# [`glvisnormals`][]
 
 A [GLSL][]/[OpenGL][] [\>=3.2][] [normal][] visualization library.
 

 A [geometry shader][] is used to visualize the normals from the same geometry
 as when drawing normally.
 

 [`glvisnormals`]: https://git.rcrnstn.net/rcrnstn/glvisnormals
 [GLSL]: https://en.wikipedia.org/wiki/OpenGL_Shading_Language
 [OpenGL]: https://en.wikipedia.org/wiki/OpenGL
 [\>=3.2]: https://en.wikipedia.org/wiki/OpenGL#Version_history
 [normal]: https://en.wikipedia.org/wiki/Normal_(geometry)

 [geometry shader]: https://www.khronos.org/opengl/wiki/Geometry_Shader
 
 ## Requirements
 
 [Geometry shader][]s require OpenGL [\>=3.2][] or the
 [`ARB_geometry_shader4`][] extension.
 
 [`ARB_geometry_shader4`]: https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_geometry_shader4.txt
 
 ## Usage
 
 Link the shader program with:
 
 -   `visnormals.vert`
 -   `visnormals.geom`
 -   `visnormals.frag`
 
 The following vertex attributes need to be set:
 
 -   `vec3 vert_position`
 -   `vec3 vert_normal` (assumed to be of unit length)
 -   `mat4 vert_model` (assumed to be an isometry, i.e. no scaling or skewing)
 
 The following uniforms need to be set:
 
 -   `mat4  view_projection`
 -   `float scale`
 -   `vec4  color`
 
 The following outputs are written by the fragment shader:
 
 -   ` vec4 frag_color`
 
 Make the shader program current and issue the same draw call as would be done
 when drawing normally.

 ## Build system
 
 This project has support for [CMake][], and uses [`cmake-cxx`][].
 
 There are several ways to use this project in another CMake-based project:
 
 -   Use [`FetchContent`][] to download it and import the targets automatically
     as part of the configure step:
 
     ```cmake
     include(FetchContent)
     FetchContent_Declare(project-name
         GIT_REPOSITORY https://example.com/user/project-name
     )
     FetchContent_MakeAvailable(
         project-name
     )
     ```
 
 -   Bundle it and import the targets with [`add_subdirectory`][].
 
 -   Use [`find_package`][] (requires that the project is [packaged](#packaging)
     or [installed](#installing)).
 
 As usual, use [`add_dependencies`][]/[`target_link_libraries`][] to declare the
 dependency.
 
 [CMake]: https://cmake.org
 [`cmake-cxx`]: https://git.rcrnstn.net/rcrnstn/cmake-cxx
 [`FetchContent`]: https://cmake.org/cmake/help/v3.14/module/FetchContent.html
 [`add_subdirectory`]: https://cmake.org/cmake/help/v3.14/command/add_subdirectory.html
 [`find_package`]: https://cmake.org/cmake/help/v3.14/command/find_package.html
 [`add_dependencies`]: https://cmake.org/cmake/help/v3.14/command/add_dependencies.html
 [`target_link_libraries`]: https://cmake.org/cmake/help/v3.14/command/target_link_libraries.html
 
 ### Configure and generate
 
 To configure and generate a build tree, use `cmake`:
 
 ```sh
 cmake -B build
 ```
 
 To set the [`CMAKE_BUILD_TYPE`][], pass e.g. `-DCMAKE_BUILD_TYPE=Release`.
 
 [`cmake`]: https://cmake.org/cmake/help/v3.14/manual/cmake.1.html#generate-a-project-buildsystem
 [`CMAKE_BUILD_TYPE`]: https://cmake.org/cmake/help/v3.14/variable/CMAKE_BUILD_TYPE.html
 
 ### Build
 
 To build, use [`cmake --build`][]:
 
 ```sh
 cmake --build build
 ```
 
 [`cmake --build`]: https://cmake.org/cmake/help/v3.14/manual/cmake.1.html#build-a-project
 
 ### Test
 
 To run tests, use [`ctest`][]:
 
 ```sh
 (cd build && ctest --output-on-failure)
 ```
 
 [`ctest`]: https://cmake.org/cmake/help/v3.14/manual/ctest.1.html
 
 ### Package
 
 To package, use [`cpack`][]:
 
 ```sh
 (cd build && cpack)
 ```
 
 [`cpack`]: https://cmake.org/cmake/help/v3.14/manual/cpack.1.html
 
 ### Install
 
 To install onto the current system, use [`cmake --install`][]:
 
 ```sh
 cmake --install build
 ```
 
 [`cmake --install`]: https://cmake.org/cmake/help/v3.14/manual/cmake.1.html#install-a-project
 

 ## License
 
 Licensed under the [ISC License][] unless otherwise noted, see the
 [`LICENSE`](LICENSE) file.
 
 [ISC License]: https://choosealicense.com/licenses/isc/