Surface Mapping One. CS7GV3 Real-time Rendering

Transcription

1 Surface Mappng One CS7GV3 Real-tme Renderng

2 Textures Add complexty to scenes wthout addtonal geometry Textures store ths nformaton, can be any dmenson Many dfferent types: Dffuse most common Ambent, specular, gloss maps Bump, normal, dsplacement maps Reflecton, refracton maps

3 Textures and Renderng Recall the Renderng Equaton: I( x, x') g( x, x')[ e( x, x') ( x, x', x") I( x', x") dx"] I(x, x ) : ntensty of lght passng from x to x g(x, x ) = (geometry factor) e (x, x ) : ntensty of lght emtted by x and passng to x r (x, x, x ) : b-drectonal reflectance scalng factor for lght passng from x to x by reflectng off x Based on last few lectures, lets smplfy ths as: I g e L df df s n.l L h.n s s L a a

4 Dffuse Map Smplest texturng drectly apples a colour to object In basc llumnaton colour s mostly based on dffuse component I g e L df df n.l L h.n s s L a a

5 Emsson Map A..a. Glow map Models lght sources on a surface Does not depend on surface normal or lght sources. I g e L df df n.l L h.n s s L a a

6 Specular Map Specular color : Gloss map Shnness Control the specular exponent n Phong lght model Or roughness n other lght models I g e L df df n.l L h.n s s L a a

7 Specular Map + Specular Exp. Map Dffuse Color Specular Color Specular Exponent Shny Dull

8 Normal Map Use texture as a nput to perturb geometrc representaton I g e L df df n.l L h.n s s L a a

9 Vsblty Mappngs Parallax mappng Shft n texture looup based on vew-ray ntersecton wth heghtfeld Can account for occlusons Alpha Mappng: Transparency mappng across prmtve Shadow mappng I g e L df df n.l L h.n s s L a a

10 Lght & Envronment Mappng Approxmaton of ncomng radance Lght maps: pre-computed ncdent flux across 2D surfaces Envronment Maps: more complex 3D loo up of ncomng flux n scene Can combne wth other maps Texture d envronment Lght Maps Merged Scene I g e L df df n.l L h.n s s L a a

11 Texture Mappng For 2D textures, we need a 3D to 2D mappng Sometmes called a projector functon Each vertex n the model wll need a (u,v) co-ordnate Normally defned by the artst and added to the vertex stream

12 Texture Mappng Components XYZ UV [0,1] U [0-wdth] V [0-heght] RGB K d? N, From: Aenne-Moller, Hanes, Hoffman Real-tme Renderng 3 rd Ed.

13 UV Mappngs

14 Example: Cylndrcal

15 Tlng, Wrappng etc. Can specfy rules for (u, v) behavour outsde [0, 1] Tlng: number of repettons of texture wthn space Tlng Mode: normal, mrror, no-tlng (clamp) The (u, v) co-ordnate can be manpulated by shader Just another nput e.g. could rotate texture co-ordnate

16 Bump Mappng Add surface geometrc detal wthout addtonal vertces A real bump dstorts the drectons of the normals (ths effects calculatons of lght reflectance) Fae bumps created by dstortng the normals although the model geometry s stll flat. e.g. A bump-map texture appled to a flat polygon.

17 Bump Mappng Use a texture map to perturb the normal to the surface Tradtonally represent ths as ether: d stored n 2 separate scalar textures (for d u and d v ) store a heghtfeld and compute or approxmate d from the surface dfferentals

18 Bump/Normal Mappng Gve the lluson of geometrc detal Shape percepton depends on lghtng cues Wthout normal mappng Wth bump mappng

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21 Normal Mappng A more commonly used method s normal mappng Also nown as dot3 bump mappng Image taen from Wpeda avalable at

22 Object Space Normal Mappng Basc Idea: Store the actual surface normal n the texture (RGB = nx, ny, nz) At each pxel, loo up the normal map, and use ths nstead of the nterpolated normal Tool support requred f generatng normals from hgh-res surfaces

23 Per-vertex Lghtng Only Normal Maps e.g. Combne wth Mesh Smplfcaton Cohen, Olano, Manocha, Appearance-preservng smplfcaton, SIGGRAPH,

24 Object Space Normal Mappng Object space has some problems: Not very flexble Strongly ted to specfc object Can t tle map or use symmetry Don t wor so well wth MIP maps or sharp edges Image from

25 Tangent Space Normal Mappng Normal s stored relatve to the tangent space of the object Sort of le a local normal Defne a local co-ordnate frame Form a co-ordnate system from normal n and tangent t and bnormal b Then defne dsplaced normal n n ths space n t b z y x z y x z y x T n n n b b b t t t n b t M t n n' b

26 Shader Setup Applcaton must send normal and tangent vector to the shader The normal s straghtforward avalable as bult n attrbute The tangent s slghtly trcy (for polygonal objects) Pass ths down as a custom attrbute B-tangent can be calculated n the shader Must be consstent wth the tangent vector to avod nterpolaton problems

27 Lghtng wth the bump map Transform lght and vew vectors nto tangent space (per vertex) Vertex Shader: varyng vec3 v; varyng vec3 l; unform vec4 L; //drectonal lght n eye space attrbute vec3 rm_tangent; attrbute vec3 rm_btangent; //here we get the btangent from applcaton //but we could calculate ths n the shader vod man(vod) { gl_poston = ftransform(); gl_texcoord[0] = gl_texturematrx[0]*gl_multtexcoord0; vec4 camera = gl_modelvewmatrxinverse*vec4(0.0, 0.0, 0.0, 1.0); vec3 vew = normalze(camera.xyz-gl_vertex.xyz); //object space vew and lght vector vec3 lght = normalze(gl_modelvewmatrxtranspose*l).xyz; } //TBNnv transforms vectors from object space to tangent space mat3 TBNnv(rm_Tangent, rm_btangent, gl_normal); l = TBNnv*lght; v = TBNnv*vew;

28 Lghtng wth the bump map Fragment Shader unform vec4 ambentcolor; unform vec4 dffusecolor; unform vec4 specularcolor; unform sampler2d dffusetex; unform sampler2d normaltex; unform float shnness; varyng vec3 v; varyng vec3 l; vod man(vod) { l = normalze(l); v = normalze(v); } vec3 n = 2.0*texture2D( normaltex, gl_texcoord[0].st ).xyz - 1.0; //tangent-space normal vec4 dffuseterm = texture2d( dffusetex, gl_texcoord[0].st)* dffusecolor *(max( 0.0, dot(n, l))); vec3 r = reflect(-l, n); //tangent-space reflecton vector vec4 specularterm = specularcolor*pow(max(0.0, dot(r, v)), shnness); gl_fragcolor = ambentcolor + dffuseterm + specularterm;

29 Tangent Space Normal Mappng

30 Tangent Space Normal Mappng Predomnantly blue: Why? No dsplacement means normal = n n tangent space n = [0 0 1] whch maps to RGB blue Dsplaced normals are relatvely close to ths Storage: Record 255*(n +1)/2 n normal map (to map to [0,255] range)