diff --git a/tutorial/706_FacetOrientation/CMakeLists.txt b/tutorial/706_FacetOrientation/CMakeLists.txt new file mode 100644 index 000000000..b61c5ba4c --- /dev/null +++ b/tutorial/706_FacetOrientation/CMakeLists.txt @@ -0,0 +1,8 @@ +cmake_minimum_required(VERSION 2.8.12) +project(706_FacetOrientation) + +add_executable(${PROJECT_NAME}_bin + main.cpp) +target_include_directories(${PROJECT_NAME}_bin PRIVATE ${LIBIGL_INCLUDE_DIRS}) +target_compile_definitions(${PROJECT_NAME}_bin PRIVATE ${LIBIGL_DEFINITIONS}) +target_link_libraries(${PROJECT_NAME}_bin ${LIBIGL_LIBRARIES} ${LIBIGL_EXTRA_LIBRARIES}) diff --git a/tutorial/706_FacetOrientation/main.cpp b/tutorial/706_FacetOrientation/main.cpp new file mode 100755 index 000000000..5a815d1f0 --- /dev/null +++ b/tutorial/706_FacetOrientation/main.cpp @@ -0,0 +1,108 @@ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +igl::viewer::Viewer viewer; +Eigen::MatrixXd V; +std::vector C(2); +std::vector RGB(2); +Eigen::MatrixXi F; +std::vector FF(2); +bool is_showing_reoriented = false; +bool facetwise = false; + +int main(int argc, char * argv[]) +{ + using namespace std; + cout<()/(double)C[pass].maxCoeff(); + HSV.rightCols(2).setConstant(1.0); + igl::hsv_to_rgb(HSV,RGB[pass]); + } + viewer.data.set_colors(RGB[facetwise]); + }; + + viewer.callback_key_pressed = + [&scramble_colors] + (igl::viewer::Viewer& /*viewer*/, unsigned int key, int mod)->bool + { + switch(key) + { + default: + return false; + case 'F': + case 'f': + { + facetwise = !facetwise; + break; + } + case 'S': + case 's': + { + scramble_colors(); + return true; + } + case ' ': + { + is_showing_reoriented = !is_showing_reoriented; + break; + } + } + viewer.data.clear(); + viewer.data.set_mesh(V,is_showing_reoriented?FF[facetwise]:F); + viewer.data.set_colors(RGB[facetwise]); + return true; + }; + + + // Compute patches + for(int pass = 0;pass<2;pass++) + { + Eigen::VectorXi I; + igl::embree::reorient_facets_raycast( + V,F,F.rows()*100,10,pass==1,false,false,I,C[pass]); + // apply reorientation + FF[pass].conservativeResize(F.rows(),F.cols()); + for(int i = 0;i
  • 703 Mesh Decimation
  • 704 Signed Distances
  • 705 Marching Cubes
    • +
  • 706 Facet Orientation
  • Chapter 8: Outlook for continuing development
    • @@ -3303,6 +3304,55 @@ this signed distance field to an indicator function and contouring reveals serious aliasing artifacts. +

    Facet Orientation

    + +

    Models from the web occasionally arrive unorientated in the sense that +the orderings of each triangles vertices do not consistently agree. Determining +a consistent facet orientation for a mesh is essential for two-sided lighting +(e.g., a cloth with red velvet on one side and gold silk on the other side) and +for inside-outside determination(e.g., using [generalized winding +numbers][#generalizedwindingnumber]).

    + +

    For (open) surfaces representing two-sided sheets, libigl provides a routine to +force consistent orientations within each orientable patch +(igl::orientable_patches) of a mesh:

    + +
    igl::bfs_orient(F,FF,C);
+
    + +

    This simple routine will use breadth-first search on each patch of the mesh to +enforce a consistent facet orientation in the output faces FF.

    + +

    For (closed or nearly closed) surfaces representing the boundary of a solid +object, libigl provides a routine to reorient faces so that the vertex ordering +corresponds to a counter-clockwise ordering of the vertices with a +right-hand-rule normal pointing outward. This method [39] assumes +that most of the universe is +empty. +That is, most points in space are outside of the solid object than inside. +Points are sampled over surface patches. For each sample point, rays are shot +into both hemispheres to compute average of the (distance weighted) ambient +occlusion on each side. A patch is oriented so that the outward side is less +occluded (lighter, i.e., facing more void space).

    + +
    igl::embree::reorient_facets_raycast(V,F,FF,I);
+
    + +

    The boolean vector I reveals which rows of F have been flipped in FF.

    + +
    +(Example 706) loads a truck model with +inconsistent orientations (back facing triangles shown darker). Orientable +patches are uniquely colored and then oriented to face outward (middle left). +Alternatively, each individual triangle is considered a patch (middle right) +and oriented outward independently. +
    (Example 706) loads a truck model with +inconsistent orientations (back facing triangles shown darker). Orientable +patches are uniquely colored and then oriented to face outward (middle left). +Alternatively, each individual triangle is considered a “patch” (middle right) +and oriented outward independently.
    +
    +

    Outlook for continuing development

    Libigl is in active development, and we plan to focus on the following features @@ -3414,7 +3464,7 @@ repository.

