真實感圖形繪制(光照模型視無關(guān))課件

1、 10800 rays used in lighting pass.Note:-improved caustic definition,-lighting effect of mirror, -reflection of caustic,-shadowing due to mirror lighting.CausticsFrom Alan Watt, “3D Computer Graphics”Standard raytracer:Diffuse table and blue ball,mirrors left, right and back, transparent red ballBi-d

2、irectional raytracer More rays in the light passSingle Pass (Conventional RTNote : caustic due to red transparent ballHenrik http:/www.gk.dtu.dk/hwjBidirectional example200 rays used in lighting pass 400 rays used in lighting passRefraction causticsHenrik http:/www.gk.dtu.dk/hwj15Direct illumination

3、 16Global Illumination17eyediagram photograph:18Original sculpture by John Ferren lit by daylight from behind.Image rendered with radiosity. note color bleeding effects.Ray traced image. A standard ray tracer cannot simulate the interreflection of light between 19Radiosity vs. Ray TracingRay-tracing

4、View-dependentSpecular and refractionRadiosityView-independent Diffuse only20Radiosity vs. Ray TracingRay tracing is an algorithmIf the camera is moved, we have to start overRadiosity is computed in object-spaceView-independent (just don't move the lightCan pre-compute complex lighting to allow

5、interactive walkthroughs 26The Rendering EquationxMuseum simulation. Program of Computer Graphics, Cornell University.50,000 patches. Note indirect lighting from ceiling.32Radiosity Overview在輻射度方法中,所有的景物表面都假設(shè)為理想的朗伯漫反射表面所有的入射光在各個方向上反射的光強都一樣整個場景被劃分為一系列的小區(qū)域(small areas, or patches 設(shè)小區(qū)域i 向外輻射的所有能量的輻射度為B

6、i,并認為在i 內(nèi)所有地方的輻射度為一個常數(shù)單位如下,表示單位立體角單位面積的瓦特數(shù):Watts / steradian * meter 2x''x'xxxDiscrete Radiosity EquationA iA jdiscrete representationiterative solutioncostly geometric/visibility calculationspatches, over which the radiosity =i B The Radiosity Matrix求解該矩陣,就可以為每一個patch 得到一個B i ,它與視點是無關(guān)的。

7、12n B B B12n E E E=111112112212221111n n n n nn F F F F F F F +=i i E B3712121112i i i i i i i i in n n n B B B E B F B E B F F B E B E =+This method is fundamentally a Gauss-Seidel relaxation (高斯-賽德爾迭代法,松弛法38(intensities needed by the 39Factory simulation. Program of Computer Graphics, Cornell Univ

8、ersity.30,000 patches.Questions?40ExampleColor bleeding is extreme in this exampleTextures are applied after solving for illumination Some meshingartifacts are visible -note the bandingaround the pictureson the wallFrom Alan Watt, “3D Computer Graphics”From Alan Watt, “3D Computer Graphics”Calculati

9、ng the Form FactorsPoint-patchPatch-patch 53Coarse patch solution (145 patchesImproved solution (1021 subpatches Adaptive subdivision (1306 subpatches54Discontinuity MeshingCreate mesh depending on expected shadow boundaries Limits of umbra and penumbraCaptures nice shadow boundaries Complex geometr

10、ic computationThe mesh is getting complexpenumbraumbrasourceblocker55Discontinuity Meshing 56With visibility skeleton & discontinuity meshingHierarchical Approach目的:減少計算形狀因子數(shù)量根據(jù)作用的重要性,面片表示成多個層次作為輻射源面片時,剖分可粗一些,作為光能接受面片時,剖分細一些。桌子和小立方體都對周圍墻面有影響,但是小立方體影響不大,微微移動小立方體,光影不會變化太大,桌子可以剖分的大一些;但是在繪制桌子時,要繪制局部

11、細節(jié),小立方體對它的影響大,桌子需要細剖分;57Lambertian Surface A Lambertian surface has constant BRDF. constant Lambertian Surface A Lambertian surface looks equally bright from any view direction. The image intensities of the surface only changes with the illumination directions. constant 61 62 Lambertian Surface For a Lambertian surface, the outgoing radiance is proportional to the in