--- title: "Per-Face Textures" canonical: "https://rmanwiki-25.pixar.com/space/REN25/20416404/Per-Face%20Textures" format: markdown --- ### Introduction RenderMan Pro Server supports per-face texture mapping, also known as Ptex. Ptex is a texture mapping system that uses the intrinsic per-face UVs of a polygonal mesh; no explicit texture parameterization is required. Ptex textures are stored along with adjacency data in a single file per primitive. Ptex uses the adjacency data to perform seamless anisotropic filtering of multi-resolution textures across surfaces of arbitrary topology. Additional technical information about Ptex textures and filtering can be found at [http://ptex.us/overview.html](http://ptex.us/overview.html) To help kick start the process of authoring Ptex files, this appnote provides details of shaders and utility programs that can be used to bake shaded results into Ptex textures. A parameter, __faceindex, which labels each face on the geometry, is required by theptexture() shading function and we provide a RIF called RifSubdivFaceIndex that will label geometry with the appropiate index. We also provide a program called ptxmake that will take a pointcloud baked in a specific way and convert the data to a Ptex file. --- ### Geometric Primitive Support One of the required parameters for the ptexture() call is __faceindex. This index is a facevarying, postive integer at each quad face of the surface, usually starting at 0. For Catmull-Clark surfaces, non-quad faces are numbered at each vertex, and the first level of subdivision of the non-quad faces will generate N-subfaces, where N is the number of vertices. For quad faces, the same faceindex` value is used on each vertex. An example of the faceindex layout is shown below. Note that the __faceindex follows special subdivision rules that will ensure the value is constant across quad-faces and that the shader parameter will be of *varying* detail. For Loop surfaces, only triangular faces are supported; each vertex of the face should be numbered with the same __faceindex value. A RIF called [RifSubdivFaceIndex.so](http://rifsubdivfaceindex.so/) is included for convenience that will take a subdivision surface without a faceindex and create the appropriate __faceindex values at each vertex. ![image](media://a044db4c-d766-45a8-96aa-5b76eb8306f4) Here is the RIB file example utilizing Ptex: ``` ##RenderMan RIBversion 3.03 Projection "perspective" "fov" [45] Format 256 256 1.0 Option "ribparse" "string varsubst" ["$"] Display "test.tif" "tiff" "rgba" WorldBegin Attribute "visibility" "camera" [1] Translate 0 0 3 Pattern "PxrPtexture" "ptex" "string filename" "./plateface.ptx" Bxdf "PxrDiffuse" "mydiffuse" "reference color diffuseColor" ["ptex:resultRGB"] SubdivisionMesh "catmull-clark" [4 4 4 4 3 3 4 4 4 4] [4 5 1 0 5 6 2 1 6 7 3 2 8 9 5 4 9 10 5 10 6 5 10 11 7 6 12 13 9 8 13 14 10 9 14 15 11 10] ["interpolateboundary" "smoothtriangles"] [0 0 1 0] [1] [] "P" [-1.0 -1.0 0 -0.3333333333333 -1.0 0 0.3333333333333 -1.0 0 1.0 -1.0 0 -1.0 -0.3333333333333 0 -0.3333333333333 -0.3333333333333 0 0.3333333333333 -0.3333333333333 0 1.0 -0.3333333333333 0 -1.0 0.3333333333333 0 -0.3333333333333 0.3333333333333 0 0.3333333333333 0.3333333333333 0 1.0 0.3333333333333 0 -1.0 1.0 0 -0.3333333333333 1.0 0 0.3333333333333 1.0 0 1.0 1.0 0] "facevarying float __faceindex" [6 6 6 6 7 7 7 7 8 8 8 8 9 9 9 9 0 1 2 3 4 5 10 10 10 10 11 11 11 11 12 12 12 12 13 13 13 13] "constant string __handleid" ["${RMANREGRESS_TESTOBJDIR}/plate"] WorldEnd ```   --- ### ptxmake A new utility program called ptxmake has been created that will take data baked into a point cloud and convert it into a Ptex texture file. The usage is as follows: `ptxmake [options] ptcfile channelname ptxfile ` ptxmake supports the following options: | | | | --- | --- | | -fedfile (fedfilename) | provide a face edge data file | | -geometry (quad|tri) | provide the geometry of the baked data quad | | -depth (byte|short|half|float) | bit depth of output image, the default is half | | -splat (none|diffusion|smooth|area) | splattering mode, the default is diffusion | | -newer (0|1) | convert if (and only if) the ptcfile is newer than the ptxfile | | -verbose | enables verbose output | | -outofcore | work out of core for large data | | -v|-version | output version string | One of the key components of a Ptex file is the face and edge connectivity data of the geometry being textured. A RIF, calledRifFaceEdgeData, has been provided that takes a surface that has been tagged with __handleid and generates a file called:__handleid.fed. This fed file can then be passed to the ptxmake program. Note, a limitation of the RifFaceEdgeData plugin is that it can only be used while rendering with prman. It will not function with catrib or prman with the -catrib option. In addition to the connectivity data, the fedfile also encodes the geometry type, so the -geom flag does not need to be used with ptxmake, except in cases where no fedfile is present. --- #### Using ptxmake The ptxmake program is used to convert the point cloud data into a Ptex file. The usage for our dragon test case is: `ptxmake -depth half -fedfile dragon.fed dragon.ptc occlusion dragon.ptx ` This takes the .fed file and the .ptc file generated during the bake pass and renders each face in the point cloud into a per-face texture in the .ptx file. This file can then be used to re-render the baked occlusion data. Notice, Ptex files support the half-float data format. The utility program ptxinfo can be used to query data about the ptx file. In our test case ptxinfo -f dragon.ptx gives the following output: `meshType: quad dataType: float16 numChannels: 1 alphaChannel: (none) numFaces: 895 hasFaceEdits: no numMetaKeys: 0 face 0: res: 7 7 (128 x 128) adjface: 85 1 6 5 adjedge: 3 3 0 1 flags: (none) face 1: res: 7 7 (128 x 128) adjface: 88 2 7 0 adjedge: 3 3 0 1 flags: (none) face 2: res: 7 7 (128 x 128) adjface: 91 3 8 1 adjedge: 3 3 0 1 flags: (none) face 3: res: 7 7 (128 x 128) adjface: 94 4 9 2 adjedge: 3 3 0 1 flags: constant face 4: res: 7 7 (128 x 128) adjface: 97 5 10 3 adjedge: 3 3 0 1 flags: constant face 5: res: 7 7 (128 x 128) adjface: 100 0 11 4 adjedge: 3 3 0 1 flags: (none) face 6: res: 7 7 (128 x 128) adjface: 0 7 12 11 adjedge: 2 3 0 1 flags: (none) ...` ` `