    2008.

    -

  • Olga Sorkine and Marc Alexa, As-rigid-as-possible Surface +

  • Olga Sorkine and Marc Alexa. As-rigid-as-possible Surface Modeling, 2007.

    • @@ -3546,6 +3596,13 @@ pseudonormal, 1987.

    +

  • Kenshi Takayama, Alec Jacobson, Ladislav Kavan, Olga + Sorkine-Hornung. A Simple Method for Correcting Facet Orientations in + Polygon Meshes Based on Ray + Casting, + 2014.

    +
    • + diff --git a/tutorial/tutorial.md b/tutorial/tutorial.md index f600032cf..da82267bd 100644 --- a/tutorial/tutorial.md +++ b/tutorial/tutorial.md @@ -97,6 +97,7 @@ lecture notes links to a cross-platform example application. * [703 Mesh Decimation](#meshdecimation) * [704 Signed Distances](#signeddistances) * [705 Marching Cubes](#marchingcubes) + * [706 Facet Orientation](#facetorientation) * [Chapter 8: Outlook for continuing development](#future) # Chapter 1 [chapter1:introductiontolibigl] @@ -2967,6 +2968,51 @@ marching cubes to contour the 0-level set (center). For comparison, clamping this signed distance field to an indicator function and contouring reveals serious aliasing artifacts.](images/armadillo-marching-cubes.jpg) +## Facet Orientation [facetorientation] + +Models from the web occasionally arrive _unorientated_ in the sense that +the orderings of each triangles vertices do not consistently agree. Determining +a consistent facet orientation for a mesh is essential for two-sided lighting +(e.g., a cloth with red velvet on one side and gold silk on the other side) and +for inside-outside determination(e.g., using [generalized winding +numbers][#generalizedwindingnumber]). + +For (open) surfaces representing two-sided sheets, libigl provides a routine to +force consistent orientations within each orientable patch +(`igl::orientable_patches`) of a mesh: + +```cpp +igl::bfs_orient(F,FF,C); +``` + +This simple routine will use breadth-first search on each patch of the mesh to +enforce a consistent facet orientation in the output faces `FF`. + +For (closed or nearly closed) surfaces representing the boundary of a solid +object, libigl provides a routine to reorient faces so that the vertex ordering +corresponds to a counter-clockwise ordering of the vertices with a +right-hand-rule normal pointing outward. This method [#takayama14][] assumes +that [most of the universe is +empty](https://www.reddit.com/r/askscience/comments/32otgx/which_as_a_is_more_empty_an_atom_or_the_universe/). +That is, most points in space are outside of the solid object than inside. +Points are sampled over surface patches. For each sample point, rays are shot +into both hemispheres to compute average of the (distance weighted) ambient +occlusion on each side. A patch is oriented so that the outward side is _less +occluded_ (lighter, i.e., facing more void space). + +```cpp +igl::embree::reorient_facets_raycast(V,F,FF,I); +``` + +The boolean vector `I` reveals which rows of `F` have been flipped in `FF`. + +![([Example 706](706_FacetOrientation/main.cpp)) loads a truck model with +inconsistent orientations (back facing triangles shown darker). Orientable +patches are uniquely colored and then oriented to face outward (middle left). +Alternatively, each individual triangle is considered a "patch" (middle right) +and oriented outward independently.](images/truck-facet-orientation.jpg) + + # Outlook for continuing development [future] Libigl is in active development, and we plan to focus on the following features @@ -3123,8 +3169,13 @@ pseudonormal](https://www.google.com/search?q=Signed+distance+computation+using+ [#sorkine_2004]: Olga Sorkine, Yaron Lipman, Daniel Cohen-Or, Marc Alexa, Christian Rössl and Hans-Peter Seidel. [Laplacian Surface Editing](https://www.google.com/search?q=Laplacian+Surface+Editing), 2004. -[#sorkine_2007]: Olga Sorkine and Marc Alexa, [As-rigid-as-possible Surface +[#sorkine_2007]: Olga Sorkine and Marc Alexa. [As-rigid-as-possible Surface Modeling](https://www.google.com/search?q=As-rigid-as-possible+Surface+Modeling), 2007. +[#takayama14]: Kenshi Takayama, Alec Jacobson, Ladislav Kavan, Olga + Sorkine-Hornung. [A Simple Method for Correcting Facet Orientations in + Polygon Meshes Based on Ray + Casting](https://www.google.com/search?q=A+Simple+Method+for+Correcting+Facet+Orientations+in+Polygon+Meshes+Based+on+Ray+Casting), + 2014. [#vallet_2008]: Bruno Vallet and Bruno Lévy. [Spectral Geometry Processing with Manifold Harmonics](https://www.google.com/search?q=Spectral+Geometry+Processing+with+Manifold+Harmonics),