying the BRDF BRDF as constant over the Sum solid angle Ω sun BRDF t t th S lid l Ω Self ‐ shadowing can be provided with a shadow map for close views
O Ocean Lighting – Sky Lighting Li hti Sk Li hti Light reflected from the sky dome is difficult Light reflected from the sky dome is difficult Approximate method for specular to diffuse BRDFs assuming an isotropic or anisotropic BRDF i i t i i t i Gaussian slope distribution Three steps: Th t Approximate environment lighting Average Fresnel reflectance A F l fl Average sky radiance
Sky Lighting – Approximate environment lighting i t li hti BRDF is proportional to the fraction of micro BRDF is proportional to the fraction of micro ‐ facets Approximation is exact when BRDF is purely specular l
Sky Lighting – Average Fresnel reflectance fl t Plot of the reflectance of anisotropic rough Plot of the reflectance of anisotropic rough surface (green), and filter function (red)
Sk Li hti Sky Lighting – Average sky radiance A k di Environment map filtering Environment map filtering The reflected light L is an elliptical Gaussian filter Environment map transformed filter
O Ocean Lighting – Refracted Lighting Li hti R f t d Li hti Light coming from the Sun and Sky also refracted Light coming from the Sun and Sky also refracted inside the water Also refracted again to the viewer Al f t d i t th i Radiance Lsea reaching the surface from below is diff diffuse
O Ocean Lighting – Result Li hti R lt Reflected sun light reflected sky light light Reflected sun light, reflected sky light, light refracted from the water to final result
S Summary of Lighting Algorithm f Li hti Al ith
E t Extensions i Local waves Local waves Support other waves than trochoids Local reflections L l fl ti Use reflection map in screen space Multiple reflections l l fl Environment map approximate sky irradiance Planet ‐ scale rendering Render a sphere with Ross BRDF
I Implementation l t ti Vertex shader projects the screen space regular Vertex shader projects the screen space regular grid Fragment shader computes the per pixel normals F t h d t th i l l and the Sun, Sky and refracted light Use a geometric progression for the wavelengths U t i i f th l th
R Result lt
R Result lt
R Result lt
C Compare to real photo t l h t
References An anisotropic phong BRDF model. Ashikhmin M., Shirley P. Journal of Graphics Tool 5(2000) GPU ‐ based real ‐ time simulation and rendering of GPU b d l i i l i d d i f unbounded ocean surface. Yang X., Pi X., Zheng L., Li S In International Conference on Computer Aided S. In International Conference on Computer Aided Design and Computer Graphics (2005) Simulating ocean water Tessendorf J ACM Simulating ocean water. Tessendorf J. ACM SIGGRAPH course notes (2001)
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